Lead Smelting Furnace

— Lead Smelting Furnace: Rotary Smelting, Slag Lead Control and Bullion Handover

A lead smelting furnace is a reduction furnace. It takes lead-bearing material in oxide, sulfate, carbonate or metallic form — battery paste, grid metal, dross, flue dust and residues — heats it with a reductant, iron and flux into a molten bath, and separates the lead as bullion that sinks to the hearth while a slag forms above. It recovers lead; it does not set its grade. What leaves the furnace is crude or hard lead bullion at about 95–98% Pb, with slag, matte and a lead-bearing filter dust; taking it to 99.97% battery-grade soft lead is the duty of kettle refining and, where bismuth and silver justify it, electrolytic refining. YuSai builds it as a complete station: short rotary furnace, burner train, enclosed charging, weighed flux, reductant and iron, tap and forehearth, a sealed enclosure with induced draught, afterburner and bag filters, sealed dust return, and a batch record closing the charge-to-bullion balance. The working band is 1,000–1,400 °C and the slag lead figure is designed, measured and reported per heat.

Product Overview

A lead smelting furnace is a reduction reactor, and the word that defines it is reduction rather than melting. Lead in a battery arrives as lead sulfate in the paste, as lead dioxide and lead monoxide alongside it, and as metallic lead in the grids and the terminals; lead in a dross or a flue dust arrives as oxide and as sulfate; lead in a residue or a concentrate arrives as sulfide, carbonate or a mixture of all of them. None of those compounds is lead metal, and no amount of heating turns them into lead metal on its own. The furnace exists to supply the two things that do: carbon at a temperature high enough to strip the oxygen, and iron to break the sulfur bond that carbon alone cannot finish. Melting is what the furnace does incidentally, because the products of that reduction have to be liquid to separate from the gangue — and it is the separation, bullion sinking and slag rising, that makes the whole thing a smelting operation rather than a chemical reaction in a pot.

That distinction fixes what this page is and what it is not. It is not a refining page: the furnace produces bullion at about 95–98% Pb and the grade of the metal that leaves the plant is set downstream, in kettles and, where the bismuth or the silver justifies it, in an electrolytic circuit — the duty covered on the lead refining machine page. It is not a battery-breaking page, although the front end it depends on is battery breaking and separation, because a furnace fed whole uncracked batteries has to carry the case, the separators and the acid through its thermal duty and its off-gas train. It is not a hydrometallurgical page: lead that arrives in a solution, a leachate or a rinse belongs in a recovery circuit. And it is not the precious-metal crucible duty covered on the precious metal smelting machine page, which melts metal that is already metal and never touches a sulfate. What this page sells is the unit that takes a solid, oxidised or sulfated lead-bearing charge and returns metallic lead bullion, a slag, a matte or speiss, and a filter dust — each with a measured weight, a measured lead content and a defined destination.

The furnace family is the first decision, and it is decided by the charge rather than by preference. A short rotary furnace — a horizontal refractory-lined drum on trunnion rollers, charged through a door, rotated to mix the bath and tapped at the end — is the most widely used unit in the secondary lead industry, and for good reason: it is a batch machine, so it can run metallics separately from pastes and change its reductant and flux between charges; it accepts fines, drosses, slag and even whole batteries; it mixes by rotation so the reduction is not limited by diffusion through a static bath; and because it can be tilted or tapped hot, it handles a tapping sequence that a stationary furnace makes awkward. A stationary reverberatory furnace is chosen where very large continuous tonnages justify it, but its slag carries 30–55% lead and must be reduced in a second furnace, so it is a two-stage plant rather than a single unit. A blast shaft is chosen where the feed is coarse and permeable and where hard, antimonial bullion is the target, at the price of a sinter plant ahead of it and a high fume load at charging, tapping and tuyere punching — and it cannot accept the fines and pastes that a rotary furnace takes in its stride. An oxygen-enriched side-blown or lance furnace is chosen where the feed is high in sulfide and the plant wants the sulfur as a saleable gas rather than fixed in a slag. The arithmetic that separates them is on this page; the model number is not.

The charge decides the furnace, and its preparation decides the slag, the off-gas and the reline interval. Grid metal is dense, melts early and needs little more than a cover flux. Paste is fine, dusty, low in density and largely sulfated, so it needs briquetting or agglomeration to keep it out of the duct, and it needs iron as well as carbon to release its lead. Drosses and flue dusts are fine and often high in antimony, arsenic and chloride, which is why they are blended rather than charged neat. Whole batteries bring their own organic load, which is why a furnace that charges them needs post-combustion. Battery casing plastic is separated before the furnace feed — a regulatory requirement in the secondary lead architecture and a refractory-life decision in practice, because chlorides from PVC separators attack linings and depress sinter quality. Wet material is dried, because water in a molten bath is not a nuisance but an explosion. Each of those is a decision taken at the front end and paid for at the furnace.

The slag system is where a lead smelter is won or lost, and it is a chemistry choice with a thermal consequence. Calcium–iron–silicate slag is the classical system and it is robust, but it melts above 1,100 °C, so the whole furnace runs hot, the off-gas volume is large and the refractory sees a harder life. A soda–iron slag built on sodium carbonate with an iron reductant melts below 800 °C, runs in practice at 850–900 °C, taps thin and easily, and captures roughly 99% of the sulfur charged in battery scrap — which is why it has become the most widely used system in small and medium secondary plants: it is simple to operate, cheap to run and forgiving of a wide range of operating parameters. Its penalty is that it is a matte rather than a true slag because of its sulfur content, that it is soluble and breaks down when it absorbs moisture and carbon dioxide, that unreacted coke and iron particles in it can combust spontaneously, and that its tolerance for sloppy fluxing is exactly what produces the published cases of lead-in-slag above 15%. This page therefore treats the slag as a designed system with a stated composition, a stated basicity window, a stated iron-to-sulfur ratio and a measured lead content — and not as an additive that is thrown in until the melt looks right.

The off-gas train follows from the chemistry and from the enclosure. The furnace is enclosed and held under induced draught, because on a secondary lead furnace the alternative to enclosure is not a clean shop but a contaminated one. The gas leaves the furnace and is post-combusted where the charge carries casing, separator or other organic material, then cooled in a quench or a surface cooler to a temperature the filter media will take, then filtered in a pulse-jet baghouse that captures the lead-bearing particulate as a collected stream rather than a discharge. Where the sulfur is not fully fixed in a soda slag, lime or sodium carbonate can be injected into the gas ahead of the filter and the captured sulfur returns to the furnace with the dust. A rotary furnace in a soda–iron configuration normally needs no scrubber behind its filter, because the sulfur went into the matte; a silicate or sulfide-fed furnace has to handle sulfur dioxide deliberately instead. Around all of it sit the enclosure, the induced-draught fan, the material-handling zones and the housekeeping provisions that keep the fugitive fraction where it can be captured.

The economics of the furnace are dominated by three things and none of them is the purchase price. The first is the lead that leaves with the slag, because slag lead is metal at market price, it recurs at every batch, and on an uncontrolled soda slag it can run above 15% of the slag mass. The second is the reductant, the iron and the soda, which are weighed per batch against the assay and whose consumption is set by the sulfur and oxygen in the feed rather than by the furnace. The third is the refractory, whose life is set by the bath temperature, by the basicity of the slag, by the chloride in the charge and, above all, by whether the furnace is run to a controlled band or pushed to whatever the burner will deliver. A plant that measures its slag assay, its additions and its lining wear per batch can manage all three; a plant that measures only its tonnage cannot manage any of them, and typically discovers the cost of all three in the same year as its first reline.

What the customer receives is bounded and documented: function-tested modules with material certificates; a site interface schedule with every service itemised; installation, electrical, fuel, water and draught checkout supervised; the first production batch run on the customer’s own charge with the flux, reductant, iron and soda schedule written against that charge; operators trained on the actual furnace and signed off against the standard operating procedure; and a performance trial that confirms the bullion grade, the slag lead figure, the batch weight and the lead balance for the material tested. The limits of the station are stated in the same document: it does not refine, it does not separate silver or bismuth, it does not accept wet, unidentified or chloride-heavy material without preparation, and it cannot carry its lining, its filter and its operator on a tonnage below the economic floor — for which the honest answer is a shared toll arrangement or a smaller unit, not a larger furnace run intermittently.

Key Facts

One batch, defined. A batch is one weighed charge to one tapped bullion lot. Furnace time on a short rotary unit is 4–6 hours from a hot start to the tap, but the cycle that decides the plant’s tonnage includes feed preparation, charge make-up, charging under enclosure, reduction, tapping, slag handling and the enclosure reset before the next charge — which is what the shift is actually paid for.
Smelting does not set the grade. Reduction smelting turns lead compounds into lead metal and takes the gangue into a slag. It does not take bullion to 99.97% and it does not separate silver, gold or bismuth from lead. Published operating figures put smelting bullion at about 95% Pb before refining, against 99% Pb for a direct hydrometallurgical route, and the battery industry’s own requirement for soft lead is 99.97% — which is why this page states the bullion grade honestly and hands the grade work to the refining step.
The slag system is the first engineering decision, not the furnace body. A soda–iron slag (sodium carbonate with iron) melts below 800 °C against over 1,100 °C for a calcium–iron–silicate slag, and in real operation the soda–iron bath runs at 850–900 °C. The choice sets the furnace’s thermal duty, its lining grade, the volume of off-gas and whether the plant needs a sulfur fixation step at all.
Slag lead is the number that shows whether the furnace is working. The discards from the furnace types in industrial service run from 2–4% Pb in a short rotary slag and 0.5–2% Pb in an electric furnace reducing reverberatory slag, through under 5% for QSL and 2–3% for KIVCET, to 3–5% for a rotary kiln, 30–55% for a reverberatory slag that still has to be reduced, and above 15% where a soda slag is run with no slag control at all. That last figure is not a furnace type; it is what an uncontrolled flux recipe produces, and it is the loss this station is designed to prevent.
Iron, not more coke, is what unlocks lead sulfate. Battery paste is largely lead sulfate, and carbon alone converts it to lead sulfide rather than to lead — the sulfide then needs iron to release the metal. Adding excess carbon to a sulfate charge does not make more lead; it makes more matte. The reductant and the iron are therefore weighed as two separate additions against the assay, and the iron-to-sulfur ratio is a controlled figure rather than a habit.
Sulfur is fixed in the slag, not emitted. In a soda–iron system roughly 99% of the sulfur charged in battery scrap is captured by the slag, and only about 1% reports to the bag-filter fume — which is why a rotary furnace in that configuration does not need an acid plant or a gas scrubber behind its filter. The corollary is that the slag is a sulfur-bearing material with its own handling requirement, not an inert residue.
The enclosure is designed, and no zero-emission claim is made. Secondary lead smelting is regulated as an enclosed operation: the furnaces, the charging areas, the tappings, the battery breaker, the dryers, the agglomerating furnace and the lead-bearing material handling are enclosed and held at negative pressure at all times and vented to a control device. This station is built to that architecture, with lead compounds designed to stay at or below 1.0 mg per dry standard cubic metre in any process vent and a facility flow-weighted average of 0.20 mg/dscm on a twelve-month rolling basis.
Feed is gated before it is charged, with the reason written down. Battery casing plastic is separated before the furnace feed because chloride from PVC separators attacks the lining and the refractory life is paid for at every reline. Wet charge is dried because water meeting a molten bath flashes at a volume ratio that turns a furnace into a mortar. Low charge levels, bridging and overfilled conveyors are named in the operating rules because each one is a documented fume release. Charges that cannot be identified and assayed are not admitted.
Bullion leaves as metal, with its numbers attached. Charge weight, bullion weight, bullion assay, slag weight and slag assay, filter dust weight and assay, and the reductant and flux additions are recorded per batch, so the lead balance is closed by measurement rather than by difference.
Capacity, power, fuel rate and footprint are engineered. Batch weight, furnace diameter and barrel length, burner rating, fuel rate, off-gas volume, filter area, induced-draught duty, refractory quantity, floor loading and the station footprint are calculated from your feed assay, your tonnage and your building’s services, and stated as figures in the process design package rather than quoted from a fixed model list.
Where the station sits. Between feed preparation and refining. It consumes a prepared charge and produces bullion for the lead refining machine, slag and dust for its own return circuit, and the assay data the whole plant is planned around. Melting already-metallic precious-metal charge in a crucible is a different duty, covered on the precious metal smelting machine page.

Product Core Selling Points

The furnace family is selected by arithmetic, then the arithmetic is published. Feed form and grade, the sulfur and carbon in the charge, the iron the sulfur needs, the batch weight the crane and the charging system can deliver, the sulfur the permit will allow and the building’s fuel, power and draught capacity — those figures choose between a short rotary furnace, a stationary reverberatory, a blast shaft and an oxygen-enriched side-blown unit, and this page shows the reasoning instead of asserting that one family is best for everything.
The smear between smelting and refining is refused. Published purity figures of 99.985% are quoted by suppliers of smelting equipment, but 99.985% is a refined-ingot number and a reduction furnace does not produce it. This page states the bullion grade the furnace actually delivers, states that refining is a separate stage on a separate page, and lets the buyer plan the two together rather than discover the difference at the assay bench.
Slag lead is a design target with a measured result. The target is stated for the furnace type being offered, the slag assay is part of the batch record, and the levers that move the number — iron addition, soda addition, slag basicity, bath temperature, hold time, slag viscosity, tapping practice — are named individually rather than folded into a claim about high recovery.
The reductant and the iron are weighed as two additions. Carbon reduces lead oxide and decomposes lead carbonate; carbon alone converts lead sulfate to sulfide; iron releases the metal from that sulfide. Treating those as one “reductant” charge is the most common way a secondary plant pays for iron twice and still loses lead to the slag, so the two are weighed separately against the assay and recorded separately.
The off-gas train is specified against the sulfur and the organic load, not against a template. Post-combustion or an afterburner for the casing and separator organics in the off-gas, a quench or surface cooler to bring the gas into the filter media’s band, reagent injection ahead of the filter where the sulfur balance asks for it, and a pulse-jet bag filter sized on the calculated volume.
The enclosure and the draught are part of the machine. The furnace, the charging opening, the tap, the forehearth and the slag handling are enclosed and held under induced draught, because a secondary lead furnace that is open to the shop transfers its emission problem into the workforce and its compliance problem into the permit review.
Dust is returned, not disposed of. Bag-filter dust from a lead furnace is lead-bearing material. It is collected in sealed containers, weighed, assayed and returned to the charge by agglomeration or briquetting, and the agglomerating equipment is sized on the dust rate rather than added later when the dust pile has become a problem.
Slag is a product with a return decision. Slag is quenched into granules or cast into blocks, sampled and assayed, and either returned to the furnace as recycle feed, sold on its antimony or tin content, or declared spent and disposed of under the applicable requirement — with the decision recorded rather than left to housekeeping.
The circuit sets the temperature, not the lining’s tolerance. Operating a bath hotter than the slag and the reduction need shortens refractory life, raises the off-gas volume, increases lead volatilisation into the filter and widens the furnace’s emission load. The working band is set from the slag melting behaviour and the reduction kinetics, and the burner is controlled to it.
The pool depth is a set figure. On a furnace with a siphon or a high slag notch, the slag port height sets the molten pool depth, and the pool depth sets the residence time the reduction reaction actually gets. It is designed and held rather than adjusted by eye.
Tapping is separated, not decanted. Bullion taps low and slag taps high, and the two streams separate in a forehearth rather than by cutting a stream. Slag that carries entrained bullion droplets is re-treated, because the lead lost in a slag is the cheapest lead in the plant to recover and the most expensive to leave in.
Feed preparation is treated as part of the plant. Battery breaking and separation, paste desulphurisation where it is chosen, drying and blending, and the plastic separation that keeps chloride out of the lining are scoped as an integrated front end, because a smelting furnace fed unprepared material is a furnace whose slag, off-gas and reline costs are all set by somebody else’s sorting.
The batch record is the product. Charge, additions, temperatures, hold time, bullion weight and assay, slag weight and assay, dust weight and assay, and the closed lead balance are issued per batch, which is what lets a plant demonstrate its yield to its own management, to a customer running a toll campaign, and to a regulator asking about the lead balance of the site.
Compliance is designed in, not argued afterwards. The station’s emission architecture, its enclosure provisions, its housekeeping provisions and its workplace exposure provisions are documented against the applicable secondary lead smelting emission standards and the occupational lead standard, so the plant is declaring measured numbers rather than defending an assumption.
A furnace that should not have been sold is a furnace that will not be reordered. Where the tonnage is too small to carry a furnace, its lining, its filter and its operator, where the lead is present as a dilute solution rather than as a solid, or where the material’s value lies in another metal entirely, this page says so and names the route that actually fits.

Application Scenarios

Secondary lead smelters running spent lead-acid batteries. Broken batteries separated into grid metal and paste, smelted to bullion for the refining kettles, with the casing plastic separated before the feed and the sulfur fixed in the slag.
Battery manufacturers running an in-house recycling loop. Prompt scrap, process rejects and returned batteries smelted inside the plant boundary so the lead returns to the grid casting line instead of leaving the site as a sold residue.
Lead-acid battery collection and consolidation operations. Regional collection points that break and separate batteries and need their own smelting capacity rather than shipping separated paste and grids to a third party.
Automotive and industrial battery recyclers handling the full size range. SLI batteries, traction batteries, motive-power and stationary cells, with the steel-case and forklift types identified at the gate because the case is the handling problem rather than the lead.
Cable and sheathing recovery operations. Lead cable sheathing stripped from copper conductor, smelted to bullion with the copper kept out of the charge so it does not report to the bullion and force a drossing step.
Lead sheet, pipe and flashing recyclers. Architectural and plumbing lead, roofing sheet, radiation shielding and tank linings, which are largely metallic and can be charged directly as a metallics batch.
Wheel-weight, solder and type-metal processors. High-antimony and high-tin lead alloys that are smelted for the alloy rather than for pure lead, with the antimony and tin reported in the bullion assay so the alloy is sold rather than diluted.
Copper and zinc smelters handling lead-bearing intermediates. Lead-bearing residues, leach residues and by-product dusts from a non-ferrous flowsheet, smelted on site so the lead is recovered as metal and does not circulate through the plant as a contaminant.
Precious metal refineries treating lead-collector and lead-bearing material. Bullion and residues in which lead was used as the collector for gold and silver, smelted so the lead is separated as bullion and the precious metals report to a stream the refinery can part — with the precious-metal recovery duty handled on the precious metal recovery and refining system page.
Anode slime and refinery residue processors. Lead-bearing anode slimes, drosses and residues from copper and lead electrorefining, smelted to recover the lead and to concentrate the antimony, bismuth and precious metals into a stream a refinery will buy.
Flue dust and baghouse residue processors. Collected dusts and filter cakes from other smelters and furnaces, agglomerated and smelted rather than stockpiled, which is the classic use of a small rotary unit.
Dross and skim recovery operations. Copper dross, antimonial dross, refining skims and litharge-bearing drosses from kettle refining, smelted for their lead and for their alloying elements.
Shot, ballast and ammunition lead recovery. Range lead, bullet trap material, fishing weights and ballast, which arrives metallic and contaminated with soil, jacket material and moisture, and is therefore screened, dried and charged as a controlled metallics batch.
Industrial sites holding a permitted lead residue. Chemical, glass, ceramics, plastics and electronics operations whose process generates a lead-bearing residue and whose permit makes on-site recovery preferable to off-site consignment.
Sites whose constraint is the permit rather than the tonnage. Operations in a jurisdiction with a strict ambient or stack lead limit, where the furnace and its enclosure, its draught and its filter are sized by the allowable emission rather than by the metal tonnage — which is why the off-gas duty is calculated before the furnace diameter is fixed.
Pilot, laboratory and teaching metallurgy facilities. Small rotary or stationary units used to establish how a particular battery paste, dross or residue behaves on a few hundred kilograms before a production plant is committed, and to train operators on charging, slagging, tapping and the enclosure discipline the full-scale unit will demand.

Applicable Raw Materials

The furnace is fed solid lead-bearing charge, and what decides whether a lot is admitted is its chemistry, its physical form and its identifiable origin rather than its commercial description. Each feed below enters the furnace at the point its condition allows: material that is dry, correctly sized, identified and inside the sulfur and chloride window is charged directly; material that is wet, fine, coated, chloride-bearing or above the antimony limit is dried, agglomerated, blended, separated or routed to a different step first. Output is stated for each feed.

Spent lead-acid battery grid metal. Cast and wrought lead-calcium and lead-antimony grids, straps, posts, terminals and intercell connectors from broken batteries, screened free of paste and case material, charged as the dense metallics fraction of a batch. Output: lead bullion with the antimony content set by the grid alloy, and a low-volume slag.
Lead-acid battery paste. Partially or fully desulphurised paste carrying lead sulfate, lead dioxide, lead monoxide and lead carbonate, agglomerated or briquetted before charging so the draught does not carry it into the duct. Output: lead bullion from the largest single lead fraction in the battery, with the sulfur disposed of into the slag or matte.
Desulphurised paste filter cake. Paste that has been leached with sodium carbonate or sodium hydroxide so that lead sulfate is converted to lead carbonate or lead hydroxide, dewatered in a filter press and dried. Output: a smelting feed that is largely lead oxide and carbonate, with the sulfur discharged as a sodium sulfate liquor rather than carried into the furnace.
Lead carbonate and lead oxide powders. Battery oxide, litharge and leady oxide from battery manufacture, oxide plant bag dust and oxide-bearing sweepings. Output: high-grade bullion, charged under a cover because the powder is the most easily entrained feed the furnace takes.
Lead cable sheathing. Extruded lead and lead-alloy sheathing stripped from power and communications cable. Output: low-antimony bullion, with the copper conductor kept out of the charge so no drossing step is forced.
Lead sheet, pipe, flashing and shielding. Architectural roofing lead, plumbing pipe and traps, radiation shielding, tank and vessel linings and lead foil. Output: bullion charged largely as metallics, with the paint, bitumen and corrosion products taken off in the slag.
Wheel balance weights. Zinc and lead balance weights, screened so the zinc fraction does not enter the lead charge. Output: bullion, with the separated zinc fraction sold or treated on its own route.
Lead-antimony and lead-tin solders and alloys. Solder dross, solder scrap, type metal, bearing metal and wiping metal. Output: alloy-bearing bullion whose antimony and tin are reported in the assay and priced rather than diluted.
Lead drosses, skims and kettle residues. Copper dross, antimonial dross, softening litharge, dezincing residues and the skims from kettle refining, together with the dross-furnace residues generated when recovering the non-lead values from them. Output: recovered lead returned to the refining circuit and a slag that carries the antimony and arsenic out of the metal.
Lead-bearing flue dust and baghouse residues. Collected dust from lead furnaces, sintering machines, dryers and agglomerating units, together with filter cakes from other smelters. Output: recovered lead from a stream that is a product rather than a waste, charged by agglomeration because the material is too fine to charge raw.
Refining and anode slime residues. Lead-bearing anode slimes, slime treatment residues and leach residues from copper and lead electrorefining. Output: bullion plus a matte or speiss that concentrates the bismuth, antimony and precious metals for a downstream refinery.
Spent lead-bearing slag. The 30–55% lead slag from a reverberatory or other first-stage furnace, and the higher-lead slags from older operations, charged as a reducing feed rather than discarded. Output: the lead recovered from the slag into bullion, with the reduced slag declining to the discard band of the furnace being used.
Lead-bearing smelter and steel-plant dusts. Electric arc furnace dust, cupola dust and baghouse catch from other metallurgical operations with a recoverable lead content. Output: recovered lead and a slag whose zinc and chloride content decides whether the material is charged neat or blended.
Lead concentrates and lead-bearing ores. Galena and mixed sulfide concentrates, oxide and carbonate lead ores, and the lead-bearing fractions of complex polymetallic ore, with the ore treated through the front end its mineralogy needs. Output: bullion, a sulfur-bearing off-gas, and a matte carrying the copper and the precious metals.
Zinc plant leach residues. Lead sulfate-bearing residues from zinc electrowinning circuits, which are sulfated material that behaves like battery paste and needs the same iron and carbon treatment. Output: recovered lead and a slag that takes the sulfur and the residual zinc out of the bullion.
Precious-metal lead-collector bullion and residues. Lead bullion and lead-rich residues in which lead was the collector for gold and silver, and the lead-bearing streams from a fire assay or a capture smelt. Output: lead bullion and a precious-metal-bearing stream that goes to the platinum group metal refining equipment or precious-metal refining route rather than being diluted into the lead.
Cathode ray tube and glass lead fractions. The leaded funnel glass and neck fractions of cathode ray tubes, and other leaded glass, charged after the phosphor and coating fractions have been removed. Output: recovered lead, with the glass formers reporting to the slag.
Electronic solder and plated-component scrap. Printed circuit board assemblies with a lead-bearing solder, solder dross from wave and reflow soldering, and lead-tinned components, blended so that the halogen-bearing board material is kept out of the charge. Output: recovered solder lead, with the copper and precious-metal fractions handled on their own routes.
Lead-shot, range and ballistic recovery material. Spent shot, bullet trap material, berm soil fractions and fishing weights, screened of soil and jacket metal and dried before charging. Output: recovered lead, with the jacket metals and the soil fraction separated before the furnace rather than reporting to the slag.
Ballast, counterweight and packing lead. Metallic lead removed from vehicle ballast, machine counterweights, diving weights and packing, often encrusted and mixed with steel. Output: recovered metallic lead, with the ferrous fraction removed by magnet before the charge is made up.
Lead-bearing foundry and machine-shop residues. Machining swarf, casting flash, grinding dust and floor sweepings from lead and lead-alloy fabrication. Output: recovered lead, with the swarf and dust briquetted and the oil-bearing fraction degreased first.
Battery case plastic and separator fractions. Polypropylene case material, polyethylene and AGM separator fractions and ebonite, which are separated from the lead feed before smelting and handled as their own product stream or as a controlled fuel or disposal material. Output: a separated plastic and separator fraction, and a lead feed with the chloride load that would otherwise attack the lining removed from it.
Battery acid and neutralised electrolyte. Sulfuric acid electrolyte drained at breaking, and the neutralised gypsum or sodium sulfate produced from it, which are handled as a liquid effluent and a solid by-product rather than charged to the furnace. Output: a neutralised salt stream for its own disposal or recovery route, and a lead feed containing no free acid and no free moisture.
Feeds admitted only after preparation. Wet or damp charge dried to the dryness criterion; fine paste and dust agglomerated or briquetted; oversized grid and case assemblies cut and separated; chloride-rich material leached, blended down or refused; high-antimony material blended to the bullion specification the plant is selling; oily or painted material degreased or burnt off in a controlled step. Output: a charge the furnace can accept without losing lead to the duct, without destroying its lining and without exceeding the bullion specification.
Feeds routed to a different step before smelting. Material whose lead is present in solution, leachate or rinse water; material whose acid, mercury, cadmium or beryllium content makes it a different class of problem; and material whose antimony, tin or precious-metal content is worth recovering in its own right, which is treated on the flowsheet that suits that metal. Output: a smelting feed that is inside specification, and by-products that are recovered on the route built for them instead of being diluted into a lead slag.
Charges that are not admitted — unidentified or unassayable. Sealed drums, closed containers, unlabelled sacks and any lot that cannot be opened, inspected, identified and sampled before charging. The furnace is the last place on a site to discover what a material contains, and the cost of discovering it there is paid in the lining, the off-gas and the bullion assay. Output: not admitted; opened, identified, sampled and approved first.
Charges that are not admitted — wet, frozen or acid-bearing. Free-draining or dripping charge, ice-bearing material, undrained batteries, wet paste and material carrying free acid. Water entering a bath of molten lead flashes to steam at a volume ratio that turns the furnace into a mortar, and free acid attacks the lining and the ducting while loading the filter with sulfate. Output: not admitted; drained, dried to the dryness criterion and neutralised first.
Charges that are not admitted — chloride-rich and PVC-bearing. Polyvinyl-chloride battery separators and cable insulation, chlorinated plastics, salt-bearing material and any feed whose chloride content is above the window the lining and the off-gas train were designed for. Chloride attacks the refractory, shortens the lining campaign, carries into the bullion and loads the abatement system, and it is the single most common reason a lead furnace relines early. Output: not admitted in bulk; the plastic separated before feed as the battery-breaking requirement demands, and the remainder leached or blended down.
Charges that are not admitted — mercury, cadmium or beryllium bearing. Mercury-contaminated lead, amalgam, mercury-cell residues, cadmium-plated and cadmium-bearing material, and beryllium-bearing alloys. These metals boil or fume below or around lead’s smelting temperature, so the furnace would volatilise them into the off-gas train, which was never sized or permitted for them. Output: not admitted; routed to a dedicated treatment step with its own abatement and monitoring.
Charges that are not admitted — reactive, explosive or oxidiser-bearing. Live or depleted ammunition and primers, sealed gas-cylinder fragments, oxidiser-contaminated dust such as nitrate, chlorate and peroxide residues, and any material that can react with a molten bath rather than dissolve in it. Output: not admitted; made safe under a competent authority’s procedure before any thermal treatment is considered.
Charges that are not admitted — radioactive or naturally occurring radioactive material. Scale, filter cake and dust from oil and gas, mineral sands and other streams that carry naturally occurring radioactive material above the clearance level, and any material found to carry a radioactive source. Output: not admitted; the site’s radiation screening gate decides the route before the material is accepted for storage, let alone for charge.

Finished Products

The station is configured around the products the plant sells or feeds forward, from crude bullion for the refining kettles through to the slag, matte and dust that each have their own market or return route. Where the plant already runs a refining kettle line, an assay bench and a slag storage area, the smelting station is delivered as the furnace, the burner system, the charging arrangement, the flux and reductant handling, the enclosure and the off-gas train; where it does not, those interfaces are inside the scope.

Crude or hard lead bullion. The primary output: charge melted, reduced, fluxed, slagged and tapped as molten metal, with the antimony, copper and bismuth content set by the charge and reported by assay. Output: lead bullion at roughly 95–98% Pb, tapped into bullion trays or transferred hot to the refining kettles.
Soft-lead-bearing bullion for battery manufacture. Bullion produced from a low-antimony grid and paste charge under a slag regime that drives the antimony, arsenic and tin into the slag rather than into the metal. Output: bullion in the low-impurity band that the refining step can take to the 99.97% soft lead the battery industry specifies.
High-antimony and hard lead bullion. Bullion produced under a reducing regime that keeps the antimony in the metal, from a high-antimony grid, dross or alloy charge. Output: antimonial bullion for the alloy market, which is a product rather than an impurity problem.
Antimony-bearing slag. The slag from a soft-bullion regime, carrying the antimony, arsenic and tin that were driven out of the metal. Output: a slag with a recoverable antimony content, sold to an antimony circuit or returned to a reduction furnace.
Matted slag and soda matte. The sulfur-bearing phase produced in a soda–iron system, which behaves as a matte because of its sulfur content and carries the sulfur charged in the battery scrap. Output: a matte that fixes roughly 99% of the feed sulfur, with its lead and antimony content assayed and its destination decided batch by batch.
Discard slag. Slag reduced to the target lead band for the furnace type being run, quenched into granules or cast into blocks. Output: granulated slag within the furnace’s design lead band, assayed before it is declared spent for disposal or sold as aggregate.
Copper matte and speiss. The matte produced where a sulfur or copper-bearing charge is smelted, and the lighter speiss phase that carries arsenic and antimony to the top of the bath. Output: matte and speiss streams sold or toll-treated for their copper, antimony, arsenic and precious-metal content.
Bag-filter dust. The fine particulate captured by the off-gas train, collected in sealed containers under the enclosure regime rather than discharged. Output: a weighed and assayed lead-bearing dust returned to the charge through the agglomerating step.
Agglomerated or briquetted recycle feed. Filter dust, fine paste screenings and floor sweepings consolidated into a chargeable form. Output: a recycle feed that re-enters the furnace without being re-entrained into the duct.
Reclaimed metallic lead from clean scrap. Sheet, pipe, cable sheathing and clean solid lead that can be melted and tapped without a full reduction regime. Output: bullion recovered at a low slag ratio, from a batch that costs less to run than a paste batch.
Batch record and closed lead balance. Charge weight and assay, reductant, iron and flux additions, bath temperature and hold time, bullion weight and assay, slag weight and assay, dust weight and assay, and the difference closed as the measured loss for that batch. Output: a batch whose lead balance can be reconstructed and defended, and a slag lead figure that can be compared against the design target.
Bullion released against assay and ready for refining. Bullion weighed, sampled and released with its assay and its batch number, in a form the kettles can charge directly. Output: a documented handover to the refining stage, on the terms set out on the lead refining machine page.

Lead Smelting Furnace Process Flow

The nine stages below are one full smelting batch, from the feed survey that decides whether a lot is admitted through to a furnace reset with the off-gas train clean and the lining inspected. Stages 3 and 5 are where the batch is actually decided: the reductant, iron and flux weighed at Stage 3 set the slag chemistry that will dissolve the gangue and capture the sulfur, and the reduction at Stage 5 is the only point at which the lead locked in lead sulfate and lead oxide can still be moved into the metal rather than into the slag. Whatever the bullion still contains — copper, antimony, tin, bismuth, silver — is not this station’s business to remove; the grade is set downstream, and that duty is described on the lead refining machine page. Engineering setpoints are fixed during process design against your own feed assay and confirmed on the first production batch.

Lead smelting furnace flow — one full smelting batch, from a surveyed feed to a tapped bullion lot and a measured slag lead figure, with the sulfur fixed in the slag, the dust returned to the charge and the off-gas released through an enclosed, filtered train.

Steps 1 — Feed Survey, Assay and Acceptance Screen. Nothing is charged before the lot has been surveyed, because every figure downstream — the iron the sulfur needs, the carbon the oxides need, the soda the slag needs, the batch weight, the bullion specification and the off-gas duty — is calculated from that survey. The lot is weighed, its form recorded, and its lead, sulfur, carbon, iron, chloride, antimony and moisture content established by sampling, by XRF on a prepared and milled surface, and by a reference determination where the lot is heterogeneous or where the result sits near a commercial or a permit boundary. The acceptance screen is then applied and the reason is written against each excluded fraction: chloride above the lining’s window, moisture above the dryness criterion, an antimony load above the bullion specification being sold, precious-metal content worth recovering separately, or an unidentified container. Where a fraction is diverted, the route sheet names the step it goes to — leaching, drying, blending, plastic separation, a precious-metal circuit or refusal — rather than leaving it on the pad. Reagent and utility input: weighing, milling and sample preparation, XRF and reference analysis, moisture determination and drying test, route sheet and batch record, acceptance checklist. Output: a surveyed and accepted charge with its slag recipe basis, its batch weight and its bullion specification confirmed, or a documented diversion with the reason stated.

Steps 2 — Battery Breaking, Separation and Desulphurisation. Batteries and mixed feed are broken, crushed and separated into grid metal, paste, casing plastic, separator material and electrolyte, and the plastic is separated before anything reaches the furnace because chloride from PVC separators attacks the lining and shortens the refractory campaign that every batch is paying for. Paste may then be desulphurised rather than charged as sulfate: a sodium carbonate or sodium hydroxide leach converts lead sulfate to lead carbonate or lead hydroxide, which has a lower solubility and a completely different behaviour in the furnace, and the sulfur leaves as a sodium sulfate liquor that is treated at the effluent plant instead of being carried into the smelting chemistry. Where desulphurisation is not used, the sulfate is instead fixed in the furnace by the soda–iron slag, which captures roughly 99% of the sulfur charged in battery scrap and leaves about 1% to report to the bag-filter fume. Grid metal is screened free of paste and case material, paste is dewatered and dried to the charge dryness criterion, and the electrolyte is drained, collected and neutralised on its own route. Reagent and utility input: battery breaker and separation plant, hammermill and sink-float or screen classification, plastic and separator separation, sodium carbonate or sodium hydroxide desulphurisation circuit, filter press, dryer, electrolyte collection and neutralisation, grid screening. Output: separated grid metal, a dried and agglomerated paste feed with its sulfur either removed or left for the slag to fix, a clean plastic and separator fraction, and a neutralised electrolyte stream.

Steps 3 — Charge Make-Up and Flux Weighing. This is the stage that decides the slag and therefore the batch, and it is arithmetic rather than judgement. Carbon is weighed against the oxygen in the lead oxides and the carbonates; iron is weighed separately against the sulfur, because carbon alone converts lead sulfate to lead sulfide and it is the iron that then releases the metal from that sulfide — which is why an excess of carbon on a sulfate charge does not produce more lead but more matte; soda ash is weighed as the sulfur binder and the slag former; and limestone, sand or a fluidiser is added where the slag’s melting behaviour or its viscosity requires it. The additions are weighed per batch on a calibrated scale, recorded in the batch record, and staged into the charge rather than thrown in as one mixture, because the order in which the reductant meets the bath changes how much of it is consumed by the atmosphere instead of by the metal. Agglomerated dust and briquetted paste are blended in at a controlled rate so that the recycle load is part of the charge design rather than an uncontrolled addition. Reagent and utility input: soda ash, coke or coal fines, iron turnings or swarf, limestone and sand, fluidiser, calibrated weighing station, agglomerated filter dust and briquetted fines, charge blending and batching record. Output: a weighed and recorded charge with its carbon-to-oxygen and iron-to-sulfur ratios set against the assay, and a slag recipe that can be repeated next batch.

Steps 4 — Furnace Preheat and Enclosed Charging. The furnace is brought to temperature before the charge goes in, and the enclosure, the induced draught and the bag filter are running before the first door is opened, because a cold furnace takes a wet or sulfated charge to the wrong reaction and an unenclosed furnace takes its first emission at the moment the door opens. Charging is done through the sealed door or the enclosed charging arrangement at a controlled rate, so the burner flame is not smothered, the bath is not thermally shocked and the gas volume leaving the furnace stays inside the duty the filter was sized for. The charge is built rather than dumped: dense grid metal first against the lining, then the briquetted paste and agglomerated dust, then the lighter fractions on top where the flame can work on them, with the bath never allowed to bridge across the barrel and never filled above its working volume. The seal, the door packing, the burner alignment, the water and air circuits and the shell temperature are checked at every charge, because a leak at the door is both a lead emission and a false draught reading. Reagent and utility input: burner start-up and preheat to the working band, induced draught and bag filter running, enclosure pressure verified, sealed charging door or enclosed feeder, crane or charging machine, charge fraction sequence, shell-temperature and seal inspection. Output: a preheated furnace with its enclosure and off-gas train verified, and a charge positioned to melt, reduce and mix without bridging.

Steps 5 — Reduction Smelting and Slag Formation. This is the reduction itself, and it runs on a temperature band and a hold time set from the slag chemistry rather than from the operator’s judgement of how the bath looks. The carbon reduces the lead oxides to metal, with the reduction of lead oxide by carbon monoxide being exothermic and therefore self-driving once the bath is hot; the carbonate fraction decomposes well below the bath temperature; and the sulfate fraction is reduced through the sulfide step that the iron completes, releasing the lead and taking the sulfur into the iron sulfide phase. The bath is rotated so that the reaction is limited by chemistry and not by diffusion, the slag is kept fluid enough to release the droplets of metal it has taken up, and the temperature is held inside the working band because overheating buys nothing in reduction and costs refractory, fuel and lead volatilised into the filter. The classical soda–iron bath runs at 850–900 °C, which is why it taps thin and easily and why it demands less of the lining and the burner than a silicate system melting above 1,100 °C. The stage ends when the bath is quiet, the slag is mobile and the design hold time has been met — the three conditions, not the clock alone. Reagent and utility input: burner at the set reduction band, barrel rotation, temperature measurement on the bath and the shell, staged carbon and iron additions, slag fluidity observation, hold-time control, bath sampling where the batch requires it. Output: a reduced bath with the lead fraction in the metal and the gangue and sulfur in a mobile slag, ready to be tapped in one pass.

Steps 6 — Tapping of Bullion, Slag and Matte. Bullion taps low and slag taps high, and the two are separated in a forehearth rather than by trying to cut a single stream. The slag port height sets the molten pool depth that the reduction reaction actually enjoyed, so it is a designed dimension and not an adjustable one; where a siphon is fitted, it holds the pool at a fixed level and lets the bullion run continuously while the slag is held back. The bullion is tapped into trays or a ladle, skimmed of the last of the entrained slag at the spout rather than letting it freeze into the ingot, and transferred hot to the refining kettles where the plant has them, so the heat in the metal is not thrown away and paid for again. The slag is tapped into a granulation launder or into block moulds, and any matte, speiss or copper-bearing phase that has formed is tapped separately, because mixing those streams is what turns a saleable by-product into a diluted waste. Every stream is weighed, identified and sampled at the tap rather than after it has cooled on the floor. Reagent and utility input: tapping tools and lances, bullion trays or ladle, forehearth and skim station, slag granulation water or block moulds, separate matte and speiss tap, weighing and sampling of each stream, hot transfer to the refining kettles. Output: a weighed and sampled bullion lot transferred for refining, a separately tapped slag, and a matte or speiss stream kept apart for its own destination.

Steps 7 — Bullion Skimming, Transfer and Refining Handover. The bullion is skimmed, weighed and released against assay, and this is where the smelting station’s responsibility ends and the refining stage’s begins. The skim taken at the spout and in the transfer ladle is a lead-rich material and returns to the charge rather than being discarded, and the bullion weight is compared with the weighed charge and the slag so the lead balance closes on measured numbers instead of on an assumption that the difference is fine. The bullion assay is established on a sample taken from the tapped metal, and the bullion is released with its batch number, its weight and its assay, in a form the kettles can charge directly. The station does not undertake to raise the grade: it reports what the metal contains — antimony, copper, tin, arsenic, bismuth, silver — and hands it to the stage that removes those elements, which is the refining circuit described on the lead refining machine page. Where the bullion’s silver or precious-metal content justifies it, the handover also routes the refining residues towards the precious-metal circuit rather than into a slag. Reagent and utility input: skim return to charge, calibrated bullion balance, sample preparation and assay, batch number and weight marking, release documentation, hot transfer or bullion tray handling, handover record. Output: a bullion lot released against assay with its batch record attached, and a documented handover to the refining stage.

Steps 8 — Slag Granulation, Assay and Return Decision. The slag is the largest single stream leaving the furnace and it is treated as a product with a decision attached. It is quenched into granules or cast into blocks so that any metallic lead caught in the viscous slag settles out and is reclaimed; it is cooled, crushed, milled and sampled; and its lead content is determined and compared with the design target for the furnace type. The comparison drives the decision: a slag inside its target band is declared and its destination set; a slag above target is returned to the furnace as a reducing feed with the iron and carbon its assay calls for, and the reason for the excursion — an iron addition short of the sulfur, a bath run too cold, a hold time cut short, a slag too viscous to release its droplets, a tapping practice that dragged metal over the notch — is identified and corrected rather than repeated. Slag is also returned where it carries antimony or tin worth recovering, and it is declared spent only when its measured content says so, with the disposal route documented. Soda slags have their own handling requirement because the sodium compounds are soluble and break down as the slag absorbs moisture and carbon dioxide, and because unreacted coke and iron in the slag can combust. Reagent and utility input: granulation water circuit or block moulds, cooling and crushing, mill and sample preparation, lead and antimony assay, return-to-charge batching, spent-slag declaration and disposal record. Output: a granulated or blocked slag with a measured lead content and a recorded decision — return, sale on its antimony or tin content, or declared spent.

Steps 9 — Off-Gas Cooling, Dedusting and Furnace Reset. The batch closes with the off-gas train cleaned, the dust accounted for and the furnace returned to a state the next charge can start from. The gas leaves the furnace, is post-combusted to burn out the organic load that comes with case and separator material, is cooled in a quench or a surface cooler to a temperature the filter media will accept, and is filtered in a pulse-jet baghouse that captures the lead-bearing particulate as a collected stream. Where the sulfur is not fully fixed in the slag, lime or sodium carbonate is injected ahead of the filter and the captured sulfur returns to the furnace with the dust; the dust itself is drawn off into sealed containers, weighed and assayed, and routed to the agglomerating step so that the fine fraction re-enters the charge instead of accumulating on the site or leaving it. The fan duty, the enclosure pressure, the filter differential pressure and the dust weight are recorded per batch, because a rising differential pressure or a falling enclosure pressure is how a bag failure and an emission problem announce themselves before a stack sample does. The furnace is then inspected — lining thickness and hot spots, the tap and the slag notch, the burner and its quarl, the seal and the door, the drive and the trunnion bearings — the slag and dust areas are cleaned with a vacuum system rather than by dry sweeping or compressed air, and the batch record is closed. Reagent and utility input: post-combustion or afterburner, quench or surface cooler, reagent injection ahead of the filter, pulse-jet bag filter and bag inspection, induced-draught fan, sealed dust collection and weighing, vacuum housekeeping, lining and burner inspection, batch record closure. Output: a cleaned off-gas train with its dust weighed and returned, a documented lining and equipment inspection, and a closed batch record for the furnace to start the next charge from.

Product Structure (Main Equipment)

The station is assembled from the seven module groups below. Materials are selected for the two environments the unit actually lives in — a bath of molten lead and sulfur-bearing slag on one side, and a working shop with a lead-in-air limit on the other: the furnace shell in boiler-quality steel plate, the lining in chrome–magnesite and magnesia–chrome brick at the slag line and high-alumina brick in the upper barrel, the burner and its quarl in heat-resistant alloy, the tap and rake tooling in refractory-coated steel, the ducting in stainless steel at the hot end, the filter media selected for lead-bearing fume, and the enclosure, the hooding and the containers in mild steel with sealed joints.

Furnace body, drive and lining

Short rotary furnace body. A horizontal refractory-lined drum on a fabricated steel shell, mounted on trunnion rollers with a riding ring, charged through a sealed door at one end and tapped at the other, with the barrel length, internal diameter and working volume set by the batch weight and the charge’s bulk density. Output: a mixing reduction vessel whose rotation keeps the bath homogeneous and the reaction off diffusion control.
Rotation drive and variable speed. A geared drive rated for the loaded barrel and the slag’s tendency to stick, with the slow speed used during melting and the higher speed used to work the bath and release the metal droplets from a viscous slag. Output: a bath that is mixed to the degree the slag chemistry needs rather than to whatever a fixed speed happens to give.
Replaceable refractory lining. Chrome–magnesite or magnesia–chrome brick at the slag line and the burner zone, high-alumina brick in the upper barrel, with the grade selected for litharge and soda attack and the thickness set for a defined campaign. Output: a lining with a known campaign length and a reline that is planned rather than forced by a failure.
Furnace shell and shell-temperature monitoring. A steel shell with thermocouples or a thermal scan arrangement at the hot zones, because a lining that has worn thin announces itself as a rising shell temperature long before it announces itself as a leak. Output: a lining wear pattern that is trended per campaign instead of discovered at the tap.
Stationary, reverberatory, blast and side-blown variants. The same station architecture offered with a stationary hearth, a vertical shaft with tuyeres and its sinter front end, or an oxygen-enriched side-blown or lance vessel, quoted where the feed, the tonnage or the sulfur product justifies the different furnace and stated with the second-stage duty each of those brings with it. Output: a furnace family matched to the flowsheet, with its own front end and its own slag consequences declared.

Burner, combustion and fuel train

Burner rated for the melt-down duty. An air-fuel or oxy-fuel burner sized on the charge’s thermal requirement rather than on the furnace’s volume, in natural gas, LPG, diesel or dual-fuel form, with the flame shape arranged so it works the bath rather than the roof. Output: a melt-down rate that matches the batch rhythm instead of extending it.
Fuel and combustion control. Ratio control with fuel, air and oxygen trim, a flame-failure safeguard, and the ability to hold a low-fire setting during the reduction phase when the reaction is supplying part of its own heat. Output: a bath held inside the working band instead of being driven past it by a burner left on one setting.
Post-combustion or afterburner. A combustion chamber that burns out the organic load carried by the off-gas when the charge includes case, separator, ebonite or other organic material, sized on the organic fraction of the charge rather than on the metal tonnage. Output: an off-gas whose organics are destroyed before the filter rather than deposited in the duct and the bags.
Oxygen enrichment provisions. Oxygen trim or enrichment available where the sulfur product, the melt rate or the off-gas volume calls for it, with the enrichment level set against the permitted gas volume rather than at the maximum the burner will take. Output: a shorter melt cycle with a smaller off-gas volume, at a consumption rate stated per batch.
Burner quarl, refractory and access. A replaceable quarl, a burner that can be withdrawn and inspected without dismantling the shell, and a sight port for observing the bath and the slag without opening the furnace. Output: a burner that can be serviced on a schedule without an unplanned shutdown.

Charging, enclosure and material handling

Sealed charging door or enclosed feeder. A charging arrangement that opens only into an induced draught, so the emission at the moment of charging is captured rather than released into the shop, with the door area and the feeder hopper inside the enclosure. Output: a charging operation that does not produce the fugitive release it would produce in an open furnace.
Total enclosure and induced draught. The furnace, its charging area, its tappings, the battery breaker, the dryers, the agglomerating unit and the lead-bearing material handling each enclosed and kept at negative pressure at all times, with the draught sized on the enclosure volume and the openings. Output: a station whose fugitive fraction is captured at source and whose workplace air is a designed condition rather than a hope.
Charge preparation and batching area. Screens, magnets, a drying arrangement where the feed needs it, briquetting or agglomeration for fines and dust, a calibrated weighing station, and a mixed-feed bunker under its own extraction. Output: a charge built to a recipe and recorded, from feed that has been dried, screened, de-ferroused and blended.
Battery breaking and separation front end. A breaker, a hammermill, screening or sink-float separation, a plastic and separator separation stage, a paste dewatering and drying stage, and an electrolyte drain and collection arrangement, delivered as the integrated front end where the plant is processing whole batteries. Output: separated grid metal, dried paste and clean plastic, with the electrolyte on its own treatment route.
Crane, charging machine and working platform. Handling equipment rated for the charge and the bullion tray weights, with the platform positioned so the operator works at the enclosure openings rather than leaning over the bath. Output: a charging and tapping operation done from a designed position instead of from wherever the operator can reach.

Tap, forehearth and slag handling

Tap hole, slag notch and siphon. A bullion tap at the low point, a slag notch or siphon whose height sets the molten pool depth, and a forehearth where the two streams separate with the skim returned to the charge. Output: bullion and slag separated as designed streams, with the pool depth held at the value the reduction was designed around.
Bullion trays, ladle and hot-transfer arrangement. Bullion trays sized so a tray is a weighable lot, or a ladle and a transfer route that carries the metal hot to the refining kettles. Output: bullion delivered to refining without being re-melted from cold.
Slag granulation or block casting. A water granulation launder with a recycled water circuit, or block moulds where granulation is not wanted, arranged so the slag cools under control and the entrained metal has the chance to settle out. Output: a slag that can be sampled representatively and returned, sold or declared spent on measured numbers.
Matte and speiss separation. A separate tap and a separate container for the matte, copper-bearing or speiss phase, with its own weighing and sampling. Output: a by-product stream sold or toll-treated for its copper, antimony and precious-metal content instead of diluted into the discard slag.
Slag handling and storage. A cooling and crushing arrangement, a mill for sample preparation, and a covered storage area under its own drainage and dust control for the slag awaiting its decision. Output: slag stored and handled without becoming a fugitive dust source of its own.

Off-gas cooling, dedusting and abatement

Quench or surface cooler. A gas cooler that brings the off-gas into the filter media’s rated temperature band, with the cooling duty calculated from the burner load, the post-combustion duty and the infiltrated air volume. Output: a filter inlet temperature that is controlled rather than dependent on the batch and the ambient weather.
Pulse-jet bag filter sized for lead-bearing fume. A fabric filter with a media selected for fine lead-bearing particulate, a cleaning cycle that does not drive the collected dust back through the bags, and a differential-pressure arrangement that shows the cleaning cycle working. Output: lead-bearing particulate captured as a collected stream, with the differential pressure as the first indicator of a bag problem.
Reagent injection ahead of the filter. Lime or sodium carbonate injection where the sulfur is not fully fixed in the slag, so the sulfur is captured with the dust and returned to the furnace rather than released. Output: a sulfur-handling route that is part of the furnace’s own circuit where the chemistry allows it.
Induced-draught fan and ducting. A fan sized on the total system volume with the margin the enclosure needs, and ducting in stainless steel at the hot end, arranged with the access and the clean-outs a lead-bearing duct requires. Output: an enclosure that holds its negative pressure with every door and tap open, rather than only when the furnace is idle.
Scrubber or acid-gas stage where the charge demands it. An absorption stage for the sulfur dioxide that a silicate or sulfide-fed furnace produces, and the reagent preparation and liquor handling that go with it, added where the charge chemistry produces acid gas and not as a standard fit. Output: an abatement train matched to the charge, with the treatment route declared rather than left to the permit application.
Emission monitoring provisions. Sampling ports, a measurement platform and the instrumentation arrangements needed for the periodic or continuous measurement of lead compounds in the process vents, together with the flow data that the facility flow-weighted average is calculated from. Output: the data required to demonstrate the stack limit and the facility average instead of arguing about a single test.

Instrumentation, control, dust return and the batch record

PLC control with a staged batch recipe. A staged sequence for preheat, charging, melt-down, reduction, tapping and shutdown, running against the batch recipe rather than the operator’s memory, with a manual mode reserved for slagging, skimming, tapping and sampling. Output: batches that are reproducible across shifts and a recipe that can be revised from a record rather than from an opinion.
Bath and shell temperature measurement. An immersion thermocouple or a lance-mounted arrangement for the bath and an infrared or thermocouple scan for the shell, with the bath reading controlling the burner and the shell reading trended against a warning threshold. Output: a reduction held inside its working band and a lining whose wear is visible in the trend.
Alarm and interlock set. Burner flame failure, off-gas temperature high, filter differential pressure high, induced-draught failure, enclosure pressure loss, cooling-water loss, rotation-drive fault, low charge level and an emergency stop, each with a defined trip action. Output: a fault that stops the batch instead of quietly emptying the filter’s collection into the shop.
Agglomerating or briquetting unit for dust return. A unit sized on the dust rate from the filter, with the binder and the mixing arrangement that turns a fine lead-bearing dust into a chargeable feed. Output: the filter dust returned to the furnace as part of the charge design rather than accumulated as a consignment.
Dust collection, weighing and sealed handling. Sealed containers, a weighing station and a dust area under negative pressure, because the dust from a lead furnace is the finest and most easily dispersed lead on the site. Output: a dust stream weighed and assayed per batch and returned under control.
Weighing, sampling and the batch record. Calibrated balances for the charge and for each product stream, sample preparation at the tap, and a batch record that closes charge, additions, bullion, slag, matte and dust against one another. Output: a lead balance per batch and a slag lead figure that can be compared with the design target.
Workplace provisions. Enclosure and local exhaust ventilation at the charging, tapping and casting positions, supplied-air islands at the tap stations, positive-pressure filtered cabs on mobile equipment, HEPA vacuum housekeeping and the change, wash and eating arrangements the occupational lead standard requires. Output: a station where the exposure controls are part of the delivery rather than a later purchase.

Product Features

A published reason for every furnace family. Short rotary, stationary reverberatory, blast shaft and oxygen-enriched side-blown units are separated on the page by the feed, the tonnage, the sulfur product and the second-stage duty each one brings, so the buyer can see why a family is being offered rather than being told it is the best one.
The bullion grade is stated honestly and the refining boundary is drawn. The page says in its first paragraph that a smelting furnace produces bullion at about 95–98% Pb and does not refine it, so a buyer does not purchase a smelting unit expecting a 99.97% soft-lead product, and so the refining stage can be planned and bought as the separate duty it is.
The slag is designed as a system, not dosed as an additive. Slag type, composition, basicity window, iron-to-sulfur ratio and reductant quantity are calculated from the feed assay and recorded per batch, which is what separates a furnace running at 2–4% lead in slag from one running above 15% on the same feed.
Carbon and iron are weighed as two separate additions. The page states the reaction sequence plainly — carbon reduces the oxides and converts lead sulfate to sulfide, iron releases the metal from that sulfide — and rejects the excess-carbon habit because on a sulfate charge it produces matte rather than lead.
Slag lead is a design target with a measured result and named levers. The target band is stated for the furnace being offered, the slag is assayed every batch, and the levers that move it — iron addition, soda addition, slag viscosity, bath temperature, hold time, tapping practice — are listed so an excursion can be corrected rather than repeated.
The sulfur is put somewhere on purpose. A soda–iron system captures roughly 99% of the battery-scrap sulfur in the matte and needs no scrubber behind its filter; a silicate or sulfide-fed system must handle sulfur dioxide in the off-gas. The page states which route the plant is buying rather than implying the problem has disappeared.
The enclosure and the draught are part of the machine. The furnace, the charging opening, the tappings, the breaker, the dryers, the agglomerating unit and the material handling are enclosed and held at negative pressure, because on a secondary lead furnace an open door is an emission, a workplace exposure and a permit consequence in one act.
The off-gas train is sized on a calculation. Post-combustion for the organic load, a quench or surface cooler to the filter media’s band, reagent injection where the sulfur balance asks for it, and a pulse-jet bag filter sized on the calculated volume from the burner, the reaction and the infiltration — not on a template matched to the furnace’s tonnage.
Filter dust is returned rather than accumulated. The dust is collected sealed, weighed and assayed per batch, and returned to the charge through an agglomerating unit sized on the dust rate, which turns the finest and most easily dispersed lead on the site into a controlled input.
Slag is given a decision instead of a pile. Every slag batch is quenched or blocked, sampled, assayed against the target and formally declared as return feed, sale material or spent residue, with the disposal route documented.
The pool depth is a designed dimension. On a furnace with a slag notch or a siphon, the slag port height sets the molten pool the reduction actually gets, so the residence time is designed rather than left to how full the furnace happens to be.
Tapping separates streams instead of decanting one. Bullion low, slag high, matte and speiss separately, each stream weighed and sampled at the tap, with the skim at the spout returning to the charge instead of being lost or re-melted.
Chloride is treated as a lining input. Battery casing plastic is separated before furnace feed, as the secondary lead emission architecture requires and as refractory life demands, and chloride-rich material is leached, blended down or refused rather than charged and paid for at the next reline.
A feed gate with mechanisms rather than warnings. The charges this station refuses — unidentified containers, wet or acid-bearing material, chloride-rich plastics, mercury, cadmium and beryllium bearing feeds, reactive and oxidiser-bearing material, radioactive material — are listed with the physical reason each one is excluded, so the rule can be applied at the gate by a receiving clerk rather than escalated to a sales contact after delivery.
Water is not used for dust suppression where it matters. The page follows the smelting-area practice that water is not used for dust suppression on lead furnace floors, because of oxide fires and the consequence of water meeting molten lead, and relies on enclosure, extraction, vacuuming and a HEPA-filtered cleaning regime instead.
Charging faults are named as emission events. Bridging, a low charge level and overfilled conveyors or feeders are listed as the three operating conditions that release fume, with the control for each, because on this duty the difference between a compliant day and an exceeded one is usually an operating habit rather than a design failure.
Shell temperature is trended so lining wear is visible. Thermocouples or a thermal scan at the hot zones give a lining campaign a visible wear curve, which is what lets a reline be scheduled against production rather than driven by a leak.
The batch record closes on measured streams. Charge, additions, bath temperature and hold time, bullion weight and assay, slag weight and assay, dust weight and assay, and the difference reported as the measured loss — which is what lets a plant demonstrate its yield to its own management, to a toll customer and to a regulator asking about the site’s lead balance.
Workplace controls arrive with the machine. Enclosure, local exhaust ventilation at the charging, tapping and casting positions, supplied-air islands at the tap stations, positive-pressure filtered cabs, HEPA vacuum housekeeping and the change, wash and eating arrangements required by the occupational lead standard are part of the delivery scope rather than a later retrofit.
Compliance is documented rather than asserted. The emission architecture and the workplace provisions are provided as design data with the measurements they rest on, so the plant’s permit application, its periodic stack testing and its exposure monitoring are supported by drawings and figures instead of by a supplier’s assurance.
Materials are chosen for the two environments the machine lives in. Boiler-quality steel plate shell, chrome–magnesite and high-alumina refractories, burners and quarls in heat-resistant alloy, stainless ducting at the hot end, media selected for lead-bearing fume, and sealed containers and enclosures throughout the material-handling side.
The station arrives as modules and leaves as a working plant. Furnace, drive and lining, burner train, charging and enclosure, front-end feed preparation, off-gas train, dust return, slag handling and the batch record arrive function-tested, and installation, the first production batch on the customer’s own feed and operator training are supervised.

Technical Parameters And Specifications

The figures below are the standard design basis and are confirmed or adjusted during process design once the feed survey is complete. Batch weight, furnace diameter and barrel length, burner rating, fuel rate, off-gas volume, filter area, draught duty, refractory quantity, lining campaign, floor loading and the station footprint are engineered to your feed assay, your lead-bearing tonnage, your shift pattern and your building’s fuel, power and draught capacity rather than taken from a catalogue of fixed models. Emission and exposure figures are quoted from the applicable secondary lead smelting and occupational lead standards as the design targets the station is built to.

Lead smelting furnace — technical parameters and specifications.

Parameter	Specification
Station type	Lead smelting station: reduction furnace with its burner and combustion train, charge preparation and batching area, sealed enclosure with induced draught, off-gas cooling and filtration, dust return, slag handling, workplace exposure controls and the batch record
Furnace family	Short rotary furnace as the standard unit for secondary lead; stationary reverberatory, blast shaft and oxygen-enriched side-blown or lance variants quoted where the feed, the tonnage or the sulfur product requires them, each with its second-stage duty declared
Applicable feed state	Solid lead-bearing material in oxide, sulfate, carbonate, sulfide or metallic form — battery grids and paste, drosses, skims, flue dusts, slags, leach residues, solders, sheathing, sheet and lead-bearing concentrates
Capacity	Engineered to your lead-bearing tonnage per shift and per day, with the batch weight, the charge volume and the number of batches per shift calculated and stated as a figure in the process design package rather than selected from a model list
Batch cycle	4–6 hours of furnace time per batch as the published range for a short rotary furnace, with the total cycle from feed preparation through charging, reduction, tapping, slag handling and reset engineered against your own feed and shift pattern
Furnace geometry	Horizontal refractory-lined drum on trunnion rollers with a sealed charging end and a tap end; internal diameter, barrel length and working volume set by the batch weight and the charge bulk density
Rotation	360° rotation at variable speed, with a slow speed for melting and a higher speed for working the bath and releasing metal droplets from the slag
Burner	Air-fuel or oxy-fuel burner rated on the charge’s thermal requirement; natural gas, LPG, diesel or dual-fuel; oxygen enrichment available, with the enrichment level set against the permitted gas volume
Fuel consumption	Engineered per batch from the charge’s thermal requirement, the moisture content, the reduction heat balance and your own fuel price, and stated in the process design package rather than quoted as a single reference figure
Working temperature band	1,000–1,400 °C for the short rotary duty; a calcium–iron–silicate slag system runs 950–1,400 °C depending on furnace and slag matrix; a soda–iron slag melts below 800 °C and runs at 850–900 °C in normal operation
Temperature control	Immersion thermocouple or lance-mounted measurement on the bath controlling the burner, plus an infrared or thermocouple scan of the shell trended against a warning threshold
Refractory lining	Chrome–magnesite or magnesia–chrome brick at the slag line and burner zone, high-alumina brick in the upper barrel, grade selected for litharge and soda attack; lining thickness set for a defined campaign and the shell temperature trended so wear is visible
Slag system	Soda–iron (sodium carbonate with an iron reductant) as the standard for battery paste, giving a low-melting sulfur-bearing matte; calcium–iron–silicate as the alternative where furnace type or residue leachability governs the choice
Slag chemistry control	Slag composition, basicity window and iron-to-sulfur ratio calculated from the feed assay and recorded per batch, with the slag kept fluid at the bath temperature so it can be tapped and so entrained metal droplets can settle out
Slag lead design target	2–4% Pb in the discard slag as the design target for a short rotary furnace. Published comparison points: 0.5–2% for an electric furnace reducing reverberatory slag, under 5% for QSL, 2–3% for KIVCET, 3–5% for a rotary kiln, 30–55% for a reverberatory slag still requiring reduction, and above 15% for a soda slag run without slag control
Reductant and flux addition	Soda ash as sulfur binder and slag former, coke or coal fines as the primary reductant, iron turnings, swarf or chips weighed separately against the sulfur, limestone or sand as slag conditioner, and a fluidiser where the slag must stay mobile; every addition weighed per batch on a calibrated scale
Desulphurisation option	Upstream paste desulphurisation with sodium carbonate or sodium hydroxide, converting lead sulfate to lead carbonate or lead hydroxide and discharging the sulfur as a sodium sulfate liquor; the alternative is to fix the sulfur in the furnace slag
Sulfur capture	Roughly 99% of the sulfur charged in battery scrap is captured by a soda–iron slag, with about 1% reporting to the bag-filter fume; a silicate or sulfide-fed furnace handles sulfur dioxide deliberately in a scrubber or an acid route
Charging	Sealed charging door or enclosed feeder opening into induced draught; charge fraction sequence designed so the bath does not bridge and is not filled above its working volume
Tapping	Bullion tapped at the low point, slag tapped or siphoned high with the slag port height setting the molten pool depth, forehearth separation of the two streams, and a separate tap for matte or speiss
Bullion grade from smelting	Crude or hard lead bullion at roughly 95–98% Pb, with antimony, copper, tin, bismuth and silver reporting to the metal and confirmed by assay of the tapped lot; grade is set downstream by kettle refining and, where required, electrolytic refining
Downstream refining interface	Bullion weighed, sampled and released with its batch number and assay for direct charging to the refining kettles; the refining duty, its temperatures and its reagent schedule are covered on the lead refining machine page
Off-gas handling	Post-combustion or afterburner for the organic load, quench or surface cooler to the filter media’s temperature band, optional lime or sodium carbonate injection ahead of the filter, and a pulse-jet bag filter with a media selected for lead-bearing fume
Lead emission design target	Lead compounds designed to stay at or below 1.0 mg per dry standard cubic metre in any process vent, and a facility flow-weighted average at or below 0.20 mg/dscm on a twelve-month rolling average calculated monthly, in line with the secondary lead smelting emission standard; a new plant is specified at 0.20 mg/dscm per process vent
Particulate emission design target	Particulate matter designed to stay at or below 50 mg per dry standard cubic metre with opacity below 20 percent for the furnace categories covered by the new source performance standards, and tighter limits applying to sources built or modified after the dates those standards specify
Total enclosure	Furnace, charging area, tappings and moulds, battery breaker, dryers, agglomerating unit, lead-bearing material handling and filter-dust processing areas each enclosed and held at negative pressure at all times and vented to a control device, following the enclosure architecture of the secondary lead smelting emission standard
Pre-furnace separation	Battery casing plastic separated from the feed before it enters a furnace, both as the pre-furnace separation requirement of that standard and to keep chloride out of the refractory
Dust return	Bag-filter dust collected sealed, weighed and assayed per batch and returned to the charge through an agglomerating or briquetting unit sized on the dust rate, using the agglomerating step the regulation defines for baghouse dust
Slag handling	Slag quenched into granules or cast into blocks so entrained metal can settle, then cooled, crushed, milled, sampled and assayed before its return, sale or spent declaration
Instrumentation and control	PLC with a staged batch recipe for preheat, charging, melt-down, reduction, tapping and shutdown, a manual mode for slagging, skimming, tapping and sampling, and trended bath, shell, draught and filter records
Alarm and interlock set	Burner flame failure, off-gas temperature high, filter differential pressure high, induced-draught failure, enclosure pressure loss, cooling-water loss, rotation-drive fault, low charge level and emergency stop, each with a defined trip action
Workplace exposure design basis	Designed to hold airborne lead exposure below the occupational permissible exposure limit of 50 micrograms per cubic metre as an eight-hour time-weighted average and to work inside the 30 microgram action level, with enclosure, ventilation, supplied-air and housekeeping provisions and support for the medical surveillance the standard requires
Site services	Electrical supply and rating, fuel supply pressure and flow, cooling-water flow and inlet temperature, compressed air, floor loading and headroom for the barrel and the charging machine, containment and drainage, and the off-gas route to atmosphere — each issued as a schedule with a value against the line
Duty and cycle	Engineered for continuous multi-shift operation with a batch rhythm set by your tonnage and the furnace campaign set by your slag chemistry and chloride load, and stated as a figure in the process design package
Materials of construction	Boiler-quality steel plate furnace shell, chrome–magnesite and high-alumina refractories, heat-resistant alloy burner and quarl, stainless steel ducting at the hot end, filter media selected for lead-bearing fume, and sealed mild-steel enclosures, hoods and containers
Installed footprint	Engineered to the furnace size and the site’s available bay, headroom, service routes and off-gas run, and stated as a figure in the process design package
Operating crew	Engineered to your shift structure; the standard crew runs the furnace and burner, the charging and tapping stations, the front-end preparation, the bag filter and dust return, and the slag handling
Mass balance per batch	Charge weight and assay, reductant, iron, soda and flux additions, bath temperature and hold time, bullion weight and assay, slag weight and assay, dust weight and assay, and the difference reported as the measured loss for that batch
Compliance basis	Design basis aligned to the secondary lead smelting national emission standards for hazardous air pollutants (40 CFR Part 63 Subpart X), the new source performance standards for secondary lead smelters (40 CFR Part 60 Subparts L and La), and the occupational lead standard (29 CFR 1910.1025)

Technical Advantages

The reduction is engineered as two reactions, because it is two reactions. Carbon strips oxygen from lead oxide and decomposes lead carbonate; iron breaks the sulfur bond that carbon can only convert to sulfide. A station that treats those as one reductant addition pays for iron it does not need on an oxide-rich charge and loses lead it should have recovered on a sulfate-rich one. Separating the two, weighing both against the assay and recording both per batch is the single largest slag-lead advantage on the page.
The slag is chosen on melting behaviour, not on tradition. A soda–iron slag melting below 800 °C against over 1,100 °C for a silicate slag is not a marginal difference: it changes the burner duty, the fuel rate, the off-gas volume, the refractory grade, the lining campaign and the volume of lead volatilised into the filter. The choice is made in process design from the feed and the permit, with its consequences stated.
Slag lead is managed against a number instead of a hope. The design target is stated for the furnace type being offered, the slag is sampled and assayed every batch, and a deviation triggers a diagnosis of iron addition, slag viscosity, bath temperature, hold time or tapping practice. That is what keeps a plant out of the published band above 15% lead in slag that uncontrolled soda fluxing produces.
Sulfur is deliberately routed. A soda–iron configuration captures roughly 99% of the battery-scrap sulfur in the matte and needs no scrubber behind its filter, which saves a whole abatement train and its reagent cost; a silicate or sulfide-fed configuration must handle sulfur dioxide and is quoted with the scrubber it needs. Either way the sulfur is accounted for on the flowsheet rather than assumed away.
The furnace is enclosed because the alternative is not a clean shop. Total enclosure at negative pressure across the furnace, the charging area, the tappings, the breaker, the dryers, the agglomerating unit and the material handling is the architecture the secondary lead emission standard requires, and it is also the only arrangement in which the fugitive fraction can be captured at all.
The off-gas train is sized from the gas the plant will actually make. Post-combustion duty from the organic content of the charge, cooling duty from the burner and the reaction, filter area from the calculated volume including infiltration, and fan duty from the enclosure openings. A filter sized on the furnace’s tonnage rather than on its gas volume is a filter that runs over its differential-pressure limit from the first week.
Water is kept away from the smelting floor on purpose. The station follows the smelting-area practice that water is not used for dust suppression where oxide and molten lead are present, and relies on enclosure, extraction, vacuuming and HEPA-filtered cleaning instead — which removes a whole class of oxide fire and water-meets-molten-lead incidents from the hazard register.
Dust becomes charge. The finest and most dispersible lead on a smelter site is the bag-filter dust, and this station is designed to collect it sealed, weigh and assay it per batch, and return it through an agglomerating unit sized on the dust rate. That converts the site’s most difficult material into a controlled input and removes the consignment that otherwise grows in a corner.
The lining is monitored rather than trusted. Shell thermocouples or a thermal scan at the slag line and the burner zone give the campaign a visible wear curve, so a reline is scheduled against production instead of being triggered by a leak — and chloride-bearing feed, which is the usual cause of an early reline, is separated or refused at the gate.
The pool depth that the reduction gets is a designed dimension. On a siphon or high-notch furnace the slag port height fixes the molten pool, so the residence time is set at the drawing board and held in operation, rather than being whatever the furnace happens to be filled to on the day.
Every stream is weighed and sampled at the tap. Bullion, slag, matte, speiss and dust each get their own weight, their own sample and their own destination, so the batch’s lead balance closes on measurements and the plant can see which stream is costing it metal instead of estimating a loss at period end.
The bullion leaves hot and the heat is not thrown away. Where the plant runs kettles, bullion is transferred as liquid metal rather than cast, cooled, stacked, re-melted and paid for twice in fuel — an operational saving that a smelting supplier quoting only the furnace will not mention.
Grade work is handed over rather than promised. The station reports the antimony, copper, tin, arsenic, bismuth and silver content of the bullion and hands it to the stage built to remove them. A supplier who quotes a 99.97% or 99.985% product from a smelting furnace is quoting somebody else’s process step, and the buyer discovers that at the assay bench.
Charging faults are treated as emission events with named controls. Bridging, a low charge level and overfilled conveyors or feeders are the three operating conditions that release fume at a lead furnace, and each has a stated control: charge level discipline, negative pressure on the furnace during charging, and a conveyor and feeder filling rule. On this duty, compliance is usually an operating habit rather than a design deficiency.
The workplace provisions are delivered with the machine. Enclosure and local exhaust ventilation at the charging, tapping and casting positions, supplied-air islands at the tap stations, positive-pressure filtered cabs, HEPA vacuum housekeeping and the change, wash and eating arrangements are part of the scope, because a lead smelter’s exposure problem cannot be retrofitted onto a finished furnace.
The feed gate is enforced at the receiving door. The refused classes are defined by physical mechanism — chloride attack, steam explosion, mercury volatilisation, oxidiser reaction, unidentified content — so a receiving clerk can apply the rule without a metallurgist present, and the refused fraction is documented with its reason rather than argued about later.
Compliance is supported with data rather than with assurance. The emission architecture, its design targets and the workplace provisions are issued as drawings, figures and instrument schedules, so the plant’s permit application, its periodic stack testing and its exposure monitoring rest on the station’s own measurements.
The batch recipe is a document that can be revised. Because additions, temperatures, hold times and stream weights are recorded against every batch, an improvement — a lower iron addition on a changing paste assay, a shorter hold on a warmer bath — can be justified from the record and then made permanent, instead of depending on which operator is on shift.
The economic floor is stated. Below a certain lead-bearing tonnage a furnace cannot carry its lining, its burner, its filter, its draught and its operator, and the honest answers are a smaller unit, a toll arrangement or a different route. A page that sells a full smelting station to an operation that needed a 2-tonne rotary unit is a page that produces an idle furnace and an unhappy buyer.
Everything that decides the plant is available before the order. The feed survey basis, the slag recipe, the batch weight calculation, the off-gas duty, the enclosure layout, the site service schedule and the emission design targets are all issued as documents, so the buyer can cost the whole project — not just the furnace — before committing to it.

Service Process

Step 1 — Feed data and duty review. You provide the feed types and their proportions, an assay or typical analysis covering lead, sulfur, carbon, iron, chloride, antimony, moisture and any precious-metal content, the physical form the feed arrives in, the tonnage per shift, the bullion specification or the refining route you intend to sell into, and the site constraints on fuel, power, draught, floor loading and headroom. We state at this stage whether each feed is chargeable as surveyed or needs drying, screening, agglomeration, plastic separation, desulphurisation, blending or refusal, and whether the tonnage clears the economic floor for a smelting station. Output: a preliminary route statement, the boundary conditions and a clear scope of supply.
Step 2 — Slag recipe and furnace configuration. The slag system, the sodium carbonate, carbon and iron additions, the slag basicity window, the batch weight, the furnace diameter and barrel length, the burner rating, the working temperature band, the off-gas volume, the filter area and the draught duty are calculated from your feed survey, with the slag lead target and the expected bullion grade written down beside them. Output: a configuration proposal with the design basis stated, plus a draft site interface schedule.
Step 3 — Laboratory smelting test on your material. A representative sample of your feed is smelted at bench scale to establish the reduction behaviour, the carbon and iron additions that release the most lead, the slag that forms and its measured lead content, the working temperature band, the bullion grade reached from that feed, and the sulfur distribution between slag and fume on real material rather than on assumption. Output: a test report with a bullion sample and a slag sample returned for your own assay.
Step 4 — Module fabrication and factory function test. Furnace body and lining, drive and trunnion assembly, burner and combustion train, charging door and enclosure, front-end preparation equipment, off-gas cooling and filter, dust return, slag handling and the control system are fabricated, assembled and function-tested before shipment, with material certificates and test records retained and issued. Output: a factory function test record and the shipping documentation set.
Step 5 — Site interface schedule and building preparation. The site services are confirmed against your building together with the foundation and refractory hearth, the floor loading for the loaded furnace and the charging machine, the containment and drainage under the tap and the slag area, the off-gas route to atmosphere and its sampling provisions, the reagent storage, and the dust and slag storage areas. Output: a signed interface schedule, equipment layout and utility connection drawings that your builder can work from.
Step 6 — Installation, enclosure verification and off-gas commissioning. Our engineers supervise setting the furnace and aligning the drive, drying out and bringing up the refractory lining on a controlled heating curve, checking out the burner and combustion controls, verifying the enclosure’s negative pressure with every door, tap and feeder open, balancing the ducting, commissioning the bag filter and the reagent injection, and proving the induced-draught duty against the calculated volume. Output: a mechanically complete station with a measured enclosure pressure and a verified off-gas duty.
Step 7 — First production batch on your own feed. The first batch is run on your feed with the slag recipe, the carbon, iron and soda additions, the temperature band and the hold time written against that feed, and the bullion grade, the slag lead figure, the batch weight and the closed lead balance measured against the process design basis. Output: a commissioned station with its setpoints recorded and a measured slag lead figure for your material.
Step 8 — Operator training and production qualification. Training covers feed survey and the acceptance screen, front-end preparation and plastic separation, charge make-up and the weighing discipline, preheat and enclosed charging, the reduction band and hold time, slag observation and fluidity, tapping and stream separation, dust return and slag handling, enclosure discipline and housekeeping, and the batch record, all taught on the actual furnace. The production trial then confirms the bullion grade, the slag lead figure, the batch weight and the lead balance, and the operators sign off the standard operating procedures. Output: trained operators, a signed SOP set and a performance certificate for the first production batches.
Step 9 — Consumables, spares and continuing process support. The refractory and patching stock, burner spares, filter bags, reagent supply arrangements, tap and rake tooling and the replacement intervals are handed over with the station, spare parts are supplied afterwards, and our engineers stay available for process troubleshooting and for re-specifying the slag recipe, the additions and the temperature band as your feed mix, your battery chemistry or your bullion specification changes. Output: continuing production support with a stocked consumables position and revised procedures as the feed changes.

Warranty And After-Sales Service

Warranty period. Twelve months from successful commissioning or eighteen months from shipment, whichever falls earlier, covering design, manufacture and assembly defects of the supplied equipment. Excluded: consumables such as refractory brick and patching material, burner nozzles and quarls, filter bags, reagents, granulation water treatment consumables and tap and rake tooling, together with damage from misuse or from a feed outside the agreed specification.
Performance commitment. Where the feed matches the tested sample, we stand behind the bullion grade, the slag lead figure, the batch weight and the lead balance established in the process design package, with the production trial as the reference point. Output: a documented performance acceptance attached to the station’s file.
Spare parts and refractory supply. Refractory brick and patching material, burner components and quarls, thermocouples, filter bags and cages, drive and trunnion parts, seal and door components, granulation pump parts and control hardware are quoted at the time of order and held available afterwards, with a recommended on-site stock list issued at handover. Output: an on-site consumables position agreed before the station enters production.
Remote support. Telephone, email and messaging support on operating questions, alarm interpretation, slag behaviour and its assay, burner and temperature problems, tank and filter differential-pressure diagnosis, and the charge recipe, whenever the station is running. Output: same-day response on operating issues.
On-site service. Engineer attendance for warranty faults, process problems and periodical check-ups, with response and attendance times agreed in the contract according to your location. Output: on-site intervention and a service report.
Lining and refractory assessment visits. Periodical measurement or thermal-scan assessment of the lining against its wear curve and its campaign target, together with a written view on how much of the remaining campaign is being consumed by the feed’s chloride load, the bath temperature and the slag basicity — so that reline planning rests on measurement rather than on experience. Output: a reline plan built from your own lining record.
Slag and lead-balance review. A periodical review of the slag assays, the reagent consumption and the closed lead balance against the design targets, with the levers that are actually moving the slag lead figure identified and a revised addition schedule issued where the feed has changed. Output: a revised slag recipe and an updated expectation of the plant’s lead recovery.
Operator retraining and refresher visits. Additional training, refresher sessions and process optimisation visits as the feed mix, the battery chemistry, the bullion specification or the permit condition changes, including re-establishing the reduction parameters after a change of feed supplier. Output: updated training and revised procedure documents.
Feed-mix change support. Where a customer adds a feed type — a new class of dross, a lead-bearing waste from another process, a different battery chemistry — we assess it against the acceptance screen, establish the carbon, iron and soda additions it needs and the slag it will produce, run a bench smelt where the answer is not obvious, and update the route sheet and the batch recipe accordingly. Output: a documented admission decision and a revised recipe for the new feed.
Documentation set. Operation and maintenance manuals, the process design package with the feed survey basis, the slag recipe and the mass balance method, the site interface schedule, equipment layout, electrical, fuel, water and ducting drawings, the alarm and interlock schedule, the batch record and lead balance templates, the spare parts catalogue, the safety and hazard assessment for the reagents and the molten metal, the exposure control and housekeeping procedure, and the emergency response plan. Output: complete documentation handover at commissioning.
Compliance support. Assistance with the emission and enclosure parameter declarations, the stack and ambient monitoring arrangements, the filter and reagent injection performance verification, the exposure monitoring programme and the handling, storage and disposal requirements for the reagents, the slag, the matte and the filter dust. Output: the technical data for your air, effluent and waste permit applications and your periodic compliance reporting.
Lifetime technical support. The process design remains yours, and our engineering team remains available for modification and expansion advice — a second furnace, an added slag reduction stage, a front-end desulphurisation circuit — for the operating life of the station. Output: long-term engineering continuity.

Frequently Asked Questions

What is the difference between lead smelting and lead refining?

Smelting is reduction and refining is separation, and they are two different furnaces with two different chemistries. A lead smelting furnace takes lead that is chemically bound, as sulfate, oxide, carbonate or sulfide in battery paste, dross, dust and residues, and uses carbon and iron at temperature to strip the oxygen and break the sulfur bond so the lead becomes metal. What comes out is lead bullion that sinks to the hearth while a slag forms above it, and that bullion runs at roughly 95 to 98 percent lead because the antimony, copper, tin, bismuth and silver in the feed went into the metal along with the lead. Refining is what raises the grade, and it is a sequence of separations rather than a reduction: copper leaves as a dross on cooling, antimony, arsenic and tin are oxidised out, silver is taken out with zinc, zinc is removed under vacuum, bismuth is removed with calcium and magnesium, and electrolytic refining takes the residue further. A supplier who quotes a 99.985 percent product from a smelting furnace is quoting a refining result, which is why we state the bullion figure honestly and describe the grade work on our lead refining machine page instead.

Which furnace type suits secondary lead, a rotary or a blast furnace?

It depends on the physical form of the feed and on what the plant intends to sell, and the arithmetic is straightforward. A short rotary furnace is the most widely used unit in the secondary lead industry because it is a batch machine that mixes the bath by rotation, accepts fines, pastes, drosses, slags and even whole batteries, and lets the reductant and flux be changed between batches. A blast shaft is chosen where the feed is coarse and permeable and where hard antimonial bullion is the product, but it needs a sinter plant ahead of it and it cannot treat the fines and battery pastes that a rotary unit takes in its stride. A stationary reverberatory furnace is chosen where very large continuous tonnages justify it, at the price of a slag carrying 30 to 55 percent lead that has to be reduced in a second furnace. An oxygen-enriched side-blown or lance furnace is chosen where the feed is high in sulfide and the plant wants the sulfur as a saleable gas. We publish that comparison and then quote the family your feed actually calls for.

What determines the lead content of the slag?

Four things, in order of influence. The first is the slag system and its melting behaviour, because a slag that is not fluid at the bath temperature traps droplets of metal instead of releasing them, and that alone moves a plant from a few percent lead in slag to the double digits. The second is the iron addition, because lead sulfate has to be reduced through a sulfide step and carbon alone will convert the sulfate to sulfide without releasing the metal, so an iron addition short of the sulfur leaves lead locked in the matte. The third is the bath temperature and the hold time, which decide how far the reduction is taken before the tap. The fourth is tapping practice, since entrained metal carried over the notch is a slag lead figure that no chemistry can explain. Published discards run from 0.5 to 2 percent for an electric furnace reducing reverberatory slag, 2 to 4 percent for a short rotary slag, under 5 percent for QSL, 2 to 3 percent for KIVCET and 3 to 5 percent for a rotary kiln, against 30 to 55 percent for an unreduced reverberatory slag and above 15 percent for a soda slag run with no slag control. Our design target for a short rotary furnace is 2 to 4 percent, assayed every batch.

Should a soda-iron slag or a calcium-iron-silicate slag be used?

The trade is between thermal duty and residue behaviour. A soda-iron slag built on sodium carbonate with an iron reductant melts below 800 degrees Celsius against over 1,100 degrees for a silicate slag, and it runs at 850 to 900 degrees in normal operation, which means a smaller burner, less fuel, a lower off-gas volume, less lead volatilised into the filter and an easier life for the refractory. It also captures roughly 99 percent of the sulfur charged in battery scrap, which is why a rotary furnace in that configuration needs no acid plant or scrubber behind its filter. Against that, the product is really a matte because of its sulfur content, the sodium compounds are soluble and break down as the slag absorbs moisture and carbon dioxide, unreacted coke and iron in the slag can combust spontaneously, and the system’s tolerance for loose fluxing is exactly what produces the published cases above 15 percent lead in slag. A calcium-iron-silicate slag is chosen where the residue’s leachability governs the permit or where the furnace type requires it, and it is charged for accordingly.

Does adding more coke recover more lead from lead sulfate?

No, and this is the most expensive misconception in secondary lead smelting. Carbon does reduce lead oxide to lead directly, and it does decompose lead carbonate. But on lead sulfate, carbon does not deliver lead metal: it converts the sulfate to lead sulfide, and that sulfide then has to be reduced by iron before the lead is released. So an excess of coke on a sulfate-rich charge does not make more lead, it makes more matte, and the plant pays for the coke, pays again for the iron it still needs, and then pays a third time for the lead that went into the matte instead of the bullion. Weighing carbon against the oxygen in the charge and iron against the sulfur in the charge, as two separate additions recorded separately, is the discipline that fixes this. On top of that, there is a temperature floor to the sulfate chemistry, since reducing lead sulfate to lead metal with lime present calls for temperatures well above the ordinary lead smelting band, which is a further reason the sulfate is better dealt with by desulphurisation or by a slag system designed to take the sulfur into a matte.

Is battery paste desulphurisation necessary before smelting?

It is not compulsory, but it is a design decision with a clear answer for most plants, and there are two legitimate routes. Desulphurising the paste first, with sodium carbonate or sodium hydroxide, converts lead sulfate into lead carbonate or lead hydroxide, which behaves in the furnace like the rest of the oxide feed and needs no sulfur chemistry at all; the sulfur leaves as a sodium sulfate liquor that the effluent plant treats, and the furnace sees a cleaner, lower-sulfur charge with a smaller off-gas duty and a lighter reagent load. Not desulphurising it means the sulfur has to be handled inside the furnace, which a soda-iron slag does very well, capturing roughly 99 percent of the sulfur in the matte and leaving about 1 percent to the bag-filter fume. The choice turns on the effluent plant’s capacity, the price of the desulphurisation reagents against the price of soda and iron, the sulfur content of the feed, and the permit condition on sulfur dioxide. We cost both routes against your own feed and your own effluent position rather than recommending one as a default.

How is lead fume controlled, and what emission limits apply?

By enclosure first, then by capture, then by filtration. A secondary lead furnace is regulated as an enclosed operation: the furnace, the charging area, the tappings and moulds, the battery breaker, the dryers, the agglomerating unit, the lead-bearing material handling areas and the filter-dust processing areas are each enclosed and held at negative pressure at all times and vented to a control device. The off-gas then goes through post-combustion where the charge carries organic material, a quench or surface cooler to bring it into the filter media’s temperature band, and a pulse-jet bag filter with media selected for lead-bearing fume. On limits, the applicable standard for existing secondary lead sources is 1.0 milligram of lead per dry standard cubic metre in any process vent, with a facility flow-weighted average of 0.20 mg per dry standard cubic metre on a twelve-month rolling average calculated monthly, and a new source is held to 0.20 mg per dry standard cubic metre per process vent. Particulate matter is limited to 50 mg per dry standard cubic metre with opacity below 20 percent for the covered furnace categories under the new source performance standards. Our station is designed to those targets and instrumented so they can be demonstrated.

Can whole batteries be charged to the furnace?

They can, but it is a decision that changes the whole plant, and it is not the configuration we recommend as a default. Charging complete batteries puts the polypropylene case, the separators and any residual electrolyte into the furnace, so the off-gas carries an organic load that has to be destroyed in a post-combustion chamber or an afterburner before the filter, and the plastic that would have been sold as a product becomes fuel instead. The casing also brings chloride, which attacks the refractory and shortens the lining campaign, and the sulfur balance changes because the case material acts as a reductant. Against that, whole-battery charging avoids the cost and the lead-dust exposure of a breaking and separation plant. The regulatory position is decisive for many plants: the secondary lead emission architecture requires a process that separates plastic battery casing material from all automotive batteries before the feed enters a furnace. Our standard station is therefore built around a breaking and separation front end, with plastic and separators removed as saleable products, and a whole-battery configuration is quoted only where the off-gas train is sized for the organics and the permit allows it.

What lead grade does the smelting furnace actually deliver?

Crude or hard lead bullion at roughly 95 to 98 percent lead, with the balance being the antimony, copper, tin, arsenic, bismuth and silver that came in with the feed and reported to the metal rather than to the slag. That figure is a property of reduction smelting rather than of our furnace, and the published comparison is instructive: smelting processes yield about 95 percent lead before refining, against about 99 percent for a direct hydrometallurgical route, and the battery industry’s own requirement for soft lead is 99.97 percent. The distance between 95 and 99.97 is covered by kettle refining and, where bismuth or silver demand it, electrolytic refining; it is not covered by the furnace. What we do commit to is that the bullion grade for your feed is established in a bench smelt before the order and confirmed on the first production batch, that the bullion is weighed and assayed per batch, and that the metal is handed to the refining stage with its numbers attached rather than with an aspiration attached.

Which feed materials are refused, and why?

Six classes, each refused for a physical reason rather than for caution. Unidentified or unassayable lots, because the furnace is the last place on a site to discover what a material contains and the discovery is paid for in the lining, the off-gas and the bullion assay. Wet, frozen or acid-bearing material, because water entering a bath of molten lead flashes to steam at a volume ratio that turns the furnace into a mortar, and free acid attacks the lining and loads the filter with sulfate. Chloride-rich and PVC-bearing feeds, because chloride attacks the refractory, shortens the lining campaign, carries into the bullion and loads the abatement system, and because the emission architecture already requires plastic casing separation before furnace feed. Mercury, cadmium and beryllium bearing material, because those metals boil or fume below or around lead smelting temperatures and would be volatilised into an off-gas train that was never sized or permitted for them. Reactive, explosive and oxidiser-bearing material, because an oxidiser meeting a molten bath reacts violently rather than dissolving in it. And radioactive or naturally occurring radioactive material, which is screened at the gate before the material is accepted for storage, let alone for charge.

How are the furnace capacity and the plant scope decided?

From your tonnage and your feed, in that order, and the figures are stated rather than assumed. The batch weight follows the lead-bearing tonnage per shift divided by the number of batches the shift can run, which is set by the furnace time per batch plus the time for charging, tapping, slag handling and reset. The furnace diameter and barrel length follow the batch weight and the bulk density of the charge, which differs sharply between dense grid metal, loose paste and agglomerated dust. The burner rating follows the thermal requirement of that charge at that moisture content, including the heat the reduction supplies itself. The off-gas volume, filter area and draught duty follow the burner, the post-combustion load and the infiltrated air. The refractory quantity and the lining campaign follow the slag chemistry and the chloride load. Fuel rate, power, water, floor loading and footprint follow from all of it. That is why we publish no model list: the arithmetic is the product, and it is issued as a process design package against your own assay so you can cost the whole plant rather than only the furnace.

What is delivered, installed, tested and warranted?

The station is delivered as function-tested modules with material certificates: the furnace body, drive, lining and shell instrumentation; the burner and combustion train; the sealed charging arrangement and enclosure; the feed preparation and batching area; the off-gas cooling, reagent injection and bag filter; the dust return; the slag handling; and the control system with its batch recipe and alarm schedule. Installation, refractory dry-out, enclosure pressure verification, ducting balance, filter and reagent commissioning and the induced-draught duty check are supervised by our engineers, and the first production batch is run on your own feed with the slag recipe and the temperature band written against that feed. The production trial confirms the bullion grade, the slag lead figure, the batch weight and the closed lead balance, and the operators are trained on the actual furnace and signed off against the standard operating procedures. The warranty runs twelve months from successful commissioning or eighteen months from shipment, whichever falls earlier, covering design, manufacture and assembly defects, with refractory and other consumables excluded. Spare parts, refractory and filter media are quoted at the time of order and held available afterwards, and our engineers remain available for feed changes, slag recipe revisions and reline planning for the operating life of the station.