Silver Refining Machine
— Silver Refining Equipment
Product Overview
The Silver Refining Machine line is the silver-only branch of a precious-metal refinery — the equipment that takes a silver-bearing feed and turns it into assay-certified fine silver, on site, in the operator’s own hands. Silver is unusual among the precious metals in that its largest secondary streams are not bullion: they are sterling and 925 scrap jewellery, coins, cutlery and holloware, silversmith sweeps and polishing dust, photographic and electroplating residues, electronic contact and solder scrap, spent catalysts, and the silver chloride residue that falls out of every precious-metal refining line as soon as chloride meets silver. All of that material is worth far more as refined metal than as scrap, and the refining step is where the value is realised.
Two routes exist, and a properly specified machine uses both where the feed demands it. Chemical reduction is the small-scale, high-selectivity route used for impure silver chloride and low-grade residues: the silver is taken into nitric acid, re-precipitated as silver chloride with hydrochloric acid or sodium chloride to strip the base metals, complexed with ammonia at pH 10–11 to convert it to soluble diamminesilver chloride, and then reduced with hydrazine hydrate at about 50 °C — the reduction rate exceeding 99% and the silver coming out above 99% purity. That product is not yet saleable fine silver, though; it is clean feed for the electrolytic stage. The second route, electrorefining, is the route that reaches the 9999 mark and the route that scales. Crude silver is melted, flux-refined and cast into anode plates; the plates are hung in a silver nitrate electrolyte; direct current drives silver from the anode into solution and out again onto the cathode as crystalline silver powder, while the impurities separate themselves by their own electrochemistry. This is the working principle of the machine: anode preparation → electrolysis → cathode deposition → impurity management.
What separates a good silver refining machine from a mediocre one is almost entirely about the impurities and the current density. Silver is the most electrically conductive of all metals and silver nitrate is a fast, forgiving electrolyte, so the temptation is to push current — and a conventional silver cell is limited to about 250–350 A/m² because higher currents heat the electrolyte, create concentration polarisation between the electrodes, and start carrying impurities across with the deposit. Running at 750 A/m² therefore requires solving three problems at once: keeping the electrolyte cool (the machine includes a chiller that holds the electrolyte temperature down, which stops the solution evaporating and keeps volatilisation and acid consumption low), keeping the silver-ion concentration uniform across the electrode gap (the machine circulates electrolyte parallel to the electrode plates, entering at the bottom and leaving at the top, which suppresses concentration polarisation and lets the cell work at a lower, more stable silver concentration), and keeping the cathode clean of shorts (an automatic stirring and scraping system lifts the silver powder off the cathode continuously, so crystals never bridge the electrode gap). Solved properly, the result is 300 kg/day of silver powder out of a single compact cell that a conventional design would need two or three of — and much less silver sitting in process as electrolyte inventory.
Impurity management is the other half of the design. Tellurium, selenium, copper, bismuth, arsenic and antimony are the classic silver impurities, and they divide into two groups. Base metals stay dissolved in the electrolyte and are bled off and recovered in the spent-electrolyte purification circuit rather than being allowed to build up until the powder fails assay. Gold, platinum, palladium and rhodium do not dissolve at all under silver-refining conditions; they collect in the anode bag as anode slime, which typically runs about 8% of the anode mass and represents the single most valuable by-product of the operation — a typical gold-silver anode slime assays 50–70% gold and 30–40% silver. Anode slime is not waste here: it is routed to nitrate parting or to a second electrolysis pass, and the gold it contains is recovered. On a silver line, the slime revenue is frequently as large as the refining margin on the silver itself.
The gas side is not an accessory either. Every stage of silver refining that touches nitric acid — dissolving crude silver to make electrolyte, boiling anode slime, running the cell — releases nitrogen oxides, which are reddish-brown, corrosive and regulated. The machine is built around that fact rather than adding a scrubber afterwards: the cell is closed with a transparent sealed fume cover with side extraction, so the operator can see the electrodes while the cell exhausts from the side rather than through a large open canopy that interferes with loading; the vapour passes through a fume-condensation system that cools it and recovers the silver carried in it; and the remaining gas goes to a multi-stage NOₓ absorption tower that operates under negative pressure, is sized for inlet loads above 30,000 mg/m³ and holds the outlet below 150 ppm at an absorption efficiency of 99.5% or better. The tower also absorbs chlorine and sulfur dioxide, and its reagents convert the nitrogen oxides to nitrogen, carbon dioxide and water, so there is no secondary pollution stream to dispose of.
The liquid side is closed-loop by design. Silver powder is washed with deionised hot water on a counter-current principle — the first wash water goes back to the electrolyte make-up tank and the second wash water becomes the first wash for the next batch — so wash water is reused rather than discharged. Spent electrolyte is purified and returned to service. The powder is dewatered, dried and sent to melting. And the finishing end — induction melting, vacuum ingot casting, granulation — produces the deliverable form the buyer wants: bars, ingots, granules or grain.
The result is a compact, closed-loop silver refinery that a jeweller, a bullion dealer, a precious-metal recycler, an e-waste processor or a smelter tankhouse can own and operate on site: higher current density than a conventional cell, tighter purity control, far less silver tied up in inventory, slime and spent electrolyte that are recovered rather than written off, and exhaust, effluent and documentation handled inside the same package.
Application Scenarios
Silver refining machines are specified wherever silver leaves a process as an impure metal, an alloy or a residue, and the operator wants the refining margin instead of a refiner’s charge.
- Jewellery manufacturers and repair workshops — refine 925 and sterling scrap, sprues, filings, polishing dust and bench sweeps into fine silver in-house and put the metal straight back into the next production order. Output: 99.99% silver for alloying, plating and re-manufacture.
- Gold and silver refineries — run silver as a dedicated circuit alongside gold, so the silver that comes out of the gold line as silver chloride or doré is finished rather than sold as a by-product. Output: 9999 silver bars and grain.
- Bullion dealers, assay offices and coin dealers — convert bought-in scrap, damaged coins, mixed silver and off-spec lots into assay-certified fine silver with a documentary trail per batch. Output: certified bars and coins stock with a Certificate of Analysis.
- E-waste and PCB recyclers — refine the silver recovered from contacts, solder, MLCCs and printed-circuit-board concentrates into saleable fine silver. Output: 99.99% silver plus gold and palladium from the same feed.
- Photographic, X-ray and imaging processors — recover silver from spent fixer, bleach-fix, hypo and wash-water precipitation sludges, and from film and paper recovery. Output: fine silver ingots from silver-bearing sludges and residues.
- Electroplating and surface-finishing plants — recover silver from spent plating baths, drag-out, anode stubs, strip solutions and ion-exchange resin. Output: recovered fine silver and recyclable electrolyte.
- Electrical, electronics and switchgear manufacturers — reclaim silver from contact tips, silver-tungsten and silver-cadmium contact scrap, brazing alloys, wire and rivet scrap. Output: 9999 silver for reuse or sale.
- Copper and lead smelters and electrorefineries — refine the crude silver and silver-gold alloy that fall out of anode slime treatment into fine silver, and monetise the associated gold. Output: fine silver ingots plus gold-bearing slime to the gold circuit.
- Silver catalyst and chemical plant operators — refine silver from spent silver catalysts, silver oxide and silver-salt process residues. Output: recovered fine silver powder and ingots.
- Solar panel and photovoltaic recyclers — refine the silver recovered from cell metallisation paste and panel processing into fine silver. Output: 99.99% silver from PV recovery circuits.
- Dental, medical and laboratory facilities — refine silver amalgam and alloy scrap, laboratory ware and bench residues. Output: high-purity silver for resale or re-alloying.
- Battery and specialty-recycling operators — refine silver from silver-zinc, silver-oxide and silver-bearing battery scrap and process residues. Output: fine silver plus recoverable base metals.
- Mints, mints’ suppliers and bullion fabricators — refine purchased scrap and returned coins to a consistent fineness before striking. Output: standardised 9999 feedstock and finished bullion.
- Traders, pawnbrokers and cash-for-gold operations — upgrade mixed and contaminated silver lots to a certified grade before resale. Output: assay-certified silver with a batch record.
- Universities, institutes and pilot facilities — bench and pilot silver electrolysis cells for process development, teaching and small-batch work. Output: analytical-grade fine silver.
Applicable Raw Materials
Route selection follows the assay, and the machine accepts a wider envelope than a fixed-output cell because the pre-treatment stage is part of the line rather than a separate purchase.
- Crude silver bullion and crude silver plate — smelted silver from anode slime treatment, cementation or furnace recovery, typically assaying 97% silver and above, which is the direct feed for electrolytic refining. Output: 99.99% silver powder.
- Silver-gold alloy (Ag-Au) from anode slime treatment — the alloy recovered from copper and lead electrorefinery anode slimes, commonly above 90% silver, and the associated doré where gold is present. Output: 99.99% refined silver, with gold recovered from the anode slime.
- Sterling and 925 scrap jewellery, cutlery and holloware — used jewellery, tableware, ornaments and damaged stock, with or without stones, plating and solder attached. Output: fine silver ingots and grain.
- Jewellery manufacturing waste — sprues, gates, filings, saw swarf, polishing dust, buffing waste and floor sweepings. Output: fine silver, with the gold content recovered from slime.
- Silver coins, medallions and commemorative stock — worn, mixed, plated or off-spec coinage, including copper-nickel-clad material after the clad layer is removed. Output: 9999 silver bars.
- Industrial silver sweepings and workshop residues — bench dust, floor sweepings, wipe rags, filter media, crucible and mould residues from silver-working shops. Output: refined fine silver.
- Electrical and electronic silver scrap — contact tips, silver-tungsten and silver-cadmium contacts, relay contacts, brazing alloys, silver wire, ribbon and rivet scrap. Output: 99.99% silver powder and ingots.
- E-waste and PCB precious-metal fractions — the silver-bearing concentrate, alloy or pregnant liquor produced by PCB processing, connector scrap and MLCC residues. Output: fine silver, plus gold, palladium and copper by-products.
- Photographic and imaging residues — silver-bearing sludges from fixer and bleach-fix recovery, hypo precipitation, film ash and spent photochemicals after metallic replacement. Output: fine silver ingots from recovered sludges.
- Spent plating baths, strip solutions and rinse water — silver electroplating and cyanide-free plating electrolytes, drag-out, strip solutions and the silver recovered from rinse water by ion exchange or electrolysis. Output: recovered fine silver and recyclable liquor.
- Silver chloride (AgCl) residue from precious-metal refining — the low-solubility silver chloride produced whenever chloride meets silver in gold, platinum and palladium refining, which is exactly the material the chemical pre-treatment stage exists to handle. Output: silver powder above 99% purity as feed to the electrolytic stage.
- Silver-bearing residues, slags and furnace products — refining residues, slags, ash, crucible and refractory scrap, and the silver recovered from spent catalysts and silver oxide. Output: fine silver after flux refining and anode casting.
- Solar cell and photovoltaic silver — silver paste and metallisation recovered from silicon cell processing and panel recycling. Output: 99.99% silver from PV recovery circuits.
- Silver alloy scrap from brazing, dentistry and battery manufacture — Ag-Cu-Zn, Ag-Cd, dental alloys and silver-oxide battery scrap. Output: fine silver plus recoverable base metals.
- Secondary silver as fine-silver feed for ultra-high purity — where 99.95% silver is available, the same machine is used to reach 99.999% (5N) for electronics and specialty applications. Output: 5N silver powder and grain.
Output Products
Every consignment leaves the line against a Certificate of Analysis, and each output is packaged in the form the buyer wants — powder, grain, granules, ingot or bar.
- Refined fine silver powder — crystalline silver deposited on the cathodes and harvested, washed and dried to a moisture content low enough for direct melting, at purity 99.99% (9999) or better. Output: 9999 silver powder of uniform particle character.
- Fine silver ingots and bars — the dried powder melted and cast into ingots, bars or cast shapes to a specified weight, with vacuum ingot casting and continuous casting available where density and surface finish matter. Output: 9999 silver bars and ingots with batch identification.
- Silver grain, granules and shot — melted and granulated silver for alloying, plating-anode manufacture and continuous-feed melting. Output: uniform silver grain and granules.
- Ultra-high-purity silver (5N) — where the feed is 99.95% silver, the same line is run to 99.999% purity for electronics, sputtering targets and specialty chemistry. Output: 5N silver powder and grain.
- Silver salts and electrolyte-grade solutions — where the buyer wants chemical form, silver nitrate solution and silver salts are produced to specification instead of metal. Output: standardised silver nitrate electrolyte and silver salts.
- Anode slime as a gold-bearing by-product — the insoluble slime that collects in the anode bags, typically around 8% of anode mass and assaying 50–70% gold with 30–40% silver, routed to gold recovery rather than discarded. Output: gold-bearing anode slime and refined gold on the associated circuit.
- Platinum-group metals captured in the slime — platinum, palladium and rhodium reporting to the anode slime from alloy and e-waste feed, separated and refined on the PGM circuit. Output: recovered Pt, Pd and Rh.
- Recovered base-metal by-products — copper, lead, bismuth, tellurium and selenium removed from the electrolyte in the purification circuit and recovered by cementation, precipitation or electrowinning. Output: base-metal salts, cement and cathode.
- Purified, returnable spent electrolyte — spent silver nitrate electrolyte that has been purified and returned to the cell, with the silver drawn out of it recovered rather than dumped. Output: regenerated electrolyte and recovered silver.
- Treated off-gas and closed-loop water — scrubbed exhaust below 150 ppm NOₓ with the scrubber reagent converting the nitrogen oxides to nitrogen, carbon dioxide and water, plus counter-current wash water recirculated to electrolyte make-up. Output: compliant emissions and reused process water.
Silver Refining Machine Process Flow
The line runs as a closed loop around the electrolytic cell: silver goes in as an anode, leaves as cathode powder, and everything that does not leave as product — slime, spent electrolyte, wash water, condenser liquor — is recovered and fed back into the circuit rather than written off. Current density is the pace-setting variable, and everything upstream and downstream of the cell is sized to keep the cell running at its design rate.
Steps 1 — Feed Assay and Route Selection. Incoming material is weighed, representatively sampled and assayed for silver content and for the impurities that decide the route — copper, bismuth, tellurium, selenium, lead, gold and the platinum-group metals. The assay sets two decisions: whether the feed is high enough grade to go straight to anode casting, or whether it needs chemical pre-treatment first, and how the anode bagging and electrolyte purification will be run so that the specific impurities present do not build up and start reporting to the cathode. Output: assay report, batch route sheet and a documented feed weight.
Steps 2 — Low-Grade Feed Pre-Treatment. Impure silver chloride, low-grade silver residues and feed carrying high silica, copper, nickel or cadmium are cleaned before they reach the cell. The material is dissolved in nitric acid, the insoluble residue is filtered off, and the dissolved silver is re-precipitated as silver chloride with hydrochloric acid or sodium chloride so that the base metals stay in the filtrate and leave the circuit. Where the silver is present as chloride, the washed silver chloride is slurried in water, ammonia is added to bring the pH to about 10–11 so that the silver converts to soluble diamminesilver chloride while base-metal impurities hydrolyse and precipitate, and the filtered silver solution is warmed to roughly 50 °C and reduced with 40–80% hydrazine hydrate at a silver-to-hydrazine mass ratio of about 1 : 0.3–0.4 over roughly 30 minutes, giving a reduction rate above 99% and a silver product above 99% purity as clean feed for anode casting. Output: clean silver powder or silver chloride, and a base-metal filtrate routed to recovery or neutralisation.
Steps 3 — Crude Silver Melting, Flux Refining and Anode Casting. Crude silver — including the high-purity powder from pre-treatment — is melted in a medium-frequency induction furnace. Where the feed carries copper, selenium or tellurium at levels that would foul the cell, sodium carbonate flux is added and air is blown across the melt surface so those elements oxidise and report to a removable slag, which is skimmed off and returned for silver recovery. The refined melt is poured into anode moulds and cast into anode plates of a controlled weight, thickness and surface condition — plate geometry is what sets the electrode spacing, and therefore the electrolyte resistance and the current distribution across the cell. Output: cast silver anode plates of uniform weight and composition, plus a slag returned to silver recovery.
Steps 4 — Electrolyte Preparation. The electrolyte is prepared by dissolving high-purity silver in nitric acid until the reaction is complete, filtering off the insoluble residue and transferring the solution to the cell. Silver and nitric acid react according to Ag + 2HNO₃ → AgNO₃ + NO₂↑ + H₂O, which is a strongly fuming reaction and the reason electrolyte preparation is done under extraction and routed to the NOₓ treatment system. The electrolyte is made up to a silver concentration of 60–150 g/L with a free nitric acid content of 10–18 g/L, and potassium nitrate is added to raise conductivity and help hold the electrolyte pH in its working band. The free-acid window is deliberately narrow: too little acid lets bismuth and other base metals hydrolyse and contaminate the silver powder, while too much re-dissolves the silver already deposited on the cathode. Output: silver nitrate electrolyte within the working specification, ready for the cell.
Steps 5 — Cell Loading and High-Current-Density Electrolysis. The cast anode plates are loaded into the cell and hung in the anode bags; where the layout allows, an overhead travelling crane is used so that plates are positioned mechanically and the operator never handles solution or reaches over the electrolyte. Direct current is applied and the cell runs at a cathode current density of 750 A/m² — about two to three times the 250–350 A/m² of a conventional silver cell — with the electrolyte circulated parallel to the electrode plates and entering at the bottom of the cell and leaving at the top. Parallel-flow circulation is what makes the high current density usable: it keeps the silver-ion concentration uniform across the electrode gap, suppresses the concentration polarisation that would otherwise force the silver concentration up, and lets the cell run at a lower and more stable silver concentration at higher throughput. A chiller cools the electrolyte and holds the temperature down so that evaporation, acid consumption and volatilisation losses stay low; the conducting bars and lugs are engineered to stay cool, and the cell is closed under a transparent sealed cover with side extraction so the process is visible and the exhaust is contained. Output: silver depositing as crystalline powder on the cathodes, base metals reporting to the electrolyte, and insoluble gold and platinum-group metals collecting in the anode bags.
Steps 6 — Silver Powder Harvesting and Scraping. Silver deposited on the cathodes is removed continuously by the automatic stirring and scraping system, which lifts the crystals off the cathode before they can bridge the electrode gap. This is not a convenience feature: bridged crystals short-circuit the cell, distort the current distribution, lower the quality of the powder still in the cell and immobilise silver as unsaleable inventory in the anode bag. Continuous scraping keeps the cell stable, and it stretches the interval between deep cleans from roughly monthly on a conventional belt-discharge cell to a continuous campaign measured in months. A single operator is sufficient for intermittent supervision while the cell runs. When the batch is complete, the electrolyte is drawn off through the discharge valve by way of the solid–liquid separator into the circulation tank, and the silver powder is discharged to the wash-and-dry unit. Output: harvested cathode silver powder and drained electrolyte routed to regeneration.
Steps 7 — Silver Powder Washing and Drying. The powder is washed in a combined washing and drying unit using deionised hot water, on a counter-current basis: first wash water is returned to the tank for electrolyte make-up, and second wash water is held back to serve as the first wash of the next batch. Washing continues until conductivity is low enough to confirm that residual nitrate has been removed, after which the powder is dewatered and dried to a moisture content low enough for clean melting. Output: dried, nitrate-free 99.99% silver powder ready for melting, and wash water recycled to electrolyte make-up.
Steps 8 — Anode Slime Collection and Treatment. Gold, platinum, palladium and rhodium do not dissolve under silver-refining conditions, so they accumulate in the anode bags as anode slime at roughly 8% of the anode mass. A typical gold-silver anode slime assays 50–70% gold and 30–40% silver, which makes it the most valuable by-product of the operation. Because its silver content is still high, it is not normally melted straight into a gold anode; it is either parted with nitric acid — silver dissolves and the gold stays as a solid, lifting the gold grade above 90% so the residue can be cast into gold anodes — or cast into a plate and given a second electrolysis pass to raise its gold content. Slime from e-waste and catalyst feed additionally carries platinum, palladium and rhodium and is routed to the PGM separation circuit. Output: gold-bearing anode slime upgraded to a castable gold anode, plus recovered silver and PGM-bearing fractions.
Steps 9 — Spent Electrolyte Purification and Regeneration. Base metals dissolve into the electrolyte continuously, and left alone they eventually contaminate the cathode powder. The machine therefore includes an electrolyte purification step: impurity-loaded electrolyte is drawn off, treated to remove the accumulated copper, bismuth, tellurium and selenium, and returned to service, so that the electrolyte can be reused instead of being remade. The silver held in the spent electrolyte is recovered in the same step rather than being neutralised to waste, which is one of the two places silver quietly disappears on an unmanaged silver line. Because the electrolyte is regenerated in place, solution-preparation frequency and its associated nitric acid demand fall, and fewer fuming make-up batches are needed. Output: purified electrolyte returned to the cell, recovered silver, and a base-metal stream to recovery.
Steps 10 — Off-Gas Condensation and Scrubbing. Fume from the cell, the melting furnace and especially from electrolyte preparation is drawn from the sealed cell through side extraction, passed through a fume-condensation system that cools the vapour and returns the silver-bearing condensate to the circuit instead of letting it escape up the stack, and then ducted to a multi-stage nitrogen-oxide absorption tower. The tower runs under negative pressure, is sized for inlet NOₓ concentrations above 30,000 mg/m³, and holds the outlet below 150 ppm at an absorption efficiency of 99.5% or better. It also absorbs chlorine and sulfur dioxide, and its reagent chemistry converts the nitrogen oxides to nitrogen, carbon dioxide and water, so there is no secondary waste to dispose of and the working area is odourless. Output: compliant, odourless exhaust, and condensed silver returned to the process.
Steps 11 — Melting, Ingot Casting and Assay Certification. The dried silver powder is melted in an induction furnace and cast into the required form — ingots, bars, cast shapes — or granulated into grain. Vacuum ingot casting and vacuum continuous casting are used where density, surface finish and freedom from porosity and oxidation matter, and a vacuum granulator where uniform grain is wanted. Each lot is re-assayed by fire assay with ICP-OES confirmation and released against a Certificate of Analysis carrying the batch number, input weight, input assay, output assay, output weight and the metal balance. Output: certified 99.99% silver bars, ingots or grain with full assay documentation.
The main chain runs vertically: assay and route selection → pre-treatment where needed → anode casting → electrolyte preparation → high-current-density electrolysis → powder harvesting → washing and drying → melting and casting → certified silver. Side branches carry anode slime to gold and PGM recovery, spent electrolyte to purification and back to the cell, wash water to electrolyte make-up, condenser liquor back to the process, slag back to silver recovery, and treated off-gas to atmosphere.
Product Structure (Main Equipment)
The set is supplied as factory-assembled, piped and functionally tested modules, with the wetted path built in high-performance polypropylene, PPH, titanium and titanium-clad copper according to duty.
- Feed Weighing, Sampling and Assay Station — platform scale, sampling bench and sample preparation equipment for feed, anodes, powder, electrolyte and finished bars, with reference to fire assay and instrument analysis. Function: fixing the feed assay that decides the route and providing the numbers for the batch metal balance.
- Pre-Treatment Reaction and Filtration Set — acid-resistant agitated reactor, ammonia and hydrazine dosing, pH control, heating, and filtration with wash capacity for the nitric-acid dissolution, silver chloride re-precipitation and ammonia-complexation route. Function: cleaning low-grade silver and impure silver chloride into cell-ready feed.
- Medium-Frequency Induction Melting Furnace — melting furnace with graphite or clay-graphite crucible, flux addition and air-blowing capability for oxidising copper, tellurium and selenium into a removable slag. Function: melting crude silver, flux-refining it and preparing a homogeneous melt for anode casting.
- Anode Casting Moulds and Anode Handling Gear — anode moulds with controlled cooling, anode stripping and dressing, anode bags, and an anode rack with overhead crane or hoist for mechanical loading. Function: producing uniform anode plates and loading them without operator contact with the electrolyte.
- Silver Electrolytic Cell — one-piece moulded high-performance polypropylene cell body with an anti-ageing additive so the shell does not become brittle with age, PPH load-bearing frame, and titanium-clad copper conducting bars for low-resistance current transfer at the anode and cathode. Function: holding the electrolyte and electrodes and carrying high current density without leakage or corrosion.
- Transparent Sealed Fume Cover and Side Extraction — hinged transparent cover plates over the cell with side suction ducting and connection to the extraction system. Function: containing acid mist and NOₓ while keeping the electrodes and the cell visible to the operator.
- Electrolyte Cooling and Circulation System — chiller with automatic start and stop on electrolyte temperature, circulation tank and pump set, and pipework arranged for parallel flow entering at the bottom of the cell and leaving at the top so the flow runs parallel to the electrode plates. Function: holding electrolyte temperature down, cutting evaporation and acid consumption, and eliminating concentration polarisation across the electrode gap.
- Automatic Cathode Scraper and Stirring Mechanism — motorised stirring and scraper assembly acting on the cathode plates, with timed or continuous operation. Function: lifting deposited silver powder off the cathodes continuously to prevent short circuits and keep the cell in a stable, high-current-density condition.
- Discharge Valve and Solid–Liquid Separator — discharge valve with a bypass through a solid–liquid separator to the circulation tank. Function: draining clear electrolyte first and discharging silver powder separately, so liquid and solid leave the cell without mixing.
- Silver Powder Washing and Drying Unit — combined wash-and-dry machine with deionised hot-water supply, counter-current wash-water storage, dewatering and controlled drying. Function: removing residual nitrate from the powder, drying it for clean melting, and recycling wash water to electrolyte make-up.
- Electrolyte Purification and Regeneration Unit — impurity removal and purification circuit with tanks, dosing, filtration and return line to the cell. Function: stripping accumulated copper, bismuth, tellurium and selenium out of the electrolyte, recovering the silver it holds and returning the purified solution to service.
- Nitrogen Oxide and Acid Gas Treatment System — fume-condensation unit with condensate return, and a multi-stage jet-spray absorption tower in anti-ageing polypropylene with circulation pump, reagent dosing, negative-pressure operation and discharge monitoring. Function: reducing inlet NOₓ above 30,000 mg/m³ to below 150 ppm at 99.5% or better absorption, absorbing chlorine and sulfur dioxide, and converting the nitrogen oxides into nitrogen, carbon dioxide and water.
- Anode Slime Collection and Handling Set — anode bags, slime washing and filtration, and slime transfer to the gold or PGM circuit. Function: capturing the gold and platinum-group metal fraction instead of losing it to the electrolyte or the drains.
- Melting, Casting and Granulating Unit — induction melting furnace, ingot and bar moulds, vacuum ingot casting machine, vacuum continuous casting machine and vacuum granulator, with inert-gas or vacuum protection. Function: converting dried silver powder into dense, oxide-free bars, ingots or uniform grain.
- Rectifier and Electrical Control Cabinet — high-current low-voltage rectifier with current and voltage control, bus bars, and PLC-based control with touch-screen HMI, alarms and interlocks. Function: holding the cell at its set current density and giving the operator a repeatable, logged process record.
- Assay and Quality-Control Laboratory — sample preparation equipment, fire-assay furnace and cupellation ware, balance, titration glassware and instrument analysis. Function: input control, in-process checking and the Certificate of Analysis that releases each batch.
- Safety and Workplace Package — local extraction, acid-resistant flooring and bunding, secondary containment for reagents, eyewash and safety shower, gas detection with interlock, and operator protective equipment including acid-resistant gloves, apron, face shield and respiratory protection. Function: protecting the operator from nitric acid and nitrogen oxide exposure and meeting workplace chemical-handling requirements.
Product Features
- Single-pass 97% to 99.99%. Crude silver assaying 97% and above goes through the machine once and comes out as 99.99% (9999) powder — no second pass, no toll refining, no settlement delay.
- High current density, compact cell. A cathode current density of 750 A/m² — roughly two to three times the 250–350 A/m² of a conventional silver cell — delivers the output of several conventional cells from one compact unit, so far less floor space and far less electrolyte inventory are needed for the same tonnage.
- Parallel-flow electrolyte circulation. The electrolyte is pumped parallel to the electrode plates and enters at the bottom and leaves at the top, which removes the concentration polarisation that normally caps silver current density and allows the cell to run at a lower, more stable silver concentration with better powder quality.
- Electrolyte cooling as standard. An integrated chiller with automatic start and stop holds the electrolyte temperature down, which cuts evaporation and volatilisation losses, reduces acid consumption and removes the acid smell from the working area.
- Fume condensation that returns metal to the process. The cell is sealed with a transparent cover, and the vapour passes through a condensation system that cools it and returns the silver-bearing condensate to the cell instead of venting it — the single largest avoidable silver loss on a nitric-acid silver line.
- Nitrogen oxide handled at the design stage. The absorption tower is sized for inlet loads above 30,000 mg/m³, holds the outlet below 150 ppm at 99.5% or better absorption, absorbs chlorine and sulfur dioxide as well, and converts the nitrogen oxides to nitrogen, carbon dioxide and water so no secondary waste stream is created.
- Continuous operation instead of monthly shutdowns. Automatic stirring and scraping prevents short circuits, keeps silver powder out of the anode bags and stretches deep cleaning from roughly a monthly stop on a conventional belt cell to a campaign measured in months.
- One-piece moulded cell, built not assembled. The cell body is moulded in a single piece from high-performance polypropylene with an anti-ageing additive, which eliminates the seam leakage of fabricated tanks and keeps the shell from becoming brittle; the frame is PPH and the conducting bars are titanium-clad copper.
- Impurities managed on both sides of the cell. Base metals are drawn out of the electrolyte in the purification circuit, and gold, platinum, palladium and rhodium are captured in the anode bags as slime, so neither group is allowed to reach the cathode or to leave the site unrecovered.
- Anode slime is revenue, not waste. At roughly 8% of anode mass and 50–70% gold content, the slime is routed to nitric-acid parting or to a second electrolysis pass that lifts the gold grade above 90% for gold anode casting — so the machine’s pay-back includes the gold, not just the silver.
- Closed-loop water and electrolyte. Counter-current powder washing sends first wash water to electrolyte make-up and second wash water to the next batch’s first wash, and spent electrolyte is purified and returned to the cell, so both water and acid demand fall and waste volume is minimised.
- Purity you can verify, not just claim. Output is established by fire assay with ICP-OES confirmation and released on a Certificate of Analysis giving input weight and assay, output weight and assay, and the metal balance — the documentation a buyer, a bank or an auditor actually asks for.
- Built for small shops and large refineries alike. The same process logic runs from bench and workshop units of a few kilograms per batch to industrial tankhouse cells of 200 kg per day and above, and capacity is added by duplicating cells rather than by redesigning the chemistry.
- One operator per cell. Mechanical plate loading, automatic scraping and automatic control mean a running cell needs only intermittent supervision, so labour is not the constraint on throughput.
- Modular and upgradeable. Supporting equipment — vacuum ingot casting, vacuum continuous casting, powder cleaning and drying, vacuum granulation, melting furnaces and the NOₓ treatment skid — is available as matched modules, so the line can be extended to a full refinery without replacing the cell.
Technical Parameters & Specifications
Values below describe the standard process envelope and product outcomes. Throughput, power, footprint and utility figures are engineered to each client’s feed assay, target throughput and site conditions, and are confirmed at design review rather than taken from a catalogue.
| Parameter | Specification |
|---|---|
| Product | Silver Refining Machine (silver electrolytic refining line, with pre-treatment, off-gas and finishing circuits) |
| Refining principle | Electrolytic refining: crude silver anode, titanium cathode, silver nitrate electrolyte, controlled direct current — anode preparation, electrolysis, cathode deposition and impurity management |
| Refined silver purity | 99.99% (9999) or better as standard output |
| Ultra-high-purity output | Up to 99.999% (5N) where the feed is 99.95% silver |
| Pre-treatment route purity | Silver powder or silver chloride above 99% purity from the chemical pre-treatment stage, as feed to anode casting |
| Feed purity for direct electrolytic refining | Crude silver and crude silver plate of 97% silver and above |
| Feed purity for the alloy route | Silver-gold alloy from anode slime treatment commonly above 90% silver; silver anodes typically above 75% silver with gold below 20% |
| Anode composition and preparation | Crude silver melted in a medium-frequency induction furnace, flux-refined with sodium carbonate and air blowing to slag off copper, tellurium and selenium where present, then cast into anode plates of controlled weight and thickness |
| Cathode material | Titanium cathode plates with scraper |
| Cathode current density | 750 A/m² (conventional silver cells run 250–350 A/m²; 600–800 A/m² is the high-current-density band) |
| Cell working voltage | Low-voltage direct current, typically 1.5–3 V per cell |
| Anode basket option | Titanium anode basket or perforated basket for loose and granular silver feed, with cast plate anodes used where the feed is castable |
| Electrolyte | Silver nitrate (AgNO₃) solution with free nitric acid, prepared by dissolving high-purity silver in nitric acid |
| Electrolyte silver concentration | 60–150 g/L Ag |
| Electrolyte free nitric acid | 10–18 g/L free HNO₃ — deliberately narrow: below the window, bismuth and base metals hydrolyse into the powder; above it, deposited silver re-dissolves |
| Electrolyte conductivity and pH control | Potassium nitrate (KNO₃) added to raise conductivity and stabilise the electrolyte working band |
| Electrolyte make-up reaction | Ag + 2HNO₃ → AgNO₃ + NO₂↑ + H₂O — a fuming reaction run under extraction and routed to the NOₓ treatment system |
| Electrolyte temperature | Actively cooled by chiller with automatic start and stop; the cell runs with the electrolyte held at a controlled temperature, and conducting bars and lugs are engineered to stay cool |
| Electrolyte circulation | Parallel flow to the electrode plates, entering at the bottom of the cell and leaving at the top, to suppress concentration polarisation |
| Electrolyte dosing and topping-up | Automatic dosing and level control from the circulation tank |
| Silver deposition form | Crystalline silver powder deposited on the cathodes and continuously removed by the automatic scraper |
| Cathode powder removal | Automatic stirring and scraping, timed or continuous, preventing crystal bridging and short circuits |
| Cooling system | Electrolyte chiller with automatic temperature control, plus cooling for the rectifier and conducting bars as required |
| Rectifier and power supply | High-current low-voltage rectifier with current and voltage control, fed from the local three-phase supply; power rating engineered per configuration |
| Electrolyte inventory | Sized against the number of cells and the target daily output; a high-current-density cell carries markedly less electrolyte per kilogram of daily output than a conventional belt cell |
| Operational supervision | One operator for intermittent supervision of a running cell, supported by mechanical plate loading |
| Anode slime yield and composition | Approximately 8% of anode mass; typical gold-silver slime assays 50–70% gold and 30–40% silver; e-waste and catalyst feed adds platinum, palladium and rhodium |
| Anode slime treatment | Nitric-acid parting to lift the gold grade above 90% for gold anode casting, or a second electrolysis pass; PGM-bearing slime routed to the PGM separation circuit |
| Electrolyte purification | Dedicated purification and regeneration circuit removing accumulated copper, bismuth, tellurium and selenium and returning purified electrolyte to the cell |
| Silver recovery | Up to 99% on a metal-balance basis, defined as silver leaving as product plus silver recovered from anode slime and regenerated electrolyte, divided by silver in the assayed anode; all remaining silver is held in recirculating circuits rather than discarded |
| Pre-treatment chemistry (low-grade and AgCl feed) | Nitric-acid dissolution, silver chloride re-precipitation with HCl or NaCl to reject base metals, ammonia complexation at pH 10–11 |
| Pre-treatment reduction | Hydrazine hydrate at 40–80% concentration, added at a silver-to-hydrazine mass ratio of about 1 : 0.3–0.4, at approximately 50 °C over about 30 minutes; reduction rate above 99% |
| Cell construction | One-piece moulded high-performance polypropylene body with anti-ageing additive; PPH load-bearing frame; titanium-clad copper conducting bars |
| Cell sealing and extraction | Transparent sealed fume cover plates with side extraction and connection to the fume-condensation and extraction system |
| Fume condensation | Condensation system cooling the cell and furnace vapour and returning silver-bearing condensate to the circuit |
| Off-gas inlet NOₓ concentration | Above 30,000 mg/m³ (about 20,000 ppm) from cell and electrolyte preparation |
| Treated NOₓ concentration | Below 150 ppm, within the applicable discharge standard |
| Scrubber absorption efficiency | 99.5% or better for nitrogen oxides, with chlorine and sulfur dioxide also absorbed |
| Scrubber reagent behaviour | Nitrogen oxides converted to nitrogen, carbon dioxide and water — no secondary pollution stream |
| Scrubber construction and duty | Multi-stage jet-spray absorption tower in anti-ageing polypropylene, operating under negative pressure, with compact footprint and low reagent cost |
| Water circuit | Counter-current powder washing with deionised hot water: first wash water to electrolyte make-up, second wash water reused as the next batch’s first wash |
| Powder drying | Combined washing and drying unit, dewatered and dried to a moisture content suitable for clean melting |
| Casting and finishing | Induction melting with ingot and bar moulds; vacuum ingot casting; vacuum continuous casting for strip, plate and tube; vacuum granulator for grain |
| Assay and quality control | Fire assay with cupellation and ICP-OES confirmation, with a Certificate of Analysis per batch recording input weight and assay, output weight and assay, and the metal balance |
| Automation and control | PLC with touch-screen HMI; current and voltage control, electrolyte temperature and circulation control, dosing, scraping cycle, scrubber and alarm management with parameter logging |
| Configuration scale | Workshop and bench units of a few kilograms per batch through to industrial tankhouse cells of 200 kg per day and above; throughput, power, footprint and utilities engineered per configuration |
| Feed forms accepted | Crude silver bullion and plate · silver-gold alloy and doré · scrap jewellery and cutlery · coins and medallions · workshop sweeps and polishing dust · electrical contacts and brazing scrap · e-waste and PCB silver concentrate · photographic and imaging sludges · spent plating baths and strip solutions · silver chloride residue · silver-bearing slags, residues and catalysts · solar-cell silver |
| Standards and compliance | CE; local air-emission, wastewater and chemical-storage requirements; closed-loop effluent design with no cyanide in the silver-refining route |
Technical Advantages
- Current density is the throughput lever, and it is designed for. A silver cell is limited by heat, concentration polarisation and short circuits, not by chemistry. Solving all three — chiller-cooled electrolyte, parallel-flow circulation and continuous cathode scraping — is what makes 750 A/m² a working number rather than a specification-sheet claim, and it is why one compact cell can match several conventional cells.
- Less silver held up in the plant. High current density means less electrolyte and less silver inventory per kilogram of daily output. On a metal that trades at a high unit value, reducing in-process hold-up is a direct reduction in working capital and in metal at risk — and it is the reason a machine like this pays back quickly.
- Metal that would otherwise go up the stack is captured. Nitric-acid silver refining loses silver as vapour unless the fume is condensed rather than diluted. Sealing the cell, condensing the vapour and returning the condensate to the circuit protects a loss stream that operators of open-canopy cells rarely even measure.
- The NOₓ problem is solved as part of the machine. The absorption tower is sized for the actual load produced by cell operation and electrolyte preparation — above 30,000 mg/m³ at the inlet — and holds the outlet below 150 ppm at 99.5% or better absorption, while also absorbing chlorine and sulfur dioxide and producing no secondary waste. Compliance is a design output, not an add-on purchase.
- Impurities are handled on both sides of the electrode gap. Base metals are bled out of the electrolyte in a purification circuit that returns clean solution to the cell, and gold and the platinum-group metals are captured in the anode bags rather than being allowed to contaminate the deposit. That is what keeps 9999 repeatable batch after batch instead of drifting with the feed.
- Slime is monetised, not discarded. At around 8% of anode mass and 50–70% gold, anode slime is usually the second-largest revenue line of a silver operation. The line captures it, washes it, and either parts it with nitric acid to lift the gold grade above 90% for gold anode casting or gives it a second electrolysis pass.
- Recovery is defined, so it can be audited. The recovery figure is stated on a metal-balance basis — product plus slime plus electrolyte silver over assayed anode silver — which means it can be checked from the batch record instead of being asserted. Both purity and recovery are confirmed on the customer’s own material during test work and verified at commissioning.
- A narrow, controlled electrolyte window instead of an approximate one. Working to 60–150 g/L silver with 10–18 g/L free acid and potassium nitrate for conductivity is what keeps bismuth out of the powder and stops the deposit re-dissolving; circulating parallel to the plates means that window can be held at a lower silver concentration and a higher current.
- Equipment life engineered into the materials. A one-piece moulded polypropylene cell with an anti-ageing additive removes the seam leakage and embrittlement that shorten the life of fabricated tanks, the frame is PPH for structural corrosion resistance, and titanium-clad copper bars hold conductivity at the current densities the cell runs.
- Water and acid demand reduced by design. Counter-current washing between the powder washer and the electrolyte make-up tank, and electrolyte purification that lets solution be reused instead of remade, both cut consumption and reduce the volume of fuming make-up batches the operator has to run.
- One operator, continuous campaign. Mechanical plate loading, automatic scraping and automatic control mean the cell is supervised rather than staffed, and deep cleaning is measured in months rather than weeks — so labour is not what limits throughput.
- A closed loop rather than a set of drains. Slime goes to gold and PGM, spent electrolyte is regenerated, wash water is reused, condenser liquor returns to the cell, slag goes back to silver recovery and the scrubber produces nitrogen, carbon dioxide and water. Fewer streams leave the site as waste, and fewer leave as unmeasured losses.
- Documentation that stands behind the metal. Every batch carries an input assay, a process record and an output Certificate of Analysis from fire assay with ICP-OES confirmation, so the product can be sold, financed or audited on the strength of its paperwork.
- The same chemistry at every scale, and an upgrade path. Workshop and industrial configurations use identical process logic, so a bench unit is a genuine pilot for an industrial cell; and the supporting modules — vacuum casting, granulation, powder drying, NOₓ treatment — let the line grow into a complete refinery without replacing what is already installed.
- Turnkey single-point accountability. One supplier owns feed testing, process design, equipment, off-gas treatment, assembly, commissioning and operator training, which removes the integration risk of building a silver refinery out of several vendors’ modules.
Service Process
YuSai delivers a silver refining machine as a complete project — from feed assay and bench test work through to a running, assay-verified refining line.
Steps 1 — Feed Characterisation and Consultation. Send a representative sample of your crude silver, scrap, residue or silver chloride, with an indication of grade and volume. Our metallurgical team assays it for silver and for the impurities that govern the route — copper, bismuth, tellurium, selenium, lead, gold and the platinum-group metals — and identifies which route suits the material: straight to anode casting, or through chemical pre-treatment first. Output: assay report and preliminary route proposal with the achievable purity.
Steps 2 — Laboratory Test Work and Process Design. Bench and pilot campaigns confirm the pre-treatment conditions where they are needed, anode composition and casting parameters, the electrolyte specification, current density and expected powder quality, and the anode slime yield and composition. The results are converted into a mass balance, flowsheet, cell and electrode sizing, rectifier rating, electrolyte volume, off-gas load, water and reagent consumption, layout and utility schedule against your throughput and site. Output: test report, process design package and firm quotation.
Steps 3 — Detailed Engineering and Manufacturing. Cell body and frame, electrodes and conducting bars, fume cover and extraction, chiller and circulation set, scraper mechanism, discharge and solid–liquid separation, powder washer-dryer, electrolyte purification unit, pre-treatment reactor, NOₓ and acid-gas treatment tower, melting and casting modules and the control cabinet are fabricated, pre-assembled on skids and piped. Output: engineered, skid-mounted modules.
Steps 4 — Factory Assembly, Testing and Acceptance. Each module is functionally tested and the line is trial-run — wherever possible on your own material — with the client invited to attend the factory acceptance test before shipment. Output: FAT-approved, pre-commissioned modules.
Steps 5 — Shipping, Installation and Commissioning. We supervise the civil interface, erection, piping, ductwork and electrical tie-in, then run an instrumented commissioning campaign on your feed until the contracted purity, throughput and recovery are demonstrated and the NOₓ outlet is verified against your local emission limit. Output: a producing silver refining line at contracted performance.
Steps 6 — Operator Training and Handover. On-site training covers safe nitric-acid and hydrazine handling, anode casting and loading, electrolyte preparation and control, current-density and temperature management, powder harvesting and washing, electrolyte purification, anode-slime handling, off-gas and effluent operation, emergency procedures and assay quality control, supported by Standard Operating Procedures and a full handover dossier. Output: trained crew and complete documentation.
Steps 7 — Process Optimisation and Ongoing Support. Remote troubleshooting, reagent and consumable supply, electrode and bag service, periodic performance audits, and recovery or capacity upgrade paths keep the line at target over its service life. Output: sustained performance and spare-part continuity.
Warranty & After-Sales Service
- Standard warranty. Twelve (12) months from commissioning, or eighteen (18) months from shipment, whichever comes first, covering structural, mechanical, electrical, control and off-gas equipment against defects in material and workmanship.
- What the warranty covers. Replacement of defective components, repair or exchange of main-process equipment, and free remote technical guidance throughout the warranty period. Consumables such as reagents, hydrazine hydrate, anode bags, filter cloth, crucibles, moulds, gaskets and electrodes, and damage caused by misuse, unauthorised modification or operation outside the agreed feed and process envelope, are excluded.
- Guaranteed performance. We warrant that, when fed material inside the agreed assay and throughput envelope and operated to the supplied SOP, the machine meets the contracted silver purity, throughput and recovery figures, verified at commissioning by fire assay and ICP-OES on the customer’s own material.
- Response commitment. Guaranteed remote response within 24 hours, on-site engineer dispatch and hotline support for breakdowns affecting production, and expedited supply of critical spares.
- Spare parts and consumables. Genuine spares, rectifier components, metering and dosing pumps, electrodes and conducting bars, anode bags, filter cloth, crucibles and moulds, tower packing, gaskets and reagent ranges are held as a stocking range to minimise downtime.
- Commissioning and start-up support. Supervised installation, commissioning on the customer’s own feed, performance verification against contract, off-gas outlet verification and an operator competence sign-off before handover.
- Wear-part schedule. A list of wear-prone and consumable parts with their expected replacement intervals is issued at handover, so the operator can plan anode bags, filters, gaskets and crucible replacement instead of discovering the need during a production run.
- Lifetime technical support. Free access to our engineering team for process questions after warranty expiry, plus optional retrofit, capacity-upgrade, recovery-improvement and reagent-optimisation services.
- Documentation. Full operating, maintenance and safety manuals, electrical drawings, P&ID, cell and electrode drawings, off-gas and scrubber documentation, spare-parts catalogue, SOPs, batch-record and CoA templates, and training material accompany every line.
- Compliance support. Assistance with local emission, effluent and chemical-storage permitting documentation, including the storage and handling requirements that apply to nitric acid and hydrazine hydrate, and with the assay and product-certification records that buyers and authorities require.
Frequently Asked Questions
Q1. What is a silver refining machine?
A silver refining machine is an industrial or workshop-scale electrolytic plant that upgrades impure silver — crude silver bullion, scrap jewellery, coins, industrial sweepings, silver-bearing residues and silver chloride from precious-metal refining — into fine silver of 99.99% (9999) purity or better. It works by electrorefining: the crude silver is melted and cast into anode plates, the plates are hung in a silver nitrate electrolyte containing 60–150 g/L silver and 10–18 g/L free nitric acid, and a controlled direct current at a cathode current density of 750 A/m² dissolves the anode and deposits crystalline silver powder on titanium cathodes. Base metals stay in the electrolyte and are removed in the purification circuit; gold, platinum, palladium and rhodium do not dissolve and are captured in the anode bags as anode slime.
Q2. How pure is the silver a silver refining machine produces?
The standard product is 99.99% (9999) silver powder, which is cast into ingots, bars or grain. Where the feed is already 99.95% silver, the same machine is run to 99.999% (5N) for electronics and specialty applications. Purity is not a fixed property of the machine: it is a function of the anode composition, the electrolyte specification, the current density and the temperature control, which is why the feed is assayed first and the process window is fixed before the equipment is sized.
Q3. How do I verify the 99.99% purity, and what should a Certificate of Analysis contain?
The output is verified by fire assay with cupellation, with ICP-OES confirmation on the same lot, and instrument analysis is used for routine in-process checking. The Certificate of Analysis issued with each batch should state the batch number, the input weight and input assay, the output weight and output assay, the impurity elements determined, and the metal balance — the arithmetic that reconciles what went in with what came out, including the silver in the anode slime and the spent electrolyte. Ask any supplier for a specimen CoA before you buy: a purity claim without a stated test method and a metal balance is a marketing number, not an assay.
Q4. What silver content should the feed have?
For direct electrolytic refining, crude silver and crude silver plate of 97% silver and above feed the anode casting stage directly. Silver-gold alloy recovered from copper and lead anode slime treatment commonly runs above 90% silver, and cast silver anodes typically run above 75% silver with gold below 20%. Materials below those grades are not rejected — they go through the chemical pre-treatment stage first and enter the cell as clean silver powder or silver chloride instead.
Q5. Can the machine refine low-grade silver, impure silver chloride or scrap below 97%?
Yes, through the pre-treatment stage. Impure silver chloride and low-grade silver residues are dissolved in nitric acid, re-precipitated as silver chloride with hydrochloric acid or sodium chloride so the base metals stay in the filtrate, then complexed with ammonia at about pH 10–11 and reduced with 40–80% hydrazine hydrate at roughly 50 °C over about 30 minutes, at a silver-to-hydrazine mass ratio of about 1 : 0.3–0.4. The reduction rate exceeds 99% and the resulting silver is above 99% purity — clean feed for anode casting and the electrolytic cell.
Q6. What current density and electrolyte does the machine run at?
The machine runs at a cathode current density of 750 A/m² — about two to three times the 250–350 A/m² of a conventional belt-discharge silver cell — in a silver nitrate electrolyte carrying 60–150 g/L silver with 10–18 g/L free nitric acid, with potassium nitrate added for conductivity and pH control. The free-acid band is deliberately narrow: below it, bismuth and other base metals hydrolyse and contaminate the silver powder; above it, the nitric acid re-dissolves silver already deposited on the cathode. Cell voltage is low-voltage direct current, typically 1.5–3 V per cell.
Q7. Why does high current density matter, and how is it achieved?
Current density is the throughput lever: it sets how much silver a cell of a given size can produce per day. It is normally capped at 250–350 A/m² because higher currents heat the electrolyte, create concentration polarisation between the electrodes and begin to carry impurities into the deposit. Three design features lift the ceiling — a chiller that holds the electrolyte temperature down and cuts evaporation and acid consumption, parallel-flow circulation entering at the bottom of the cell and leaving at the top so the silver-ion concentration stays uniform across the electrode gap, and an automatic scraping and stirring system that continuously removes silver powder from the cathode so crystals never bridge the gap and short-circuit the cell.
Q8. How does the machine stop silver from being lost in the exhaust?
By sealing the cell and condensing the vapour rather than diluting it. Open refining cabinets draw a large volume of air across the cell, which evaporates solution and carries silver out with the vapour as an unmeasured loss. On this machine the cell is closed under a transparent sealed fume cover with side extraction, and the vapour passes through a fume-condensation system that cools it and returns the silver-bearing condensate to the process. Only the residual nitrogen oxide goes on to the scrubbing tower.
Q9. How is the nitrogen oxide from nitric acid handled?
Nitrogen oxides are produced whenever nitric acid meets silver — in electrolyte preparation (Ag + 2HNO₃ → AgNO₃ + NO₂↑ + H₂O), in anode slime boiling and in the cell itself. Cell and furnace fume is drawn from the sealed cover, condensed, and ducted to a multi-stage nitrogen-oxide absorption tower operating under negative pressure, sized for inlet concentrations above 30,000 mg/m³ (about 20,000 ppm). The treated outlet is held below 150 ppm at an absorption efficiency of 99.5% or better. The tower also absorbs chlorine and sulfur dioxide, and its reagent converts the nitrogen oxides to nitrogen, carbon dioxide and water, so no secondary waste stream is generated and the working area is odourless.
Q10. What happens to the gold and platinum-group metals in the anode slime?
They are captured, not lost. Gold, platinum, palladium and rhodium do not dissolve under silver-refining conditions and collect in the anode bags at roughly 8% of the anode mass. A typical gold-silver anode slime assays 50–70% gold and 30–40% silver, so it is usually the second-largest revenue line of the operation. Because its silver content is still high, it is normally either parted with nitric acid — silver dissolves and the gold residue is lifted above 90% so it can be cast into gold anodes — or cast into a plate and given a second electrolysis pass. Slime from e-waste and catalyst feed is routed to the platinum-group-metal separation circuit.
Q11. Is the silver left in the spent electrolyte recovered?
Yes. Base metals accumulate in the electrolyte as the cell runs, and the machine includes a purification and regeneration circuit that strips copper, bismuth, tellurium and selenium out of the solution, recovers the silver it holds, and returns purified electrolyte to the cell. This does two things: it stops impurities from building up until they contaminate the silver powder, and it avoids the two silent losses on an unmanaged silver line — silver neutralised to waste with the spent solution, and silver immobilised in a cell that has to be drained and remade.
Q12. How does daily capacity translate into batch size, anode weight and number of cells?
Daily capacity is the product of three variables, not a standalone figure: the weight of silver in the anodes loaded per cell, the current density and therefore the deposition rate, and the number of cells. In practice an operator loads a batch of anode plates, runs the cell until the plates are consumed, discharges the powder and reloads — so daily output equals the silver dissolved per cycle multiplied by the number of cycles, multiplied by the number of cells. Ask any supplier for the anode weight, the cycle time and the cathode area behind a quoted daily figure; a daily number without those three variables cannot be checked or compared.
Q13. How many operators are needed, and how often does the cell need cleaning?
One operator is enough for intermittent supervision of a running cell. Anode plates are positioned mechanically — with an overhead travelling crane where the layout allows — so the operator never handles solution or reaches across the electrolyte, and the automatic scraper removes the silver powder continuously. Continuous scraping also keeps powder out of the anode bags and prevents crystal bridging, so deep cleaning moves from roughly a monthly shutdown on a conventional belt-discharge cell to a campaign measured in months.
Q14. What utilities, floor space and reagents are required?
The machine needs a three-phase supply for the rectifier and drives, cooling water for the electrolyte chiller and rectifier, a fume-extraction and scrubbing connection, and a level, acid-resistant floor with bunding and secondary containment. Reagents are nitric acid for electrolyte preparation and anode slime treatment, potassium nitrate for electrolyte conductivity, sodium carbonate flux for anode refining, sodium chloride or hydrochloric acid and ammonia for pre-treatment, hydrazine hydrate for reduction, and the scrubber reagent. Power rating, footprint, cooling-water demand and reagent consumption are all engineered to the configuration — they scale with daily throughput, cell count and feed grade, and are fixed at design review rather than published as a fixed table.
Q15. Can the machine produce 999.9 or 999.99 (4N or 5N) silver?
Yes. 99.99% (9999) is the standard output, and where the feed is 99.95% silver, the same machine is run to 99.999% (5N). Reaching 5N is a matter of feed quality and process discipline rather than a different machine: the anode must be clean, the electrolyte must be kept within its silver and free-acid window, the current density and temperature must be held, and the powder must be washed free of nitrate before melting. Because 5N is a documentation claim as much as a metallurgical one, it is released against fire assay and ICP-OES results on the same batch.
Q16. How much does a silver refining machine cost, and what drives the price?
Cost is driven by five things: daily throughput, which sets the cell size, the cathode area and the rectifier rating; feed grade and impurity profile, which set whether pre-treatment, flux refining and additional electrolyte purification are needed; the level of automation, such as mechanical plate loading, automatic scraping and PLC control; the off-gas package, because the nitrogen-oxide absorption tower and fume condensation are sized to the actual acid load rather than being a fixed add-on; and the finishing scope, meaning whether melting, vacuum ingot casting, continuous casting and granulation are included or the customer already owns them. Because the price is a function of the feed and the target output, it is quoted after assay and test work rather than published as a list figure for a model number.
Q17. What warranty, installation and support are included?
A standard 12-month warranty from commissioning, or 18 months from shipment, whichever comes first, covering material and workmanship defects with defective-part replacement and free remote support, backed by a guaranteed-performance clause confirming the contracted purity, throughput and recovery at commissioning. Delivery includes supervised installation, commissioning on the customer’s own feed, off-gas outlet verification, on-site operator training with full SOPs and a handover dossier, a wear-part schedule with replacement intervals, a 24-hour remote response commitment, stocked spares and consumables, compliance support for emission and chemical-storage permitting, and lifetime technical support after warranty expiry.
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