Silver Electrolysis Machine

— Silver Electrolysis Machine: 99.99% Silver from Scrap

A silver electrolysis machine takes silver-bearing scrap that starts between 80% and 90% and returns it as 99.99% (9999 fine) silver in one continuous electrolytic operation. Crude silver is charged into titanium baskets wrapped in high-density filter bags instead of being melted and cast into anode plates, a rotating titanium drum or a titanium plate carries the cathode, and a dilute nitric acid electrolyte is held inside its working window while direct current dissolves the silver at the basket and deposits it on the drum as crystal. YuSai Machinery builds the machine as a complete unit — basket loading and bag sealing, electrolyte make-up and regeneration, high-frequency rectifier and busbar, circulation and cooling, drum harvest, crystal rinsing and drying, fume condensation and nitrogen-oxide abatement — and configures it around your own scrap assay, so that gold, platinum and palladium leave the machine as a saleable anode slime rather than as a loss in the rinse water.

Product Overview

A silver electrolysis machine is a self-contained electrolytic unit that upgrades silver-bearing scrap into fine silver. The input is metallic scrap and the output is crystalline silver: the feed is graded, charged into titanium baskets, immersed in a silver nitrate electrolyte carried in dilute nitric acid, and put under a controlled direct current so that the silver at the anode dissolves into solution and comes back out on the cathode as crystal. Base metals dissolve with the silver and stay in the liquor as nitrates, lead and bismuth are held out of the deposit by the acid window and hydrolyse instead, and gold, platinum, palladium and rhodium do not dissolve at all and are retained at the anode as slime. Nothing that is not silver follows the silver to the cathode, and the whole design problem is holding that condition steady for the length of a campaign.

The electrochemistry is simple to state. At the basket anode, metallic silver loses an electron and enters the solution as the silver ion, Ag − e⁻ = Ag⁺. At the drum cathode, the silver ion gains an electron and returns as metal, Ag⁺ + e⁻ = Ag, so the cell is written as Ag (anode) | AgNO₃, HNO₃, H₂O | Ag (cathode). The electrolyte is made by dissolving high-purity silver in nitric acid, Ag + 2HNO₃ → AgNO₃ + NO₂↑ + H₂O, and it is made up at 10–15% nitric acid by volume in demineralised water before being set to its working silver concentration. What makes the cell a purification step rather than a shuttle is where everything else goes: copper stays in solution and is removed on the bleed schedule, lead and bismuth are precipitated by the working acid band instead of being co-deposited, and the gold and the platinum group metals never enter the solution at all. Two streams therefore carry every impurity — the electrolyte and the anode slime — and the machine is designed around controlling both.

Current density is the parameter that decides how fast the machine works and how clean the product is, and it is the number most often missing from a silver electrolysis machine specification. Mixed 80–90% scrap is run at 300–500 A/m² of cathode area, and that band is a deliberate choice rather than a limitation of the hardware: the same machine takes up the 600–800 A/m² band on clean granulated silver, and the rectifier, busbar, circulation and cooling are sized for it. Scrap carries more copper, lead, bismuth and tin per kilogram of silver than a smelter’s cast anode does, and the rate at which those elements are dragged into the cathode deposit rises with current density, so the machine is set to the density the feed can hold and the extra capacity is spent on the feeds that can take it. Raising the density is paid for in three further currencies: the resistive drop across the electrode gap, the tendency of the basket charge to compact and slow its own dissolution as its silver content falls, and deposit morphology, because a crystal grown too fast at a starved boundary layer turns nodular and starts to bridge the gap.

The basket charge changes the geometry of the problem compared with a cast plate. A plate presents one flat dissolving surface and consumes evenly from the outside in; a basket is a packed bed, and the liquor has to reach the inner charge through the pack while the slime being released has to be carried out of it. That is why the basket is bagged on the outside rather than lined on the inside, why the pack is graded so that the charge does not screen its own flow, why the liquid level is held at least 15 cm above the top of the basket, and why circulation is run at a rate that keeps silver ions moving into the pack instead of being drawn from the outer face only. It is also why the machine is generous with cathode area: the drum is sized against the dissolution rate of the pack, not against the current the rectifier could deliver.

The electrolyte is the second thing that has to be held rather than set, and both of its boundaries are live in normal operation. Silver is held at 60–150 g/L with 10–18 g/L of free nitric acid, and the two failure modes sit on opposite sides of the same setpoint, which is why the liquor is titrated and corrected on a schedule rather than adjusted after a quality excursion. Below the free-acid window the bismuth and other base metals hydrolyse and the precipitate contaminates the crystal; above it the acid re-dissolves silver already deposited and drives the silver concentration up. Temperature is part of the same control: the machine holds the electrolyte below a 50 °C ceiling with the chiller set to start at 40 °C, because warmth lowers the electrolyte resistance and improves deposition kinetics but also raises evaporation, acid consumption and the quantity of silver carried out of the cell in the vapour.

The liabilities of the process are specific, and the machine contains them rather than describing them. Nitric acid mist and nitrogen oxides are generated at the cell and far more intensively at electrolyte make-up, where silver reacts with nitric acid, so both the cell and the make-up vessel are closed and extracted from the side, the vapour passes a condenser that returns entrained silver to the circuit, and the residual stream goes to a multi-stage absorption tower. Crystal bridging between basket and drum is a short circuit waiting to happen, which is why the drum is harvested on a 2–3 hour interval instead of being allowed to load. The anode bags are changed on a batch basis, because a bag that is left too long stops passing liquor, blinds the basket face and quietly converts a high-current-density machine into a low-current-density one. And the electrolyte and the slime are assayed every campaign, because those two streams are where an unmanaged machine loses both metal and grade.

Because scrap composition varies from one supplier and one lot to the next, and because a refining machine is judged on its ingot assay as much as on its output, YuSai configures the machine from your own material rather than from a fixed model list. Basket count, cathode area, rectifier rating, circulation rate, cooling duty, exhaust volume and effluent duty are set against your assay and your monthly silver volume, and the resulting figures are stated in the process design package. Configuration is engineered rather than selected from a catalogue, and the same platform is scaled up by adding basket and cathode area or scaled down to a single cell for a workshop that refines its own scrap. Working as a silver electrolysis machine manufacturer from the feed assay backwards rather than from a standard cabinet, we would rather revise the basket and bag specification than supply a machine that cannot hold the grade.

Key Facts

Silver purity: cathode crystal at 99.99% (9999 fine) from feed above 80% silver, and up to 99.999% where a second electrolysis pass on the crystal is specified.
Feed accepted: 80–90% silver scrap — old 925 jewellery, silverware and holloware, coin and bullion stock, silver solder and brazing scrap, contact and silver-plated scrap — charged into titanium baskets without being melted and cast into anode plates first.
Anode form: four or more titanium baskets wrapped in 100–150 mesh high-density filter bags, held with the electrolyte at least 15 cm above the top of the basket pack, so that the insoluble fraction stays at the anode as slime.
Cathode and harvest: rotating titanium drum as standard, with the crystal peeled off continuously and harvested on a 2–3 hour interval at design current; polished stainless steel or titanium plates are used where a plate cathode is preferred.
Electrolyte: a silver nitrate solution carried in dilute nitric acid, prepared at 10–15% nitric acid by volume for make-up and held at 60–150 g/L silver with 10–18 g/L of free nitric acid, with potassium nitrate available where the conductivity or the pH band needs help.
Current density and cell voltage: 300–500 A/m² of cathode area on mixed scrap feed, held deliberately below the 600–800 A/m² band that clean cast feed allows, because impurity transfer to the cathode rises with density; the cell runs at 2–5 V DC, read as a diagnostic rather than as a productivity handle.
Electrolyte temperature: held below a 50 °C ceiling, with the chiller set to start at 40 °C; warmer liquor lowers resistance but raises evaporation, acid consumption and the silver carried out in the vapour.
Two silver-bearing streams stay inside the circuit: the fume condenser returns vaporised electrolyte to the tank and the rinse-water cascade returns its first cut to electrolyte make-up, so neither evaporation nor washing is a metal loss.
Configuration: basket count, cathode area, rectifier rating, circulation rate, cooling duty, exhaust volume and effluent duty are engineered to your scrap assay, monthly silver volume, target product form and site conditions rather than selected from a fixed catalogue of models.

Product Core Selling Points

The machine takes scrap, not cast anodes. A conventional silver circuit requires the feed to be melted, fluxed and cast into anode plates before it can be refined, and every hour that silver spends in the furnace and in the anode mould is metal sitting in process rather than metal being refined. On this machine the feed is graded, granulated where the form requires it and charged straight into titanium baskets, so the melting step is limited to the final ingot cast and to the residual anode stock that comes back from each campaign.
Basket anodes with sealed filter bags, because that is where the value is. Gold, platinum, palladium and rhodium do not dissolve in a nitrate electrolyte. The bag holds them at the anode from the first minute of the run and lets the slime be drawn as a discrete, weighable, assayable stream, which is what allows the metal balance for the batch to close. Bag mesh is matched to the feed: a fine 150 mesh bag for finely divided residues, a coarser 100 mesh for granulated jewellery scrap where drainage matters more than retention.
A rotating drum cathode that clears itself. Silver deposits as a crystal and, left in place, it bridges the electrode gap, shorts the cell and distorts the current distribution across every other electrode. The drum rotates through the liquor and the crystal is peeled from its surface on a short interval, so the deposit never reaches bridging thickness, the cathode surface is refreshed continuously, and the machine holds its current instead of being throttled back as the deposit builds.
Dilute nitric acid at 10–15% by volume is the make-up standard. The working solution is made from high-purity silver and nitric acid in demineralised water rather than acquired as a proprietary reagent, and the acid strength is set at make-up and then monitored as free acid in grams per litre during the campaign. Both ends of the window matter: below it, bismuth and other base metals hydrolyse and the floc reports to the crystal as a grade loss that cannot be corrected afterwards; above it, the acid re-dissolves silver that has already been deposited.
Current density is set to the feed, not to the brochure. Mixed 80–90% scrap is run at 300–500 A/m² of cathode area. The band is chosen because impurity transfer to the cathode rises with current density, and scrap carries more copper, lead and bismuth per kilogram of silver than a cast anode from a smelter does. When the same machine is fed clean granulated silver, it is taken up into the 600–800 A/m² band, and the rectifier, busbar, circulation and cooling are sized for that headroom from the start.
The electrolyte is regenerated on the machine. Copper dissolves alongside the silver and accumulates in the liquor; as its concentration climbs, the deposition window narrows and copper begins to co-deposit, which shows up first as a change in crystal appearance and then in the assay. Impurity-loaded electrolyte is drawn off, treated so that the accumulated elements leave the circuit, re-acidified to its working pH and returned to the tank, with the silver it holds recovered in the same step instead of being neutralised to waste.
A pulse rectifier with PLC control, sized for the duty. The machine runs a high-frequency switch-mode rectifier with PLC and touchscreen control, adjustable voltage and current limits, a staged take-up programme and per-cathode current verification. Pulse output is used to keep the deposit fine-grained and coherent and to interrupt the growth habit that produces nodules and dendritic bridges, and the event log is written against the batch so that a drift in current or voltage can be traced to the hour it started.
Rinsing is counter-current, so the silver comes back. Entrained electrolyte would carry silver and nitrate out of the machine in the wash water. The crystal is rinsed with demineralised hot water in a cascade in which the first rinse is returned to the tank as electrolyte make-up and the second rinse becomes the first rinse of the next batch; rinsing continues until the rinse water reads neutral and its conductivity stops falling, and the crystal is then dewatered and dried.
Nitric acid mist and nitrogen oxides are contained at the machine. The cell runs under a transparent closed cover with side extraction, the vapour passes a condenser that returns entrained silver to the circuit, and the residual stream goes to a multi-stage absorption tower before release. Making up the electrolyte is the more intensive of the two fume sources, so make-up runs in its own closed vessel under extraction rather than at the open tank.
Drying, melting and assaying are part of the machine, not off-machine work. Crystal from the drum goes through a combined rinsing and drying unit, is dried to a moisture content fit for clean melting, and is then melted under a flux cover in an induction furnace, cast and sampled. The machine is delivered with a certificate of analysis per lot and a batch record that reconciles the charged weight, the product weight and the slime weight.
A compact unit that one operator can run. The machine is laid out so that loading, harvest, rinsing, bag change and titration are done from one working side, with mechanical handling for the basket assemblies where the layout allows. One operator is sufficient for intermittent supervision while the cell runs, which is the difference between a refining capability that exists on paper and one that survives a normal production week.
Materials chosen stream by stream for nitric acid service. Integrally formed polypropylene cell bodies with an anti-ageing additive rather than welded-seam construction, polypropylene homopolymer structural frames, titanium baskets and titanium-clad copper conductor bars, bakelite insulation between the bars and the tank, and PP and PVDF wetted parts and ducting throughout the fume path.
Configuration is engineered rather than catalogued. Basket count, cathode area, rectifier rating, circulation rate, cooling duty, exhaust volume and effluent duty are set from your assay and your monthly silver volume, and the resulting figures are stated in the process design package. What matters in this machine is how much silver is in the feed, what base metal load comes with it and what current the drum can carry — not a nominal daily figure.

Application Scenarios

Jewellery workshops and manufacturers refining their own scrap. Bench sweeps, filings, polishing dust, rejected castings and old 925 stock are refined in-house and returned to production as fine silver instead of being sold at a scrap discount or sent out for toll refining.
Precious metal recyclers taking mixed silver scrap. A machine that accepts 80–90% feed without an anode casting step is what allows a recycler to buy mixed silver-bearing material, run it in batches and sell certified fine silver rather than an intermediate.
Gold and silver exchange shops, pawn operations and bullion dealers. Old jewellery, coin, medallion and bullion stock with a grade that varies batch to batch, refined to a uniform 9999 grade with a certificate of analysis for each lot.
Refiners desilverising gold-rich material. Where a gold-bearing alloy or a gold doré carries silver above the ceiling that a gold cell can tolerate, the silver is taken out on this machine first, so that the residual gold-rich plate can be cast into a gold anode instead of passivating in a chloride electrolyte.
Smelters and refineries handling anode slime and doré. Silver recovered from copper and lead anode slime, and the associated doré and cement silver, brought to a saleable 9999 product rather than shipped as an intermediate.
E-waste and printed circuit board recyclers. Silver recovered from contacts, relays, silver-plated components, solder and the silver-bearing fractions of mixed electronic scrap after the copper and ferrous fractions have been separated.
Photographic, X-ray and imaging processors. Silver recovered as cemented silver or as a reduced residue from fixer, bleach-fix and wash water, dried and charged into baskets as clean feed for the machine.
Electroplating and surface finishing shops. Silver plating anode stubs, spent silver plating baths and drag-out silver taken back to fine silver and returned to the plating line or sold.
Solar photovoltaic cell recyclers. Silver recovered from the metallisation paste and the etched wafer fractions of end-of-life panels, where silicon and the other layer materials are separated before the silver is charged to the cell.
Catalyst and chemical processors. Spent silver catalysts, silver oxide and silver salt residues reduced to metallic silver and run through the machine, with the support material separated beforehand.
Mints, assay offices and laboratories. Small-volume, high-value work where the feed is well characterised and the requirement is a documented purity rather than throughput, served by the same platform in a single-cell configuration.
Contract and toll refiners. Third-party scrap refined in campaigns where the machine must reconfigure quickly between feeds and every batch has to close on a weighed metal balance and an assay certificate.
Small and medium refineries entering precious metal refining. A single-machine starting point that establishes a refining capability on the customer’s own scrap, with basket and cathode area added in parallel as volumes grow rather than a plant being designed for a volume that has not yet appeared.

Applicable Raw Materials

Each feed below is charged to the machine at the point its composition requires. Material that is already metallic and reasonably coarse — granulated silver, cast grain, cut plate, heavy jewellery — goes into the titanium baskets as it is; fine material such as polishing dust, sweeps ash, cemented silver and reduced residues is dried, fluxed and consolidated into granulated form first, because a loose powder pack screens its own flow and blinds the bag. Material carrying chloride is converted to metallic silver before it reaches the machine, because silver chloride will not dissolve anodically in a nitrate electrolyte. Output is stated for each feed.

Old 925 sterling jewellery and silverware. The reference feed for this machine: alloyed silver at roughly 80–92.5% with the balance copper, arriving as chains, rings, holloware, cutlery and damaged stock that would cost more to sort than to refine as a batch. Output: 99.99% silver crystal and a copper-bearing electrolyte bleed.
Bench sweeps, polishing dust and filings from jewellery manufacture. Fine, high-surface-area material carrying abrasive, rouge and workshop dirt, which is ashed or burnt off, fluxed and granulated before it is charged. Output: 99.99% silver crystal and a slag returned for silver recovery.
Silver solder and brazing alloy scrap. Feed running from about 60% to 95% silver depending on grade, with zinc, cadmium, copper or phosphorus in the balance, granulated and charged as a blend. Output: 99.99% silver crystal and a base-metal laden bleed.
Coin, medallion and bullion stock below fine grade. Old coinage and medallion stock whose grade varies from lot to lot, refined to a single declared 9999 grade with an assay certificate per batch. Output: 99.99% silver crystal and certified ingot.
Granulated crude silver and shot from upstream smelting. Cast grain or shot that needs no further preparation and can be charged directly into the baskets, which is the fastest route through the machine. Output: 99.99% silver crystal with a low-yield slime.
Silver doré from gold cyanidation and gravity concentrate smelting. Silver carrying gold, copper and platinum group metals, where the gold content sets how the batch is charged and how the residual basket charge is finished. Output: 99.99% silver crystal and gold-bearing anode slime.
Silver recovered from copper and lead anode slime. Slime-derived silver arriving as doré, cement or a reduced residue, charged according to its physical form and its gold content. Output: 99.99% silver crystal, with any remaining gold and PGM declared and routed onward.
Cemented silver and reduced silver residues. Fine, metallic and usually high grade but physically unsuitable for charging loose, so it is dried, fluxed and consolidated before it goes into the basket. Output: consolidated basket feed, then 99.99% silver crystal.
Silver-plated and contact-bearing electronic scrap fractions. Contacts, relays, switches, pins and silver-plated components, concentrated and pre-treated so that the copper and ferrous fractions are separated before the silver-bearing concentrate is charged. Output: 99.99% silver crystal and a separated base metal fraction.
Photographic, X-ray and imaging silver. Cemented or reduced silver from fixer, bleach-fix and wash water, delivered as a damp cake or a powder, dried and granulated for basket charging. Output: 99.99% silver crystal and a treated liquor stream.
Spent silver plating baths, anode stubs and drag-out silver. Plating-side silver recovered as metal, with plating salts and organic load removed before the material reaches the machine. Output: 99.99% silver crystal returned to the plating line or sold.
Silver catalysts, silver oxide and process salt residues. Recovered after the support material has been separated, reduced to metallic silver and charged as a granulated blend. Output: 99.99% silver crystal and a separated support fraction.
Residual basket charge and partly dissolved material returning from a campaign. Material that has not fully dissolved at the end of a campaign is bagged out, washed, dried and returned to a following batch or to the melting shop rather than being sold as scrap. Output: recycled basket charge and recovered silver.

Finished Products

The machine is configured around the product form the customer sells, from cathode crystal to certified bar. Where a melting shop already exists on site, the machine is supplied with the harvest, rinsing and drying stages and the customer casts; where it does not, melting, casting and assaying are included so that the machine delivers finished metal.

99.99% silver crystal. The primary product: crystalline cathode silver at the 9999 grade, rinsed free of entrained electrolyte, dewatered and dried, ready either for sale as crystal or for the melting stage. Output: dried 99.99% silver crystal with a lot assay.
9999 fine silver ingots and bars. Crystal melted in an induction furnace and cast into the bar or ingot weight the market requires, marked with weight and batch number. Output: certified 99.99% silver bar with certificate of analysis.
99.999% silver where a second pass is specified. Crystal re-run through the same machine as a second electrolysis pass, which is the route to the higher figure; the requirement is agreed against the end use rather than assumed. Output: 99.999% silver crystal or bar with a supporting assay.
Silver granules and grain. Where the product is sold as grain rather than as bar, the melt is granulated, dried, screened and packed to a declared grade. Output: packed silver grain at a declared grade.
Vacuum-cast and continuously cast silver. Where density, surface finish and freedom from porosity and oxidation matter, vacuum ingot casting or vacuum continuous casting is used instead of open casting. Output: high-finish silver bar or ingot for investment and industrial use.
Gold-bearing anode slime. The most valuable by-product of the machine, running at roughly 8% of the charged anode mass and typically assaying 50–70% gold with 30–40% silver; bagged out, washed free of entrained electrolyte, dried, weighed and assayed. Output: washed and assayed gold-rich slime with the silver and PGM fractions declared.
Nitric-parted gold residue. Slime from a feed with a high gold content is parted with nitric acid, which dissolves the silver and lifts the residual gold grade above 90% before it leaves for the gold circuit. Output: gold residue above 90% grade and a silver-bearing parting liquor returned to the machine.
Platinum group metal fraction from the slime. Where the feed carried platinum, palladium or rhodium, that fraction is separated from the slime and declared by metal content before it leaves for the PGM refining line. Output: PGM-bearing concentrate with declared metal content.
Regenerated electrolyte. Spent liquor from which the accumulated copper, bismuth and other impurities have been removed, re-acidified to its working pH and returned to the tank. Output: electrolyte returned to service at the working specification.
Silver recovered from the electrolyte bleed and the rinse-water cascade. The silver held in the liquor drawn off for regeneration, and the silver carried in the first rinse cut, are both returned to the circuit rather than neutralised to waste, which is where an unmanaged machine quietly loses metal. Output: recovered silver returned to the basket charge.
Condensed silver returned from the fume. Vaporised electrolyte captured by the condenser and returned to the tank, so that evaporation is a handling issue rather than a metal loss. Output: silver-bearing condensate returned to the cell.
Compliant off-gas and effluent. Cell and make-up vessel off-gas treated through condensation and multi-stage nitrogen-oxide absorption before release, and process effluent neutralised, metal-polished and either recirculated or discharged at the agreed limits. Output: emission and effluent records filed with the batch.
Batch documentation. Every lot is released with the charged weight and assay, the electrolyte analysis at make-up and at draw-off, the slime weight and assay, the product assay and the metal balance for that lot. Output: certificate of analysis and batch record.

Silver Electrolysis Machine Process Flow

The nine stages below are the standard flowsheet of the machine, from grading the incoming scrap through to a certified assay. Stages 2 and 5 are the two that decide the grade, and stages 6 and 8 are the two most often missing from competing machine specifications: the rinse water and the spent electrolyte are the streams in which an unmanaged machine loses both metal and purity. Basket count, cathode area, rectifier rating, circulation rate, cooling duty and exhaust volume are fixed during process design against your own feed assay.

Silver electrolysis machine process flow — nine stages from 80–90% silver scrap to a certified 9999 fine product, with the electrolyte regenerated and the gold-bearing anode slime recovered inside the same machine.

Steps 1 — Feed Grading and Basket Charge Preparation. Incoming material is weighed, sampled and assayed before anything is charged, and it is graded at the same time because the physical form decides how it can be charged. Silver is determined by fire assay with cupric chloride titration or an ICP-OES cross-check, gold by fire assay, and the base metal and platinum group metal inventory by ICP-OES. Four figures from that assay govern the rest of the run. The silver content sets the charge weight that matches the basket volume and the current the drum can carry. The gold and platinum group metal content sets the slime expectation for the batch and whether the slime will be parted afterwards. The copper, lead, bismuth and tin load sets the current density the batch can hold and the point at which the electrolyte must be drawn off for regeneration. And the physical form decides preparation: coarse material and cast grain are charged directly, fine dust, sweeps ash, cemented silver and reduced residues are dried, fluxed and granulated so that the pack does not blind its own bag, and anything carrying chloride is converted to metallic silver before it goes near the tank. The assay output is a batch route sheet that fixes the charge weight, the basket and bag specification, the target current density and the campaign length. Output: assay report, batch route sheet and a documented charged weight.

Steps 2 — Electrolyte Make-Up from Silver and Nitric Acid. The working solution is a silver nitrate electrolyte carried in dilute nitric acid, and it is made on site rather than bought in as a proprietary reagent. High-purity silver or cathode crystal is dissolved in nitric acid in demineralised water until the reaction is complete — Ag + 2HNO₃ → AgNO₃ + NO₂↑ + H₂O — the insoluble residue is filtered off, and the liquor is transferred to the tank and brought to its working specification of 60–150 g/L silver with 10–18 g/L of free nitric acid, with potassium nitrate added where the conductivity or the pH band needs help. The make-up acid strength is set at 10–15% nitric acid by volume, which is the practical band for a machine of this size: strong enough to dissolve the make-up silver at a workable rate, dilute enough to keep the reaction and the fume load controllable in a closed vessel. Both ends of the free-acid window are live. Below it, bismuth and other base metals hydrolyse and the floc reports to the cathode crystal as a grade loss that cannot be corrected afterwards. Above it, the acid re-dissolves silver that has already been deposited, which is a recovery loss and which drives the silver concentration upward until the electrolyte has to be corrected anyway. The dissolution reaction is strongly fuming, so make-up runs in a closed vessel under extraction with the gas routed straight to the absorption plant; the made-up liquor is then titrated for silver and for free acid and recorded against the batch. More first campaigns disappoint because the electrolyte was never assayed than for any other single reason. Output: electrolyte at 60–150 g/L silver with 10–18 g/L free acid, a make-up record, and NO₂ routed to the absorption tower.

Steps 3 — Basket Loading, Bag Sealing and Cell Immersion. The prepared charge is loaded into titanium baskets and each basket is enclosed in a high-density filter bag before it goes anywhere near the tank; bag mesh is matched to the feed, with a 150 mesh bag for finely divided material and a coarser 100 mesh bag for granulated jewellery where drainage matters more than retention. The pack is filled so that liquor can move through it rather than around it, without being tamped into a solid bed that would screen its own flow and slow its own dissolution. The bagged assemblies are then carried to the machine on a handling frame and immersed to depth, with the electrolyte level held at least 15 cm above the top of the basket pack so that the whole charge works and the slime released from the upper part of the pack settles inside the bag rather than against the basket face. Conductor bars, hooks and contact faces are cleaned and dressed, the spacing between basket and cathode is set with a gauge, and the per-position contact resistance is checked. A resistive contact or a mis-set basket does not fail immediately: it redistributes current across the remaining positions, shows up later as a localised burn or an unexplained low current on one drum section, and is far harder to diagnose once the cover is on and the cell is full. Output: bagged and immersed basket assemblies with verified spacing and contact, and the cell charged to its working level.

Steps 4 — Rectifier Take-Up and Deposit Seeding. The rectifier is set to the current and voltage programme fixed in process design and the current is brought up on a ramp rather than switched on at its full value, because the first minutes decide the structure of everything that grows afterwards. A modest initial current produces a coherent, fine-grained seed layer that stays coherent as it thickens; a cold start at full current produces a burst of nodules, high local current density at the contact edges and a deposit that sheds back into the liquor later in the run as fine silver that has to be recovered from the electrolyte. Pulse output from the high-frequency rectifier is used at this stage to interrupt the dendritic growth habit and to keep the seed layer dense. Per-position current is verified during the take-up, so that a poor contact or a mis-set basket is found in the first hours rather than at the bag change. Cell voltage is checked against the design figure, and the conductor bar and lug temperatures are confirmed stable, before the machine is left to run. Output: stable current distribution across the cathode, a coherent seed deposit established, and the corrected settings recorded against the batch.

Steps 5 — Basket-Anode Electrolysis with Drum Harvest. The machine then runs at 300–500 A/m² of cathode area on mixed scrap feed, held deliberately below the 600–800 A/m² band that the same hardware occupies on clean granulated silver, because impurity transfer to the cathode rises with current density and scrap carries more base metal per kilogram of silver than a smelter’s anode does. At the basket the silver dissolves as Ag − e⁻ = Ag⁺, the copper dissolves alongside it and stays in the liquor, the lead and the bismuth are held out of the deposit by the acid window and hydrolyse instead, and the gold and platinum group metals do not dissolve at all and are retained in the bag. At the rotating drum the silver ion is reduced as Ag⁺ + e⁻ = Ag and deposits as crystalline metal, which the drum carries out of the liquor and the blade peels off. Harvest is continuous in the sense that it never has to wait for a campaign to end — the crystal is drawn on a 2–3 hour interval at design current, so the deposit never reaches the thickness at which it would bridge the gap and short the cell. A chiller holds the electrolyte below a 50 °C ceiling and starts at a 40 °C set point, and circulation keeps the silver concentration at the drum face close to the bulk concentration so that the machine does not have to be run at a higher silver concentration than the process needs. The cell runs under a transparent closed cover with side extraction throughout. Output: 99.99% silver crystal, a copper-bearing electrolyte and a gold-bearing anode slime held at the anode.

Steps 6 — Crystal Rinsing, Dewatering and Dryness Check. Crystal lifted from the drum carries a film of electrolyte, and that film is silver and nitrate leaving the circuit unless it is handled deliberately. The crystal therefore goes straight from the drum into a rinsing and dewatering unit rather than being left in an open tray. Rinsing is counter-current with demineralised hot water: the first cut is returned to the tank as electrolyte make-up, and the second cut is held back to become the first rinse of the following batch, so the water and the silver that it holds stay inside the machine. The first cut is hot because the solubility of the entrained salts falls sharply as the rinse water warms, which is what makes a small number of rinses sufficient instead of a long wash. Rinsing continues until the water draining from the crystal reads neutral and its conductivity stops falling, which is the practical endpoint: a rinse checked by pH alone will pass while nitrate is still present. The rinsed crystal is then dewatered mechanically and dried to a moisture content fit for clean melting, screened, weighed and sampled against the batch number. Output: dried 99.99% silver crystal with the nitrate removed, a rinse-water cascade returned to the circuit, and a lot sample.

Steps 7 — Anode Slime Bag Change and Slime Recovery. The bag is where the insoluble fraction of the whole batch accumulates: gold, platinum, palladium, rhodium, and any silver that did not dissolve with the balance of the charge. Bags are changed on a batch basis — typically every two to three days of running, and more often when the feed is finely divided — because a bag that is left in service stops passing liquor and blinds the basket face, which throttles the batch and lowers the effective current density without any alarm being raised. At the change the assembly is lifted, drained over the tank so that the entraining liquor returns to the circuit, and the bag is opened over a wash station. The slime is washed free of entrained electrolyte, dried, weighed and assayed. It runs at roughly 8% of the charged anode mass and typically assays 50–70% gold with 30–40% silver, which is high enough that the slime is not normally melted straight into a gold anode: it is either parted with nitric acid, so that the silver dissolves and the residual gold grade rises above 90% for the gold circuit, or cast and given a second electrolysis pass. Partly dissolved residual charge that did not give up its silver in the campaign is washed, dried and returned to a following batch or to the melting shop, and the platinum group metal fraction is separated and declared by metal content where the feed carried one. Output: washed and assayed gold-rich slime, a PGM fraction where present, and residual charge returned to the machine.

Steps 8 — Spent Electrolyte Regeneration and Rinse-Water Return. Copper dissolved from the scrap does not follow the silver to the cathode, which is exactly why 80–90% alloyed feed can be run on this machine without a pretreatment step; but it does accumulate, and once its concentration in the liquor is high enough the deposition window narrows and copper begins to co-deposit. That change shows up first as a shift in crystal appearance and then in the assay, and by then the batch has already been run. Impurity-loaded electrolyte is therefore drawn off on the bleed schedule rather than after an excursion. It is transferred to the regeneration vessel, where the accumulated impurities are taken out of the circuit, the liquor is re-acidified to its working pH and its silver is recovered rather than neutralised to waste, and the regenerated electrolyte is returned to the tank with a fresh titration against the batch record. In the same stage the rinse-water cascade is closed: the first cut from the most recent batch goes back into the circuit, the second cut becomes the first rinse of the next one, and the small quantity of water that leaves the machine leaves as moisture in the dried crystal or as neutralised effluent. The condenser on the fume path is emptied on the same schedule, and the silver-bearing condensate returns to the tank. Output: regenerated electrolyte with its silver recovered, a rinse-water cascade closed to the circuit, and a bleed record against the batch.

Steps 9 — Induction Melting, Ingot Casting and Purity Release. The dried crystal is melted in an induction furnace under a flux cover, treated against gas absorption on the melt surface, sampled and cast into ingots, bars or granulated grain, with vacuum ingot casting or vacuum continuous casting where the product form calls for density and surface finish rather than weight alone. Silver melts at 961 °C, and the moulds are preheated before pouring so that the bar face does not carry the cold-shut and surface porosity that a cold mould produces. Each lot is then re-assayed on a sample drawn from the released batch, by fire assay with a cupric chloride titration or an ICP-OES cross-check, and the batch is not released until the certificate of analysis confirms the grade. The documentation set holds the charged weight and assay, the electrolyte analysis at make-up and at draw-off, the campaign record from the PLC event log, the slime weight and assay, the product weight and assay, and the metal balance that reconciles them — which is what connects the bar in the customer’s hand to the scrap lot that produced it. Output: certified 9999 fine silver ingot, bar or grain, and a certificate of analysis with a closed metal balance.

Product Structure (Main Equipment)

The machine is assembled from the five equipment groups below. Materials of construction are selected stream by stream for nitric acid service: integrally formed polypropylene for the cell body rather than welded-seam construction, with an anti-ageing additive where the liquor is warm and strongly acid; polypropylene homopolymer for the structural frame and basket support; titanium for everything that touches the basket charge and the cathode surface; titanium-clad copper for the conductor bars, with bakelite insulation between the bars and the tank; and PP and PVDF wetted parts along the whole fume path.

Cell body, basket assemblies and containment

Integrally formed polypropylene cell body with an acid-resistant finish, a sloped internal floor that keeps crystal and slime moving towards the discharge point instead of accumulating in a corner, and a discharge valve with a solid-liquid separation detail so that the liquor can be drawn off from under the basket assemblies without carrying the crystal with it.
Titanium baskets with perforated walls and reinforced rims, sized to the batch and the cathode area; basket count is set in process design, and the support frame holds each basket at a fixed spacing so that the cathode-to-basket distance is identical at every position.
High-density filter bags, 100–150 mesh depending on the feed, sized to the basket and closed with a sealed seam so that the insoluble fraction is retained rather than washing out through the bag mouth.
Transparent closed cover in sections, sitting on the cell body with the extraction connection at the side, so that the electrode positions and the liquor can be inspected while the headspace stays closed.
Basket handling frame or lifting points on the assemblies, so that a loaded basket is moved to and from the tank mechanically rather than by hand over the liquor.

Cathode assembly, harvest and current delivery

Rotating titanium drum cathode as the standard cathode for this machine, carried on acid-resistant bearings with an insulated drive, rotating slowly enough that the liquor film on the drum is continuously renewed and fast enough that the deposit is carried clear of the liquor for the blade.
Crystal blade and discharge chute peeling the deposit from the drum surface on a continuous basis, with the interval between harvests set at 2–3 hours at design current rather than left to the operator’s judgement.
Titanium cathode plates where a plate cathode is preferred, hung in parallel with the baskets and spaced with a gauge, for customers who want a stationary cathode system.
Titanium-clad copper conductor bars and lugs sized for the machine’s current with a low-resistance contact face, cooling surfaces adequate to hold the bar temperature down, and bakelite insulation between the bars and the tank to eliminate stray-current corrosion of the containment.
Busbar and inter-cell connections arranged so that a single position can be isolated and checked for current without shutting the machine down.

Rectifier, controls and instrumentation

High-frequency switch-mode rectifier with adjustable voltage and current limits, pulse output for deposit control, a staged current take-up programme and the current range the machine’s cathode area requires; single-phase supply for a compact unit and three-phase for installations where the load profile calls for it, at the local voltage and frequency.
PLC with a touchscreen operator interface covering rectifier control, the take-up programme, circulation and drum rotation, temperature control, harvest sequencing and the alarm annunciation, with a per-position current display so that a weak contact is visible on the screen rather than inferred from a low output.
Event log and batch record, writing current, voltage, temperature, circulation status and alarm history against the batch number, so that a drift in any of them can be traced back to the hour it began.
Level, temperature and flow instrumentation in the tank and the circulation loop, including a temperature controller that starts and stops the chiller on the measured electrolyte temperature rather than on a fixed schedule.

Electrolyte circuit, cooling and fume path

Circulation pump and piping sized to keep the silver concentration uniform through the basket pack and across the drum surface, with a filtration leg that takes out fine silver and slime carry-over before it can be re-deposited on the drum.
Chiller and heat exchange loop holding the electrolyte below the 50 °C ceiling and starting at the 40 °C set point, sized against the electrical energy dissipated in the cell rather than against the tank volume.
Electrolyte make-up and regeneration vessels, closed and extracted, with agitation and metered nitric acid dosing for make-up, and a regeneration vessel in which the bleed is treated, re-acidified and returned to the tank.
Fume condenser on the cell and the make-up vessel, cooling the vapour below its dew point so that entrained electrolyte returns to the tank as condensate instead of leaving as a metal loss.
Multi-stage nitrogen-oxide absorption tower downstream of the condenser, sized to the extraction volume of the machine and the fume load released during make-up, with the scrubber liquor managed as part of the site’s effluent scheme.

Rinsing, drying and finishing

Rinsing and dewatering unit taking crystal directly from the drum or the tray, with a counter-current cascade in which the first rinse cut returns to the tank as electrolyte make-up and the second cut becomes the first rinse of the next batch.
Dryer bringing the crystal to a moisture content fit for clean melting, with the temperature set low enough that the crystal is dried rather than oxidised, and a discharge arranged so that the dried crystal can be sampled before it is melted.
Induction melting furnace with a graphite or clay-bonded crucible, a flux cover for the melt, and a mould set with preheat, for casting bars, ingots or granulated grain.
Assay and sampling equipment, including sample splitting, drying and preparation for fire assay or ICP-OES, so that each lot can be sampled on site and released against a certificate of analysis.

Product Features

Basket-anode charging removes the anode casting step. Granulated, cemented, powdered and coarse metallic feed is charged into titanium baskets rather than melted and cast into plates, which takes a melting step and its metal inventory out of the flowsheet and lets a batch be started from material that has already been assayed.
Titanium baskets with sealed 100–150 mesh bags. The insoluble fraction is retained where it can be weighed and assayed rather than migrating to the cathode, and the mesh is matched to the feed so that drainage through the pack is not sacrificed to retention.
Rotating titanium drum cathode with continuous peel. The drum carries the deposit out of the liquor and the blade removes it before it can reach bridging thickness, so the machine holds its current instead of being throttled back as the deposit builds.
Harvest on a 2–3 hour interval at design current. The interval is set from the deposition rate rather than left to the operator, which keeps the drum surface refreshed and the current distribution even across the cathode.
Dilute nitric acid electrolyte at 10–15% by volume for make-up, brought to 60–150 g/L silver with 10–18 g/L of free nitric acid and corrected on a titration schedule, with potassium nitrate available where the conductivity or the pH band needs help.
Current density set to the feed. 300–500 A/m² on mixed 80–90% scrap, and up to the 600–800 A/m² band on clean granulated silver, with the rectifier, busbar, circulation and cooling sized for the higher band from the start.
Cell voltage read as a diagnostic. The working band is 2–5 V DC, and a rising voltage at constant current is worked through in a fixed order — contacts, basket condition, silver concentration, free acid, temperature — instead of being answered with more current.
Electrolyte temperature held below a 50 °C ceiling with the chiller starting at the 40 °C set point, which keeps the resistance low without paying for it in evaporation, acid consumption and silver in the vapour.
Fume contained at both sources. A closed cell cover and a closed make-up vessel, side extraction, a condenser that returns silver-bearing condensate to the circuit, and a multi-stage absorption tower on the residual stream.
Counter-current rinsing with the first cut returned. The crystal is rinsed with demineralised hot water until the drainage reads neutral and its conductivity stops falling, and the first rinse cut goes back into the electrolyte circuit rather than to the drain.
Electrolyte regenerated in place with its silver recovered. Impurity-loaded liquor is drawn off on the bleed schedule, treated, re-acidified and returned to the tank, which cuts both the frequency of make-up and the nitric acid demand of the machine.
Slime handled as a value stream. The bags are changed on a batch basis, the slime is washed, dried, weighed and assayed, and it is either nitric-parted to raise the gold grade above 90% or cast for a second electrolysis pass, with any PGM fraction declared by metal content.
Rinsing, drying, melting and assaying inside the machine scope. The customer receives certified metal rather than a wet powder, and every lot is released with a certificate of analysis and a metal balance that closes.
Materials selected for nitric acid service stream by stream. Integrally formed polypropylene cell bodies with an anti-ageing additive, PPH structural frames, titanium baskets and drum, titanium-clad copper conductor bars, bakelite insulation, and PP and PVDF wetted parts and ducting.
Cleanable and reconfigurable between feeds. The cell can be drained, the baskets and bags changed and the electrolyte corrected between batches, which is what allows one machine to run mixed scrap, cement silver and doré in sequence with a documented assay at each step.
Engineered configuration rather than a fixed catalogue. Basket count, cathode area, rectifier rating, circulation rate, cooling duty, exhaust volume and effluent duty are set from your assay and your monthly silver volume, and the figures are stated in the process design package.

Technical Parameters And Specifications

Parameter	Specification
Primary function	Electrolytic upgrading of silver-bearing scrap into 99.99% cathode silver, with the gold and platinum group metals recovered as anode slime
Feed silver content	80–90% silver accepted as standard, and above 60% for solder and brazing scrap blends; fine and powdery feed is granulated before charging
Feed gold content	Any content that the feed can present; gold does not dissolve and reports to the anode bag, and a high gold content is a slime value rather than a process limit
Feed physical form	Granulated silver, cast grain or shot, cut plate, coarse jewellery, consolidated residues; fine dust, sweeps ash, cemented silver and reduced residues are dried, fluxed and granulated first
Chloride-bearing feed	Converted to metallic silver before charging; silver chloride will not dissolve anodically in a nitrate electrolyte
Anode form	Titanium baskets charged with prepared silver and wrapped in a high-density filter bag; no anode casting step is required
Basket count and cathode area	Set in process design from the batch weight, the charge density of the feed and the current the cathode area carries
Filter bag mesh	150 mesh for finely divided residues and 100 mesh for granulated jewellery, in a sealed bag sized to the basket
Electrolyte level	Held at least 15 cm above the top of the basket pack so that the whole charge works and the slime settles inside the bag
Cathode material	Rotating titanium drum as standard; titanium or polished stainless steel plates where a stationary cathode system is preferred
Harvest mechanism	Blade peel of the drum surface with the crystal discharged to the rinsing unit; harvest interval 2–3 hours at design current
Cathode current density	300–500 A/m² on mixed 80–90% scrap feed, and up to the 600–800 A/m² band on clean granulated silver; the density is set to the base metal load of the batch because impurity transfer to the cathode rises with density
Cell voltage	2–5 V DC across the working band; a rising voltage at constant current is treated as a fault indicator and worked through as contacts, basket condition, silver concentration, free acid and temperature
Rectifier type	High-frequency switch-mode rectifier with adjustable voltage and current limits and pulse output for deposit control
Rectifier control mode	Constant current or constant voltage as the flowsheet specifies, with a staged take-up programme at the start of each batch
Cell supply	Single-phase for compact configurations and three-phase for installations that call for it, at the local voltage and frequency
Electrolyte system	Silver nitrate carried in dilute nitric acid, with potassium nitrate available where the conductivity or the pH band requires it
Electrolyte make-up acid strength	10–15% nitric acid by volume in demineralised water at make-up, then monitored as free acid during the campaign
Silver concentration in electrolyte	60–150 g/L Ag
Free nitric acid	10–18 g/L; below the window bismuth and other base metals hydrolyse into the crystal, above it re-dissolves silver already deposited
Electrolyte acid control	Titrated and corrected on schedule during the campaign, and re-acidified to the working pH during regeneration
Electrolyte temperature	Held below a 50 °C ceiling, with the chiller starting at a 40 °C set point on the measured electrolyte temperature
Conductor bar and lug temperature	Engineered to stay below 70 °C in continuous operation
Electrolyte circulation	Forced circulation through the basket pack and across the drum face, with a filtration leg removing fine silver and slime carry-over
Electrolyte regeneration	Impurity-loaded liquor drawn off on the bleed schedule, treated, re-acidified and returned to the tank, with its silver recovered rather than neutralised
Current density control	Per-position current display and logging, so that a weak contact or a blinded basket is visible before it affects the assay
Rinsing	Counter-current rinse with demineralised hot water; the first rinse cut returns to the tank as electrolyte make-up and the second becomes the first rinse of the next batch
Rinsing endpoint	Rinse water draining from the crystal reads neutral and its conductivity stops falling; pH alone does not confirm that nitrate has been removed
Drying	Crystal dried to a moisture content fit for clean melting, with the drying temperature set low enough that the crystal is dried rather than oxidised
Melting	Induction furnace with a graphite or clay-bonded crucible, a flux cover on the melt and preheated moulds; silver melts at 961 °C
Product forms	Silver crystal, granulated grain, and cast ingots or bars, with vacuum ingot or vacuum continuous casting where density and surface finish require it
Product purity	99.99% (9999 fine) as standard; 99.999% where a second electrolysis pass on the crystal is specified against the end use
Anode slime	Roughly 8% of the charged anode mass, typically assaying 50–70% gold with 30–40% silver, plus the platinum group metal fraction where the feed carries one
Slime handling	Bags changed on a batch basis, typically every two to three days of running and more often on finely divided feed; slime washed, dried, weighed and assayed
Slime parting	Nitric acid parting to lift the residual gold grade above 90% for the gold circuit, or casting for a second electrolysis pass
Fume control	Transparent closed cover with side extraction, closed make-up and regeneration vessels, fume condenser returning silver-bearing condensate to the circuit, and a multi-stage nitrogen-oxide absorption tower
Water quality	Demineralised water for electrolyte make-up and for rinsing, held to a low-microsiemens specification, since chloride and hardness in the make-up water end up in the electrolyte
Effluent handling	Segregated process effluent, neutralised, metal-polished and either recirculated or discharged at the agreed limits, with the analysis filed against the batch
Instrumentation and control	PLC with touchscreen operator interface, rectifier and take-up control, circulation and drum rotation, temperature control, per-position current and cell voltage logging, alarm annunciation and an event log written against the batch
Operating labour	One operator for intermittent supervision while the cell runs, with basket handling by frame or lifting point and bag changes done from the working side of the machine
Operating consumables	Nitric acid, potassium nitrate where specified, demineralised water, filter bags, flux, crucible and mould consumables, and scrubber liquor make-up
Verification	Fire assay with cupric chloride titration or ICP-OES confirmation; every lot released against a certificate of analysis with a closed metal balance
Capacity, basket count, cathode area, power, footprint and utilities	Engineered to your feed assay, monthly silver volume, target product form and site conditions
Installation	Indoor, on a level floor, with the containment, bunding, ventilation and segregated drainage arrangements shown on the layout drawing

Technical Advantages

The machine is sized to the feed’s impurity load, not to a catalogue number. Mixed 80–90% scrap is run at 300–500 A/m² of cathode area because the rate at which copper, lead and bismuth are dragged into the deposit rises with current density, while the same hardware takes up the 600–800 A/m² band on clean granulated silver. The machine’s headroom is therefore a real capability rather than a specification figure, and it is spent only on the feeds that can absorb it.
No anode casting step, so the silver is not locked up in the furnace. A cast-plate circuit holds a working inventory in the melter, in the moulds and in anode stock; charging baskets from assayed scrap shortens the time between buying material and selling certified metal, which matters more to a machine of this size than a marginal difference in throughput.
The basket and bag specification is matched to the feed rather than fixed. Pack grading, bag mesh, immersion depth and circulation rate are chosen together, because a basket that screens its own flow will silently derate the machine — the current stays where it was set while the dissolution rate falls away, and the batch simply takes longer without any alarm.
A drum cathode that removes the main cause of throttling. Crystal left on the cathode bridges the gap, shorts the machine and distorts the current across every other position. Continuous peel on a 2–3 hour interval keeps the deposit below bridging thickness, which is what allows the machine to hold its current density for the whole campaign instead of tapering off as the deposit builds.
The deposit is controlled while it forms, not corrected afterwards. Pulse output from a high-frequency rectifier, a staged take-up programme and a coherent seed layer together hold the deposit fine-grained and dense, which reduces nodular growth, reduces silver shed back into the electrolyte, and keeps the crystal easy to rinse.
Both silver-bearing losses are closed by design. The fume condenser returns vaporised electrolyte to the tank and the counter-current rinse cascade returns its first cut to electrolyte make-up, so evaporation and rinsing are handling questions rather than losses. Those are the two places a small silver machine quietly gives away metal, and neither is visible on a production report.
The rinse endpoint is a measurement, not a habit. Rinsing continues until the drainage reads neutral and its conductivity stops falling. A rinse judged by pH alone passes while nitrate is still entrained, and that nitrate goes into the melt, into the slag and into the assay as a discrepancy nobody can explain afterwards.
Electrolyte regeneration on the machine rather than off it. Copper accumulates as the scrap is refined, and regenerating the bleed in place — with its silver recovered and the liquor returned to the tank — cuts both the make-up frequency and the nitric acid demand, and avoids the far more expensive habit of neutralising silver-bearing liquor to waste.
The fume is contained at the source, which keeps the scrubber small. Make-up is the more intensive fume source and it is closed and extracted like the cell; a condenser takes the silver out of the vapour before the absorption tower sees it, so the tower is sized for the residual load rather than for the whole vapour volume.
Materials are specified for nitric acid service stream by stream. Integrally formed polypropylene cells with an anti-ageing additive instead of welded seams, PPH frames, titanium baskets and drum, titanium-clad copper bars with bakelite insulation, and PP and PVDF wetted parts along the fume path — the difference between a machine that runs for years and one that leaks at a seam in its first.
The batch record closes on metal. Charged weight and assay in, product weight and assay out, slime weight and assay alongside, and the electrolyte analysis at both ends of the campaign. That is what makes the machine’s figures checkable on the customer’s own material, and it is what a refiner needs when the material is somebody else’s.
One platform, configured rather than re-engineered. Basket and cathode area are added in parallel as volume grows, so a single-cell machine that validates the route on a customer’s own scrap can be extended into a multi-position installation without replacing the unit or re-learning the process.

Service Process

Step 1 — Feed Sample and Site Data Review. Send a representative sample of the scrap, residue, cement silver or slime-derived feed with an indication of grade, monthly volume and the product form you intend to sell. Our metallurgical team assays it for silver and gold by fire assay with an ICP-OES cross-check, screens the base metal and platinum group metal load, and reviews the site information that decides the configuration: available floor area, power supply, water quality, drainage, ventilation route and the acid handling and storage arrangements. Where the feed is a mixed or variable stream, two or three samples taken across normal production are more useful than one ideal one, because the machine is configured against the range, not the best case.

Step 2 — Bench and Pilot Electrolysis Test. The sample is charged and run at bench and pilot scale to confirm the basket and bag specification, the make-up acid strength and the working silver concentration, the free-acid band the feed needs, the current density the batch can hold and the harvest interval it implies, the expected crystal quality and rinse behaviour, the anode slime yield and composition, and the bleed rate at which the electrolyte has to be drawn off. Where the feed carries chloride, or where the physical form needs granulating, that step is tested as well. The output is a test report stating the achievable purity on your material, the expected slime yield and the working parameters the machine will be configured to.

Step 3 — Machine Configuration and Engineering Package. The machine is then specified against the tested feed: basket count and cathode area, rectifier rating, circulation and filtration rate, cooling duty, exhaust volume, rinse-water arrangement and effluent duty, together with the layout, the containment and bunding, the ventilation route and the utility schedule. Because capacity is engineered rather than selected from a catalogue, the process design package states the figures that follow from your assay and your monthly silver volume, and the same figures are the ones the site is built to.

Step 4 — Fabrication, Assembly and Factory Run-In. The cell, basket assemblies, drum and blade, frame, rectifier, circulation and cooling package, extraction and condenser, absorption tower and the rinsing, drying and melting stages are fabricated and assembled as a unit. The machine is then wet-run at the factory: the cell is filled, circulation and temperature control are tested, the drum and blade are run through a harvest cycle, the extraction and condenser are proved, the rectifier is taken through its take-up programme, and the control and alarm functions are checked against the same list the customer will use at site. Witness testing and a pre-shipment inspection can be arranged where the project requires it.

Step 5 — Dispatch, Installation and First Campaign. The machine is shipped with the layout drawing, the utility schedule and the commissioning procedure, and is installed and commissioned by our engineers, either on site or with remote supervision where local conditions require it. Commissioning includes making up the first electrolyte, charging the first batch from the customer’s own material, taking the rectifier through its first take-up, running the first harvest and the first bag change, and completing the first full campaign with the rinse and the metal balance. The first campaign is run with us on the floor rather than on a manual, because the two stages where a new operator loses material are the harvest interval and the rinse endpoint.

Step 6 — Operator Certification and Handover. Operators are trained on the machine they will actually run: basket preparation and bag sealing, charge weights against basket volume, make-up and titration, the take-up programme, harvest and bag change timing, the rinse endpoint check, drying and melting, sample taking, and the fault tree for a rising cell voltage or a low current position. Training covers the safety routine around nitric acid, the nitrogen-oxide alarm and the extraction interlock, and the acid handling and storage arrangements. Handover is against the commissioning list, the process design package, the drawings, the operating and maintenance manuals and the spare parts list, and operators are signed off against the tasks they will perform unsupervised.

Step 7 — Campaign Reviews and Consumable Planning. After handover we review the first campaigns against the batch records: achievable purity, slime yield and composition, electrolyte consumption and bleed frequency, bag life, nitric acid consumption, harvest interval and the actual rinse water balance. Those reviews are what turn a commissioned machine into a stable one, because the correct bleed schedule and bag interval for a customer’s own scrap are found in their records rather than in a specification. Consumable planning — filter bags, flux, crucibles and moulds, scrubber liquor, spare electrodes and seals — is set from the same records so that the machine is not stopped by a consumable that was never ordered.

Warranty And After-Sales Service

The machine is supplied with a twelve-month warranty from commissioning or eighteen months from dispatch, whichever falls first, covering design, materials and workmanship on the cell body, basket assemblies, drum and drive, frame, conductor bars, rectifier and control system, circulation and cooling package, extraction and condenser, absorption tower and the rinsing, drying and melting stages. Wear parts are excluded as a matter of course and are listed as such in the offer: filter bags, crucibles, moulds, blades, seals, gaskets, scrubber liquor and the flux and reagent consumables are wear or consumable items rather than warranted components. Full terms, including the exclusions and the claim procedure, are stated in the contract rather than summarised here.

Commissioning by our engineers. Installation supervision, commissioning, electrolyte make-up, the first charged batch and the first full campaign are part of the delivery, with the acceptance criteria agreed in the contract and signed off against the commissioning list.
Operator training and certification. Training is delivered on the installed machine against the tasks the operators will perform unsupervised, including basket preparation, loading and bag sealing, make-up and titration, the take-up programme, harvest and bag change timing, the rinse endpoint check, drying and melting, sampling, and the safety routine around nitric acid and nitrogen oxides.
Spare parts and wear-part availability. A commissioning spares kit ships with the machine, including filter bags, seals and gaskets for the first campaigns, and a recommended first-year spares list is issued with the offer. Wear parts are held as standard items so that a bag, blade or seal is not the reason a machine stands idle.
Technical support and remote diagnosis. Support is available through the commissioning and warranty period and afterwards on an agreed basis, including remote review of the PLC event log and the batch records, which is usually enough to identify a rising cell voltage, a weak contact, a blinded basket or a drifting electrolyte before it reaches the assay.
Process support when the feed changes. Where a customer’s feed stream changes — a new scrap source, a higher gold content, a different alloy — the working parameters are re-derived against a fresh sample rather than extrapolated from the old batch. The machine is the same; the bag specification, current density, bleed rate and rinse schedule may not be.
Documentation set. The machine is delivered with the process design package, general arrangement and layout drawings, the utility schedule, electrical and P&ID drawings, the operating and maintenance manuals, the spare parts list, the commissioning and acceptance records, and a certificate of analysis for the first campaign.
Assay and metal balance discipline. Every batch on the machine is documented with the charged weight and assay, the electrolyte analysis at make-up and at draw-off, the slime weight and assay, the product weight and assay, and the metal balance that reconciles them. Where a batch does not close within the agreed tolerance, that record is what allows the cause to be found in the process rather than argued about at the assay.

Frequently Asked Questions

What is a silver electrolysis machine, and what does it replace?

A silver electrolysis machine is a self-contained electrolytic unit that upgrades silver-bearing scrap into 99.99% fine silver. Feed that starts between 80% and 90% silver is charged into titanium baskets, immersed in a silver nitrate electrolyte carried in dilute nitric acid, and put under a controlled direct current, so that the silver dissolves at the basket and deposits on the cathode as crystal while the base metals stay in the liquor and the gold and platinum group metals stay in the bag. It replaces the same duty that chemical refining is often used for at workshop scale, and it also removes the melting and anode-casting step that a conventional cast-plate silver cell requires: on this machine the scrap goes into the basket as assayed material rather than through a furnace and an anode mould first. It is also used in reverse as a desilverising machine, where taking silver out of a gold-rich alloy is what allows the residual gold plate to be run in a gold cell at all.

What purity does a silver electrolysis machine produce?

Cathode crystal at 99.99%, which is the 9999 fine grade, from feed above 80% silver, and up to 99.999% where a second electrolysis pass on the crystal is specified. The figure is not a property of the machine alone: it depends on the assay of the feed, the base metal load that the batch brings with it, the current density the batch is run at, the free-acid window held during the campaign and the discipline of the rinse at the end. That is why the achievable purity on your own material is confirmed in a bench or pilot test and stated in the process design package rather than quoted from a table, and why every lot is released against a certificate of analysis rather than against a nominal grade.

Why does this machine charge titanium baskets instead of casting anode plates?

Because casting an anode costs a melting step, a flux bill and a working inventory of silver sitting in the furnace, the moulds and the anode stock – and for scrap at 80% to 90% silver it buys nothing that the basket does not already provide. The basket accepts granulated silver, cast grain, cut plate, coarse jewellery and consolidated residues as assayed material, holds the insoluble fraction in the same way a bagged plate does, and lets a batch be started the day the material is graded and assayed. Plates remain the better answer where the feed is already a smelter’s cast anode and the object is the highest possible current density on a uniform dissolving surface; the basket is the better answer for a machine that has to handle whatever scrap arrives.

What is the advantage of a rotating drum cathode?

The drum keeps the deposit thin and the cathode surface fresh. Crystal left on a cathode grows until it bridges the gap to the basket, at which point the machine is short-circuited, the current distribution across every other position is distorted and the quality of the crystal still in the tank falls away. A drum carries the deposit out of the liquor and a blade peels it off on a 2-3 hour interval, so the deposit never reaches bridging thickness and the machine holds its current for the whole campaign instead of being throttled back as the load builds. The rotation also keeps the liquor film at the cathode face renewed, which is the same boundary-layer control that would otherwise have to be provided by more aggressive circulation.

What electrolyte does the machine use, and why is it made up at 10-15% nitric acid?

The electrolyte is a silver nitrate solution carried in dilute nitric acid, made on site by dissolving high-purity silver in nitric acid in demineralised water, Ag + 2HNO3 -> AgNO3 + NO2 + H2O, filtering off the insoluble residue and bringing the liquor to 60-150 g/L of silver with 10-18 g/L of free nitric acid. The make-up acid strength is set at 10-15% nitric acid by volume: strong enough to dissolve the make-up silver at a workable rate, dilute enough to keep the reaction and the fume load controllable in a closed vessel. Both ends of the free-acid window are live in service. Below it, bismuth and other base metals hydrolyse and the precipitate reports to the crystal as a grade loss that cannot be corrected afterwards. Above it, the acid re-dissolves silver that has already been deposited.

What current density does the machine run at, and how is it chosen?

Current density on this machine is set by the feed rather than by the hardware, which is why mixed 80-90% scrap is run at 300-500 A/m² of cathode area, while the same machine takes up the 600-800 A/m² band on clean granulated silver. The rectifier, busbar, circulation and cooling are sized for that headroom from the start, so the higher band is a real capability rather than a specification figure. The choice is a feed decision rather than a hardware limit: impurity transfer to the cathode rises with current density, and scrap carries more copper, lead, bismuth and tin per kilogram of silver than a smelter’s cast anode does, so raising the density on a dirty feed buys throughput and pays for it in grade. Three further costs come with density – the resistive drop across the electrode gap, the tendency of the basket pack to slow its own dissolution as its silver content falls, and deposit morphology.

How often is the crystal harvested, and how often are the anode bags changed?

The drum is harvested on a 2-3 hour interval at design current, which is set from the deposition rate rather than left to the operator’s judgement. The anode bags are changed on a batch basis, typically every two to three days of running and more frequently when the feed is finely divided, because a bag left too long stops passing liquor and blinds the basket face. A blinded basket does not raise an alarm: the current stays where it was set while the dissolution rate falls away, so the batch simply takes longer and the effective current density drops without anyone noticing. That is why the bag interval is written into the operating routine and why the slime weight is recorded at every bag change rather than only at the end of a campaign.

Where do the gold and the platinum group metals end up?

They stay at the anode. Gold, platinum, palladium and rhodium are insoluble under silver electrolysis conditions, so they never enter the solution and are retained inside the high-density filter bag as anode slime. Slime runs at roughly 8% of the charged anode mass and typically assays 50-70% gold with 30-40% silver, which makes it the most valuable by-product of the machine rather than a waste. Because its silver content is still high, it is not normally melted straight into a gold anode: it is either parted with nitric acid, so that the silver dissolves and the residual gold grade rises above 90% for the gold circuit, or cast and given a second electrolysis pass. Where the feed carried platinum group metals, that fraction is separated and declared by metal content before it leaves the plant.

What happens to the copper in 925 scrap?

It dissolves anodically alongside the silver and stays in the electrolyte as copper nitrate, so it does not follow the silver to the cathode – which is exactly why alloyed 80-90% feed can be run on this machine without a chemical pretreatment step. Copper nevertheless accumulates in the liquor, and once its concentration is high enough the deposition window narrows and copper begins to co-deposit. That change shows up first as a shift in the appearance of the crystal and then in the assay, and by the time it is visible in the assay the batch has already been run. Impurity-loaded electrolyte is therefore drawn off on the bleed schedule, regenerated so that the accumulated copper and bismuth leave the circuit, re-acidified to its working pH and returned to the tank, with the silver it holds recovered in the same step.

What feed must not go into the machine?

Chloride-bearing material, and only that is an absolute boundary: silver chloride will not dissolve anodically in a nitrate electrolyte, so anything arriving as chloride is converted to metallic silver before it is charged. Alongside that are practical limits rather than prohibitions. Feed that is very low in silver carries so much base metal that the bleed frequency and the acid demand stop making sense, and it is normally concentrated or pretreated first. Fine dust, sweeps ash and loose powders must be granulated rather than charged loose, because a loose pack screens its own flow and blinds the bag. And feed carrying organic material or plastics is ashed or burnt off beforehand, since organics in the cell create their own problems in the electrolyte and the deposit.

How is the crystal rinsed, and how do I know the rinse is finished?

Crystal goes straight from the drum into a rinsing and dewatering unit and is rinsed counter-current with demineralised hot water, in a cascade where the first cut returns to the tank as electrolyte make-up and the second cut is held back to become the first rinse of the next batch. The first cut is hot because the solubility of the entrained salts falls as the water warms, which is what makes a small number of rinses sufficient instead of a long wash, and because the water and the silver it carries stay inside the machine. The rinse is finished when the water draining from the crystal reads neutral and its conductivity stops falling. A rinse judged by pH alone will pass while nitrate is still entrained in the crystal, and that nitrate goes into the melt and into the slag.

How is silver recovered from the fume?

Two things happen at the cell and at the make-up vessel: nitric acid mist and nitrogen oxides are generated, and some electrolyte is carried out of the tank as vapour. Both sources are closed and extracted from the side, and the vapour passes a condenser before it reaches the absorption tower. The condenser cools the vapour below its dew point, so the entrained electrolyte returns to the tank as condensate instead of leaving as a metal loss, and the make-up vessel – which releases the more intensive fume load, because that is where silver reacts with nitric acid – is closed and extracted in the same way. The residual stream then goes to a multi-stage nitrogen-oxide absorption tower sized for what is left after the condenser, not for the whole vapour volume.

What does the machine consume, and what drives the operating cost?

The consumables are nitric acid, potassium nitrate where the flowsheet specifies it, demineralised water, filter bags, flux, crucible and mould consumables and scrubber liquor make-up, together with the electricity for the rectifier, the circulation pump, the chiller and the extraction fan. In practice the running cost is driven by four things rather than by the electricity bill: how much nitric acid the make-up and the regeneration demand, how often the bags are changed, how much silver is lost in the rinse water and the bleed, and how much of the base metal load has to be taken out through the electrolyte. That is why the bleed schedule and the bag interval are set from the batch records after the first campaigns, and why those two numbers matter more to the cost per kilogram than any figure on the equipment specification.

Can the machine reach 99.999% silver?

Yes, by running the crystal through the machine a second time as a second electrolysis pass. That is a specification decision rather than a default: the second pass has its own small cost in acid, power and handling, and it is only worth carrying where the end use actually requires the higher figure – investment product, certain electronic and scientific applications, or a customer specification that names it. Where it is specified, the pass is run against a re-assayed electrolyte and a clean basket charge, and the resulting product is certified in the same way as a single-pass lot. Refiners who need both grades normally run standard 9999 as the main product and schedule second-pass campaigns when the higher grade is required.

How is the machine configured for my volume, and what information do you need?

Capacity on this machine is engineered rather than selected from a catalogue, and it follows from four inputs: the silver content and base metal load of your feed, the monthly silver volume you intend to run, the product form you sell, and the site conditions. From those, we size the basket count, the cathode area, the rectifier rating, the circulation and filtration rate, the cooling duty, the exhaust volume, the rinse-water arrangement and the effluent duty, and we state the resulting figures in the process design package. The silver content of the feed matters more than the tonnage, because the basket volume and the current density are set against it; the base metal load decides the bleed rate. Send a representative sample and the site data, and the configuration follows.

How is the silver verified, and what documentation comes with each batch?

Each lot is verified by fire assay of a sample drawn from the released batch, with a cupric chloride titration or an ICP-OES cross-check, and the batch is not released until the certificate of analysis confirms the grade. Alongside the certificate, the batch record holds the charged weight and assay, the electrolyte analysis at make-up and at draw-off, the slime weight and assay, the product weight and assay, and the metal balance that reconciles them – which is what connects the bar in the customer’s hand to the scrap lot that produced it. That record is also what allows a batch that does not close within tolerance to be diagnosed in the process rather than argued about at the assay, and it is what a toll refiner needs when the material belongs to somebody else.

What warranty, installation and operator training are included with the machine?

The machine carries a twelve-month warranty from commissioning or eighteen months from dispatch, whichever falls first, covering design, materials and workmanship on the cell, basket assemblies, drum and drive, frame, conductor bars, rectifier and control system, circulation and cooling package, extraction and condenser, absorption tower and the rinsing, drying and melting stages. Wear and consumable items – filter bags, crucibles, moulds, blades, seals, scrubber liquor and reagents – are excluded and listed as such in the offer. Installation supervision, commissioning, electrolyte make-up, the first charged batch and the first full campaign are part of the delivery, operators are trained and signed off on the tasks they will run unsupervised, and after handover the first campaigns are reviewed against the batch records to fix the bleed schedule and the bag interval for your own scrap.