Silver Electrolysis Equipment

— Silver Electrolysis Equipment: 99.99% Silver Refining Cells

Silver electrolysis equipment is an electrorefining circuit that dissolves cast crude-silver anodes in a silver nitrate electrolyte and deposits the silver on the cathode as 99.99% crystals at a cathode current density of 750 A/m². YuSai Machinery engineers the whole circuit — feed assay and anode specification, anode bagging and cell loading, silver nitrate electrolyte make-up, rectifier and busbar, parallel-flow circulation and cooling, automatic crystal scraping, electrolyte regeneration, fume condensation and nitrogen-oxide abatement — around your own anode assay, so that the gold, platinum and palladium leave the plant as a saleable anode slime rather than as a loss.Configuration: cell count, cathode area, rectifier rating, circulation rate, cooling duty, exhaust volume and effluent duty are engineered to your anode assay, monthly silver volume, product form and site conditions rather than selected from a catalogue of fixed models.

Product Overview

Silver electrolysis equipment is an electrorefining circuit that passes a direct current through cast crude-silver anodes immersed in a silver nitrate electrolyte, dissolves the silver at the anode and deposits it on the cathode as crystals of 99.99% purity, at a cathode current density of 750 A/m². The input is metallic: the crude silver or doré has already been melted and cast into anode plates, and the process is governed by how quickly that anode can be dissolved, how cleanly the silver can be kept in solution, and how completely the impurities can be kept out of the cathode deposit. YuSai Machinery builds the complete line — feed assay and anode specification, anode bagging and cell loading, electrolyte make-up, rectifier and busbar, circulation and cooling, automatic crystal harvesting, electrolyte regeneration, fume condensation and nitrogen-oxide abatement, and the washing, drying, melting and casting stages that follow.

The electrochemistry is simple to state and demanding to run. At the anode, metallic silver loses an electron and enters the electrolyte as the silver ion, Ag − e⁻ = Ag⁺. At the cathode, the silver ion gains an electron and comes back out as metal, Ag⁺ + e⁻ = Ag, so the cell is written as Ag (anode) | AgNO₃, HNO₃, H₂O | Ag (cathode). What makes the cell work as a purification step rather than as a shuttle is what happens to everything that is not silver. Copper and other base metals dissolve anodically alongside the silver and stay in solution as nitrates, so they accumulate in the electrolyte instead of following the silver. Lead and bismuth hydrolyse in the working pH band and precipitate, which is why they must not be allowed to reach the cathode as a hydrolysed floc. Gold, platinum, palladium and rhodium do not dissolve in nitric acid at all and report to the anode bag as insoluble slime. The silver is therefore concentrated and the impurities are separated into exactly two places — the electrolyte and the anode slime — and the whole design is a matter of controlling those two streams.

Current density is the parameter that sets both the throughput and the quality of the product, and it is the number most often missing from a silver electrolysis equipment specification. A conventional silver cell runs at 250–350 A/m². High-current-density practice occupies a 600–800 A/m² band, this line is designed around 750 A/m², and industrial high-current-density silver electrorefining cells are published as operating above 1,000 A/m² depending on the composition of the doré being processed. Raising the current density is paid for in three currencies: the resistive drop across the electrolyte gap, which rises with current and with the amount of silver and base metal held in the liquor; the tendency of the anode face to passivate as its silver content falls away and the residual surface becomes gold-rich; and deposit morphology, because a deposit grown too fast at a starved boundary layer turns nodular and dendritic and can bridge the gap to the anode. Boundary-layer control is therefore part of the deposition stage rather than an accessory: circulation keeps the silver concentration at the cathode face close to the bulk concentration, agitation is set to the design rate, and the temperature is held in band, which lowers the electrolyte resistance and improves the deposition kinetics at the same time.

The electrolyte is a silver nitrate solution in nitric acid, and the operating window is narrow in both directions. Silver is held at 60–150 g/L with 10–18 g/L of free nitric acid, and potassium nitrate is added where the conductivity and the pH band need help. If free acid falls below the window, bismuth and other base metals hydrolyse and the precipitate contaminates the silver crystal, which is a grade problem that cannot be corrected afterwards. If free acid rises above the window, the acid re-dissolves silver that has already been deposited, which is a recovery problem and also forces the silver concentration up. The two failure modes are on opposite sides of the same setpoint, which is why the electrolyte is titrated and corrected on a schedule rather than adjusted after a quality excursion, and why the temperature is held at a 40 °C set point by a chiller that starts and stops on the measured electrolyte temperature: warmth lowers the resistance, but evaporation, acid consumption and volatilisation losses all climb with it.

The process liabilities are specific and the design contains them rather than describing them. Nitric acid mist and nitrogen oxides are generated at the cell and, far more intensively, during electrolyte preparation, where silver reacts with nitric acid according to Ag + 2HNO₃ → AgNO₃ + NO₂↑ + H₂O. Both the cell and the make-up vessel are therefore 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 nitrogen-oxide absorption tower. Silver crystals bridging the electrode gap are a short-circuit waiting to happen, which is why scraping is continuous rather than scheduled. Anode passivation as the plate is consumed is managed by current and voltage intervention and by reading cell voltage as a diagnostic. And the electrolyte and the anode slime are assayed every campaign, because those two streams are where an unmanaged silver line quietly loses both metal and grade.

Because anode composition, gold content, impurity profile and required product vary widely between one project and the next — and because a silver electrolyte line is judged on its anode slime and its ingot assay as much as on its throughput — YuSai sizes the number of cells, the cathode area, the rectifier rating, the circulation rate, the cooling duty, the exhaust volume and the effluent duty from your own anode assay and monthly silver volume, and states the resulting figures in the process design package. Capacity is engineered rather than selected from a catalogue, and the same platform is scaled up or down accordingly. Working as a silver electrolysis equipment manufacturer from the anode backwards rather than from a standard cabinet, we would rather revise the anode specification than supply a cell that cannot hold the grade.

Key Facts

Silver purity: cathode crystals at 99.99% (9999 fine) silver from an anode above 75% silver, and in practice above 97%; 99.999% where a second electrolysis pass is specified.
Cathode current density: 750 A/m² is the design point, against the 250–350 A/m² of a conventional silver cell. High-current-density silver electrorefining cells in industrial service are published as operating above 1,000 A/m² depending on the composition of the silver doré anodes being processed.
Cell voltage: 1–3 V DC per cell in the normal working window. Voltage rises with the silver concentration in the liquor, with circuit resistance and with anode passivation, which is why a rising cell voltage at constant current is read as a fault to be diagnosed rather than as a productivity setting.
Electrolyte: silver nitrate at 60–150 g/L silver with 10–18 g/L of free nitric acid, held inside that window deliberately, with potassium nitrate available to raise conductivity and stabilise the pH band.
Electrolyte temperature: held at a 40 °C set point by the chiller, which starts and stops on the electrolyte temperature; conductor bars and lugs are engineered to stay below 70 °C.
Anode slime: about 8% of the anode mass, typically assaying 50–70% gold with 30–40% silver, and carrying the platinum group metals; it is the most valuable by-product of the line.
Two silver-bearing losses are closed by design: the fume condensation system returns vaporised electrolyte to the circuit, and spent electrolyte is regenerated in place and returned to the cell instead of being remade or neutralised.
Configuration: cell count, cathode area, rectifier rating, circulation rate, cooling duty, exhaust volume and effluent duty are engineered to your anode assay, monthly silver volume, product form and site conditions rather than selected from a catalogue of fixed models.

Product Core Selling Points

High current density is the design point, not an upgrade. The cell is engineered for a cathode current density of 750 A/m² and above, against the 250–350 A/m² of a conventional silver cell. Electrode spacing, busbar cross-section, contact pressure, circulation rate and cooling duty are all sized for that regime from the start, rather than a low-density design being pushed harder and expected to hold its grade.
The electrolyte window is controlled, not approximated. Silver is held at 60–150 g/L with free nitric acid at 10–18 g/L, and both are titrated and corrected on a schedule. The window is deliberately narrow in both directions: too little free acid lets bismuth and other base metals hydrolyse and report to the cathode crystal, and too much re-dissolves the silver already deposited.
Parallel-flow circulation, which is what makes the current density usable. Electrolyte enters at the bottom of the cell and leaves at the top, flowing parallel to the electrode plates. That 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.
Anode bagging that keeps the gold out of the product. Gold, platinum, palladium and rhodium do not dissolve under silver-refining conditions. High-density filter bags hold them at the anode as slime from the first minute of the run, so the value stays recoverable instead of migrating to the cathode as contamination.
Automatic scraping and conveyor discharge, so the cell clears itself. Silver deposits as a crystalline powder that will bridge the electrode gap and short-circuit the cell if it is left in place. The scraper lifts the crystals off both faces of the cathode as they form, and a conveyor built into the cell floor carries them across the sloped front section straight into the washing and drying unit.
Electrolyte regenerated in place. Copper, bismuth and other impurities stripped from the anodes accumulate in the liquor and eventually co-deposit. Impurity-loaded electrolyte is drawn off, treated so that those elements leave the circuit, re-acidified to its working pH and returned to service — which cuts both the frequency of electrolyte make-up and its nitric acid demand.
The silver that leaves in the fume is recovered. Vapour from the cell, from electrolyte preparation and from the melting furnace passes a condensation system that cools it and returns the silver-bearing condensate to the circuit, so evaporation stops being a metal loss, before the residual stream is ducted to the nitrogen-oxide absorption tower.
Materials selected for nitric acid service stream by stream. Integrally formed polypropylene cell bodies with an anti-ageing additive instead of welded-seam construction; polypropylene homopolymer structural frames; titanium-clad copper conductor bars; bakelite insulation between the bars and the tank; titanium and stainless steel cathodes; and PP and PVDF wetted parts and ducting.
Anode slime treated as a value stream, not as a waste. Slime is washed free of entrained electrolyte, dried, weighed and assayed for silver, and where the feed carried platinum group metals that fraction is separated and declared by metal content before it leaves for the PGM line. Residual anode plates return to the melting shop rather than being sold as scrap.
Counter-current washing with the water returned. First wash water goes back to the tank as electrolyte make-up and second wash water becomes the first wash of the next batch, so both the water and the dissolved silver stay inside the circuit. Washing continues until the residual nitrate is low enough to confirm that the crystal is clean.
Cleaning is scheduled by campaign, not by shift. Continuous scraping stretches the interval between deep cleans from roughly monthly on a belt-discharge cell to a campaign measured in months, and a single operator is sufficient for intermittent supervision while the cell runs.
Harvest, melt and assay are inside the scope. Washing, drying, fluxing, induction melting, ingot or granule casting, sampling and a certificate of analysis are supplied as part of the line, so the customer receives certified fine silver rather than a wet powder.

Application Scenarios

Silver refineries treating doré from gold cyanidation and gold electrowinning. Doré bars carrying silver with gold, copper and platinum group metals are parted in the silver cell, with the gold held back in the anode bag and the silver leaving as 9999 fine crystal.
Desilverising before gold electrolysis. Where a gold doré carries silver above the ceiling the gold cell can tolerate, the silver is taken out here first, so that the residual gold-rich plate can be cast into a gold anode instead of passivating in a chloride electrolyte.
Copper and lead smelters processing anode slime. Silver recovered from copper and lead anode slime, and from the associated doré and cement silver, upgraded to a saleable 9999 product rather than shipped as an intermediate.
Integrated precious metal refineries. A silver cell that sits between the smelting shop and the gold line, taking the silver-rich fractions out of the flowsheet and returning gold-bearing slime to the gold circuit.
Jewellery, silverware and holloware manufacturers. Sterling 925 scrap, bench sweeps that have been ashed and melted, and silver-copper alloys from coin and tableware manufacture, refined in-house and returned to the workshop as fine silver rather than sold at a discount.
Coin melt and bullion operations. Old coin, medallion and bullion stock with a silver content that varies batch to batch, refined to a uniform 9999 grade with an assay certificate per lot.
E-waste and printed circuit board recyclers. Silver recovered from contacts, silver-plated components, solder and the silver-bearing fractions of mixed electronic scrap after they have been concentrated and cast into anodes.
Photographic, X-ray and imaging processors. Silver recovered as cemented silver or as a reduced silver residue from fixer, bleach-fix and wash water, refined into saleable metal instead of being sent out as a regulated waste.
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 have to be separated before the silver can be cast and refined.
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.
Catalyst and chemical processors. Spent silver catalysts, silver oxide and silver salt residues reduced and cast into anodes, with the support material separated before the cell.
Contract and toll refineries. Third-party crude silver refined in campaigns, where the cell must be quick to reconfigure between feeds and every batch must close on a weighed metal balance and a certificate of analysis.
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 smaller cell configuration.

Applicable Raw Materials

Each feed below enters the circuit at the point its composition requires. Material that is already metallic is melted, fluxed and cast into anode plates; material that arrives as a powder, a cement or a slime is dried, fluxed and consolidated into a cast anode rather than fed loose; material carrying chloride is converted to metallic silver before it is cast, because silver chloride will not dissolve anodically in a nitrate electrolyte. Output is stated for each feed.

Silver doré bars from gold cyanidation and gravity concentrate smelting. The classic feed, carrying silver with gold, copper and platinum group metals, and cast directly into anode plates once the gold content has been checked against the ceiling the cell can hold. Output: 99.99% silver crystals, and gold-bearing anode slime to the gold circuit.
Crude silver ingots and bullion above 97% silver. High-grade feed that goes straight to anode casting with no intermediate chemical step. Output: 99.99% silver crystals and a low-yield slime.
Crude silver scrap between 75% and 97% silver. Feed carrying enough copper, lead or bismuth that it is fluxed and air-blown during melting so those elements oxidise into a removable slag before the anode is cast. Output: refined anode plates, a base-metal slag returned for silver recovery, and 99.99% cathode silver.
Sterling 925 silver scrap, jewellery and holloware. Alloyed feed with a predictable 7.5% copper content, which reports to the electrolyte and is managed by the bleed schedule rather than by pretreatment. Output: 99.99% silver crystals and a copper-bearing electrolyte bleed.
Silver-copper coin alloys, solders and brazing alloys. Feed with a copper or zinc matrix, cast into anodes with the flux and blowing conditions set from the assay. Output: 99.99% silver crystals and a base-metal stream to recovery.
Cemented silver, silver powder and reduced silver residues. Fine, high-surface-area material that must be dried, fluxed and consolidated into a cast anode, because loose powder will not survive in an anode bag. Output: cast anode plates, then 99.99% silver crystals.
Silver chloride and silver salt residues. Converted to metallic silver before casting, since chloride is not compatible with the nitrate electrolyte; the conversion is carried out in a closed vessel with the off-gas routed to the absorption tower. Output: metallic silver feed for anode casting, and a base-metal filtrate.
Silver recovered from copper and lead anode slime. Slime-derived silver, typically arriving as doré, cement or a reduced residue depending on the upstream route. Output: 99.99% silver crystals, with any remaining gold and PGM declared and routed onward.
Silver-bearing fractions from electronic and electrical scrap. Contacts, silver-plated components, relays, switches and solder, concentrated and melted into anodes after the copper and ferrous fractions have been separated. Output: 99.99% silver crystals and a base-metal slag.
Silver recovered from photographic, X-ray and imaging chemistry. Cemented silver or a reduced silver residue from fixer, bleach-fix and wash water, prepared and cast as an anode feed. Output: 99.99% silver crystals and a treated liquor stream.
Spent silver plating baths, anode stubs and drag-out silver. Plating-side silver recovered as metal, with the plating salts and organic load removed before the material reaches the melt. Output: 99.99% silver crystals returned to the plating line or sold.
Silver catalysts, silver oxide and silver salt process residues. Recovered from spent catalyst and process residue after the support material has been separated. Output: 99.99% silver crystals and a separated support fraction.
Gold-rich silver alloy plate and residual anode stock. Partly dissolved anode plates and silver-rich alloy returned from the gold circuit, re-melted and re-cast into fresh anodes rather than sold as scrap. Output: recast anode plates and 99.99% silver crystals.

Finished Products

The line is configured around the product form the customer sells, from cathode crystal to certified bar. Where the customer already operates a melting shop, the line is delivered with the harvest, washing and drying stages only; where it does not, melting, casting and assay are included.

99.99% silver crystals. The primary product: crystalline cathode silver at 9999 grade, washed free of entrained electrolyte, dried and 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 bars or ingots of the weight the market requires, marked with weight and batch number. Output: certified 99.99% silver bar with certificate of analysis.
Vacuum-cast and continuously cast silver. Where density, surface finish and freedom from porosity and oxidation matter, vacuum ingot casting and vacuum continuous casting are used instead of open casting. Output: high-finish silver bar or ingot for investment and industrial use.
Silver granules and grain. Where the product is sold as grain rather than as bar, the melt is granulated and the grain is dried, screened and packed. Output: packed silver grain at a declared grade.
Gold-bearing anode slime. The most valuable by-product of the line, running at about 8% of the anode mass and typically assaying 50–70% gold with 30–40% silver; washed, dried, weighed and assayed, and either parted with nitric acid to raise the gold grade above 90% or cast into a second anode for the gold circuit. Output: washed and assayed gold-rich slime with the silver and PGM fractions declared.
Platinum group metal fraction from the slime. Where the feed carried platinum, palladium and 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.
Recast anode plates from residual anode stock. Partly dissolved plates that reached the end of their dissolution cycle are returned to the melting shop and cast into fresh anodes rather than being written off. Output: remelted anode plates returned to the cell.
Regenerated electrolyte. Spent electrolyte from which the accumulated copper, bismuth and other impurities have been removed, re-acidified to its working pH and returned to the cell. Output: electrolyte returned to service at the working specification.
Silver recovered from the electrolyte bleed. The silver held in the electrolyte drawn off for purification 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. Output: recovered silver returned to the anode melt.
Condensed silver returned from the fume. Vaporised electrolyte captured by the condensation system and returned to the circuit, 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 vessel off-gas treated through condensation and 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 anode weight and assay, the electrolyte analysis, the slime weight and assay, the product assay and the metal balance for that lot. Output: certificate of analysis and batch record.

Silver Electrolysis Equipment Process Flow

The nine stages below form the standard silver electrolysis flowsheet, from the anode assay through to certified fine silver, regenerated electrolyte and a declared gold-bearing slime. Step 3 is the stage that decides the grade and Step 8 is the stage most often missing from competing equipment specifications: the electrolyte and the anode slime are the two streams in which an unmanaged silver line loses both metal and purity. Cell count, electrode area, current density, circulation rate, cooling duty and stage count are fixed during process design against your own anode assay.

Silver electrolysis process flow — from a cast crude-silver anode to certified 9999 fine silver, with the electrolyte and the anode slime kept inside the circuit.

Steps 1 — Silver Feed Assay and Anode Specification. Incoming material is weighed, representatively sampled by riffling and splitting, and assayed before anything is melted. Silver is determined by fire assay with cupric chloride titration or ICP-OES, gold by fire assay with an ICP-OES cross-check, and the base metal and platinum group metal inventory by ICP-OES. Three figures from that assay govern the rest of the design. The silver content decides whether the feed can be cast straight into an anode or needs flux refining first. The gold content decides the plateau at which the anode stops dissolving cleanly, and therefore how the anode is bagged, how the residual plate is scheduled, and how much value will report to the slime. The copper, lead, bismuth, tellurium and selenium figures set the flux, the blowing time during melting, the bleed rate during the campaign and the level at which the electrolyte must be drawn off for regeneration. The assay output is a route sheet that fixes the anode specification, the electrolyte composition, the target current density and the campaign length. Reagent and utility input: weighing and riffling equipment, sample splitting, fire assay apparatus, titration glassware, ICP-OES, XRF for screening; sodium carbonate flux where the feed requires it. Output: assay report, anode specification, batch route sheet and a documented feed weight.

Steps 2 — Anode Bagging and Cell Loading. The cast anode plates are dressed, the lugs are formed and the plate is weighed, because the anode weight is what the cell current is set against. Each plate is then enclosed in a high-density filter bag before it goes anywhere near the cell, and this is a functional stage rather than a finishing detail: gold, platinum, palladium and rhodium are insoluble in the nitrate electrolyte and will report to the cathode as contamination if they are free to move, so the bag holds them at the anode from the first minute of the run. The bagged assemblies are hung on the anode frame, and where the layout allows, an overhead travelling crane positions them mechanically so that the operator never reaches over the electrolyte. Conductor bars, hooks and contact faces are cleaned and dressed, the plate is checked for straightness, and the electrode spacing is set with a gauge — a bowed plate or a resistive contact changes the inter-electrode distance along its length, shows up later as a localised burn or an unexplained low current on one cathode, and is difficult to diagnose once the cell is closed and full. The cell is then charged to its working level with electrolyte and the electrodes are immersed to depth. Reagent and utility input: anode bagging or membrane material, anode hangers, hooks, frames, spacing gauges, busbar cleaning and contact dressing, overhead crane or handling frame, level indication. Output: bagged, hung and weighed anode assemblies with verified contact and spacing; cell charged and ready to energise.

Steps 3 — Silver Nitrate Electrolyte Make-Up. The electrolyte is a silver nitrate solution in nitric acid, and how it is made up decides how the cell behaves for the whole campaign. High-purity silver is dissolved in nitric acid until the reaction is complete — Ag + 2HNO₃ → AgNO₃ + NO₂↑ + H₂O — the insoluble residue is filtered off, and the liquor is transferred to the cell and made up to the working specification. That specification is a silver concentration of 60–150 g/L with 10–18 g/L of free nitric acid, potassium nitrate being added where the conductivity or the pH band needs help. Both bounds are deliberate and both fail in a different direction: below the free-acid window, bismuth and other base metals hydrolyse and the precipitate contaminates the cathode crystal as a grade loss that cannot be corrected afterwards; above the window, the acid re-dissolves silver that has already been deposited, which is a recovery loss and drives the silver concentration up. The dissolution reaction is strongly fuming, so make-up is carried out in a closed vessel under extraction with the gas routed straight to the absorption plant, and the made-up liquor is titrated for silver and free acid and recorded against the batch — because the single most common cause of a disappointing first campaign is an electrolyte that was never assayed. Reagent and utility input: nitric acid with metered dosing, high-purity silver or cathode crystal for make-up, potassium nitrate where specified, closed electrolyte preparation vessel with agitation, extraction and level control, filtration, heating and circulation pump, deionised water, silver and free-acid titration. Output: electrolyte at 60–150 g/L silver with 10–18 g/L free acid; electrolyte make-up record; NO₂ routed to the absorption tower.

Steps 4 — Rectifier Commissioning and Current Ramp. 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. The reason is deposit structure: a modest initial current produces a coherent, fine-grained seed layer of silver crystals that stays coherent as it thickens, whereas a cold start at full current produces a burst of nodules, high local current density and a deposit that sheds back into the electrolyte later in the run. Individual cathode currents are verified during the ramp, because a poor contact or a mis-set electrode found on the first day costs a shift, while the same fault found at harvest costs the campaign. Cell voltage is checked against the design figure and the busbar temperature is confirmed to be stable before the ramp is complete. Where the anode carries a silver content that tends to passivate its own face, or where the liquor is unusually concentrated, an alternating component can be superimposed on the rectifier output so that the polarity reverses for part of every cycle and the anode face is kept active rather than becoming film-bound. Reagent and utility input: DC rectifier with adjustable voltage and current and, where specified, an adjustable superimposed alternating component, staged current programme, per-cathode current check, insulation and spacing verification, busbar temperature monitoring. Output: stable current distribution across the cathode set; coherent seed deposit established; corrected settings recorded against the batch.

Steps 5 — Electrolysis at High Cathode Current Density. This is the stage that sets the plant output. The cell runs with a cathode current density of 750 A/m² — between two and three times the 250–350 A/m² of a conventional silver cell and inside the 600–800 A/m² band of high-current-density practice, with industrial silver electrorefining cells published as running above 1,000 A/m² depending on the composition of the doré being processed. At the anode the silver dissolves as Ag − e⁻ = Ag⁺ while the copper and other base metals dissolve alongside it and stay in the liquor, and the lead and bismuth that hydrolyse in the working pH band are kept out of the deposit by holding the acid window. At the cathode the silver ion is reduced as Ag⁺ + e⁻ = Ag and deposits as crystalline metal. A chiller holds the electrolyte at a 40 °C set point, which limits evaporation, acid consumption and volatilisation losses while lowering the electrolyte resistance. Circulation runs parallel to the electrode plates, entering at the bottom of the cell and leaving at the top: that flow pattern keeps the silver-ion concentration uniform across the electrode gap and suppresses the concentration polarisation that would otherwise force the silver concentration up, and it is the mechanism that makes the high current density usable at all. The cell runs under a transparent sealed cover with side extraction, so the process remains visible while the exhaust is contained, and one operator is sufficient for intermittent supervision. Reagent and utility input: rectifier at design current, magnetic circulation pump, chiller with a 40 °C set point, parallel-flow bottom inlet and top outlet, agitation, sealed transparent cover with side extraction, continuous cell voltage and per-cathode current logging, silver and free-acid titration. Output: silver depositing as crystals on the cathodes at 99.99%, base metals reporting to the electrolyte, and insoluble gold and platinum group metals collecting in the anode bags.

Steps 6 — Automatic Silver Crystal Scraping and Discharge. Silver deposits as a crystalline powder, and crystals left on the cathode grow until they bridge the electrode gap, which short-circuits the cell, distorts the current distribution across the remaining electrodes, lowers the quality of the powder still in the cell and immobilises silver as unsaleable inventory in the anode bag. The scraper therefore runs continuously rather than on a schedule: it removes the crystals from both faces of the cathode as they form, and a conveyor built into the cell floor carries them across the sloped front section and discharges them directly into the washing and drying unit. Because the cell clears itself, the interval between deep cleans stretches from roughly monthly on a conventional belt-discharge cell to a campaign measured in months, and production is interrupted only at long intervals for scheduled maintenance. When the campaign is complete, the cell is de-energised, the electrolyte is drawn off through the discharge valve by way of the solid–liquid separator and into the circulation tank, and the cell is emptied for the harvest of residual anode plates and anode slime. Reagent and utility input: automatic scraping mechanism on both cathode faces, cell-floor conveyor and sloped discharge section, solid–liquid separator, discharge valve, circulation and collection tanks, residual anode lifting gear. Output: harvested silver crystal transferred to the wash-and-dry stage; drained electrolyte routed to regeneration; residual anode plates and bags recovered.

Steps 7 — Crystal Washing, Drying and Grading. The crystal carries entrained electrolyte, and electrolyte left on the crystal takes silver, nitrate and base-metal salts back out of the circuit in the wash water and introduces chloride and nitrate into the melt. Washing is therefore counter-current rather than a single rinse: the crystal is washed with deionised hot water in a combined washing and drying unit, the first wash water is returned to the tank for electrolyte make-up, and the second wash water is held back to serve as the first wash of the next batch, so that both the water and the dissolved silver remain inside the process. Washing continues until the residual conductivity of the wash water confirms that the nitrate has been removed, after which the crystal is dewatered and dried to a moisture content low enough for clean melting. The dried crystal is screened and graded, weighed, sampled and held for the melting stage, with the lot number tied back to the anode batch. Reagent and utility input: deionised hot water, combined washing and drying unit, counter-current wash cascade with return to electrolyte make-up, conductivity measurement, dewatering, drying, screening and weighing. Output: dried, nitrate-free, screened 99.99% silver crystal ready for melting, and wash water returned to electrolyte make-up.

Steps 8 — Anode Slime Recovery and Electrolyte Regeneration. The campaign closes on the two streams that carry the residual value and the accumulated impurity respectively, and both are recovered rather than written off. The anode bags are opened and the slime is washed free of entrained electrolyte, dried, weighed and assayed: it runs at about 8% of the anode mass and typically assays 50–70% gold with 30–40% silver, which makes it the most valuable by-product of the line. 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 gold stays as a solid whose grade rises above 90% for the gold circuit, or cast into a plate and given a second electrolysis pass. Where the feed carried platinum, palladium and rhodium, that fraction in the slime is separated and declared by metal content before it leaves the plant. The silver taken up by the parting liquor returns to the silver cell. In parallel, the impurity-loaded electrolyte drawn off during the campaign is regenerated: the accumulated copper, bismuth and other elements are removed, the liquor is re-acidified to its working pH, and the silver held in it is recovered rather than neutralised to waste. Regenerating in place lowers both the frequency of electrolyte make-up and its nitric acid demand, and cuts the number of fuming make-up batches in a year. Reagent and utility input: anode bag opening and slime washing station, filter press or vacuum filter, drying oven, slime and electrolyte assay by fire assay and ICP-OES, nitric acid for parting, electrolyte purification vessel with agitation and pH control, re-acidification and transfer pumps. Output: washed and assayed gold-rich slime with silver and PGM fractions declared; purified electrolyte returned to the cell at the working specification; recovered silver returned to the anode melt; residual anode plates returned to the melting shop.

Steps 9 — Induction Melting, Ingot Casting and Assay. The dried crystal is melted in an induction furnace, treated against gas absorption, sampled and cast into the product form the customer sells — ingots, bars, or granulated 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 a uniform grain is wanted. Each lot is re-assayed by fire assay with an ICP-OES cross-check, marked with its weight and batch number, and released against a certificate of analysis carrying the batch number, the input weight and assay, the output weight and assay, the slime weight and assay and the metal balance for the lot. The certificate is what connects the bar in the customer’s hand to the anode lot that produced it, and it is also the reason the purity figure on this page is checkable on the customer’s own material rather than only on a specification sheet. Reagent and utility input: medium-frequency induction melting furnace with graphite-clay crucible or equivalent, flux and mould set, vacuum ingot casting, vacuum continuous casting or granulation equipment where specified, marking and weighing equipment, sampling and fire assay, ICP-OES cross-check, certificate of analysis preparation. Output: certified 99.99% silver ingots, bars or grain with full assay documentation and a closed lot metal balance.

Product Structure (Main Equipment)

The line is assembled from the four equipment groups below. Materials of construction are selected stream by stream: integrally formed polypropylene for cell bodies rather than welded-seam construction, with an anti-ageing additive where the liquor is strongly oxidising; polypropylene homopolymer for structural frames and support work; titanium-clad copper for the conductor bars and lugs; bakelite insulation between the bars and the tank body; high-density filter fabric for the anode bags; titanium and stainless steel for cathodes; and PP and PVDF for wetted parts, piping and ducting.

Cell bodies, covers and process containment

Electrolytic cell body. An integrally formed polypropylene tank, produced without welded seams so that the electrolyte cannot weep through a joint, with the wall thickness, ribbing and base support set by the hydrostatic load of the working volume. Where the liquor or the site calls for it, high-density polyethylene, PVC or FRP construction is used instead. Output: a corrosion-resistant cell that holds its dimensions and does not develop seam leaks in nitric acid service.
Cell frame and structural support. A polypropylene homopolymer support structure carrying the cell, the electrode frames and the conductor bars, with the load path kept clear of the busbar insulation. Output: dimensional stability at operating temperature and a rigid electrode array.
Transparent sealed cover. A transparent cell cover that closes the process while leaving the electrodes visible for inspection, fitted with a gasket line and secured so that the extraction draws from under the cover rather than from the room. Output: contained exhaust, a visible process and a clear workshop floor.
Side extraction plenum and ducting. Extraction taken from the side of the cell body rather than from a hood above it, because sealing the cell is what makes the extraction economic: a small, well-directed air volume removes the mist that collects under the cover, instead of a large open hood diluting it into the workshop. Output: captured acid mist and nitrogen oxides with a reduced exhaust volume to treat.
Anode slime and residue handling. Bag emptying, slime washing and filtration equipment, plus the collection vessels for the drained electrolyte and cell washings, arranged so that no metal-bearing stream is handled over an open floor drain. Output: contained slime and electrolyte streams for recovery.
Cell and floor containment. Bunding, drip trays and a segregated floor drainage path under the cell and the electrolyte preparation area, with the drainage directed to the effluent plant rather than to the storm system. Output: containment of spills and wash-down within the process boundary.

Electrode assemblies and current delivery

Cast silver anodes and anode bags. Anode plates cast to the cell’s geometry with formed lugs and a dressed face, enclosed in high-density filter bags that retain insoluble gold and platinum group metals at the anode. Anode moulds and a casting arrangement are supplied as part of the equipment scope. Output: weighed, bagged anode assemblies that hold the slime where it can be recovered.
Titanium basket anodes for granulated feed. For feed that cannot be cast into a plate, a titanium basket holds the granular silver so that it dissolves in the cell without being recast, with the basket lined so that the residue is retained. Output: a route for granulated and cemented silver that avoids a second melting step.
Titanium cathode plates. Titanium sheet cathodes on which the silver crystallises, selected for the duty because titanium resists the nitrate electrolyte, releases the crystal easily on scraping and does not contaminate the deposit. Stainless steel plate is available where the process calls for it. Output: a cathode surface that produces a clean, easily harvested crystal.
Rotating titanium drum cathode. A rotating drum cathode with an internal scraper, where the layout and capacity call for continuous harvesting and a compact footprint. Output: continuous crystal removal from a cell with no plate handling.
Titanium-clad copper conductor bars. Anode and cathode conductor bars in titanium-clad copper, with the plating graded so that the current-carrying copper is protected from the acid mist and the contact faces stay clean. Output: low-resistance current delivery with a long service life in an acid atmosphere.
Bakelite and polymer insulation. Interlocking insulation between the conductor bars and the tank body, and at every point where the busbar passes near a structural member, to prevent stray current from finding a path through the frame. Output: no stray-current corrosion of the structure or the tank.
Anode frames, hooks and hangers. Anode frames and hangers that set the plate position and hold the spacing square, together with the handling gear for lifting and setting plates. Output: uniform electrode spacing across the array.

Power supply, circulation and thermal control

DC rectifier. A direct-current rectifier rated for continuous duty at the high-current-density operating point, with adjustable voltage and current and, where specified, an adjustable superimposed alternating component for anodes whose face tends to become film-bound. Input is configured to the site supply, single-phase for the smaller cell configurations and three-phase for industrial duty, at the local voltage and frequency. Output: a stable, controllable current at the design current density with an adjustable waveform where the feed requires it.
PLC control and operator interface. PLC control with a touchscreen interface covering rectifier start and stop, current and voltage setting, circulation and scraping sequences, temperature control and alarm annunciation, with an event log that writes the campaign record against the batch. Output: repeatable campaigns and a process record that stands behind the batch documentation.
Circulation pump and piping. A magnetic-drive circulation pump with PP or PVDF wetted parts, piped so that the electrolyte enters at the bottom of the cell and leaves at the top, parallel to the electrode plates. Output: uniform silver concentration across the electrode gap and suppression of concentration polarisation.
Electrolyte cooling set. A chiller with a 40 °C set point on the electrolyte temperature, starting and stopping on the measured temperature, with a heat exchanger and the associated control loop. Cooling is not a comfort measure: it limits evaporation, acid consumption and the volatilisation of silver-bearing electrolyte, and it holds the crystal quality stable. Output: electrolyte held in band, with acid consumption and fume load reduced.
Circulation and sieve tanks. Working tanks for the circulation loop and a sieve tank for separating crystal from electrolyte at discharge, sized from the cell volume and the campaign length. Output: a closed circulation loop and a clean solid–liquid split at discharge.
Electrolyte preparation vessel. A closed, agitated and extracted vessel for dissolving silver in nitric acid, with metered acid addition, fume extraction to the absorption plant and the instrumentation to bring the liquor to specification before it is transferred. Output: electrolyte made to the working specification with the fume contained.

Harvesting, electrolyte regeneration and finishing

Automatic scraping mechanism and cell conveyor. A scraper that works both faces of the cathode and a conveyor built into the cell floor, discharging across the sloped front section directly into the washing and drying unit. Output: continuous harvest with no plate handling and no bridging between electrodes.
Crystal washing and drying unit. A combined washing and drying unit operating on a counter-current cascade with deionised hot water, with temperature control and a drying stage that brings the crystal to a moisture content fit for melting. Output: dried, nitrate-free silver crystal with the wash water returned to the circuit.
Solid–liquid separator. A separator at the cell discharge line that splits the crystal from the electrolyte before the liquor is returned to the circulation tank, so that the electrolyte is recovered rather than carried out with the product. Output: clean electrolyte return and a dry harvest stream.
Electrolyte purification and regeneration set. A purification vessel with agitation and pH control in which the impurity-loaded electrolyte is treated so that copper, bismuth and the other accumulated elements leave the circuit, after which the liquor is re-acidified to its working pH and returned to the cell, with the silver content recovered in the same step. Output: regenerated electrolyte at the working specification and recovered silver returned to the melt.
Fume condensation system. A condenser on the cell and vessel off-gas path that cools the vapour and returns the silver-bearing condensate to the circuit instead of letting it escape up the stack. Output: recovered silver and a reduced load on the scrubbing stage.
Nitrogen-oxide and acid-mist absorption tower. A multi-stage absorption tower operating under negative pressure, sized for the nitrogen oxide load generated by electrolyte preparation and cell operation and absorbing chlorine and sulphur dioxide as well as nitrogen oxides, with its reagent chemistry converting the nitrogen oxides to nitrogen, carbon dioxide and water so that no secondary waste is generated. Output: compliant, odourless exhaust with an emission record per batch.
Induction melting furnace. A medium-frequency induction furnace with a crucible and flux set for melting crystal, with a sampling arrangement and casting moulds, or vacuum ingot casting, vacuum continuous casting and granulation equipment where the product form requires them. Output: molten silver ready to cast, or granulated grain.
Casting, marking and weighing. Ingot and bar moulds, a casting station, and marking and weighing equipment to identify each bar with its weight and batch number. Output: marked, weighed silver bars or ingots traceable to their anode lot.
Assay and testing station. Sample preparation, fire assay apparatus, titration glassware and an ICP-OES or atomic absorption instrument for the anode, electrolyte, slime and product assays on which the batch is released. Output: the assay basis for the certificate of analysis and the metal balance.

Product Features

High-current-density cell engineered as a whole. Electrode spacing, conductor bar section, contact pressure, circulation rate and cooling duty are sized for 750 A/m² from the start, so the current density is a design premise rather than a derated promise.
Integrally formed polypropylene cell body. Produced without welded seams, so the nitric acid electrolyte cannot weep through a joint, with an anti-ageing additive compounded into the material and a polypropylene homopolymer frame carrying the load.
Transparent sealed cover with side extraction. The process stays visible for inspection while the headspace is closed and extracted from the cell side, which is both a containment measure and what keeps the exhaust volume that has to be treated economically small.
Titanium-clad copper conductor bars with bakelite insulation. Current-carrying copper protected from the acid atmosphere, low-resistance contacts, and interlocking insulation that prevents stray current from finding a path through the tank or the frame.
Titanium cathode with automatic two-face scraping. A cathode surface that releases the crystal cleanly, and a scraper that works both faces continuously so the deposit cannot bridge the electrode gap.
Cell-floor conveyor discharging straight to the wash unit. The crystal leaves the cell mechanically and enters the washing stage without being shovelled, bagged or transferred by hand.
Counter-current crystal washing. First wash returned to electrolyte make-up and second wash reused as the next batch’s first wash, so water and dissolved silver both stay inside the circuit.
Parallel-flow electrolyte circulation. Bottom inlet and top outlet, flowing parallel to the plates, which is the mechanism that makes the high current density usable rather than a claim on a specification sheet.
Chiller with a 40 °C electrolyte set point. Automatic start and stop on the measured electrolyte temperature, holding evaporation, acid consumption and silver volatilisation losses down, with conductor bars and lugs engineered to stay below 70 °C.
Electrolyte purification and regeneration in place. Impurity-loaded liquor is treated, re-acidified and returned to the cell, with the silver in it recovered in the same step, so the electrolyte is reused instead of remade.
Fume condensation that returns silver to the circuit. Vaporised electrolyte is condensed and returned, which converts an evaporation loss into a handling step.
Multi-stage nitrogen-oxide and acid-mist absorption. Negative-pressure tower sized for the load from electrolyte preparation and cell operation, absorbing chlorine and sulphur dioxide as well as nitrogen oxides, with no secondary waste stream.
Anode slime recovered as a value product. Bag emptying, washing, filtration, drying and assay are part of the equipment scope, and the PGM fraction is declared by metal content where the feed carries it.
Melting, casting and assay inside the line. Induction melting, open or vacuum casting, granulation, marking and weighing, with fire assay and ICP-OES verification and a certificate of analysis per lot.
PLC control with a campaign record. Rectifier start and stop, current and voltage setting, circulation and scraping sequences, temperature control, per-cathode current and cell voltage logging, and an event log that writes against the batch number.

Technical Parameters And Specifications

Parameter	Specification
Primary function	Electrolytic refining of crude silver and silver doré into 99.99% cathode silver, with the gold and platinum group metals recovered as anode slime
Feed silver content	Above 75% Ag, and in practice above 97% for direct anode casting; lower grades are flux refined during melting first
Feed gold content	Held below the plateau at which the anode face stops dissolving cleanly; where the assay exceeds it, the gold is parted upstream so the residual plate can be cast into a gold anode
Anode form	Cast silver plates with formed lugs, or a titanium basket for granulated, cemented and powdered feed
Anode bagging	High-density filter bags retaining insoluble gold, platinum and palladium at the anode from the first minute of the run
Cathode material	Titanium sheet plate as standard; stainless steel plate where the process specifies it; rotating titanium drum cathode for continuous harvest
Cathode current density	750 A/m² design point, against 250–350 A/m² for a conventional silver cell and inside the 600–800 A/m² high-current-density band; above 1,000 A/m² is published for industrial high-current-density silver electrorefining cells depending on the silver doré composition
Cell voltage	1–3 V DC per cell in the normal working window; rising voltage at constant current is read as a fault indicator rather than as a control handle
Rectifier control	Adjustable voltage and current, constant-current or constant-voltage mode as the flowsheet specifies, with an adjustable superimposed alternating component where anode passivation requires it
Cell supply	Single-phase for compact cell configurations and three-phase for industrial duty, at the local voltage and frequency
Electrolyte system	Silver nitrate in nitric acid, with potassium nitrate where the conductivity or the pH band requires it
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	40 °C set point, held by a chiller that starts and stops on the measured electrolyte temperature
Conductor bar and lug temperature	Engineered to stay below 70 °C in continuous operation
Circulation pattern	Parallel flow, entering at the bottom of the cell and leaving at the top, parallel to the electrode plates
Circulation function	Holds the silver-ion concentration uniform across the electrode gap and suppresses the concentration polarisation that would otherwise force the silver concentration up
Electrode spacing	Set with a gauge and held square by the anode frame; a spacing or contact fault is corrected before the cell is energised
Harvesting	Automatic scraping on both cathode faces, with a cell-floor conveyor discharging across the sloped front section into the wash-and-dry unit
Crystal washing	Counter-current cascade with deionised hot water; first wash returned to electrolyte make-up, second wash held as the next batch’s first wash
Wash endpoint	Residual conductivity of the wash water below the level that confirms the entrained nitrate has been removed
Crystal drying	Dried to a moisture content fit for clean melting, then screened, weighed and held for the melt
Cell cleaning interval	Deep clean on a campaign basis rather than the roughly monthly cycle of a conventional belt-discharge cell, with continuous scraping in between
Anode slime yield	About 8% of the anode mass
Anode slime composition	Typically 50–70% gold with 30–40% silver, plus the platinum group metal fraction where the feed carries one
Anode slime treatment	Nitric acid parting to raise the gold grade above 90% for the gold circuit, or casting into a second anode for a further electrolysis pass
Electrolyte regeneration	Impurity-loaded liquor drawn off, treated so copper and bismuth leave the circuit, re-acidified to working pH and returned, with the silver content recovered in the same step
Residual anode handling	Partly dissolved plates returned to the melting shop and recast, or finished in a titanium basket without recasting where the cell is fitted for it
Fume control	Transparent sealed cell cover with side extraction, then a condensation system returning silver-bearing condensate to the circuit
Nitrogen oxide abatement	Multi-stage absorption tower under negative pressure, sized for the load generated by electrolyte preparation and cell operation, also absorbing chlorine and sulphur dioxide, and generating no secondary waste
Materials of construction — cell body	Integrally formed polypropylene with an anti-ageing additive and no welded seams; HDPE, PVC or FRP where specified
Materials of construction — structure	Polypropylene homopolymer frame and support work
Materials of construction — busbar and insulation	Titanium-clad copper conductor bars and lugs, with interlocking bakelite insulation between the bars and the tank
Materials of construction — wetted parts	PP and PVDF piping, ducting, pump internals and filter media
Product purity	99.99% (9999 fine) silver at the cathode, from an anode above 75% silver; 99.999% where a second pass is specified
Product forms	Silver crystal, granules or grain, and cast ingots or bars, with vacuum ingot or continuous casting where the finish and density require it
Verification	Fire assay with cupric chloride titration or ICP-OES confirmation; each lot released against a certificate of analysis with a closed metal balance
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 control, circulation and scraping sequences, temperature control, per-cathode current and cell voltage logging, alarm annunciation and an event log written against the batch
Capacity, cell count, electrode area, power, footprint and utilities	Engineered to your anode assay, monthly silver volume, target product form and site conditions
Installation	Indoor, on a level floor, with the containment, bunding and segregated drainage arrangements shown on the layout drawing

Technical Advantages

Throughput from current density rather than from cell volume. At 750 A/m² against the 250–350 A/m² of a conventional silver cell, a cell of the same working volume carries two to three times the cathode current, and the electrode array, rectifier, circulation and cooling are all engineered for that duty rather than derated from it. High-current-density silver electrorefining cells in industrial service are published above 1,000 A/m² depending on the doré composition, which is the headroom this design is built into.
The boundary-layer limit is addressed instead of being discovered. Concentration polarisation is what caps cathode current density long before the rectifier does, so parallel-flow circulation, agitation and uniform electrode spacing are treated as process equipment rather than as accessories. A cell that ignores this underperforms its own specification on the first campaign.
Crystal quality held by voltage discipline. Voltage is read as a diagnostic, not used as a productivity lever: within the 1–3 V window silver deposition is the favoured reaction, and a rising cell voltage at constant current is worked through in a fixed order — contacts, spacing, silver concentration, free acid, temperature, anode condition. Correcting the fault rather than raising the current is what keeps the crystal at 9999.
The two silver-bearing loss paths are closed. Fume condensation returns vaporised electrolyte to the circuit, and the electrolyte bleed is regenerated and returned with its silver recovered rather than neutralised, so the metal that would otherwise leave in the stack or the effluent plant stays in the balance.
Electrolyte economics rather than electrolyte consumption. Regenerating in place reduces the frequency of make-up, the nitric acid demand that comes with it and the number of fuming make-up batches in a year, at the same time as it removes the accumulated impurities that would otherwise start co-depositing into the crystal.
Anode slime treated as a revenue line, not a residue. At about 8% of the anode mass and typically 50–70% gold with 30–40% silver, the slime is usually the largest single value stream after the silver itself. Bag opening, washing, filtration, drying, assay and the PGM declaration are inside the equipment scope, so that value is measured and recovered rather than estimated.
A route for feed that cannot be cast. Granulated, cemented and powdered silver is run from a titanium basket instead of being melted twice, and residual anode plates are finished in the basket or returned to the melting shop, so material does not have to be cycled through the furnace to be recovered.
Grade protected at the point where it is decided. The free-acid window is the difference between a clean crystal and one contaminated by hydrolysed bismuth, and the window is held by titration on a schedule rather than adjusted after an excursion — because a grade failure at the cathode cannot be corrected downstream without a second melting and refining pass.
Materials matched to nitric acid service stream by stream. Integrally formed polypropylene without welded seams, a polypropylene homopolymer frame, titanium-clad copper bars, bakelite insulation, titanium cathodes and PP and PVDF wetted parts, selected for the chemistry rather than for first cost.
Compliance engineered into the cell rather than added downstream. Sealed cover, side extraction, condensation and a negative-pressure absorption tower are part of the line, and the reagent chemistry of the tower converts the nitrogen oxides to nitrogen, carbon dioxide and water so that abatement does not create a secondary waste to dispose of.
Batch traceability from anode to bar. Anode weight and assay, electrolyte analysis, campaign record, slime weight and assay, product assay and metal balance are held together against the lot number and released with a certificate of analysis, which is what allows the purity figure to be checked on the customer’s own material.
Configuration stated in writing before manufacture. Cell count, cathode area, rectifier rating, circulation rate, cooling duty, exhaust volume and effluent duty are engineered from your anode assay and monthly silver volume, and the resulting figures are set out in the process design package rather than left to be discovered at commissioning.

Service Process

Step 1 — Feed Characterisation and Consultation. Send a representative sample of your crude silver, doré, cement silver, residue or slime-derived feed with an indication of grade and the volume you intend to process. Our metallurgical team assays it for silver and gold by fire assay with an ICP-OES cross-check, and for the impurities that govern the route — copper, lead, bismuth, tellurium, selenium and the platinum group metals — and identifies which route suits the material: straight to anode casting, flux refining during melting, or a pretreatment step first. Output: assay report and a preliminary route proposal with the achievable purity and the expected slime yield.

Step 2 — Laboratory Test Work and Process Design. Bench and pilot campaigns confirm the anode composition and casting parameters, the electrolyte specification and the free-acid window, the current density, the expected crystal quality, the anode slime yield and composition, and the bleed and regeneration schedule. The results are converted into a mass balance, a flowsheet, cell and electrode sizing, the rectifier rating, the electrolyte volume, the circulation and cooling duty, the off-gas load, water and reagent consumption, a layout and a utility schedule against your throughput and site. Output: test report, process design package and firm quotation.

Step 3 — Detailed Engineering and Manufacturing. The cell body and frame, electrodes and conductor bars, bag assemblies, transparent cover and side extraction, chiller and circulation set, scraper and cell conveyor, discharge and solid–liquid separation, crystal washing and drying unit, electrolyte preparation vessel, purification and regeneration set, fume condenser, nitrogen-oxide absorption tower, melting and casting modules, marking and weighing equipment and the control cabinet are fabricated, pre-assembled on skids and piped. Output: engineered, skid-mounted modules.

Step 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.

Step 5 — Shipping, Installation and Commissioning. We supervise the civil interface, erection, piping, ducting and electrical tie-in, then run an instrumented commissioning campaign on your feed until the contracted purity, throughput and recovery are demonstrated and the nitrogen-oxide outlet is verified against your local emission limit. Output: a producing silver electrolysis line at contracted performance.

Step 6 — Operator Training and Handover. On-site training covers safe nitric acid handling, anode casting and bagging, cell loading and electrode spacing, electrolyte make-up and titration, current density and temperature control, crystal scraping and washing, electrolyte purification and regeneration, 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.

Step 7 — Process Optimisation and Ongoing Support. Remote troubleshooting, reagent and consumable supply, electrode, bag and filter service, periodic performance audits where the crystal assay, the electrolyte analysis and the slime yield are reviewed against the design, and recovery or capacity upgrade paths keep the line at target over its service life. Output: sustained performance and spare-part continuity.

Warranty And After-Sales Service

Warranty period. Twelve months from commissioning or eighteen months from shipment, whichever falls first, covering design, materials and workmanship of the equipment supplied, with the terms and the excluded wear parts stated in the contract.
Wear part and consumable clarity. Anode bags, filter media, gaskets, pump seals and scraper elements are identified as consumables with their expected service intervals declared up front, so that the operating cost of the line is visible before it is commissioned rather than after.
Spare parts availability. A recommended commissioning and first-year spares set is quoted with the line, and spare parts remain available through the equipment’s service life with lead times stated at order.
Remote support. Telephone, email and messaging support for operating questions, alarm interpretation, crystal quality problems, cell voltage deviations and process troubleshooting while your line is running. Output: same-day response on operating issues.
On-site service. Engineer attendance for warranty faults, process problems and periodical check-ups, with response and attendance times agreed in the contract according to your location. Output: on-site intervention and a service report.
Assay and metal balance verification service. Periodic verification of the product assay and the electrolyte and slime analyses against your own laboratory results, so that the performance of the line is tracked over time rather than assumed from commissioning. Output: verification report against the batch records.
Operator retraining and refresher visits. Additional training, refresher sessions and process optimisation visits as your feed mix, anode assay or product requirement changes. Output: updated training and revised procedures.
Documentation set. Operation and maintenance manuals, process flow diagram, cell and electrode drawings, electrical and control drawings, layout, spare parts catalogue, safety data for nitric acid and the reagents used, and the emergency response plan covering acid exposure, nitrogen oxide release and electrical isolation. Output: complete documentation handover.
Compliance support. Assistance with emission and effluent parameter declarations, absorption tower performance verification, and the handling, storage and disposal requirements for acid-bearing process liquors and for the intermediates generated in the line. Output: technical data for your permit applications.
Lifetime technical support. The process design remains yours, and our engineering team remains available for modification and expansion advice for the operating life of the line. Output: long-term engineering continuity.

Frequently Asked Questions

What is silver electrolysis equipment used for?

Silver electrolysis equipment refines crude silver into high-purity silver by dissolving a cast anode in a silver nitrate electrolyte and depositing the silver on a cathode as crystals. It sits between the smelting shop and the market: material that has been melted and cast into anode plates goes into the cell, 99.99% silver comes out as cathode crystal, and the gold, platinum, palladium and rhodium that will not dissolve are held back in the anode bag as slime. It is the standard route wherever the silver has to be brought to a marketable purity with a documented assay, and it is also used in reverse as a desilverising step, where taking the 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 silver electrolysis achieve?

Cathode silver at 99.99%, which is the 9999 fine grade, from an anode above 75% silver and in practice above 97% silver. Where a higher figure is required, the route is a second electrolysis pass on the crystal, which is specified rather than assumed: the purity is a function of the anode assay, the electrolyte condition and the discipline held during the campaign, so the achievable figure is confirmed on your own material in the laboratory test and stated in the process design. The purity is verified by fire assay with a cupric chloride titration or an ICP-OES cross-check, and the lot is released against a certificate of analysis rather than against a nominal grade.

What cathode current density does the cell run at, and why does it matter?

The design point is 750 A/m² of cathode area, against the 250–350 A/m² of a conventional silver cell and inside the 600–800 A/m² band that high-current-density silver practice occupies. Industrial high-current-density silver electrorefining cells are published as operating above 1,000 A/m² depending on the composition of the silver doré being processed, which is the headroom the design is built into. Current density is the single parameter that sets both throughput and product quality. Raising it buys production and costs three things: the resistive drop across the electrolyte gap, the tendency of the anode face to passivate as its silver content falls, and deposit morphology, because a crystal grown too fast at a starved boundary layer turns nodular and can bridge the electrode gap.

What electrolyte composition does the silver cell use, and why is the free nitric acid window so narrow?

The electrolyte is a silver nitrate solution in nitric acid, held at 60–150 g/L of silver with 10–18 g/L of free nitric acid, with potassium nitrate added where the conductivity or the pH band needs help. Both bounds matter and they fail in opposite directions. If free acid falls below the window, bismuth and other base metals hydrolyse and the precipitate reports to the cathode crystal, which is a grade failure that cannot be corrected without melting and refining the lot again. If free acid rises above the window, the acid re-dissolves silver that has already been deposited, which is a recovery loss and also forces the silver concentration up. Because the two failure modes sit on either side of the same setpoint, the electrolyte is titrated and corrected on a schedule during the campaign rather than adjusted after a quality excursion.

What happens to the gold and the platinum group metals in the anode?

They do not dissolve. Gold, platinum, palladium and rhodium are insoluble under silver electrolysis conditions, so they report to the anode bag and collect as anode slime at about 8% of the anode mass, typically assaying 50–70% gold with 30–40% silver. That slime is usually the most valuable by-product of the line. 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 into a plate 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 silver content does the anode need before it can be run in the cell?

Above 75% silver is the working threshold, and in practice above 97% is what goes straight to anode casting. Feed above 75% but below the practical figure is fluxed and air-blown during melting so that copper, lead and bismuth oxidise into a slag that is skimmed off before the anode is cast. The gold content sets a second limit: where the gold is high enough that the anode face stops dissolving cleanly as its silver is used up, the plate is left as a residual anode and either returned to the melt or given a desilverising pass, and the castability of that residue is what the anode specification is built around.

Where does the copper go, and what happens when it builds up in the electrolyte?

Copper dissolves anodically alongside the silver and stays in the electrolyte as copper nitrate, so it does not follow the silver to the cathode. That is why sterling scrap and coin alloys can be run without a pretreatment step. It does mean, however, that the copper has to be taken out of the circuit eventually: as its concentration rises the deposition window narrows and copper begins to co-deposit, which shows up as a change in crystal appearance and then in the assay. Impurity-loaded electrolyte is therefore drawn off on the bleed schedule, regenerated so that the copper, bismuth and other accumulated elements leave the circuit, re-acidified to its working pH and returned to the cell, with its silver content recovered in the same step.

Why is the cell temperature held at 40 °C?

Warmer electrolyte has a lower resistance and better deposition kinetics, so cooling is not applied to slow the reaction down. The set point is held because above it the losses climb faster than the benefit: evaporation rises, nitric acid consumption rises with it, and the vapour that leaves the cell carries silver with it, so a warm cell is a cell that loses metal up the stack. A chiller running at a 40 °C set point, starting and stopping on the measured electrolyte temperature, keeps the resistance low without paying for it in acid and metal loss, and it also holds the crystal quality steady across the campaign. The conductor bars and lugs are engineered separately to stay below 70 °C.

Why is the cell closed and extracted rather than run under an open hood?

Because a sealed cell is what makes the extraction economic and the workshop habitable. Nitric acid mist and nitrogen oxides collect under the cover, and a small, well-directed air volume drawn from the side of the cell body removes them at the point of generation. An open cell under a large hood has to be diluted with a far greater air volume to reach the same working condition, which means a much larger scrubber, a much larger fan and a much larger operating cost for the same emission result. The cover on this line is transparent, so the electrodes and the electrolyte remain visible for inspection while the headspace stays closed.

Why is the anode bagged before it goes into the cell?

Because the anode is where the insoluble material accumulates, and if it is free to move it will migrate to the cathode and report to the product as contamination. The bag holds the gold, platinum, palladium and rhodium at the anode from the first minute of the run, so they can be recovered as slime instead of being found in the crystal assay at the end of the campaign. Bagging is also what makes the slime weighable and assayable as a discrete stream, which is what allows the metal balance for the lot to close.

How is the silver crystal harvested without stopping the cell?

A scraper works both faces of the cathode continuously and lifts the crystals off as they form, and a conveyor built into the cell floor carries them across the sloped front section straight into the washing and drying unit. Continuous removal is not a convenience: crystals left in place bridge the electrode gap, short-circuit the cell, distort the current distribution across the remaining electrodes and lower the quality of the powder still in the cell. Because the cell clears itself, the interval between deep cleans stretches from roughly monthly on a conventional belt-discharge cell to a campaign measured in months, and one operator is sufficient for intermittent supervision.

Can granulated or cemented silver be refined without casting an anode plate?

Yes. Granulated, cemented and powdered silver is loaded into a titanium basket rather than being melted into a plate, which removes a melting step and the metal inventory that sits in the furnace with it. The basket carries the same bagging function, so the insoluble residue is still retained at the anode and recovered as slime. Residual anode plates that have reached the end of their dissolution cycle can also be finished in a basket without being recast, or returned to the melting shop and cast into fresh anodes.

Can silver chloride or low-grade silver scrap be fed to the cell directly?

Not directly, and this is the one boundary worth stating plainly: silver chloride will not dissolve anodically in a nitrate electrolyte, so chloride-bearing material has to be converted to metallic silver before it can be cast and run. Low-grade scrap that carries enough copper, lead or bismuth is fluxed and air-blown during melting to take those elements out as a slag before the anode is cast. Both conversions are part of the line’s scope where the feed requires them, and the route is set from the assay during feed characterisation rather than discovered after the material has been melted.

What is the difference between silver electrolysis and aqua regia refining?

Aqua regia refining dissolves the metal chemically and then brings it back out of solution by precipitation or reduction, so the purification is done by chemistry in a vessel and the operator’s control is over reagent addition and reaction conditions. Silver electrolysis dissolves the metal anodically under an applied current and deposits the purified metal directly as crystalline cathode metal, so the purification is done electrochemically and the operator’s control is over current density, electrolyte composition and temperature. For silver the electrolytic route is normally preferred because it produces a directly saleable crystal at 99.99% without consuming the quantity of acid an aqua regia route requires, and because the impurities are separated into two recoverable streams. Aqua regia remains the route for gold-bearing material and for the parting of anode slime where the chemistry requires it.

How long does a campaign run, and how often does the cell need cleaning?

Anodes are loaded and residual plates and slime discharged at the end of an electrolysis cycle, with the frequency set in process design from the anode weight, the anode assay and the current density rather than by a fixed calendar. Between those cycles the cell runs continuously, and because the crystal is scraped away as it forms, the deep clean is a campaign-scale job rather than a routine one — the difference between a cell that is cleaned roughly monthly and one that is cleaned between campaigns. The electrolyte and the anode slime are assayed at each cycle, and those two results are what decide whether the bleed schedule or the anode specification needs to change.

What capacity can you supply, and how is it configured?

Capacity is engineered to your anode assay and your monthly silver volume rather than taken from a catalogue of fixed models. What matters in this line is the silver content of the anode, the gold and base metal load, and the number of cells and electrode area needed to carry the target current at the design current density, so two plants quoted at the same daily silver output can require very different cell counts depending on what is in the anode. We size the number of cells, the cathode area, the rectifier rating, the circulation rate, the cooling duty, the exhaust volume and the effluent duty from your analysis and your target silver volume, and we state the resulting figures in the process design package. The layout is modular, so a line that validates the route on one campaign can be extended in parallel rather than replaced.

How is the silver product verified, and what documentation comes with it?

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 specified grade. The documentation set for the lot holds the anode 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. That is what connects the bar in the customer’s hand to the anode lot that produced it, and it is why the purity and recovery figures for this equipment are checkable on the customer’s own material rather than only on a specification sheet.