Silver Refining Process

— Silver Refining Process: Turnkey Silver Refining Plant and Equipment

The YuSai silver refining process and plant is a turnkey silver refinery with two routes. Hydrometallurgical refining — nitric acid dissolution, chloride precipitation, ammonia complexation and hydrazine reduction — serves low-grade and chloride feed, at a reduction rate above 99% and purity above 99%; electrolytic refining — crude silver anodes in a silver nitrate electrolyte with titanium cathodes — produces 99.99% (9999 fine) silver above the 999.0 LBMA Good Delivery minimum, recovering above 99% from 97% crude silver. The cell runs at 750 A/m², two to three times the 250–350 A/m² of a belt-discharge cell, with electrolyte at 60–150 g/L silver, 10–18 g/L free nitric acid and about 40 °C. A carbonate flux and oxidising blow remove copper, tellurium, selenium and bismuth before casting, and anode slime — about 8% of the anode mass, 50–70% gold — is parted to raise gold grade above 90%.

Product Overview

The silver refining process is the aqueous and electrochemical route that turns impure silver — mine doré, copper and lead electrorefinery anode slime, jewellery and silverware scrap, photographic and plating waste, electronic scrap fractions and silver-bearing solutions — into fine silver of a defined grade. Silver is unusual among the precious metals in that the industrial route to 9999 quality is a single, well-characterised step: electrolysis in a silver nitrate electrolyte, where a crude silver anode dissolves and pure silver deposits on the cathode. Everything upstream exists to make that step succeed and everything downstream exists to make sure nothing of value leaves with the waste. Silver is also the most widely used precious metal by volume: it is the highest-conductivity metal in commercial use, the standard contact and conductor material in electronics, a core component of photovoltaic cells and brazing alloys, a catalyst in ethylene oxide and formaldehyde production, and an antibacterial agent in medical and consumer products. Because that demand is met from a mix of mine supply and recycling, and because the metal is spread thin across an enormous number of manufactured parts, secondary silver is one of the largest single streams in the precious-metals recovery industry.

A silver refinery is a process plant, not a machine, and its design follows the feed. Crude silver from copper and lead anode slime is treated by pre-refining and electrolysis; silver recovered as silver chloride from precious-metal refining circuits is treated by the chemical route, because silver chloride will not dissolve in nitric acid until it has been converted; low-grade sweeps, film and ash need incineration and pre-concentration before either route applies; and silver that is alloyed with gold in a doré bar needs a parting step before the silver can be refined to grade. This plant is engineered to run that whole sequence at a single site: preparation (crushing, milling, screening, incineration, ashing, blending, sampling and assay), pre-refining (fluxing with sodium carbonate and an oxidising air blow to slag off copper, tellurium, selenium and bismuth; cupellation where lead is present; zinc and chlorine treatments where silver must be separated from lead or from gold), anode casting into crude silver plates, electrolytic refining in high current density cells, chemical refining for chloride and low-grade feed, slime and liquor treatment, and melting, casting and assay. The wider circuits this page belongs to — a precious metal hydrometallurgical refining plant for the aqueous route, a precious metal recovery and refining system for the front end that concentrates feed, and the platinum-group-metal lines covered by platinum group metal refining equipment — are designed to hand off to one another, so a silver circuit is rarely a stand-alone purchase.

The chemical route is the plant’s answer to feed that a cell cannot take. Silver chloride is dissolved through nitric acid where a wet route is required — 3Ag + 4HNO₃ → 3AgNO₃ + NO + 2H₂O — then re-precipitated with hydrochloric acid or sodium chloride as Ag⁺ + Cl⁻ → AgCl so that silica and base-metal impurities separate out on filtration. The washed silver chloride is slurried in water and converted with ammonia liquor to a soluble complex at pH 10–11 — AgCl + 2NH₃·H₂O → Ag(NH₃)₂Cl + 2H₂O — during which the remaining base metals hydrolyse and precipitate and are filtered off. The clear silver solution is warmed to about 50 °C and hydrazine hydrate is dosed slowly with agitation at a silver-to-hydrazine mass ratio of 1 : 0.3–0.4 as a 40–80% solution; within about 30 minutes grey-white silver is reduced out according to 4Ag(NH₃)₂Cl + N₂H₄·H₂O + 3H₂O → 4Ag + N₂ + 4NH₄Cl + 4NH₃·H₂O, at a reduction rate above 99% and a silver purity above 99%. Hydrazine is chosen deliberately: it is a strong, fast reductant that introduces no new impurity to the silver. Where the silver must reach 9999 grade it then goes forward to the electrolysis section as an anode plate rather than being sold as chemically reduced powder.

Electrolysis is where the grade and the throughput are actually set. Crude silver anodes are hung in bags in a silver nitrate electrolyte; current is applied through titanium-clad copper conductor bars; silver dissolves from the anode and deposits as dendritic crystals on titanium cathode plates. The plant runs the cell at 750 A/m² cathode current density — the conventional horizontal belt-discharge cell operates at 250–350 A/m² and a high current density horizontal cell at 600–800 A/m², so the same physical cell footprint produces two to three times the silver — and it achieves that without losing quality because the two factors that normally force a low current density are controlled: the electrolyte circulation pattern is arranged to flow parallel to the electrodes with bottom inlet and top outlet, which suppresses the concentration polarisation between anode and cathode, and the electrolyte is cooled to about 40 °C by a refrigeration unit that starts and stops on temperature, which cuts evaporation and acid consumption and keeps the liquor inside the window where crystal growth stays coherent. Electrolyte management runs continuously in parallel: silver concentration is held between 60 and 150 g/L and free nitric acid between 10 and 18 g/L, copper and bismuth are drawn off before they can co-deposit, and silver recovered from bleed, rinse and spent liquors is returned to the circuit. The result is silver powder that assays 99.99% or better run after run, which is why the plant also mechanises what happens next: an automatic stirring and scraping system knocks the crystals off the cathode so the electrodes never short, a belt conveyor carries the powder out through a ramp at the front of the cell directly into a container for washing and ingot casting, and a sealed transparent cover with side extraction keeps the aisle clear and the operator out of the acid mist.

The result is a compact, closed-loop silver refinery that a mine, smelter, precious-metal refiner, jewellery manufacturer, e-waste processor or plating shop can own and operate on site: 9999 fine silver as ingot, granule or anode, gold and platinum-group metals recovered from the slime rather than surrendered to a third party, recovery above 99% with the last fraction pulled out of rinse water, spent electrolyte and dilute solutions, and off-gas, dust and effluent treated inside the same package. Capacity, footprint and utilities are engineered to the individual case rather than sold from a catalogue — the sizing that matters is the silver content of the feed, the target product and the batch rhythm — and every consignment is released against a Certificate of Analysis from fire assay with ICP-OES confirmation.

Application Scenarios

A silver refining process and plant is specified wherever silver-bearing material exists in volume, the silver is below saleable grade, and the operator wants to own the refining margin and the assay rather than sell a mixed product at a discount. The scenarios below are the configurations we build most often.

Copper and lead electrorefineries — treat anode slime from copper and lead electrolysis on site, recover silver as 9999 ingots and raise the gold grade of the residue for its own circuit, instead of shipping slime to a third-party refiner. Output: 9999 silver ingots, gold-rich residue above 90% Au.
Precious-metal refineries and assay houses — add or replace a silver refining line with high current density cells, sealed covers and side extraction, and a dedicated chemical route for the silver chloride produced by gold and PGM refining. Output: certified Ag 99.99% and chemically reduced silver powder.
Silver mines and doré producers — refine doré bars and gravity or flotation concentrates into saleable fine silver on site, with a pre-refining and anode casting step in front of the cell. Output: 9999 fine silver bars for the bullion market.
Gold refineries with silver by-product — separate silver from gold-silver alloy by silver electrolysis or by the Miller chlorine route, and refine the silver to grade rather than selling a cyanide or chloride residue. Output: Ag 99.99% plus gold collected in the anode bag.
E-waste and PCB recyclers — feed the silver-bearing alloy, contact scrap, connector plating and pregnant liquor produced by the front end of an e-waste line into a silver refining circuit. Output: 9999 silver ingots, with gold and palladium finished on the same site.
Jewellery, silverware and hollowware manufacturers — refine 925 sterling scrap, bench sweeps, polishing dust, filings and floor residues in-house and return the metal to production within days. Output: Ag 99.99% for alloying or ingot sale.
Photographic, X-ray and imaging processors — recover silver from spent fixer, bleach-fix, wash water, film and ash, and see the silver through to ingot rather than selling sludge. Output: recovered silver metal and treated effluent for discharge.
Electroplating and surface-treatment shops — recover silver from plating baths, drag-out, strip and rinse solutions, including cyanide-bearing liquors where the feed requires it. Output: electrolytic silver and recyclable liquor.
Electrical and electronics manufacturers — refine silver contacts, brazing alloy scrap, sputtering targets, thick-film paste residue and rejected assemblies. Output: 9999 silver for reuse or sale.
Photovoltaic and solar-panel recyclers — recover the silver-bearing fraction from end-of-life modules and production scrap as a concentrate, and refine it to grade as volumes build. Output: refined silver from the module silver fraction.
Catalyst and chemical producers — recover silver from spent ethylene oxide and formaldehyde catalysts, and from silver-bearing process residue and filter cake. Output: refined silver and decontaminated residue.
Bullion traders, banks and fabricators — convert mixed, contaminated or off-spec silver back to assay-certified 9999 metal with full batch traceability. Output: certified ingots and granules with assay documents.
Medical, dental and laboratory operations — refine silver alloy scrap, amalgam residues, crucibles, electrodes and bench waste with documented mass balance. Output: high-purity silver for reuse or sale.
Universities, institutes and pilot facilities — bench and pilot silver refining trains for process development, teaching and small-batch production. Output: analytical-grade silver and reproducible process data.

Applicable Raw Materials

Every consignment leaves the plant against a Certificate of Analysis produced by fire assay with cupellation and confirmed by ICP-OES, and each product is packed in the form its buyer wants — ingot, granule, crystal, powder or anode plate.

9999 fine silver ingots — electrolytic silver crystals melted in an induction furnace in a graphite-clay crucible and cast in cast steel moulds to Ag 99.99% (9999 fine), above the 999.0 parts per thousand minimum fineness required for LBMA Good Delivery silver, and available in the bar weights and grain markings your market requires. Output: assay-certified silver ingots.
Fine silver granules and shot — where the buyer prefers melting stock, the same metal is granulated or cast as shot for alloying and anode production. Output: Ag 99.99% granules.
Electrolytic silver crystals and powder — cathode crystals washed, dewatered and dried to a defined residual conductivity, supplied where the user melts, blends or processes the metal directly. Output: washed and dried silver crystals above 99.99%.
Chemically reduced silver powder — from the ammonia complexation and hydrazine reduction route, at a reduction rate above 99% and a purity above 99%, for customers whose feed is chloride-based. Output: silver powder above 99% purity.
Refined silver up to 99.995% — where a specification beyond 9999 is required, electrolyte purity, current density and re-electrolysis are set to reach 99.995% on request. Output: 5N silver to specification.
Silver anode plates — cast crude silver anodes for an existing electrolysis line, and refined silver anodes used as consumable anodes in plating, electroforming and oxygen-transfer processes. Output: cast silver anode plates.
Gold-rich residue and gold product — anode slime is treated by nitric acid parting or a second electrolysis to raise the gold grade above 90% for the gold circuit; where gold is finished on site it leaves as gold powder or ingot. Output: gold-rich residue above 90% Au, or refined gold.
Copper and base-metal by-products — copper, bismuth, tellurium and selenium removed in pre-refining and electrolyte purification are recovered as slag, salt, cement or cathode rather than discarded. Output: saleable base-metal by-products and inert slag.
Treated off-gas, effluent and recycled water — scrubbed cell and reactor off-gas with NOₓ below the applicable discharge limit at 99.5% or better absorption, and neutralised, metal-polished water recirculated to the wash and rinse loop. Output: compliant emission, discharge and recirculated water.
Batch documentation — input assay, process record and output Certificate of Analysis for every lot, in the form banks, bullion buyers and environmental authorities require. Output: Certificate of Analysis and batch traceability record.

Output Products

Every consignment leaves the line against a Certificate of Analysis produced by fire assay with ICP-OES confirmation, and each product is packed in the form its buyer wants — ingot, granule, granulate or powder. Fineness is reported as parts per thousand against an internationally recognised standard.

Au99.99 (Grade I) gold ingots — electrolytic cathode gold melted and cast to the Shanghai Gold Exchange Au99.99 (Grade I) standard gold ingot specification, in weights and dimensions agreed with the buyer. Output: 99.99% gold ingots, assay-certified per batch.
99.999% fine gold — where the buyer’s end use requires five-nines metal, the cathode gold is recast and passed a second time through the same electrolytic cell. Output: 99.999% gold ingots or granules.
LBMA-specification cast bars — vacuum and inert-gas casting to any LBMA-approved trading specification the customer requires, delivered without porosity, shrinkage cavities or surface ripple. Output: cast bars to a nominated trading specification.
Investment-grade gold granules and granulate — gold melted and granulated rather than cast where the buyer needs a free-flowing, easily weighed and easily redissolved form. Output: gold granules of controlled size distribution for alloying or plating.
Gold in sponge and powder form — the reduced gold intermediate, washed to neutral and dried, supplied where the customer routes it to powder metallurgy, catalyst preparation or a plating bath rather than to a bar. Output: sponge gold and fine gold powder at 99.9% and above.
Silver chloride and recovered silver — the silver chloride recovered from the anode bag and from nitric acid pre-treatment, reduced and melted to silver metal; where a silver electrolytic circuit is added, refined further. Output: silver metal at 99.95% and above, or silver chloride for onward sale.
PGM-bearing anode slime and residue — the insoluble fraction of the anode and the electrolyte bleed, which concentrates platinum, palladium and rhodium. Output: a PGM-bearing residue routed to a platinum-group-metal refining circuit.
Spent electrolyte and recovered gold from electrolyte bleed — electrolyte removed from the circuit when impurity levels rise, with the contained gold recovered by reduction before the liquor goes to effluent treatment. Output: recovered gold plus a treated chloride liquor.
Treated off-gas and neutralised effluent — acid fume and nitrogen oxides absorbed in the scrubber train and the acid effluent neutralised, so that both streams leave the plant within local emission and discharge limits. Output: compliant stack emission and neutralised effluent for discharge or reuse.
Batch documentation and metal balance — an assay certificate, a batch record of feed weight, product weight, residues and losses, and a full parameter log from the PLC. Output: an auditable batch file for every refining lot.

Silver Refining Process Flow

The plant runs as a staged route in which silver-bearing feed is first prepared and pre-refined, then refined either chemically or electrolytically depending on its form, with the slime circuit, the electrolyte purification loop, the dilute-stream recovery loop and the gas and effluent circuits running continuously in parallel with the metal chain rather than behind it.

Figure: Silver refining process flow — ten stages from feedstock receiving and pre-refining to certified 9999 fine silver, with anode slime treatment, electrolyte purification, dilute-stream recovery and NOₓ abatement inside the same plant.

The main chain runs vertically through receiving → preparation → pre-refining and anode casting → chemical refining of chloride and low-grade feed → electrolytic refining → powder washing and drying → anode slime treatment → electrolyte purification → melting and casting. Side branches route dust and incineration off-gas to collection, slime to the gold circuit, spent electrolyte and rinse water to silver recovery, regenerated electrolyte and eluate back to the cell, slag and base-metal by-products to sale, and neutralised water to the wash and rinse loop.

Steps 1 — Feedstock Receiving, Sorting and Assay. Incoming material is weighed, photographed and logged batch by batch, then sorted by type — crude silver, doré, anode slime, silver chloride, jewellery scrap, sweeps, plated components, film and ash, photographic or plating liquor, or silver-bearing solution — because each stream follows a different preparation and refining route. A representative sample is drawn from every lot and assayed by XRF and fire assay with cupellation, confirmed by ICP-OES, and each batch is tagged for traceability from the gate to the finished ingot. Output: sorted, weighed, assayed and barcoded batch with a route sheet.

Steps 2 — Mechanical Preparation and Pre-Concentration. Solid feed is crushed, milled and screened so that melting or dissolution acts completely rather than on the surface only; sweeps, buffing dust and floor residue are homogenised and blended so that a sample represents the whole batch; photographic film, paper, plastics and ion-exchange material are incinerated or ashed to a silver-bearing ash; and oily, coated and plated material is stripped or burn-off treated as the assay requires. Output: milled, homogenised or ashed feed at a grade the next stage can handle, with dust captured and returned.

Steps 3 — Pre-Refining and Silver Anode Casting. Material carrying copper, tellurium, selenium, bismuth or lead is melted with a sodium carbonate flux and given an oxidising air blow across the melt so those elements report to a slag that is separated before casting; lead-bearing bullion is treated by cupellation, silver is separated from lead bullion by the zinc route, and where silver must be parted from a gold-rich alloy the chlorine treatment converts it to silver chloride for skimming or to the anode bag. The cleaned silver is then cast into crude silver anode plates — typically above 75% silver with gold below 20%, and above 97% where the feed allows — with the surface dressed and the lugs formed for the cell. Output: crude silver anode plates at ≥ 97% Ag, plus slag and collected base-metal by-products.

Steps 4 — Nitric Acid Dissolution and Chloride Precipitation. Low-grade, chloride and heavily contaminated feed that cannot be cast into a workable anode is treated chemically. Silver is dissolved in nitric acid — 3Ag + 4HNO₃ → 3AgNO₃ + NO + 2H₂O — and the solution is filtered to remove silica and insoluble residue; the dissolved silver is then re-precipitated with hydrochloric acid or sodium chloride as Ag⁺ + Cl⁻ → AgCl, filtered and washed so that the base metals, which stay in solution, are separated from the silver. Gold and the platinum-group metals are insoluble in nitric acid and remain in the residue for their own circuit. The reaction runs in an enclosed reactor with a sealed mouth, and the nitrogen oxide produced is drawn to the scrubbing tower. Output: washed silver chloride, a base-metal liquor, and a gold or PGM-bearing residue.

Steps 5 — Ammonia Complexation and Hydrazine Reduction. The washed silver chloride is slurried in water and converted with ammonia liquor at pH 10–11 into a soluble silver ammonia complex — AgCl + 2NH₃·H₂O → Ag(NH₃)₂Cl + 2H₂O — during which residual base metals hydrolyse and precipitate and are filtered off. The clear silver solution is warmed to about 50 °C, and hydrazine hydrate is dosed slowly with agitation at a silver-to-hydrazine mass ratio of 1 : 0.3–0.4 as a 40–80% solution. Within about 30 minutes grey-white silver is reduced out — 4Ag(NH₃)₂Cl + N₂H₄·H₂O + 3H₂O → 4Ag + N₂ + 4NH₄Cl + 4NH₃·H₂O — at a reduction rate above 99% and a purity above 99%. Output: silver powder above 99% purity, at a reduction rate above 99%, for washing, drying and, where required, electrolysis to 9999 grade.

Steps 6 — Silver Electrolytic Refining. Crude silver anode plates are hung in anode bags and immersed in a silver nitrate electrolyte carrying 60–150 g/L silver with 10–18 g/L free nitric acid; titanium plates serve as cathodes and current is delivered through titanium-clad copper conductor bars. Current is applied at 750 A/m² cathode current density — well above the 250–350 A/m² of a conventional belt-discharge cell and within the 600–800 A/m² band of high current density horizontal cells — and the anode dissolves while coherent silver crystals deposit on the cathode. The electrolyte is circulated parallel to the electrodes with a bottom inlet and top outlet to suppress concentration polarisation, and a refrigeration unit holds it at about 40 °C, which limits evaporation and acid consumption and keeps crystal quality stable. Free acid is held in the 10–18 g/L window so that bismuth and other base metals cannot hydrolyse into the powder, without re-dissolving the deposit. Output: electrolytic silver crystals at Ag ≥ 99.99%, and a silver-bearing anode slime.

Steps 7 — Silver Powder Collection, Washing and Drying. The crystals are knocked from the cathodes by an automatic stirring and scraping mechanism, which also prevents short circuits between cathode and anode, and fall onto the conveyor built into the cell floor. A ramp at the front of the cell discharges them directly into a container for washing, dewatering and drying; the powder is washed counter-currently to a defined residual conductivity so that entrained electrolyte and silver nitrate are recovered rather than lost, and the wash water returns to the silver recovery loop. Because the cell clears itself, continuous production is interrupted only at long intervals for a scheduled clean rather than by routine bottom scraping. Output: washed, dewatered and dried silver crystals above 99.99%, plus silver-bearing rinse water returned to recovery.

Steps 8 — Anode Slime Treatment and Gold Recovery. Everything the anode rejects collects in the bag as anode slime, around 8% of the anode mass, typically assaying 50–70% gold with 30–40% silver. That slime cannot go directly to a gold anode because its silver content is too high, so it is either parted with nitric acid — silver dissolves, gold stays insoluble, and the two are separated by filtration — or melted and cast into a second anode for a further silver electrolysis pass. Both routes raise the gold grade of the residue to above 90% for the gold circuit, and the silver nitrate liquor produced by parting returns to the electrolysis cell. Output: gold-rich residue above 90% Au, and silver nitrate liquor returned to the cell.

Steps 9 — Electrolyte Purification and Dilute-Stream Recovery. Copper, bismuth and other impurities stripped from the anodes accumulate in the electrolyte, and above a controlled level they begin to co-deposit and degrade the powder; the plant therefore draws off and purifies electrolyte continuously — by crystallisation, cementation, selective precipitation and ion exchange or resin capture — and returns regenerated liquor to the cell. In parallel, the dilute silver that would otherwise be neutralised is recovered rather than discharged: rinse and wash water, spent and bleed electrolyte, stripping and plating solutions, photographic fixer and low-concentration leach liquors are treated by resin or activated-carbon capture, cementation or electrowinning, which works from low concentrations upward. Wastewater is segregated, neutralised, metal-polished and recirculated. Output: regenerated electrolyte returned to the cell, recovered silver from dilute streams, and polish water for recirculation.

Steps 10 — Melting, Casting and Certificate of Analysis. The dried silver crystals or reduced powder are melted in an induction furnace in a graphite-clay crucible, treated against gas absorption before pouring, and cast in preheated cast steel moulds to ingots; granulation, continuous casting and vacuum ingot casting are available where the product form requires them. Every lot is re-assayed by fire assay with cupellation and confirmed by ICP-OES, marked and weighed, and released against a Certificate of Analysis. Output: certified Ag 99.99% (9999 fine) silver ingots, granules or anode plates with full assay documentation.

Product Structure (Main Equipment)

The plant is supplied as factory-assembled, piped and functionally tested modules on a turnkey basis, with the wetted path built from high-performance polypropylene with anti-ageing additive, PPH, titanium, titanium-clad copper, glass-lined or enamelled steel and stainless steel according to duty.

Feedstock Receiving, Sorting and Weighing Station — weighbridge or platform scale, sorting benches, barcode tagging and batch-record station. Function: establishing the mass balance and traceability chain that all downstream metal accounting depends on.
Crushing, Milling and Screening Unit — jaw or hammer crusher, ball or hammer mill, screen deck and dust extraction, with magnetic separation for ferrous material. Function: reducing solid feed to a uniform particle size so that melting and dissolution act completely rather than on the surface only.
Incineration, Ashing and Calcination Furnace Set — incinerator or asher for photographic film, paper, plastics and ion-exchange material, and a calciner for sweeps, filter cake and organic-bearing residue. Function: converting bulky low-grade silver-bearing material into a compact ash that the refining route can accept.
Blending, Homogenisation and Sampling Station — ribbon or cone blender, riffle and rotary sample dividers, and sample-preparation bench. Function: producing feed that is homogeneous enough for a sample to represent the whole batch, which is what makes the assay — and therefore the settlement — defensible.
Pre-Refining Melting Furnace and Fluxing System — melting furnace with flux dosing and an air or oxygen blowing lance for the oxidising blow, slagging and tapping arrangement, and fume extraction. Function: removing copper, tellurium, selenium and bismuth into a slag before the silver is cast into an anode, which is the step that decides how clean the electrolyte will stay.
Anode Casting Machine and Anode Moulds — anode casting table with preheated moulds, anode trolley, lug-forming and surface-dressing equipment. Function: producing dimensionally consistent crude silver anode plates with sound lugs, so that current distribution across the cell stays even.
High Current Density Silver Electrolysis Cell — cell body moulded in one piece from high-performance polypropylene with anti-ageing additive, and a PPH support frame, with sealed transparent cover, side extraction connections, bottom inlet and top outlet circulation ports and an integrated discharge ramp. Function: the refining step itself — dissolving crude silver at the anode and depositing 9999 silver crystals at the cathode at 750 A/m².
Horizontal Belt-Discharge Silver Electrolyser — horizontal trough cell with a mechanical conveyor running along the floor for fully continuous automatic powder discharge, available where the throughput profile favours continuous operation over single-cell batching. Function: unattended continuous silver production at large tonnage, with the option of a sealed side-extraction design.
Titanium Cathode Plates and Anode Bags — titanium cathode plates with prepared surfaces for coherent crystal growth, and anode bags sized to retain slime while passing electrolyte freely. Function: collecting the refined silver in a form that can be scraped off cleanly, and keeping anode slime out of the cathode deposit.
Conductor Bar and Busbar Set — titanium-clad copper conductor bars, cell-to-cell busbars and connections. Function: carrying current at low resistance, resisting acid vapour, and avoiding the corrosion and voltage drop of plain copper.
Electrolyte Circulation, Filtration and Storage System — circulation pumps, filtration, elevated storage tanks, metering and make-up vessels, and level and flow control. Function: holding silver concentration at 60–150 g/L and free nitric acid at 10–18 g/L, and keeping the circulation pattern parallel to the electrodes.
Electrolyte Cooling System — refrigeration unit with automatic temperature control, plate or coil heat exchanger and interconnecting pipework. Function: holding the electrolyte at about 40 °C, which cuts evaporation and acid consumption and keeps the working aisle free of acid vapour.
Silver Powder Automatic Scraping and Stirring Mechanism — motor-driven scraper and agitator set working across the cathode plates on a controlled cycle. Function: removing crystal build-up from the cathode continuously, preventing cathode-to-anode short circuits and keeping the cell running for months between scheduled cleans.
Powder Conveyor and Discharge Unit — mechanical conveyor along the cell floor and a front ramp discharging into a transport container. Function: moving silver powder out of the cell to washing and casting without manual collection and without interrupting electrolysis.
Silver Powder Washing, Dewatering and Drying Machine — counter-current washer, centrifuge or dewatering screw and controlled drying oven. Function: removing entrained electrolyte to a defined residual conductivity, recovering the silver nitrate with it, and delivering dry powder for melting.
Nitric Acid Dissolution and Precipitation Reactor Set — enclosed reactors in glass-lined or enamelled steel, titanium, titanium-clad and anti-ageing PP with agitation, heating, sealed mouth, condensing and vacuum transfer connections. Function: dissolving silver and precipitating silver chloride under sealed conditions for feed that cannot be cast into an anode.
Ammonia Complexation and Hydrazine Reduction Reactor Set — agitated reactor with pH control, ammonia and hydrazine dosing, temperature control to about 50 °C and exhaust connection. Function: converting silver chloride into a clean silver solution and reducing it to silver powder above 99% purity at a reduction rate above 99%.
Filtration and Solution Transfer Skid — vacuum filter trays, plate-and-frame filter press, candle filters for slime and fine residue, vacuum receivers, glass elevated storage tanks and solution transfer piping. Function: clarifying liquor, washing and dewatering precipitates and residues, and moving high-value solution by vacuum rather than pouring.
Anode Slime Treatment and Parting Unit — parting reactor, filtration, washing and re-anode casting equipment for the nitric acid parting and second-electrolysis routes. Function: raising the gold grade of the slime above 90% and returning the silver nitrate liquor to the electrolysis circuit.
Electrolyte Purification and Ion-Exchange Unit — crystallisation, cementation and selective-precipitation vessels, resin-packed columns with loading, elution and regeneration circuits, and activated-carbon capture. Function: drawing copper, bismuth and other base metals out of the circulating electrolyte before they reach the cathode, and recovering silver from dilute liquors.
Dilute-Stream Recovery Unit — electrowinning cells working from low concentrations upward, cementation and scavenger precipitation equipment. Function: recovering the silver in rinse water, spent electrolyte, plating and photographic liquors instead of neutralising metal to waste.
Sealed Cell Cover, Side Extraction and Flue-Gas Condensation System — transparent sealed cover with side extraction ducting, cold-water circulation condenser and gas–liquid separator with condensate return to the process. Function: containing acid mist at the cell, returning the silver carried in the vapour to the process instead of losing it to atmosphere, and keeping the workshop environment clean.
Nitrogen Oxide and Acid Gas Treatment System — multi-stage jet-spray absorption tower with gas–liquid separators, circulation pumps and tank, alkali dosing and neutralisation with pH control. Function: absorbing nitrogen oxides, nitric and hydrochloric acid mist and chlorine-bearing vapour from dissolution, parting and cell operation at 99.5% or better efficiency and holding the outlet below the applicable discharge limit.
Dust Collection Unit — cyclone, bag or sleeve filter with ductwork and induced draught fan. Function: capturing silver-bearing dust from crushing, milling, incineration, melting and casting so that it re-enters the circuit instead of the environment.
Wastewater Neutralisation and Polishing Unit — neutralisation reactor, settling tank, sludge filter press and polish-water loop with metal analysis. Function: compliant discharge and recirculation of process water.
Induction Melting, Granulation and Ingot Casting Line — medium-frequency induction melting furnace, graphite-clay crucible, granulator, preheated cast steel moulds, ingot marking, weighing and cooling arrangement, with vacuum ingot casting available. Function: converting dried silver crystals and powder into void-free 9999 ingots, granules or anodes at controlled temperature and atmosphere.
Assay and Quality-Control Laboratory — XRF analyser, fire-assay furnace with cupellation equipment, sample-preparation bench, potentiometric titration for silver in solution and ICP-OES. Function: input control, electrolyte and product checking, and the Certificate of Analysis that releases each batch.
PLC Automation and Control Cabinet — PLC with touch-screen HMI, rectifier current and voltage control, cell voltage monitoring, dosing, temperature, pH, flow, level, extraction and scrubbing control, with parameter logging, alarms and interlocks. Function: repeatable, safe, traceable operation and a defensible metal-accounting record.
Safety and Workplace Package — cell and reactor fume hoods, local extraction, acid-proof flooring and matting, secondary containment, eyewash and safety shower, gas-detection interlocks and operator protective equipment. Function: operator protection and compliance with workplace chemical-handling rules.

Product Features

Two refining routes in one plant. Electrolytic refining for metallic silver feed and the nitric acid, chloride, ammonia and hydrazine chemical route for silver chloride, low-grade and contaminated feed are designed as one flowsheet, so the plant is not limited to whichever route the supplier happens to build.
Pre-refining built in, not optional. Fluxing with sodium carbonate and an oxidising air blow before anode casting, plus cupellation, zinc and chlorine treatments, are part of the flow — which is what keeps copper, tellurium, selenium and bismuth out of the electrolyte instead of letting them co-deposit with the silver.
High current density electrolysis. The cell runs at 750 A/m² cathode current density, two to three times the 250–350 A/m² of a conventional belt-discharge cell, so the same footprint produces two to three times the silver — and it does so without losing crystal quality, because circulation and temperature are controlled rather than allowed to drift.
Electrolyte composition held in a defined window. Silver is maintained at 60–150 g/L with free nitric acid at 10–18 g/L: enough acid to prevent bismuth and other base metals from hydrolysing and contaminating the powder, but not so much that the deposited crystals redissolve.
Electrolyte cooling with automatic control. A refrigeration unit holds the electrolyte at about 40 °C and starts and stops on temperature, which reduces evaporation and acid consumption, stabilises crystal growth and keeps acid vapour out of the working aisle.
Parallel-flow electrolyte circulation. Electrolyte flows parallel to the electrode array with a bottom inlet and top outlet, which reduces concentration polarisation between anode and cathode — the mechanism that normally forces a cell to run at low current density.
Sealed cells with side extraction. Transparent sealed covers with side extraction contain acid mist at source, improve the workshop environment and make loading and unloading the cell easier than a large overhead hood permits.
Flue-gas condensation that returns silver to the process. A cold-water circulation condenser and gas–liquid separator cool the vapour, and the silver-bearing condensate goes back to the process rather than being vented — the single largest avoidable silver loss in an open-hood cell.
Automatic powder removal without short circuits. A motorised stirring and scraping system knocks crystals off the cathodes on a controlled cycle, which prevents cathode-to-anode shorting and eliminates the manual scraping that is both a labour cost and a powder-loss point.
Belt discharge directly to washing and casting. Powder falls onto the conveyor built into the cell floor and leaves through a front ramp straight into a container for washing, dewatering and drying, so production does not stop for collection.
Long runs between scheduled cleans. Because the cell clears its own floor and the anodes are bagged, the cell runs continuously for months between scheduled bottom cleans rather than being shut down monthly — the direct cause of a large part of the acid saving, since every shutdown carries a boiling and clean-down cost.
Anode slime treated, not discarded. Slime at roughly 8% of the anode mass and typically 50–70% gold is parted with nitric acid or given a second electrolysis to raise the gold grade above 90%, and the silver nitrate liquor returns to the cell.
Electrolyte purified on a cycle. Copper and bismuth are drawn off by crystallisation, cementation, selective precipitation and ion exchange before they reach the cathode, and regenerated liquor goes back to the cell — the difference between a plant that holds 9999 grade over years and one whose product drifts.
Dilute streams still pay. Rinse water, spent and bleed electrolyte, plating and photographic liquors, and low-concentration leach solutions are treated by resin or carbon capture, cementation and electrowinning working from low concentrations upward, instead of being neutralised to waste.
Corrosion-engineered wetted path. High-performance polypropylene with anti-ageing additive for the cell body, PPH for the frame, titanium-clad copper for conductor bars, titanium for cathodes, and glass-lined or enamelled steel and titanium for the reactors are selected against the real duty — nitric acid, silver nitrate, ammonia, hydrazine and chloride liquor — rather than one material used everywhere.
Cyanide-free standard route. The standard chemical and electrolytic flows use nitric acid, hydrochloric acid, sodium chloride, ammonia, hydrazine hydrate and sulfite, with no cyanide salt anywhere in the process — which removes the most heavily regulated reagent class from the site and simplifies permitting and workplace safety.
Purity held by re-purification, not by hope. Electrolyte control, current density, cell temperature and, where required, a second electrolysis pass are specified per feed, delivering Ag ≥ 99.99% (9999 fine) as standard and up to 99.995% on request.
Low hold-up of high-value metal. Continuous discharge, fast batch reactions and small working volumes mean that less silver is tied up in solution, on cathode surfaces or in filter cakes at any moment — a direct reduction in working capital and metal at risk.
Batch accountability. Weighing, sampling and assaying are tied to a batch record from receiving to dispatch, and every consignment is released against an assay certificate from fire assay with cupellation and ICP-OES confirmation.
Modular and scalable. The same process logic runs from bench and pilot trains to multi-tonne industrial refineries; capacity is added by duplicating cells, reactors, purification and recovery trains rather than by redesigning the chemistry.

Technical Parameters & Specifications

Values below describe the standard process envelope and product outcomes. Throughput, cell count, footprint, power and utility figures are engineered to each client’s feed assay, target product and site conditions, and are confirmed at design review.

Parameter	Specification
Product	Silver Refining Process and Plant (integrated silver refining plant: preparation, pre-refining, chemical refining and electrolytic refining)
Metals recovered	Silver (Ag) as the primary product; gold (Au) from anode slime, with copper, bismuth, tellurium and selenium as by-products
Process routes	Electrolytic refining: pre-refining → crude silver anode casting → silver nitrate electrolysis → powder washing and drying → melting and casting. Chemical refining: nitric acid dissolution → chloride precipitation → ammonia complexation → hydrazine hydrate reduction → washing, drying and, where required, electrolysis to 9999 grade. Both routes share the preparation, slime, purification, recovery and off-gas sections
Plant configuration	Turnkey, skid-mounted and modular: feedstock preparation section · pre-refining and anode casting section · electrolysis section · chemical refining section · washing, drying and melting section · slime and electrolyte purification section · off-gas and effluent treatment section · assay laboratory
Overall silver recovery	Above 99% by the electrolytic route from crude silver feed, with slime silver, spent electrolyte, rinse water and dilute solutions returned to the circuit
Refined silver purity	Ag ≥ 99.99% (9999 fine) as standard, above the 999.0 parts per thousand minimum fineness for LBMA Good Delivery silver; 99.995% on request
Chemical-route purity and yield	Reduction rate above 99% and silver purity above 99% in a single pass from silver chloride, before any electrolysis
Crude silver anode specification	Typically above 75% Ag with Au below 20% and minor copper and bismuth; above 97% Ag where the feed allows, for direct refining to 99.99%
Electrolyte composition	Silver nitrate electrolyte at 60–150 g/L Ag, with potassium nitrate where conductivity or pH adjustment is required
Free nitric acid content	10–18 g/L — sufficient to prevent hydrolysis of bismuth and other base metals into the silver powder, and controlled so that deposited crystals are not redissolved
Cathode current density	750 A/m² standard operating point; high current density horizontal cells run the 600–800 A/m² band, compared with 250–350 A/m² for a conventional belt-discharge cell
Electrode materials	Anode: cast crude silver plates in anode bags. Cathode: titanium plates. Conductor bars: titanium-clad copper
Cell construction materials	Cell body moulded in one piece from high-performance polypropylene with anti-ageing additive; support frame in PPH; sealed transparent cover with side extraction; one-piece moulding eliminates electrolyte leakage at joints
Electrolyte circulation	Circulation parallel to the electrode array, bottom inlet and top outlet, to suppress concentration polarisation between anode and cathode
Electrolyte temperature control	Refrigeration unit with automatic start and stop, holding the electrolyte at about 40 °C to limit evaporation, reduce acid consumption and stabilise crystal growth
Powder handling	Automatic stirring and scraping of cathodes, conveyor discharge along the cell floor, front ramp to container; counter-current washing to a defined residual conductivity, dewatering and controlled drying
Pre-refining chemistry	Sodium carbonate flux with oxidising air blow to slag off copper, tellurium, selenium and bismuth; cupellation where lead is present; zinc treatment for silver in lead bullion; chlorine treatment where silver must be parted from gold
Chemical-route chemistry	Nitric acid dissolution (approximately 50% strength) · silver chloride precipitation with hydrochloric acid or sodium chloride · ammonia complexation at pH 10–11 · hydrazine hydrate reduction
Reduction conditions	Silver solution warmed to about 50 °C · hydrazine hydrate at 40–80% strength dosed at a silver-to-hydrazine mass ratio of 1 : 0.3–0.4 · reduction time about 30 minutes with agitation
Anode slime	Approximately 8% of the anode mass, typically 50–70% Au with 30–40% Ag plus minor impurities; treated by nitric acid parting or by a second electrolysis to raise the gold grade above 90%
Electrolyte purification	Crystallisation, cementation, selective precipitation, ion exchange and activated-carbon capture to remove accumulated copper and bismuth and return regenerated liquor to the cell
Dilute-stream recovery	Resin and activated-carbon capture, cementation and electrowinning working from low silver concentrations upward; applied to rinse water, spent and bleed electrolyte, plating and photographic liquors and low-grade leach solutions
Filtration and transfer	Vacuum filter trays, plate-and-frame filter press, candle filters for slime and fine residue, vacuum solution transfer and elevated storage tanks
Off-gas treatment	Sealed cell cover and side extraction · cold-water circulation condenser and gas–liquid separator with condensate return to the process · multi-stage jet-spray absorption tower with alkali neutralisation for nitrogen oxides, nitric and hydrochloric acid mist and chlorine-bearing vapour
Scrubber absorption efficiency	≥ 99.5% for nitrogen oxides, acid mist and acid gases, with outlet concentration within the applicable local discharge standard
Dust control	Cyclone and bag or sleeve filter capture on crushing, milling, incineration, melting and casting, with collected silver-bearing dust returned to the process
Wastewater treatment	Segregated collection, neutralisation, metal precipitation and polishing, with polished water recirculated to the wash and rinse loop
Melting and casting	Medium-frequency induction melting in graphite-clay crucibles · granulation · preheated cast steel moulds · vacuum ingot casting · ingot marking, weighing and cooling
Product forms	Ingots · granules and shot · electrolytic crystals · chemically reduced powder · silver anode plates, to the client’s specification
Assay and quality control	XRF · fire assay with cupellation · potentiometric titration · ICP-OES, with a Certificate of Analysis per batch
Automation	PLC with touch-screen HMI; rectifier current and voltage, cell voltage, dosing, temperature, pH, flow, level, extraction and scrubbing control; parameter logging, alarms and interlocks
Feed forms accepted	Crude silver and bullion · doré · copper and lead anode slime · silver chloride and refinery residue · photographic film, fixer and ash · plating bath, drag-out and strip solution · electronic and electrical scrap fractions · jewellery scrap and sweeps · spent silver catalyst · silver-bearing process liquor and dilute solution
Plant scale	Engineered from laboratory and pilot trains to industrial refineries; cell count, reactor sizes and throughput are fixed at design review from the feed assay, target product and batch rhythm
Footprint, power and utilities	Configured to the customer’s building, available headroom and utility supply; electrical supply, cooling duty, extraction volume and reagent storage are engineered per project
Working voltage and power supply	Rectifier output and working voltage configured to the cell arrangement and supplied to the local standard, with electronic voltage stabilisation
Standards and compliance	CE; product grade referenced to the 999.0 parts per thousand LBMA Good Delivery minimum fineness for silver; local air-emission, wastewater and chemical-storage requirements applied at design

Technical Advantages

Throughput comes from current density, not from buying more floor space. Running at 750 A/m² against the 250–350 A/m² of a conventional belt-discharge cell means the same cell produces two to three times the silver, and the anode plates in the cell at any moment hold proportionally less of the working capital. For a refiner whose constraint is building footprint or capital, this is the single largest lever in the plant.
The two things that normally cap current density are both controlled. Cells are run at low current density because concentration polarisation forms between anode and cathode and because the electrolyte heats and evaporates. Parallel-flow circulation with bottom inlet and top outlet addresses the first; refrigeration holding the electrolyte at about 40 °C addresses the second. High current density here is a control outcome, not an overdriven cell.
Grade is protected at the electrolyte, not checked afterwards. Free nitric acid at 10–18 g/L keeps bismuth and other base metals from hydrolysing into the powder, silver at 60–150 g/L keeps conductivity and cathode quality in balance, and continuous purification draws copper and bismuth off before they can co-deposit — which is why 99.99% and better is repeatable rather than occasional.
Silver lost through the exhaust is recovered, not vented. An open silver cell evaporates solution and carries metal out with the vapour. Sealing the cell, extracting from the side and condensing the vapour returns that silver to the process; over a year of continuous operation this is frequently worth more than the cost of the condenser.
Pre-refining decides how long the electrolyte lasts. Every unit of copper, tellurium, selenium and bismuth removed by the sodium carbonate flux and oxidising blow is a unit that does not accumulate in the cell, does not require electrolyte bleed, and does not risk reporting to the cathode. Doing this before casting is the cheapest purification available in the flowsheet.
The gold in the slime is monetised instead of discounted. Slime is around 8% of the anode mass and typically 50–70% gold but too silver-rich for a gold anode. Parting it with nitric acid or giving it a second electrolysis pass raises the gold grade above 90% and returns the dissolved silver to the cell — turning what many refiners sell as a wet residue into two finished metals.
Electrolysis is interrupted for maintenance on a schedule, not on a scrape cycle. Automatic stirring and scraping clears the cathodes and the cell floor continuously, so short circuits are avoided, powder quality does not drift through accumulated fines, and the cell runs for months between scheduled cleans rather than being shut down monthly with the acid and labour cost that implies.
Both refining routes are covered, so the feed envelope is wide. A plant that can only electrolyse cannot process silver chloride, photographic sludge or heavily contaminated sweeps without selling them on; a plant that can only run wet chemistry cannot economically produce 9999 ingots at volume. Running nitric acid dissolution, chloride precipitation, ammonia complexation and hydrazine reduction alongside high current density electrolysis is what lets a single site take whatever silver-bearing material the market offers.
Hydrazine reduction is chosen for what it does not add. It is strongly reducing, reacts quickly and introduces no new impurity into the silver — the reason it is the preferred reductant for silver chloride — and it is dosed at a controlled mass ratio of 1 : 0.3–0.4 at about 50 °C, so consumption is measured rather than guessed.
Dilute streams are treated as product. Electrowinning, resin and carbon capture and cementation all work from low concentrations upward, so rinse water, spent electrolyte, plating and photographic liquors and low-grade leach solutions add recovered metal rather than effluent charges — and because they also cut the metal load reaching the wastewater plant, they reduce treatment cost at the same time.
Corrosion protection matched to each duty. Nitric acid, silver nitrate, ammonia, hydrazine and chloride liquor attack materials differently and carry different contamination risks. Moulding the cell in one piece from polypropylene with anti-ageing additive, framing in PPH, using titanium-clad copper for conductors and titanium for cathodes, and specifying glass-lined or enamelled steel, titanium and PP for the reactors extends equipment life and removes the metal contamination that a wrongly chosen material causes.
Cyanide-free route reduces the compliance burden. Removing cyanide from the standard flows removes the most tightly regulated reagent class from the site — its storage, its transport documentation, its exposure monitoring and its effluent limits — which shortens permitting and lowers the cost of running the plant day to day.
Base metals become by-products rather than disposal. Copper, bismuth, tellurium and selenium removed in pre-refining and electrolyte purification, and the inert slag and decontaminated residue that remain, leave as saleable streams or inert material instead of as tipping fees.
Metal accounting that stands up to scrutiny. Weighing, sampling and assay management are integrated into the control system from the gate onward, so every batch carries an input assay, a process record and an output Certificate of Analysis — the documentation banks, bullion buyers and auditors require when a single consignment can be worth more than the equipment that produced it.
Low in-process inventory of a high-value product. Continuous discharge, short batch reactions and small working volumes mean less silver is held in solution, on cathodes or in filter cake at any moment — a direct release of working capital and a reduction in metal at risk per day of operation.
Reliable supply position for a market in structural deficit. With The Silver Institute forecasting a sixth consecutive annual supply deficit in 2026 and recycling reaching only about 193.9 million ounces in 2024 against total demand above a billion ounces, refineries that can turn low-grade secondary material into 9999 metal are the marginal source of supply — and the plant is built for exactly that material.
Turnkey single-point accountability. One contractor owns test work, process design, equipment, assembly, commissioning and operator training, which removes the integration risk of assembling a silver refinery out of several vendors’ modules.

Service Process

YuSai delivers a silver refining process and plant as a full turnkey project, from feed characterisation and bench test work to a running, assay-verified silver refinery.

Steps 1 — Feed Characterisation and Consultation. Send representative samples of your crude silver, doré, anode slime, silver chloride, sweeps, film, ash, plating or photographic liquor, or silver-bearing solution. Our metallurgical team runs XRF, fire assay with cupellation and ICP-OES, identifies the silver, gold and impurity levels, checks the base-metal, organic and chloride load, determines which route the material needs, and proposes the achievable purity and recovery. Output: assay report and preliminary route proposal.

Steps 2 — Laboratory Test Work and Process Design. Bench and pilot campaigns confirm pre-refining flux and blowing conditions, anode composition, electrolyte make-up and current density, chemical-route dissolution, complexation and reduction conditions, reagent consumption, slime treatment and expected recovery, and are converted into a mass balance, flowsheet, equipment list, cell and reactor sizing, utility schedule and plant layout against your throughput, site and local emission and discharge rules. Output: test report, process design package and firm quotation.

Steps 3 — Detailed Engineering and Manufacturing. Crushing, milling, incineration and blending equipment, pre-refining and anode casting units, electrolysis cells with covers, extraction and cooling, dissolution, complexation and reduction reactors, filtration and transfer skid, slime parting and electrolyte purification units, dilute-stream recovery, NOₓ and acid-gas treatment tower, dust collection, wastewater plant, melting and casting line and control cabinet are fabricated, pre-assembled on skids and piped. Output: engineered, skid-mounted modules.

Steps 4 — Factory Assembly, Testing and Acceptance. Each module is functionally tested and the whole train is trial-run, wherever possible on your own material, with the client invited to attend the factory acceptance test before shipment. Output: FAT-approved, pre-commissioned modules.

Steps 5 — Shipping, Installation and Commissioning. We supervise the civil interface, erection, piping, ductwork and electrical tie-in, then run an instrumented commissioning campaign on your feed until the contracted purity and recovery are demonstrated and the off-gas, dust and effluent results are verified against your local limits. Output: a producing silver refinery at contracted performance.

Steps 6 — Operator Training and Handover. On-site training covers safe nitric acid and ammonia working, cell loading and unloading, anode casting, electrolyte make-up and purification, current density and temperature control, powder washing and drying, slime parting, melting and casting, off-gas and effluent operation, emergency procedures and assay QC, supported by Standard Operating Procedures and a full handover dossier. Output: trained crew and complete documentation.

Steps 7 — Process Optimisation and Ongoing Support. Remote troubleshooting, reagent, crucible, mould, anode bag and resin supply, periodic performance audits and recovery or capacity upgrade paths keep the plant at target over its service life. Output: sustained performance and spare-part continuity.

Warranty & After-Sales Service

Standard warranty. Twelve (12) months from commissioning, or eighteen (18) months from shipment, whichever comes first, covering structural, mechanical, electrical, control, thermal and scrubbing equipment against defects in material and workmanship.
What the warranty covers. Replacement of defective components, repair or exchange of main-process equipment, and free remote technical guidance throughout the warranty period. Consumables such as reagents, crucibles, moulds, anode bags, cathode plates, resin, activated carbon and filter cloth, and damage caused by misuse, unauthorised modification or operation outside the agreed feed and process envelope, are excluded.
Guaranteed performance. We warrant that, when fed material inside the agreed assay and throughput envelope and operated to the supplied SOP, the plant meets the contracted silver purity and recovery figures, verified at commissioning by fire assay with cupellation and ICP-OES.
Response commitment. Guaranteed remote response within 24 hours, on-site engineer dispatch and hotline support for breakdowns affecting production, and expedited supply of critical spares.
Spare parts and consumables. Genuine spares, furnace elements, crucibles, moulds, anode bags, titanium cathode plates, rectifier components, metering pumps, circulation and dosing pumps, ion-exchange resin, activated carbon, filter cloth, tower packing and reagent ranges are held as a stocking range to minimise downtime.
Commissioning and start-up support. Supervised installation, commissioning on the customer’s own feed, performance verification against contract, off-gas, dust and effluent verification, and an operator competence sign-off before handover.
Lifetime technical support. Free access to our engineering team for process questions after warranty expiry, plus optional retrofit, capacity-upgrade, recovery-improvement and electrolyte-optimisation services.
Documentation. Full operating, maintenance and safety manuals, electrical drawings, P&ID, cell and reactor documentation, scrubber and furnace documentation, spare-parts catalogue, SOPs and training material accompany every plant.
Compliance support. Assistance with local air-emission, effluent, cyanide-free process certification and chemical-storage permitting documentation, and with the assay and product-certification records that bullion buyers and authorities require.

Frequently Asked Questions

Q1. What is the silver refining process?

The silver refining process is the sequence of operations that turns impure silver-bearing material into fine silver of a defined grade. It has four parts. Preparation reduces the material to a uniform, assayed feed — crushing, milling, screening, incineration or ashing, blending and sampling. Pre-refining removes the base metals that would otherwise contaminate the electrolyte: the silver is melted with a sodium carbonate flux and given an oxidising air blow so copper, tellurium, selenium and bismuth report to a slag, then cast into crude silver anode plates. Refining follows one of two routes — electrolysis in a silver nitrate electrolyte, where silver dissolves from the anode and deposits as pure crystals on a titanium cathode, or the chemical route of nitric acid dissolution, silver chloride precipitation, ammonia complexation and hydrazine reduction. Finishing washes, dries, melts and casts the silver into 9999 fine ingots, and treats the anode slime, spent electrolyte, rinse water and off-gas so that no metal and no pollutant leaves the plant.

Q2. What is the difference between electrolytic silver refining and chemical silver refining?

They are complementary, and this plant runs both. Electrolytic refining is the volume route to 9999 grade: a crude silver anode is dissolved electrochemically in silver nitrate electrolyte and pure silver is deposited on a titanium cathode. It is fast, needs little reagent per kilogram, and is the standard industrial route for metallic feed that can be cast into an anode. Chemical refining is the route for feed that cannot be cast — silver chloride from gold and platinum-group-metal refining, low-grade residues, photographic sludge and heavily contaminated material. Silver is dissolved in nitric acid, re-precipitated as silver chloride to separate the base metals, converted with ammonia to a soluble complex at pH 10–11, and reduced with hydrazine hydrate at a reduction rate above 99% and a purity above 99%. Choosing between them is a question of feed form and target grade, and the useful answer is usually to have both.

Q3. What purity of silver can the plant produce?

Ag ≥ 99.99% (9999 fine) as the standard product from the electrolytic route, which is above the 999.0 parts per thousand minimum fineness required for LBMA Good Delivery silver. Where a specification beyond 9999 is required, electrolyte purity, current density, cell temperature and, where necessary, a second electrolysis pass are set to reach 99.995% on request. The chemical route delivers silver powder above 99% purity directly, and that powder is normally electrolysed onward to 9999 where the market grade is required.

Q4. What crude silver content does the electrolysis cell need?

Crude silver feed of 97% and above is refined directly to 99.99%. A typical anode for a silver cell assays above 75% silver with gold below 20% and minor copper and bismuth, and it refines perfectly well at that level — the silver content of the anode sets how often electrolyte has to be purified and how much slime is generated, not whether the cell works. Where the feed is a low-grade melt, the anode recipe, fluxing and blowing conditions are set at test work so that the anode is sound and the impurity load is manageable. Feed that is genuinely too low-grade, or is in chloride form, goes to the chemical route instead.

Q5. Why does the cathode current density matter so much?

Because it sets throughput per litre of cell and per square metre of floor. A conventional horizontal belt-discharge silver cell runs at 250–350 A/m²; this plant runs at 750 A/m², within the 600–800 A/m² band of high current density cells, which is two to three times the production from the same cell footprint. Running high current density normally risks two problems — concentration polarisation between anode and cathode, and electrolyte heating with evaporation and acid loss — and this plant controls both: electrolyte is circulated parallel to the electrode array with a bottom inlet and top outlet, and a refrigeration unit holds it at about 40 °C. The result is high throughput without the crystal-quality penalty that normally comes with pushing current.

Q6. Why is free nitric acid controlled between 10 and 18 g/L?

Silver nitrate electrolyte carries 60–150 g/L silver together with 10–18 g/L free nitric acid, and the free acid window is one of the two or three parameters that decide whether the product is 9999 or scrap. Too little acid and bismuth and other base metals hydrolyse and precipitate into the silver powder. Too much and the nitric acid redissolves the silver crystals as fast as they deposit, cutting current efficiency and degrading the deposit. Silver concentration is held in the same way: it sets conductivity and the balance between crystal growth and dendrite formation, and it is the number the circulating electrolyte loop is continuously corrected to.

Q7. How much silver does the anode slime contain, and what happens to it?

Anode slime is generated at roughly 8% of the anode mass and typically assays 50–70% gold with 30–40% silver plus minor impurities. Because its silver content is too high for a gold anode, it is not sent directly to gold electrolysis. It is either parted with nitric acid — the silver dissolves, the gold stays insoluble, and the two are separated by filtration — or melted and cast into a second anode for a further silver electrolysis pass. Both routes raise the gold grade of the residue above 90% for the gold circuit, and the silver nitrate liquor produced by parting returns to the electrolysis cell. In practice the slime is often the most valuable single stream in a silver refinery.

Q8. How does the plant handle the acid mist and nitrogen oxides from the cell?

Silver electrolysis and nitric acid dissolution both generate nitrogen oxides and acid mist, and both are contained at source. The cell is closed with a sealed transparent cover and extracted from the side rather than through a large overhead hood, so the aisle stays clear and loading and unloading are easy. The vapour passes through a cold-water circulation condenser and gas–liquid separator, and the silver-bearing condensate returns to the process — this is metal recovery as much as pollution control. What remains goes to a multi-stage jet-spray absorption tower with gas–liquid separation and alkali neutralisation, which absorbs nitrogen oxides, nitric and hydrochloric acid mist and chlorine-bearing vapour at 99.5% or better efficiency and holds the outlet within the applicable local discharge limit.

Q9. What recovery rate can the plant achieve?

Above 99% by the electrolytic route from crude silver feed, and above 99% reduction in the chemical route from silver chloride. A headline figure means little on its own, however, so the plant is designed so that the streams that usually dilute a recovery figure are treated as process streams: slime silver is recovered in the parting step, spent and bleed electrolyte is purified and its silver returned, rinse and wash water is decanted and its silver recovered by resin capture or electrowinning, and filter wash liquor goes back to the circuit. Recovery is verified at commissioning on the customer’s own feed, and the mass balance is documented batch by batch.

Q10. Is the process cyanide-free?

The standard route is cyanide-free: it uses nitric acid, hydrochloric acid, sodium chloride, ammonia, hydrazine hydrate, sodium carbonate and sulfite, none of which are cyanide salts. That matters commercially as well as environmentally — removing cyanide removes the most tightly regulated reagent class from the site, together with its storage requirements, transport documentation, exposure monitoring and effluent limits. Where a customer’s own upstream process delivers cyanide-bearing feed, such as spent silver plating baths, the plant can be specified to handle it with the appropriate recovery and treatment sections; this is agreed at design review.

Q11. Can the plant treat silver-bearing solutions, fixer and plating liquors as well as solid feed?

Yes. Dilute silver is recovered rather than neutralised, by electrowinning, resin or activated-carbon capture, cementation or selective precipitation — methods that work from low concentrations upward. Feed that falls into this group includes rinse and wash water, spent and bleed electrolyte, silver plating baths and drag-out, strip solutions, photographic fixer and bleach-fix, and low-concentration leach liquors. Because recovering this silver also removes the metal load reaching the wastewater plant, it reduces effluent treatment cost at the same time as it adds recovered metal, which is what makes the dilute-stream section worth installing rather than merely compliant.

Q12. How is gold in the feed handled?

Gold is insoluble in nitric acid, so it separates naturally. In the electrolytic route it reports to the anode slime and is recovered from there by parting or a second electrolysis. In the chemical route it remains in the insoluble residue when silver is dissolved in nitric acid, and is filtered off for the gold circuit. Where the feed is a gold-silver alloy with gold as the major component, the silver is removed first — by electrolysis where the silver content is above 75%, or by the chlorine route where silver must be converted to silver chloride and skimmed or collected in the anode bag — so that the remaining gold can go forward at a higher grade. Where gold is finished on the same site, the plant can be integrated with the gold refining line.

Q13. What information is needed for a quotation?

For a quotation we need a representative sample or assay of your feed giving silver and gold content and the main impurities; the material type and physical form, including whether the silver is metallic, in chloride form, plated onto another metal, or in solution; the target throughput and batch rhythm; the product form and purity you intend to sell, whether that is 9999 ingots, granules, crystals or anode plates; available floor area, headroom and utilities; and your local air-emission, wastewater and chemical-storage requirements. A sample and an assay are what allow us to confirm which route your material needs and what purity and recovery are achievable, and the performance figures in the quotation are based on that test work rather than on a catalogue.

Q14. What warranty and support are included?

The plant is delivered turnkey with a standard 12-month warranty from commissioning, or 18 months from shipment, whichever comes first, covering defects in material and workmanship with defective-part replacement and free remote support, backed by a guaranteed-performance clause confirming the contracted silver purity and recovery at commissioning. Delivery includes supervised installation, commissioning on your own feed, off-gas, dust and effluent verification, on-site operator training with full SOPs and a handover dossier, a 24-hour remote response commitment, stocked spares and consumables, and lifetime technical support after warranty expiry.