Gold Electrolytic Cell

— Gold Electrolytic Cell

A gold electrolytic cell is the apparatus that refines gold electrochemically to Au99.99 and, on a second pass, to 99.999%: a cast crude-gold anode hangs in a chloroauric acid electrolyte at 60–70 °C as the positive electrode of a low-voltage DC circuit, the anode dissolves as the tetrachloroaurate ion, and the gold redeposits on the cathode while the silver, platinum group metals and base metals alloyed with it are rejected as anode slime or held in solution. YuSai Machinery builds it as an engineered unit — tank and containment, electrode frame and spacing, titanium-clad copper busbars and racks, series connection and rectifier match, circulation and thermal loops, an enclosed headspace with condensate return, and voltage, current and busbar monitoring. Cathode area, electrode count, spacing, cell volume and rectifier rating follow from the anode assay and the target daily gold output, and the arithmetic is issued in the process design package. It dissolves a solid anode; gold already in solution is a separate duty.

Product Overview

A gold electrolytic cell is an electrorefining cell. A cast anode of crude gold is hung in the cell and made the positive electrode of a direct current circuit; the anode dissolves, gold leaves the plate as the tetrachloroaurate ion, and the same gold is reduced back onto the cathode as coherent metal while the silver, copper, nickel and other metals alloyed with it are left behind in the electrolyte or in an insoluble residue at the anode. The cell is the classical chlor-auric acid electrorefining cell — the design family known as the Wohlwill cell — and everything about the hardware follows from the fact that both the feedstock and the electrochemical reactant are the same solid plate. That is what separates this vessel from a solution-side cell: an electrowinning tank has no anode to dissolve, and a cementation vessel uses no current at all. Three different machines, three different sizing exercises, and a cell specified for one duty will not do the work of another.

Why the cell, and not the plant around it, is the informative unit comes down to where the numbers are fixed. The daily output of a line is the gold deposited on cathode faces, so it is the product of cathode area, current density and time. The power the line draws is the product of the current and the cell voltage, so it is the product of cathode area and the voltage budget of one cell. The working capital tied up in the circuit is the product of cell volume and working gold concentration. All three of those figures are properties of a single cell, multiplied by the number of cells; get the cell right and the line is right, and get the cell wrong and no amount of rectifier capacity repairs it.

The cell voltage is where most of the practical engineering lives, and it is worth separating into its parts because the parts behave differently. The first two are electrochemical: the potential needed to dissolve gold at the anode and the potential needed to deposit it at the cathode. The third is ohmic: current passing through an electrolyte of finite conductivity across a gap of finite width, which is the term that spacing and temperature act on directly. The fourth is purely electrical: contact resistance at the hanger faces, clamp faces and busbar joints. Published figures for gold cells differ by a factor of several, and the reason is almost never a disagreement about electrochemistry — it is that one figure is quoted for a single electrode pair, another for a complete cell at the terminals, and a third for the rectifier output across a line of cells in series, at different spacing, different current density and different temperature. This page quotes cell voltage per cell at the terminals, at the design current density and inside the working temperature band, and states the spacing that the figure assumes.

Temperature is not a comfort setting in this cell. Electrolyte conductivity rises with temperature and so does the rate at which gold ions can be transferred to the cathode face, which is why the cell is specified to run in the 60–70 °C band rather than at ambient: below the band the electrolyte resistance in the voltage budget grows and the cell cannot sustain the current density it was built for. The cost of running hot is that the electrolyte evaporates, and what evaporates carries gold. That is why the cell is an enclosed vessel with a transparent viewing panel and why the vapour path is taken to a condensate return rather than straight to the extraction duct — the enclosure is a metal-recovery device before it is a ventilation device, and the loss figure of below 0.02% of the gold charged is a consequence of it rather than a promise about it.

Cell geometry also decides how much gold the process ties up. The electrolyte has to be rich in gold to carry the plating reaction, so cell volume converts directly into gold held as solution, and a cell is therefore a four-to-five figure quantity of metal in kilograms before any anode has been hung in it. Two cell designs with the same cathode area can hold very different inventories if their volumes differ, and closing the gap between the plates, shortening the tank and trimming the settled electrolyte volume are all inventory decisions as much as they are electrical ones. YuSai issues the cell volume together with the corresponding working-inventory figure so the customer can price that capital rather than discover it.

Because anode composition, silver load, base metal profile and target daily output vary so much between one refinery and the next, a cell is not selected from a fixed model list. Electrode count, cathode area, spacing, tank dimensions, electrolyte volume, circulation rate, thermal duty, enclosure and duct connection, containment and drainage, and the rectifier rating that has to match all of them are derived from your anode assay and your intended output, and the resulting cell drawings, voltage budget and inventory figure are issued before manufacture. A single cell validating a route on a few kilograms a day and a cell line running a production refinery are the same engineering exercise at two sizes, built from the same component family.

Key Facts

The cell is the unit of design. Output, voltage, current, spacing and volume are all cell-level figures: they are derived from the anode assay and the target daily output, and they are the numbers the customer can check with a clamp meter, a ruler and an ampere-hour meter.
The capacity figure means fine gold deposited on the cathode. A cell rated by daily output is rated by the gold actually plated out of solution onto the cathode over a campaign, not by the weight of anode charged into it and not by the weight of crystal recovered after washing.
One ampere-hour of charge is 2.45 g of gold, at 100% current efficiency. Gold enters solution and returns to the cathode as the Au(III) species, so the electrochemical equivalent is 196.97 g/mol divided by three faradays; 3,600 C therefore corresponds to about 2.45 g of gold. Real output is that figure reduced by the current efficiency established on your own anode.
Cathode current density is quoted on the cathode face area, and it is the figure that sets the cell size. The cell is designed to run up to 1,000 A/m² on the cathode face, against the 200–800 A/m² band that conventional electrolytic gold and silver cells occupy; cathode area then follows directly from the current the rectifier is asked to deliver.
Cell voltage is the sum of four things, and it is quoted per cell at the terminals. Anode dissolution potential, cathode deposition potential, the resistance of the electrolyte across the gap, and the contact and conductor losses. That is why the same cell is quoted at different values by different suppliers when the basis is not stated.
Inter-electrode spacing is the lever on electrolyte resistance. The gap between the anode face and the cathode face multiplies directly into the ohmic part of the cell voltage, and it is the one geometric variable that can be tightened in design rather than paid for in power.
The cell runs enclosed because it runs hot. The working temperature band is 60–70 °C, and at that temperature the electrolyte evaporates and will carry gold out of the cell with it; the enclosure and the condensate return path are part of the cell, not an accessory.
Contact resistance is the first suspect when a cell voltage rises. Hanger faces, clamp faces and busbar joints are the components that change state between campaigns, and they are checked before voltage, current density or chemistry are blamed.
Cells are connected in series, so one current serves the line. Cell count and rectifier output are matched on that basis: the line carries a single current, and the rectifier output voltage covers the sum of the per-cell potentials plus the conductor drop.
The electrolyte in a cell is gold held as solution. Cell volume and working concentration together are a kilogram figure of gold that is neither feedstock nor product, which is why cell geometry is chosen to keep the volume down rather than up.
Nothing is taken from a catalogue. Electrode count, cathode area, spacing, cell volume, cell count, rectifier rating, circulation duty, thermal duty, containment and the utility interfaces are engineered to the anode assay, the silver load and the target daily gold output.

Product Core Selling Points

A cell specified from the electrode geometry up. The sequence runs anode assay, then current, then cathode area, then electrode count, then spacing, then cell volume, then cell count. Every number in the cell is downstream of a number the customer can measure on their own material.
The voltage budget is written down and handed over. Anode potential, cathode potential, electrolyte ohmic drop and contact losses are stated separately for the proposed cell, so a voltage excursion during operation can be traced to one of four known components instead of being answered by turning the rectifier up.
Spacing controlled to the millimetre, along the full immersed length. The electrode frame and the spacing comb hold every cathode at the design distance from its anode, and the cell drawing records the nominal gap and its tolerance, because a gap that varies along the plate produces a current distribution that varies with it.
Busbars sized to the current, with the contacts treated as a wear item. Titanium-clad copper conductors are sized to carry the cell current at a temperature rise the insulation and the working environment allow, and hanger and clamp faces are machined, dressed and re-checked as routine maintenance.
Series connection designed as a system, not assembled on site. Cell count, rectifier output voltage and the conductor drop across the line are designed together, so the rectifier is not oversized to cover an assumed voltage the line never draws.
The cell is matched to the rectifier, not the other way round. Current rating follows from cathode area and the design current density; the voltage window covers the working band plus the headroom the start-up ramp requires.
Circulation arranged to sweep the electrode faces. The flow path runs parallel to the electrode planes, enters low and leaves high, so the liquor sweeps each face and the denser gold-rich solution at the bottom of the tank does not stratify into a region the current cannot reach.
Thermal control inside the cell circuit. The working temperature band is held by a control loop with the probe located where it reads liquor the electrodes are actually in, because the electrolyte resistance that appears in the cell voltage depends on the temperature at the electrodes.
A closed headspace that pays for itself. The enclosure and the condensate return path put evaporated electrolyte back into the cell rather than through the extraction system, which is what keeps metal loss below 0.02% of the gold charged.
Containment and drainage designed with the cell. Each cell stands over an acid-resistant containment tray with a defined drain point so that a leak is recovered as liquor rather than lost to the floor.
Cell-level acceptance testing before shipment and again on site. Hydrostatic testing of the tank, insulation resistance, contact resistance at every hanger and clamp, circulation flow verification, temperature loop verification and an interlock test are recorded cell by cell.
A cell that can be cleaned, drained and re-charged between campaigns. Turnaround is designed rather than improvised: drain points, lifting provision, bag and membrane access, and a slime removal route that does not require the tank to be dismantled.
The cell can be extended into a cell line later. Additional cells, additional electrode pairs and additional rectifier capacity are added to a validated installation rather than replacing it.
Cell geometry chosen to keep the gold inventory down. A tighter cell volume with the same cathode area holds less gold as working inventory — the design decision that most directly affects how much capital sits inside the circuit.

Application Scenarios

Refineries converting anode plates instead of shipping semi-refined bars. Operations that already cast crude gold anodes and want the refining step inside their own building, with the cell specified to the anode they actually produce.
Plants replacing a manual or undersized cell. Existing installations where the tank was bought as a cheap tank and now limits output, current density or deposit quality, and where the constraint has to be found in the geometry rather than in the rectifier.
Operations adding cell capacity to an existing line. Additional cells tied into an existing rectifier and busbar arrangement, where the electrical match between the new cells and the installed supply is the first design question.
Refineries whose output is limited by cell voltage rather than by current. Sites running at a rectifier limit because their voltage budget is larger than it needs to be, where spacing, contact quality and temperature are the recoverable losses.
Plants where the working capital tied up in the circuit has become the constraint. Businesses whose gold inventory in electrolyte has grown to a level they no longer want to fund, and for whom a smaller cell volume at the same cathode area is the whole objective.
Jewellery manufacturers and casting houses refining their own returns. Bench sweeps, sprues, rejected castings and old gold consolidated and cast into anodes, then run through a cell sized to the workshop rather than to a refinery.
Gold mines and elution plants refining doré on site. Mine bullion upgraded where the silver and base metal load allows direct electrolysis, in cells sized to the mine’s daily doré production rather than to a central refinery’s throughput.
Precious metal traders and assay offices establishing lot value. Buyers of mixed karat scrap who need a measured fine-gold content and a saleable product form, in a cell designed for lot-by-lot turnaround.
Electronic scrap and PCB recycling operations. Gold recovered from connector, finger and plating strip liquors as cemented powder or sludge, melted to anodes and refined in a cell whose counting and turnaround suit frequent small lots.
Copper, lead and nickel electrorefiners running slime circuits. Operations that concentrate gold with silver and the platinum group metals in anode slime and reduce it back to metal, and that need a cell matched to a slime-derived anode rather than to doré.
Plating and surface finishing companies. Gold recovered from plating baths, strip liquors and rinses, re-melted into anodes and refined to a grade the plating line can accept.
Secondary refineries running toll campaigns. Multi-customer operations that need cells which can be drained, cleaned, re-bagged and re-charged quickly between lots, with spacing, volume and current programme re-specified from one campaign to the next.
Pilot, laboratory and university facilities. Small cells used to establish how a particular anode behaves on a few kilograms before a production line is committed, and to train operators on electrode handling and spacing discipline.
Operations building a refinery in stages. Buyers who intend to start with one or two cells and add more as volumes grow, and who need the first cell to be electrically and geometrically compatible with the cells that come later.
Sites where service access and headroom, not throughput, drive the design. Buildings with restricted access or limited headroom, where cell height, lid clearance and lifting provision are the binding constraints on the design.
Plants where the cell has to fit an existing ventilation and effluent scheme. Operations whose exhaust capacity, duct routing or effluent treatment is already fixed, and where the enclosure, duct connection and drain arrangement of the cell have to be matched to it.

Applicable Raw Materials

Every feed below reaches the cell as a cast anode. The assay is taken before the anode is cast, because the cell is specified against it: the silver figure sets the tolerable dissolution regime and the cleaning frequency, the platinum group metal figure sets the value held in the cell residue, and the base metal figure sets how fast the electrolyte has to be bled. Feeds that arrive as powder, sludge or cemented precipitate are melted and cast into anodes before they come near the cell. Output is stated for each feed.

Mine doré and smelted bullion. Bar and button doré from carbon elution or gravity circuit smelting, containing gold with silver and a moderate base metal load, cast or re-cast to the anode envelope the cell accepts and run directly where the silver figure allows. Output: fine gold cathode deposit; silver-bearing residue retained in the cell.
Cast crude gold anode plates. Plates cast from consigned gold, returned cathode gold, cemented powder or ion-exchange product, melted under flux and cast to a controlled thickness and envelope — the standard anode for a secondary refinery. Output: fine gold cathode deposit; anode residue to the silver and platinum group metal circuits.
Gold reduced from chloride or aqua regia liquor. Powder produced by selective reduction, washed free of residual nitrate and chloride, dried and melted to a plate; the normal interface between a wet chemical refining line and a cell. Output: fine gold cathode deposit.
Karat scrap after inquartation and parting. 18K, 14K and 9K scrap and old gold melted with silver or copper, granulated and parted in nitric acid so that the silver and base metals leave before the gold is cast to anodes. Output: fine gold cathode deposit; silver nitrate liquor to the silver circuit.
Bench sweeps, polishing dust and workshop residues. Incinerated, milled, blended and sampled material from jewellery manufacture, smelted to an anode after organic burn-off and removal of ferrous contamination. Output: fine gold cathode deposit; slag returned for re-milling.
Gold recovered from anode slime. Gold leached out of copper, lead or nickel electrorefining slime, reduced back to metal, melted and cast — frequently the highest-value lot a cell sees. Output: fine gold cathode deposit; platinum group metals separated upstream and from the cell residue.
Electronic scrap gold concentrate. Gold from fingers, connectors, package substrates and plating strip liquors recovered as cemented powder or sludge and cast to anodes; the base metal load is usually the reason the material is electrolysed rather than sold as a concentrate. Output: fine gold cathode deposit; copper and nickel held in the electrolyte and bled off.
Deplated and stripped coating gold. Gold recovered from stripped watch cases, spectacle frames, connectors and decorative ware, collected as foil or powder and consolidated into an anode. Output: fine gold cathode deposit.
Dental and laboratory alloy scrap. Dental casting alloys, laboratory crucibles, electrodes and precious metal ware, parted where necessary and cast to anodes sized to the cell. Output: fine gold cathode deposit; platinum group metal fraction to the PGM circuit.
Gold–silver and gold–PGM alloy scrap. Au–Ag strip, Au–Pt and Au–Pd brazing alloys and similar material where the anode is high grade in gold but carries a platinum group metal load that reports to the cell residue rather than to the electrolyte. Output: fine gold cathode deposit; platinum group metal concentrate from the cell residue.
Recycled bullion, coin and bar material. Old bars, coins and bullion whose provenance requires re-refining before resale, cast directly to anode plates from the melted material. Output: fine gold cathode deposit with a fresh certificate of analysis.
Electrowon and cemented gold. Cathode sludge and cemented precipitate from solution-side recovery circuits, dried and melted to anodes; the standard route by which gold recovered from a liquor is brought up to bullion standard. Output: fine gold cathode deposit.
Second-pass cell feed. First-pass cathode gold cast back into anodes and returned to the cell where a higher grade is required, with the cell re-specified for a feed that is already at bullion standard. Output: high-grade fine gold cathode deposit.

Finished Products

The cell delivers a plated product, a residue that stays inside the tank, and a set of streams that leave the circuit on a defined schedule. All of them are weighed and assayed against the lot, which is what makes the cell’s mass balance checkable rather than rhetorical.

Fine gold cathode deposit. The primary product: coherent gold plated onto the cathode face, harvested when the cathode has taken up its design load. Output: cathode gold crystal at Au ≥ 99.99%.
Certificated fine gold ingot. The deposit washed free of adhering electrolyte, dried, melted under flux and cast to the required form and weight, released against an analysis. Output: Au ≥ 99.99% ingot, button or granule with a certificate of analysis.
Higher-grade product from the second pass. Where the customer’s specification or a downstream qualification requires it, first-pass gold becomes the anode of a second cell cycle. Output: 99.999% gold.
Silver-bearing cell residue. The insoluble fraction that forms at the anode face and is retained inside the cell by the bag or membrane rather than allowed to reach the cathode. Output: washed, dried, weighed and assayed silver chloride residue declared by metal content.
Platinum group metal fraction. The part of the anode that neither dissolves nor plates, held with the silver residue and separated before it leaves for the PGM line. Output: PGM-bearing concentrate declared by metal content.
Residual anode plate. The undissolved remainder of a spent plate, together with hanger residues and material recovered from the cell floor. Output: remelt stock returned to anode casting — not sold as scrap.
Electrolyte bleed. Liquor withdrawn on the schedule the electrolyte assay dictates, carrying the silver and base metals that have accumulated in solution. Output: gold recovered from the bleed before the liquor leaves; silver-bearing bleed to the silver circuit.
Rebuilt electrolyte. Bleed make-up liquor adjusted back to the working composition and returned to the cell, so that the volume and the inventory in the circuit are held rather than allowed to grow. Output: electrolyte returned to the cell at the working composition.
Recovered condensate. Electrolyte evaporated from the hot cell and condensed on the vapour path, returned to the tank rather than vented. Output: condensate returned to the cell, recovering the metal it carries.
Cell-side by-product streams. Rinse water from the harvested cathode, filter media and container rinses, and containment liquor from the tray, all collected rather than sewered. Output: residual metal recovered; effluent to neutralisation.
The cell record itself. Voltage, current, busbar temperature and ampere-hour readings per cell and per campaign, filed with the anode, electrolyte, residue and product assays. Output: per-cell process record issued with the batch.
Cell drawings and the voltage budget. The as-built geometry, spacing, electrode schedule and the four-part voltage budget the cell was designed against. Output: as-built cell documentation issued at handover.

Gold Electrolytic Cell Process Flow

The nine stages below are the standard cell sequence, running from the assay that fixes the cell geometry through installation, current ramp, the campaign itself and the turnaround. Steps 1 to 4 are the stages that decide whether the cell will behave: the assay fixes the current and the cathode area, the tank and containment fix the geometry, the electrode and spacing set-up fixes the current distribution, and the busbar and contact work fixes the last term of the voltage budget. Engineering setpoints — electrode count, spacing, immersion depth, cathode area, design current density, cell voltage window, working temperature band, circulation duty, level control and residue removal schedule — are fixed during process design against your own anode assay and target daily output.

Gold electrolytic cell process flow — from the anode assay that fixes the geometry to a cleaned cell ready for the next campaign, with the four-part voltage budget and the ampere-hour count running alongside.

Steps 1 — Cell Specification from the Anode Assay. The lot is weighed, sampled by riffling and splitting and assayed before any cell geometry is fixed, because the assay is the input to every number that follows. Gold is determined by fire assay with an ICP-OES cross-check, silver by titration or ICP-OES, and the base metal and platinum group metal inventory by ICP-OES. Three figures from that assay drive the cell design: the gold content sets the effective anode area and therefore the current the cell can carry, the silver content sets the tolerable dissolution regime and how often the anode has to be inspected and the cell cleaned, and the platinum group metal content sets the value that will be held inside the tank as residue. The target daily output of fine gold and the number of cells are then fixed together, and the cathode area follows from the current the rectifier will deliver at the design current density. Output: cell specification, electrode schedule and the four-part cell voltage budget.

Steps 2 — Tank Fabrication and Containment Assembly. The cell body is formed as a single integrally moulded or welded tank in polypropylene or PPH with an anti-ageing additive, ribbed where the design requires it and closed at the base so that the tank can stand in service without weeping at a seam. Tank dimensions follow from the electrode envelope, the settled electrolyte volume and the spacing the design calls for, with the walls and base checked by hydrostatic test before the cell leaves the works. The tank is then set on its acid-resistant containment tray with the drain point at the low corner, the tray sized to hold the working volume that could be released by a leak, and the assembly levelled so that the electrodes hang vertically. Output: a leak-tested cell on its containment tray, ready for electrode installation.

Steps 3 — Electrode Cascade and Spacing Set-Up. Anodes and cathodes are hung alternately in the cell, each anode standing between two cathodes so that both faces of every plate work. Each anode is fitted with its bag or membrane frame before it goes near the tank, the hanger faces are cleaned and dressed, and each plate is checked for straightness — a bowed plate changes the gap along its own length and produces a current distribution that follows the bow. The spacing comb or spacer system is then set so that the clear distance between the anode face and the cathode face is the design value along the whole immersed length, with the immersion depth recorded for each row. Output: a loaded cell with uniform spacing and verified immersion depth.

Steps 4 — Busbar Assembly and Contact Verification. The titanium-clad copper busbars are installed on their insulated supports with the conductor section that carries the cell current, and the anode and cathode hangers are clamped to them with machined contact faces that sit flat rather than on a single edge. Every clamp is torqued to specification and the contact resistance of every hanger and clamp is measured and recorded as a baseline, because contact resistance is the component that changes between campaigns and the first thing to check when a cell voltage rises. The series connection to the neighbouring cell and the rectifier is completed and the polarity is verified at the terminals before any electrolyte is charged. Output: a verified current path with a recorded contact-resistance baseline per electrode.

Steps 5 — Electrolyte Charging, Circulation and Thermal Holding. The cell is charged with electrolyte to the working level, either from the make-up vessel or from the rebuilt liquor returned from the previous campaign, and the circulation path is started before the current so that the liquor is moving when the first ampere is applied. Flow is arranged parallel to the electrode planes, entering low in the tank and leaving high, so that the stream sweeps each plate face and the denser gold-rich liquor at the bottom does not settle into a stagnant layer the current cannot reach. The thermal loop brings the cell into the working band and holds it there, with the probe reading liquor the electrodes are actually standing in, since the conductivity term in the cell voltage depends on the temperature at the plates rather than in the pipework. Output: a cell at working level, in circulation and at temperature.

Steps 6 — Current Ramp and Cathode Seed Formation. Current is applied on a ramp rather than switched straight to the design value, because the first minutes decide the character of the deposit: a modest initial current produces a coherent, fine-grained layer that later growth can build on, whereas a cold start at full current produces nodules that shed back into the electrolyte and contaminate the liquor. Cell voltage, cell current, busbar temperature and the individual cathode readings are verified as the current steps up, and the ramp is only taken to the design current density once the voltage is behaving as the budget predicted. The ampere-hour count for the campaign starts at the moment the plates are under full load. Output: a seeded cathode set running at the design current with a verified voltage.

Steps 7 — Deposition at the Design Current Density. The cell runs with a cathode current density up to 1,000 A/m², against the 200–800 A/m² band conventional electrolytic gold and silver cells occupy, and the geometry of the cell is what makes that figure usable rather than merely stated. Tight spacing keeps the ohmic term of the voltage small, circulation at each plate face keeps the gold concentration at the cathode close to the bulk value, the working temperature keeps the electrolyte conducting, and the electrode schedule keeps current density even across the whole face rather than concentrated where the plates stand closest. The ampere-hour count is the campaign’s clock: the mass plated onto the cathode is the ampere-hours passed multiplied by 2.45 g per ampere-hour, reduced by the current efficiency established on the material. Output: fine gold cathode deposit accumulating against the ampere-hour target.

Steps 8 — Cell Voltage Decomposition and Fault Isolation. Cell voltage is read as a diagnostic, not as a control handle. A change at constant current is worked through the voltage budget in a fixed order: the contact term first, by comparing per-electrode readings and checking hanger and clamp faces; then the ohmic term, by checking spacing, immersion depth, level and temperature; then the electrochemical terms, by checking the anode face and the electrolyte composition; and only then the current programme itself. Voltage applied above the working window is not deposition current — it is consumed decomposing water and evolving gas, and it drives the deposit towards roughness, so the response to a rising voltage is to find the component that changed and not to raise the setpoint. Busbar temperature is monitored continuously on the same loop. Output: a fault localised to one of four voltage components, with the cell record updated.

Steps 9 — Cathode Withdrawal, Cell Turnaround and Residue Recovery. When the ampere-hour target is reached the cell is taken out of service in a defined order — current off, circulation held briefly, then cathodes lifted — and the deposit is washed free of adhering electrolyte before drying, with the wash water collected and returned rather than sewered. The residue retained at the anode during the campaign is removed from the bags or membranes, washed, dried, weighed and assayed, and the residual anode plate and cell-floor material go back to the melting station to be cast into fresh anodes. The tank, lid, viewing panel, vapour path, filter media and containment tray are cleaned on the same schedule, the electrolyte is sampled and bled as the assay dictates, and the emptied cell is inspected before the next anode set is loaded. The lot mass balance is closed and issued with the cell record. Output: harvested cathode gold, declared residue and a cleaned cell ready for the next campaign.

Product Structure (Main Equipment)

The cell is supplied as six groups of equipment. Materials are selected for hot chlor-auric acid service and for the small quantity of liquor that inevitably leaves the tank: tank and lid in polypropylene or PPH with an anti-ageing additive, conductors in titanium-clad copper, wetted pipework in PP and PVDF, viewing panels in transparent polymer, and bag or membrane media in acid-resistant woven polymer.

Cell tank, lid and containment

Cell tank body. Integrally formed polypropylene or PPH tank with an anti-ageing additive, ribbed where the design requires it and sealed at the base, dimensioned from the electrode envelope, the design spacing and the settled electrolyte volume so that the cell holds the liquor the electrode schedule needs rather than a nominal tankful. Output: the process vessel, hydrostatically tested before shipment.
Tank base, plinth and levelling provision. Sealed base with levelling points that let the cell be set so the electrodes hang vertically, because a tank out of level puts the anode and cathode faces out of parallel and distorts the current distribution along the plates. Output: a level cell with vertical electrodes and even immersion depth.
Cell lid and transparent viewing panel. Sealed lid carrying the transparent panel that closes the headspace while keeping the electrode faces and the deposit visible, so film build-up, deposit character and liquor level can be judged without breaking containment. Output: an enclosed cell with the process observable in service.
Containment tray and drain point. Acid-resistant tray beneath the cell, sized to hold the liquor that a leak would release, with the drain at the low corner piped to a recovery point so that spillage is collected as liquor instead of reaching the floor drain. Output: spill containment with recoverable liquor.
Tank fittings and connections. Level connection, circulation inlet and outlet, charging connection, drain valve, thermal probe pocket and vapour outlet, all in PP or PVDF, positioned so that the flow path runs parallel to the electrode planes, entering low and leaving high. Output: a defined hydraulic and vapour interface on the tank.
Load-bearing frame and access provision. Structural frame or plinth carrying the loaded cell and its containment, arranged so that the cell can be approached on the working side for inspection, sampling and electrode handling without standing over the tank. Output: safe access for routine inspection and turnaround.

Electrode frame, hangers and spacing system

Anode hanger bars and contact blocks. Titanium-clad copper hangers that carry each anode at its recorded immersion depth, with machined contact faces that sit flat on the busbar rather than on an edge; the hanger is the anode’s only electrical connection and its condition is the first suspect in the voltage budget. Output: anode assemblies mounted at verified depth with dressed contacts.
Cathode hanger bars and supports. Matched hangers for the cathode set with insulated supports and a lifting provision, so that a cathode can be lifted, weighed and returned without being dragged across the tank edge or shorted against a neighbouring plate. Output: cathodes handled and positioned without damage or contact.
Spacing comb and spacer system. Insulated comb or spacer assembly that holds every cathode at the design clear distance from the anode faces on both sides along the full immersed length, with the nominal gap and its tolerance recorded on the cell drawing. Output: uniform inter-electrode spacing and even current distribution.
Cathode plates. Titanium plates selected for clean stripping and freedom from second-metal contamination, or pure gold seed sheets where a titanium contact is excluded by the customer’s own specification; supplied as a matched set with the geometry the electrode schedule calls for. Output: the deposition surface and the deposit carrier.
Anode bag and membrane frames. Acid-resistant bag or membrane assembly and its frame, fitted to each anode to retain the insoluble residue at the anode face and keep it out of the cathode deposit, sized so that the bag does not touch the cathode or restrict circulation. Output: residue contained at the anode with the deposit protected.
Electrode lifting and setting frame. Lifting frame and setting gauges for anodes, cathodes, lids and bag assemblies, so that loading and unloading follow a repeated method and the spacing set in commissioning is reproducible at every turnaround. Output: repeatable electrode loading and spacing at every campaign.

Busbar, current distribution and series connection

Cell busbars. Titanium-clad copper conductors sized to carry the cell current at a temperature rise that the insulation and the working environment allow, with insulated supports, machined contact faces and a section that keeps the conductor drop inside the voltage budget written for the cell. Output: even current distribution with a conductor loss inside the design budget.
Compression clamps and contact hardware. Clamps, bolts and contact shims selected for repeated assembly, torqued to a recorded value at every campaign so that contact resistance is a controlled quantity rather than an unknown that grows between turnarounds. Output: reproducible contact resistance across campaigns.
Series link and polarity marking. Inter-cell connection hardware linking the cell to its neighbour in the line so that one current serves all cells, with polarity and current direction marked at the terminals for verification before charging. Output: verified series connection and rectifier polarity.
Contact-resistance measurement points. Accessible, clearly identified measurement points at every hanger, clamp and cell joint, so that the contact term of the voltage budget can be read electrode by electrode rather than inferred from the cell total. Output: contact term measured per electrode and trended.
Busbar temperature sensing. Sensors on the conductor bars wired to the same monitoring loop as cell voltage and cell current, so that a rising contact resistance is caught as a temperature rise before it becomes a voltage problem. Output: conductor temperature monitored and logged per cell.

Electrolyte charging, circulation and thermal control

Electrolyte charging and make-up connection. Charging line, metering and valves that let the cell be filled from the make-up vessel or from rebuilt liquor returned from the previous campaign, with the fill recorded against the lot. Output: cell charged to the working level with a recorded liquor source.
Circulation pump and piping. Acid-resistant pump with PP or PVDF wetted parts, pipework and distribution header arranged to deliver liquor parallel to the electrode planes, entering low and leaving high, at the rate the electrode area requires. Output: a swept electrode stack without stagnant regions or stratification.
Flow distribution and return header. Inlet distribution and outlet weir arranged so that every electrode pair sees comparable flow, since a plate starved of circulation runs at a higher effective current density than its neighbours in the same cell. Output: comparable flow at every electrode pair.
Thermal control loop. Heating and, where the duty requires it, cooling with a probe located in liquor the electrodes actually stand in, holding the cell inside the 60–70 °C working band, because the conductance of the liquor — and therefore one term of the cell voltage — depends on the temperature at the plates. Output: cell held inside the working temperature band.
Level control and make-up dosing. Level sensing with metered make-up matched to the rate at which liquor leaves the cell with the vapour, so that the cell neither runs down in level nor drifts in composition between shifts. Output: cell level and composition held inside the control band.
Filtration ahead of the cell. Bag or cartridge filtration that removes suspended solids which would otherwise blind the bag media, settle in the tank and plate onto the cathode, with the filter housing accessible for change-out without draining the cell. Output: particle-free liquor at the electrode stack.
Bleed take-off and sampling points. Bleed point and sampling valves arranged so that the liquor can be drawn for assay and the bleed taken on the schedule the results dictate, rather than when the cell begins to behave badly. Output: electrolyte assay trend and a bleed taken on measurement.

Cell enclosure, vapour path and condensate return

Enclosed headspace and sealed perimeter. Sealed lid and perimeter gaskets that close the cell headspace rather than leaving it open to the workshop, arranged so that the panels can be opened for inspection and returned to a sealed condition quickly. Output: an enclosed cell headspace under extraction.
Condensate return. Condenser on the vapour path that turns evaporated electrolyte back into liquor and returns it to the cell, which is the equipment that holds metal loss below 0.02% of the gold charged rather than letting it leave through the duct. Output: condensate returned to the cell and metal loss contained.
Vapour duct and extraction connection. Ductwork and connection sized to the enclosure volume and run at negative pressure so that any leakage is inward, with the connection arranged to suit the site’s existing exhaust route where one exists. Output: controlled vapour extraction at the cell headspace.
Acid mist and chlorine abatement interface. Connection to the alkali scrubbing stage with a demister, and a nitrogen oxide absorption stage where nitrate-based pre-treatment is also operated on site, with the scrubber liquor sampled and logged. Output: abated off-gas with a logged scrubber record.
Tray and floor liquor handling. Connection from the containment tray and the cell area to the collection point for wash water and spill liquor, so that liquor leaving the cell hydraulically is recovered rather than sewered. Output: cell-area liquor routed to recovery and neutralisation.

Instrumentation, cell record and turnaround tooling

Cell voltage and current instrumentation. Per-cell voltage measurement and cell current measurement with the instruments selected for a chloride environment and arranged so the voltage can be read at the terminals the design figure refers to. Output: cell voltage read on the stated basis.
Busbar temperature monitoring and interlocks. Continuous conductor temperature measurement on the same loop as voltage and current, with interlocks that take the rectifier out of service on an abnormal reading rather than allowing a fault to run to the end of a campaign. Output: faults stopped at the cell rather than in the product.
Control panel and operator interface. Panel controlling the rectifier, the circulation pump, the thermal loop and the dosing, running a staged ramp at the start of a campaign with a manual mode for intervention and for fault investigation. Output: repeatable campaigns and a controlled current ramp.
Per-cell campaign record. Storage and retrieval of voltage, current, busbar temperature and ampere-hour readings per cell and per campaign, filed with the anode, electrolyte, residue and product assays so that a deviation can be traced to the electrode, the liquor or the supply. Output: per-cell process record issued with the batch.
Turnaround tooling and spares set. Setting gauges, contact dressing tools, spare gaskets, clamps, bag media and seals, and the lifting gear needed to empty, clean and re-load the cell, held on site so that turnaround does not wait on a delivery. Output: cells turned around on schedule without external support.
As-built cell documentation. Cell drawings with the geometry, spacing, electrode schedule and the four-part voltage budget the cell was designed against, plus the containment, utility interface and drain arrangement. Output: as-built cell documentation handed over at commissioning.

Product Features

The cell is specified from the electrode geometry outward. Anode assay, then current, then cathode area, then electrode count, then spacing, then tank dimensions, then cell volume, then cell count. Each step is a documented calculation and each is handed over, so the customer can follow how their own material produced the cell they receive.
Cell voltage is delivered as a four-part budget. Anode potential, cathode potential, electrolyte ohmic drop and contact loss are stated separately, with the current density, spacing and temperature the figures assume. A voltage excursion during operation can therefore be attributed to one component instead of being treated as an unexplained drift.
The voltage basis is stated explicitly. The published spread in gold cell voltages is a difference in basis — one electrode pair against a whole cell against the rectifier output across a line — and the cell is quoted per cell at the terminals, at the design current density and inside the working temperature band, with the spacing that the figure assumes written down.
Spacing is a controlled dimension, not a site decision. The spacing comb and the setting gauges fix the clear distance between anode and cathode faces along the full immersed length, and the tolerance is recorded on the drawing, because spacing errors appear as current distribution errors before they appear as a voltage change.
Contact resistance is measured, recorded and trended. Every hanger, clamp and cell joint has a measurement point and a recorded baseline, so the contact term can be read electrode by electrode and a rise is caught before it turns into a hot joint.
Conductors sized to the current and to the temperature rise. Busbar sections are selected against the cell current and the allowable conductor temperature rather than against a nominal rating, keeping the conductor loss inside the budget the cell was designed against.
Series connection designed as one system with the rectifier. Cell count, the summed per-cell potentials, the conductor drop along the line and the rectifier output are matched together, so one current serves the line and the rectifier is not oversized to cover a voltage the line never draws.
The rectifier is matched to the cell, not chosen from a stock list. Current rating follows from cathode area and design current density; the voltage window covers the working band plus the headroom the start-up ramp requires.
Circulation designed into the tank, not added to it. Inlet and outlet positions are part of the cell design so the flow runs parallel to the electrode planes, entering low and leaving high, sweeping every face and preventing the denser gold-rich liquor from settling into a layer the current cannot reach.
Thermal control reads the liquor the electrodes stand in. The probe position is a design decision, because the conductance term of the cell voltage depends on the temperature at the plates rather than in the pipework or the header.
A cell volume that is also an inventory decision. The tank is dimensioned to the electrode envelope and the settled volume the design needs, and the corresponding gold inventory in the circuit is issued as a figure so that capital tied up in solution is a known cost rather than an emergent one.
Enclosed headspace with condensate return. The lid, panel and vapour path close the cell because the cell runs hot, and the condensate returns the evaporated liquor to the tank so that metal loss stays below 0.02% of the gold charged and the working atmosphere stays free of acid mist.
Containment and drainage designed with the cell. A containment tray with a defined drain point under each cell, and cell-area liquor routed to collection, so a leak is a recovered loss rather than an environmental incident.
Everything visible without breaking containment. The transparent panel keeps the electrode faces, the deposit and the liquor level in view during a campaign, which is what allows the operator to judge deposit character and clean-up need without opening the cell.
Turnaround designed as a procedure. Drain points, lifting provision, bag and membrane access, a defined unloading order and a slime route that does not require the tank to be dismantled, so that cleaning between campaigns is planned work rather than an improvised stoppage.
Acceptance tested cell by cell. Hydrostatic test of the tank, insulation resistance, contact resistance at every electrode, circulation flow verification, thermal loop verification, level and dosing verification and an interlock test are recorded per cell before shipment and again on site.
A cell that extends into a cell line. Additional cells, additional electrode pairs and additional rectifier capacity are added to a validated installation, with the series connection and the conductor schedule extended rather than rebuilt.
Materials chosen stream by stream. Polypropylene and PPH with an anti-ageing additive for tank, lid and frame, titanium-clad copper for conductors and hangers, titanium or pure gold for cathodes, acid-resistant woven polymer for bags and membranes, and PP and PVDF for wetted pipework — matched to hot chloride duty rather than to a general chemical plant specification.
The cell is documented as built. Anode and cathode schedules, spacing with tolerance, tank geometry, the voltage budget, containment and utility interfaces, drain arrangement and the campaign record template are issued at handover, so the cell can be maintained, extended or duplicated without re-deriving the design.
No catalogue model number. Cell dimensions, electrode count, cathode area, spacing, cell volume, cell count, rectifier rating, circulation and thermal duty, enclosure and duct connection, containment and utility interfaces are engineered to your anode assay, silver load and target daily output.

Technical Parameters And Specifications

The engineering setpoints below are the standard design basis for a cell in this family and are confirmed or adjusted during process design once the anode assay is known. Where a value is not fixed here, the cell is dimensioned to your material and your target output and the resulting figure is issued in the process design package with the calculation behind it.

Gold electrolytic cell — technical parameters and specifications.

Parameter	Specification
Process duty	Anodic electrorefining of crude gold: a cast gold anode is dissolved in the cell and the gold is redeposited on the cathode while the other metals are rejected
Cell type	Vertical-plate plate-and-frame cell with alternating anodes and cathodes, each anode standing between two cathodes, enclosed headspace and integral circulation
Connection arrangement	Cells connected in series so that one current serves the line; rectifier output voltage matched to the sum of the per-cell potentials plus the conductor drop
Feed gold content	Au ≥ 92% for direct running, Au ≥ 95% preferred; the cell is dimensioned on the assay rather than on the nominal figure
Feed silver content	The first cell-level design constraint: silver forms an insoluble chloride at the anode face, so the silver figure sets the dissolution regime, the cleaning frequency and the spacing the cell is built with
Feed platinum group metal content	Reports to the residue retained inside the cell rather than to the electrolyte or the deposit; established in the feed assay and separated from the cell residue
Feed forms accepted	Mine doré and smelted bullion, cast crude gold anode plates, gold reduced from chloride or aqua regia liquor, karat scrap after parting, bench sweeps and workshop residues, slime-derived gold, electronic scrap gold concentrate, deplated coating gold, dental and laboratory alloy scrap, Au–Ag and Au–PGM scrap, recycled bullion and coin, electrowon and cemented gold, second-pass cell feed
Feed preparation	Melting under flux and casting to the anode envelope the cell accepts; incineration and milling of sweeps; drying, fluxing and consolidation of powder, sludge and cemented precipitate
Anode geometry	Cast to a controlled thickness and envelope, with the plate straightness, hanger position and immersion depth fixed in process design so that the spacing holds along the immersed length
Anode plate thickness	Fixed in process design within the range the hanger and spacing system accepts; historical published chlor-auric acid practice worked plates of about 4 mm, and the cell accepts whatever thickness your casting practice and campaign length require
Cathode medium	Titanium plate selected for clean stripping, or a pure gold seed sheet where a titanium contact is excluded by the customer’s own product specification
Cathode area basis	Cathode current density is quoted on the immersed cathode face area, and cathode area follows from the current the rectifier delivers at the design current density
Cathode current density	Up to 1,000 A/m² on the cathode face, against the 200–800 A/m² band conventional electrolytic gold and silver cells occupy
Electrochemical equivalent	2.45 g of gold per ampere-hour from the Au(III) species at 100% current efficiency (196.97 g/mol divided by three faradays, over 3,600 s); delivered mass is this figure reduced by the current efficiency
Output basis	Daily output is quoted as fine gold deposited on the cathode over a campaign, calculated from cathode area, design current density and hours under load, then adjusted by the current efficiency established on the material
Electrode count and schedule	Alternating anode and cathode arrangement with both faces of every plate working; electrode count, plate size and row spacing fixed from the anode assay and target output
Inter-electrode spacing	Set at the closest clear distance between the anode face and the cathode face that keeps electrolyte resistance low without risking deposit bridging, and held along the full immersed length by the spacing system; classical published practice ran about 3 cm between plate faces, and a modern high current density cell is set from the deposit morphology control the material allows
Immersion depth	Recorded per row; the working plate area of both anode and cathode follows from it, so it is a measured dimension on the cell drawing rather than a nominal fill level
Cell voltage, basis	Quoted per cell at the terminals, at the design current density and inside the working temperature band, with the spacing the figure assumes stated alongside it
Cell voltage, working window	1–3 V per cell; gold deposition is the favoured reaction only inside this window
Cell voltage, components	Anode dissolution potential, cathode deposition potential, electrolyte ohmic drop across the gap (current density × spacing ÷ conductivity) and contact and conductor loss; each is stated separately in the design package
Published voltage spread	Values quoted elsewhere for gold cells differ mainly because the basis differs — a single electrode pair, a complete cell, or the rectifier output across a series line — and because spacing, current density and temperature differ
Cell voltage above the window	Consumed by water decomposition and gas evolution rather than by gold deposition, and it drives the deposit towards roughness and poor adhesion; the response is to locate the component that changed
Contact resistance	Measured and recorded electrode by electrode as a commissioning baseline, with measurement points provided at every hanger, clamp and cell joint; it is the first term checked when a cell voltage rises
Busbar material and section	Titanium-clad copper conductors with machined contact faces, insulated supports and a section sized to carry the cell current at a conductor temperature rise the insulation and working environment allow
Busbar temperature	Monitored continuously on the same loop as cell voltage and cell current, with a rectifier interlock on an abnormal reading
Rectifier match	Current rating set by cathode area at the design current density; voltage window covering the working band plus the headroom the start-up ramp requires
Current ramp	A staged ramp from a fraction of the design current, because the initial current decides the character of the seed deposit; a cold start at full current produces nodules that shed into the liquor
Electrolyte volume per cell	Derived from tank geometry and the settled electrode envelope; the corresponding quantity of gold held as working inventory in the cell is issued as a figure in the process design package
Circulation path	Parallel to the electrode planes, entering low in the tank and leaving high, so that the stream sweeps each plate face and the denser gold-rich liquor does not stratify into a stagnant layer
Circulation duty	Sized to the electrode area and the design current density so that the gold concentration at the cathode face stays close to the bulk value at full load
Working temperature band	60–70 °C, held by the thermal loop, because electrolyte conductance and the transfer of gold to the cathode face both depend on it
Temperature measurement point	In liquor the electrodes stand in, since the conductance term of the voltage depends on the temperature at the plates rather than in the pipework
Level control	Automatic level sensing with make-up dosing matched to the rate at which liquor leaves with the vapour, so the cell neither runs down in level nor drifts in composition
Filtration	Bag or cartridge filtration ahead of the electrode stack, removing solids that would blind the bag media, settle in the tank or plate onto the cathode
Tank material	Polypropylene or PPH with an anti-ageing additive, integrally formed and sealed at the base, with welded rib reinforcement where the design requires it
Tank and containment arrangement	Each cell on an acid-resistant containment tray sized to hold the liquor a leak would release, with the drain at the low corner piped to recovery
Lid and viewing panel	Sealed lid with a transparent polymer panel, so the electrode faces, the deposit and the liquor level can be seen without breaking containment
Vapour path and condensate return	Condenser on the cell vapour line returning evaporated electrolyte to the tank, with extraction run at negative pressure, an alkali scrubbing stage with a demister, and nitrogen oxide abatement added where nitrate-based pre-treatment is also operated
Wetted materials	Polypropylene and PPH with an anti-ageing additive, titanium-clad copper, titanium, acid-resistant woven polymer for bags and membranes, PP and PVDF for wetted pipework
Instrumentation	Cell voltage, cell current, busbar temperature, liquor temperature and level continuously measured; per-cell readings retained with the campaign record and the ampere-hour count
Interlocks	The rectifier is taken out of service automatically on an abnormal voltage, current or busbar temperature reading rather than allowed to run to the end of a campaign
Deposit grade	Au ≥ 99.99% as the standard cathode product, released against an analysis; 99.999% where first-pass gold is cast back into anodes for a second pass
Gold recovery into the cathode	99% and above of the gold in the anode under the design window; the balance reports to the cell residue, the residual anode and the electrolyte, each of which is recovered
Residue inside the cell	Insoluble silver chloride and platinum group metal fraction retained at the anode by the bag or membrane, washed, dried, weighed and declared by metal content at every turnaround
Residue quantity basis	Predictable from the feed assay rather than discovered at cleaning: the silver in the anode reports to the cell as an insoluble chloride, so an anode carrying one kilogram of silver forms roughly 1.33 kg of silver chloride, a stoichiometric ratio that lets the residue load and the cleaning schedule be planned
Residual anode handling	Spent plate, hanger residue and cell-floor material returned to the melting station and cast into fresh anodes rather than sold as scrap
Design life items	Bag and membrane media, gaskets, seals, cathode plates and conductor contacts treated as wear items with a site stock list and a replacement interval set from the campaign record
Acceptance testing	Hydrostatic test of the tank, insulation resistance, contact resistance at every electrode, circulation flow verification, thermal loop verification, level and dosing verification and an interlock test, recorded per cell before shipment and again on site
Documentation	Cell drawings and as-built geometry, electrode schedule, spacing with tolerance, four-part voltage budget, containment and utility interfaces, drain arrangement, operating procedure, campaign record template and spare parts list
Capacity, cathode area, electrode count, spacing, cell volume, cell count, rectifier rating, containment and utilities	Engineered to your anode assay, silver load and target daily gold output and site conditions rather than taken from a catalogue of fixed models
Site interfaces	DC connection point, electrical supply for rectifier, pump, heating and controls, liquor charging and bleed connections, exhaust duct connection, condensate return, wash water and cell-area drainage, lifting access and headroom

Technical Advantages

A cell specified from the material, with the arithmetic visible. The design sequence from assay to current to cathode area to electrode count to spacing to tank volume is documented and handed over, so the customer can follow how their own anode produced the cell they receive rather than accepting a nominal model number. Result: a cell the customer can audit against their own metallurgy.
Cell voltage delivered as a budget rather than as a rating. Four components, stated separately, with the current density, spacing and temperature each figure assumes. Result: a voltage rise during operation is attributed to a component instead of being answered by turning the rectifier up.
The voltage basis is written down, which is where most confusion starts. A single electrode pair, a complete cell and a series line all give different numbers, and the same cell gives different numbers at different spacing and current density. Result: buyers comparing quotations are comparing a defined quantity, and the cell is not judged against a figure that was never about the same thing.
Spacing held as a controlled dimension. The comb and the setting gauges fix the clear gap along the immersed length, and the tolerance is on the drawing. Result: current distribution stays even across the plate area that the cathode area figure assumes.
The contact term treated as a wear item with a baseline. Measurement points, machined contact faces, a torque value and a recorded baseline at every electrode. Result: contact resistance is a trend line, not a surprise, and a hot joint is caught before it becomes a voltage problem.
Conductors sized to the current, not to a nominal rating. Titanium-clad copper busbars selected against cell current and allowable conductor temperature. Result: the conductor loss stays inside the budget the cell was designed against.
One current, one voltage sum. Cells in series with the conductor drop designed in and the rectifier output matched to the summed potentials. Result: a line that behaves as one electrical system rather than a set of cells sharing an oversized supply.
Spacing, spacing, temperature and circulation treated as one lever set. Reducing the gap lowers the ohmic term but narrows the margin against deposit bridging; circulation and temperature are what buy that margin back. Result: a cell that can run at high current density without paying for it in deposit grade.
Temperature measured where it matters. The probe reads liquor the electrodes stand in. Result: the conductance term of the voltage is controlled on the temperature the electrochemistry actually sees.
Circulation built into the tank geometry. Inlet and outlet positions, distribution header and return weir designed with the cell. Result: every electrode pair sees comparable flow, so current density is even across the stack rather than concentrated where circulation is weakest.
The gold inventory is an issued figure. Cell volume and the quantity of gold it holds as working liquor are stated together. Result: the most under-discussed cost of electrolytic gold refining is priced before the cell is built rather than discovered on the balance sheet.
The cell runs hot and closed. The lid, panel and condensate return are part of the vessel because a hot chloride electrolyte evaporates and carries gold. Result: metal loss below 0.02% of the gold charged, and a working atmosphere free of acid mist.
The residue load is predictable in advance. Silver in the anode reports to the cell as an insoluble chloride at a stoichiometric ratio, so the residue load and the cleaning schedule follow from the feed assay. Result: turnaround is planned from the assay rather than discovered at the cleaning.
Turnaround designed into the hardware. Drain points, lifting provision, bag access and an unloading order that does not require dismantling the tank. Result: cleaning between campaigns is scheduled work, and the cell is not idle waiting for access.
Acceptance is tested cell by cell, twice. Hydrostatic, insulation, contact, flow, thermal, level and interlock checks before shipment and again on site, recorded per cell. Result: a cell that is known to be right before the first anode is charged.
A cell that grows into a line. Series links, conductor schedule and rectifier matching designed for extension. Result: a pilot cell becomes the first cell of a line rather than stranded capital.
No model number to hide behind. Every dimension and duty is engineered to your assay, silver load and target output. Result: two customers with different material get two different cells, and neither is sold capacity it cannot use.

Service Process

Step 1 — Enquiry and anode data review. You provide the anode material type, an assay or typical analysis with the silver and base metal figures, the target monthly gold volume and any site constraints such as headroom, access, existing rectifier capacity, exhaust routing or floor area. We state whether the material can be run directly or needs a pre-treatment step first. Output: preliminary cell concept and a clear scope of supply.
Step 2 — Laboratory electrolysis test. A representative sample is cast to a small anode and run through a cell cycle at bench scale to establish the achievable current density, the deposit character, the cathode area that will be needed and the current efficiency on your material rather than on an assumption. Output: test report with the plated sample returned for your own assay.
Step 3 — Cell sizing and voltage budget. We issue the electrode schedule, cathode area, current, spacing with tolerance, tank dimensions, cell volume, the four-part voltage budget, the cell count and the rectifier match, together with the corresponding figure for gold held as working inventory. Output: process design package with the cell sizing calculation.
Step 4 — Cell drawings and interface design. Cell drawings, containment and drainage arrangement, layout, civil loading, DC connection, electrical supply points, water and heating connections, exhaust and condensate connections, and the lifting and headroom requirements are defined against your building. Output: cell drawings and utility interface schedule.
Step 5 — Manufacture and factory acceptance testing. Tanks, lids, panels, electrode assemblies, spacing systems, busbars, containment trays, piping, control panel and instrumentation are fabricated and assembled, with the hydrostatic, insulation, contact-resistance, flow, thermal, level and interlock tests recorded per cell before shipment. Output: factory acceptance test record per cell.
Step 6 — Shipment, installation and commissioning. Equipment ships with the documentation set, and our engineers supervise setting and levelling of the tanks, containment and drainage, electrode loading to the spacing recorded on the drawings, busbar assembly and torque, electrical and control checkout, duct and condensate connection, and water commissioning of the circulation and thermal circuits. Output: mechanically complete cells ready for electrolyte charging.
Step 7 — Operator training and procedure handover. Operating procedures, electrode loading and spacing discipline, contact dressing and torque practice, safe handling of hot chlor-auric acid electrolyte and acid mist, voltage diagnosis against the four-part budget, sampling, and turnaround practice are taught on site with the installed cells. Output: trained operators and a signed procedure set.
Step 8 — Production trial and performance acceptance. The cells are run on your own anode material against the ampere-hour target, and acceptance is confirmed against measured gold recovery into the cathode, deposit grade, cell voltage at the design current density, residue metal content and effluent concentration. Output: performance test certificate and the first certificate of analysis.
Step 9 — Cell optimisation and extension. Voltage components, spacing, current density, temperature and circulation are reviewed against the accumulated campaign record as your feed mix changes, and additional cells, electrode pairs or rectifier capacity are designed into the line as output grows. Output: continuing cell-level optimisation and extension engineering.

Warranty And After-Sales Service

Warranty period. Twelve months from successful commissioning or eighteen months from shipment, whichever falls earlier, covering design, manufacture, assembly and workmanship of the supplied cell equipment. Excluded: consumables such as bag and membrane media, filter elements, gaskets, seals and cathode wear items, and damage from misuse or from anode material outside the agreed specification.
Performance commitment. Where the anode material matches the tested sample, we stand behind the gold recovery into the cathode, the deposit grade, the cell voltage at the design current density and the achievable current density, with the production trial as the reference point. Output: documented performance acceptance.
Geometry commitment. Tank dimensions, electrode count, spacing and immersion depth are supplied as as-built figures against the design drawings, and the cell is warranted to hold the spacing tolerance that the current distribution figure depends on. Output: as-built geometry confirmed at handover.
Spare parts. Wear and critical spares — bag and membrane media, gaskets and seals, conductor contacts, clamps, cathode plates, pump and valve parts, filter elements, probes and control components — are quoted at the time of order and held available afterwards, with a recommended on-site stock list issued at handover. Output: spare parts list and supply at cost.
Remote support. Telephone, email and messaging support on operating questions, alarm and interlock interpretation, cell voltage diagnosis against the four-part budget, and contact-resistance or spacing queries, whenever your cells are running. Output: same-day response on operating issues.
On-site service. Engineer attendance for warranty faults, geometry or contact problems, and periodical check-ups including re-measurement of contact resistance and spacing, with response and attendance times agreed in the contract according to your location. Output: on-site intervention and a service report.
Operator retraining and refresher visits. Additional training, refresher sessions and cell optimisation visits as your feed mix, anode quality or product standard changes, including re-establishing the electrode schedule and current programme after a change of anode source. Output: updated training and procedure revisions.
Documentation set. Cell drawings with as-built geometry, electrode and spacing schedule, the four-part voltage budget, operation and maintenance manuals, process flow and piping and instrumentation diagrams, layout drawings, electrical drawings, spare parts catalogue, safety data for the reagents handled and an emergency response plan. Output: complete documentation handover.
Compliance support. Assistance with emission and effluent parameter declarations, enclosure and extraction performance, condensate and scrubber verification, and the handling, storage and disposal requirements for the electrolyte and residue streams. Output: technical data for your permit applications.
Lifetime engineering support. The cell design remains yours, and our engineers remain available for modification and extension — additional electrode pairs, a larger cathode area, higher current density, a further cell in the series line — for the operating life of the installation. Output: long-term cell-level engineering continuity.

Frequently Asked Questions

What is a gold electrolytic cell?

A gold electrolytic cell is the vessel in which a cast crude-gold anode is hung and made the positive electrode of a direct current circuit, so that the anode dissolves into a chloride electrolyte and the gold is redeposited as coherent metal on a cathode. The cell contains the electrodes, the electrolyte, the circulation that keeps the liquor moving across the plate faces, the thermal loop that holds the working temperature, the busbars that carry the current in and out of every plate, and the enclosed headspace that captures the vapour a hot chloride electrolyte produces. The cell is the unit in which the process numbers are actually fixed: cathode area and current density together set the daily output of fine gold, the voltage budget of one cell times the current sets the power, and the cell volume times the working concentration sets the gold held as working inventory. Everything else in the plant exists to feed it with anodes, take its product away and treat its off-gas and effluent.

What is the difference between a gold electrolytic cell and a gold refining plant?

A cell is one vessel and its immediate equipment; a plant is the arrangement of cells plus everything around them. A cell contains electrodes, electrolyte, busbars, circulation, thermal control, enclosure and vapour path. A plant adds anode casting and handling, electrolyte make-up and storage, the rectifier and switchgear for the whole line, the exhaust scrubbing train, effluent neutralisation, the melting, washing and assay station, and the buildings, containment and services that hold them. Buying a cell means the customer already has the feed preparation, the product finishing and the utility infrastructure, and needs the vessel and its sizing done properly. Buying a plant means all of that is designed together, and the cell count is then one of the outputs rather than the starting point.

How is cathode current density defined, and why do suppliers quote such different figures?

Current density is a current divided by an area, so a figure without its area basis is meaningless. The meaningful basis for deposition is the immersed cathode face area actually doing the plating, which for a plate-and-frame cell means both faces of every cathode plate. Figures quoted as anode current density, or per cathode plate without stating whether one face or two are counted, will differ from a cathode face figure by a factor of two or more before any process difference is considered. The cell is specified at up to 1,000 A/m² on the cathode face, against the 200–800 A/m² band conventional electrolytic gold and silver cells occupy, and the figure is linked to the geometry that supports it: spacing, circulation, temperature and electrode schedule. A current density quoted without those is a claim rather than a specification.

Why do published cell voltages for gold cells range from about one volt to about five?

Because the basis differs, not because the electrochemistry does. One manufacturer quotes the potential across a single electrode pair; another quotes a complete cell measured at its terminals, which adds the busbar and contact losses at both electrodes; a third quotes the rectifier output across a line of cells in series, which adds the conductor drop between cells and reflects the number of cells strung together. Spacing and current density then move the ohmic term, and temperature moves the conductivity that term depends on. The classical published design basis for a chlor-auric acid refining cell sat near the top of that range with a wide gap between the plates, while modern high current density cells sit lower because the gap is tighter and the liquor is held hot. This cell is quoted per cell at the terminals, at the design current density and inside the working temperature band, with the spacing the figure assumes stated alongside it.

What are the components of gold electrolytic cell voltage?

Four. The anode term is the potential required to dissolve gold from the plate; the cathode term is the potential required to deposit it; the ohmic term is the current density multiplied by the gap between the plates and divided by the conductivity of the liquor; and the contact term is the resistance at hanger faces, clamp faces and busbar joints at both electrodes. The first two are electrochemical and are what they are; the last two are engineering, and they are the two that a properly built cell keeps small. That is why the voltage budget is issued as four separate figures: when the total moves during a campaign, the component that moved tells you whether to look at contacts, geometry, temperature or the anode face.

What inter-electrode spacing should a gold electrolytic cell be built with?

The closest clear distance between the anode face and the cathode face that keeps the ohmic term of the voltage low without narrowing the margin against deposit bridging, circulation starvation or a bowed plate touching through. Spacing is the one geometric variable that can be tightened in design instead of paid for in power, so it is worth tightening — but every millimetre removed also removes margin, and the margin has to be bought back with circulation, temperature control and deposit morphology control. Historical published practice for this type of cell ran a gap of about three centimetres between plate faces; a modern cell running at high current density is set from what the material and the deposit allow rather than from a nominal figure, and the value and its tolerance are recorded on the cell drawing and held by the spacing system along the full immersed length.

How is the daily output of a cell calculated?

From three quantities and one correction. Cathode area sets the deposition surface; current density sets the current per unit of that surface, so current equals area times current density; and hours under load set how long that current is applied. The mass deposited is then the charge passed multiplied by the electrochemical equivalent of gold from the Au(III) species, which is about 2.45 grams per ampere-hour at 100% current efficiency, reduced by the current efficiency actually achieved on the material. A cathode area carrying 1,000 A/m² passes 1,000 amperes per square metre, which over twenty-four hours is 24,000 ampere-hours, or about 58.8 kilograms of gold as a theoretical maximum before the current efficiency correction. The delivered figure is that number reduced by the efficiency, and it is quoted as fine gold on the cathode rather than as anode charged or crystal recovered.

How many cells do I need for a given daily output?

The count follows from the arithmetic rather than from a stock list. Divide the target daily output by what one cell delivers, where one cell’s delivery is its cathode area times the design current density times hours under load times the electrochemical equivalent times the current efficiency. Partial cells do not exist, so the count is rounded up and the spare capacity is absorbed by running a shorter campaign, a slightly lower current density or a slightly different plate schedule. Two practical corrections apply: the number of cells also has to leave room for one cell being cleaned or turned around while the rest are running, and the cells are in series, so the rectifier output voltage rises with the count while the current stays the same.

What determines the tank size and the electrolyte volume?

The electrode envelope and the spacing, with a margin for circulation, level variation and the settled volume at the bottom of the tank. Width and length follow from the plate size, the number of electrodes and the gaps between them; the depth follows from the immersed length the cathode area figure assumes plus the liquor above the plates. That settled volume is not free — the electrolyte carries gold at its working concentration, so tank volume converts directly into gold held as solution, and a cell with the same cathode area but a bigger tank holds more gold doing nothing. YuSai therefore treats volume as a design output and issues the corresponding working-inventory figure alongside the cell dimensions.

What happens if the circulation is switched off while the cell is running?

The ohmic term of the voltage is unaffected, but the deposition term is not: the layer of liquor immediately against the cathode is stripped of gold ions as soon as current flows, and if that boundary layer is not refreshed, the current that cannot be spent on gold is spent on decomposing water and evolving gas instead. The symptoms appear in a known order — cell voltage climbs at constant current, the deposit turns dark, rough and poorly adherent, and gas evolution at the plate disturbs the crystal further. That is why circulation starts before the current is applied and is held for a period after the current is removed. It is also why circulation is on the interlock loop rather than left to an operator to restart.

How is the residue removed from the cell, and how often is the cell cleaned?

The insoluble residue forms at the anode face and is held there by the bag or membrane fitted around each anode, so it does not have to be recovered from the tank bottom or separated out of the cathode deposit. At turnaround the anode is lifted with its bag, the bag is opened and its contents are washed free of entrained liquor, dried, weighed and assayed, and the residual plate goes back to the melting station. Cleaning frequency follows from the feed assay rather than from a fixed interval: the silver in the anode reports to the cell as an insoluble chloride, and because that conversion is stoichiometric — roughly 1.33 kilograms of silver chloride for every kilogram of silver charged — the residue load per campaign is predictable in advance and the cleaning schedule is planned from it. Anode inspection for surface film is a routine in-campaign check and does not require a full turnaround.

Which materials survive service inside a gold electrolytic cell?

The service environment is a hot chloride electrolyte with acid mist above it, so the selection is specific. Tanks, lids, frames and containment are polypropylene or PPH with an anti-ageing additive, integrally formed and sealed at the base; conductors and hanger bars are titanium-clad copper, which gives the conductivity of copper with a titanium surface in contact with the liquor; cathodes are titanium plate or pure gold seed sheet; bag and membrane media are acid-resistant woven polymer; and wetted pipework, ducting and fittings are PP or PVDF. Stainless steel and ordinary carbon steel have no place in contact with this liquor, and the design does not depend on painted or coated surfaces for corrosion protection.

Can a single cell be expanded into a cell line later?

Yes, and it is designed for it. Because the cells are in series, extending means adding cells into the same current path, extending the busbar and conductor schedule and confirming that the rectifier’s voltage window covers the summed per-cell potentials plus the additional conductor drop, while the current rating is unchanged. The first cell is therefore specified with the same electrode schedule, spacing and busbar arrangement as the cells that will follow, so the extension is an addition rather than a replacement. The practical limits are the available floor area, the containment and drainage arrangement, the exhaust capacity and the rectifier’s voltage headroom, all of which are checked at the design stage of the first cell.

How small can a single gold electrolytic cell be?

A cell can be built to validate a route on a few kilograms a day, and below that the economics turn on things other than the tank. The fixed items do not scale down indefinitely: the rectifier, the circulation pump, the thermal loop, the enclosure and condensate return, the containment and the control panel are all needed whatever the cathode area, and the electrolyte inventory is set by the tank volume rather than by the throughput, so a very small cell holds proportionally more gold as working liquor per kilogram refined. Campaign turnaround also becomes a larger fraction of the calendar. The practical answer is that a small cell is a valid way to prove a material and to train operators, and the decision to go into production is made on the throughput at which the fixed equipment and the working inventory stop dominating the cost per kilogram.

What is the electrolyte in a gold electrolytic cell, and why does it run hot?

The electrolyte is a gold chloride liquor in hydrochloric acid, in which gold is carried as the tetrachloroaurate species — the same chemistry the classical chlor-auric acid refining cell used, which is why the anode has to be a cast plate of crude gold rather than a powder. It runs hot because both the conductance of the liquor and the rate at which gold can be transferred to the cathode face improve with temperature, so the cell is held in the 60–70 °C band to make the design current density usable at all. That working band is also why the cell is closed: a hot chloride electrolyte evaporates, the vapour carries gold with it, and the enclosure and condensate return are what bring that metal back into the tank instead of out through the duct.

What determines the cell’s working gold inventory, and why does it matter?

The electrolyte volume of the cell multiplied by the working gold concentration. Both are design outputs: the volume comes from tank geometry, and the concentration is set by what the plating reaction needs to conduct. The product is a quantity of gold that is neither feedstock nor product — it is working capital held in solution, and it is recovered only by bleeding the liquor and recovering the gold from the bleed on a defined schedule. It matters because refining businesses scale the tank up without redesigning the volume down, and the inventory scales with it. That is why cell geometry is chosen to keep the settled volume to what the electrode envelope actually needs, and why the working-inventory figure is issued with the cell dimensions rather than left to be discovered.

What is included in the acceptance test before the cell is handed over?

The tank is hydrostatically tested, the insulation resistance of the electrical installation is measured, the contact resistance of every hanger, clamp and cell joint is measured and recorded as a commissioning baseline, circulation flow is verified at every electrode pair, the thermal loop is verified against its set point, level and dosing are verified against their control band, and the interlocks are function-tested by inducing an abnormal reading and confirming that the rectifier is taken out of service. The same set is repeated on site after installation. The records are issued cell by cell, so the first campaign starts from a documented baseline rather than from an assumption, and a voltage or temperature trend later in the life of the cell is compared against a number rather than against a memory.