Gold Refinery Machine
Gold Refinery Technical Guide
Gold Refinery Machine: Aqua Regia Refining and Gold Electrolysis
Gold refining is used to raise the purity of crude gold, scrap gold, alloy gold or recovered gold powder before it is made into gold bars, jewelry, coins, industrial wire, sheet or plate. Higher purity improves market value, color stability and downstream processing quality.
In industrial gold refining, the two common routes are aqua regia refining and gold electrolysis. Aqua regia is usually selected for low-purity material, recovered gold powder, filings, scrap and mixed gold-bearing material. Gold electrolysis is not normally the first step for low-grade feed; it requires higher-grade gold, usually 22K or above, and the gold must be prepared into anode plates before refining to Au99.99 or higher.
Refining Purpose
Why refine gold before melting, casting or minting?
Raw gold, recovered gold and jewelry scrap can contain silver, platinum, copper, iron, lead, zinc and other impurities. These elements change gold color, reduce value and may affect later melting, rolling, bar casting or coin minting.
Silver and platinum can make the color lighter. Copper can make the color darker. When gold is ground into powder or gold foil, different impurity levels can even make the appearance turn purple, red, dark brown or black. Refining removes these impurities so the final gold has better purity, density and commercial value.
Choosing the refining route
- Low-purity gold: aqua regia refining is usually the first choice because it can handle lower-grade feed without first making anode plates.
- 22K gold and above: gold electrolysis is more suitable when the feed has already been upgraded and the target is stable Au99.99 or Au99.999.
- Environmental requirements: aqua regia systems must include proper ventilation, waste gas handling and local approval.
- Gold inventory: electrolysis requires gold to be pressed or cast into anode plates, so it occupies valuable gold during the cycle.
- Final product: refined gold powder or cathode gold is usually washed, dried, melted and cast into bars or ingots.
Method I
Aqua regia refining for low-purity gold
Aqua regia refining dissolves impure gold, crude gold, gold alloy or gold-containing material into chloroauric acid. Sodium bisulfite is then used as the reducing agent to precipitate gold powder. This route is practical for low-content gold-bearing material because the feed does not need to be cast into anode plates first. After purification, washing, drying and melting with flux, the final gold can reach a golden yellow color and purity above 99%.
Aqua regia ratio: 1 part concentrated nitric acid and 3 parts concentrated hydrochloric acid. The original chemical reaction is commonly expressed as 3HCl(aq) + HNO3(aq) -> 2H2O(l) + NOCl(g) + Cl2(l).
Method II
Gold electrolysis system for Au99.99 refining
Gold electrolysis is suitable for 22K gold and above when stable high purity is required. It is not recommended for low-content raw material directly. Before electrolysis, the gold normally needs pretreatment and must be pressed or cast into anode plates. The electrolyte also needs dissolved gold content before stable operation. This means gold is occupied in two places: the anode plates and the gold-containing electrolyte.
The system uses the gold chloride electrolysis method proposed by E. Wohlwill. Impure high-grade gold is used as the anode. During electrolysis, gold and impurities dissolve from the anode, while high-purity gold is deposited at the cathode. CDOCAST gold electrolysis equipment can refine gold to Au99.99, and special process requirements can produce gold with 99.999% purity.
- Feed requirement: normally 22K gold or above, and higher purity feed gives more stable refining results.
- Not suitable as the first treatment for very low-content gold-bearing material.
- Gold occupation: the process requires gold anode plates and gold dissolved in electrolyte before operation.
- High current density electrolysis technology: around 1000A/m2.
- Typical electrolysis cycle: about 20-22 hours.
- 5kg/day system electrolyte volume: about 12-13L, containing 120-150g/L gold, which can occupy up to about 2kg of gold in electrolyte.
- Electrolyte temperature: around 60-70°C, with condensing device to reduce electrolyte and gold loss.
- Main equipment material: high-performance polypropylene with titanium clad copper conductive parts.
Selection Comparison
Aqua regia refining vs gold electrolysis
| Item | Aqua Regia Refining | Gold Electrolysis System |
|---|---|---|
| Suitable material | Low-purity gold, crude gold, gold alloy, recovered gold powder, filings and gold-containing recovery material. | 22K gold and above, high-grade gold anode plates and high-purity refining projects. |
| Purity target | Usually above 99% after chemical refining, washing, drying and smelting; it can also be used as a pretreatment route before higher-purity refining. | Au99.99 standard; 99.999% can be achieved with special process requirements. |
| Investment | Lower equipment investment and simple process layout, but stronger acid fume and waste treatment requirements. | Higher system investment and requires anode plate preparation plus gold-containing electrolyte, both of which occupy valuable gold during the refining cycle. |
| Environmental control | Requires ventilation, mist separator, waste gas treatment and local approval. | Cleaner operation, but electrolyte must be maintained and replaced on time. |
| Best use case | Small and medium chemical refining, low-purity scrap gold treatment and recovery material pretreatment. | Professional refinery line, high-grade feed, Au99.99 gold ingot production and stable cathode gold quality. |
Technical Notes
Key points buyers should understand before choosing a refining method
Aqua regia is for low-content feed
Aqua regia can treat low-purity gold, recovered gold powder, filings and mixed gold-bearing material. It is often the more practical first step when the material cannot be directly made into a stable anode plate.
Electrolysis needs higher-grade gold
Gold electrolysis is not a direct solution for very low-content raw material. The feed usually needs to be 22K or above, and in many refinery lines it is first pretreated, melted and cast into anode plates. The electrolyte also needs dissolved gold content, so the buyer must calculate gold occupation before choosing this route.
Gold inventory matters
Because gold is expensive, buyers should consider how much gold will be occupied during electrolysis. A 5kg/day electrolysis system may use 12-13L electrolyte containing 120-150g/L gold, so the electrolyte alone can occupy up to about 2kg of gold, not including anode plates.
Aqua regia gas must be treated
The main risk is acid mist, nitrogen oxides, chlorine and nitrosyl chloride, not simply “sulfide waste gas”. A proper system needs ventilation, mist separation, scrubber treatment and local environmental approval.
Pure gold deposits at the cathode
In Wohlwill gold electrolysis, impure high-grade gold dissolves from the anode. High-purity gold is deposited at the cathode. This distinction is important when explaining the process to technical buyers.
Electrolyte condition controls quality
When impurity ions build up in the electrolyte, cathode gold quality can drop. The electrolyte should be monitored, replaced or treated to recover remaining gold and maintain stable purity.
5kg Aqua Regia Flow Reference
How a practical aqua regia refining and waste gas treatment line works
For a 5kg gold refining workflow, the aqua regia route is usually built around acid storage, acid metering, dissolving, solid-liquid separation, reduction precipitation, fine filtration, washing, drying and melting. This is a practical route for low-content gold material because the material can enter chemical dissolution first instead of being prepared into electrolysis-grade anode plates.
A typical line can include hydrochloric acid and nitric acid storage tanks, 50L acid metering tanks, 50L gold dissolving titanium reactor, aqua regia fine filter, 150L reduction PPH reactor, sodium sulfite or hydroxylamine reducing agent, sponge gold fine filter, hot water washing, oven drying and final torch or electric melting.
Waste gas treatment should not be ignored
- High-concentration acidic waste gas and nitrogen oxides should pass through condenser and vacuum pump system.
- The waste gas treatment system may include an 800L treatment tank, circulating water tank and automatic chemical dosing system.
- Acidic gas is normally treated by an alkaline spray tower before discharge.
- The reference flow uses a caustic scrubber tower and centrifugal fan for compliant exhaust.
- Smoke and organic gas from drying, melting and casting should also be collected separately.
Complete Refinery Line
Gold refinery and purification process
A complete gold refinery machine line is not only one electrolytic tank. For electrolysis, the practical process is: crude gold -> crushing or granulating -> nitric acid impurity removal -> electrolyte preparation -> anode plate casting -> electrolysis -> washing -> drying -> ingot casting. For low-content material, aqua regia refining is often used before this high-purity route.
Large raw gold pieces are crushed or granulated to improve dissolution speed and process stability.
Nitric acid removes base metals such as iron, copper, lead and zinc while gold remains undissolved.
After washing and drying, gold is melted by an intermediate frequency furnace and cast into anode plates.
The anode plate is hung in gold-containing electrolyte and refined into high-purity cathode gold.
Collect cathode gold and wash it to remove electrolyte residue and soluble impurities.
Dry washed gold in an oven before the next melting or ingot casting process.
Refined gold is melted and cast into ingots, bars or customer-required specifications.
When impurity ions exceed the standard, the electrolyte should be replaced or treated to recover remaining gold.
Equipment Scope
What equipment is usually included in a gold refinery machine line?
The final configuration depends on feed material, target purity, daily capacity and local environmental requirements. For aqua regia refining, the system may include acid tanks, impurity removal kettle, dissolving kettle, reduction kettle, mist separator, filter plates, precision filter, support platform, vacuum unit, chiller, pipe fittings and power distribution cabinet.
For gold electrolysis, the line usually includes gold dissolution wind cabinet, titanium bucket, electrolyte preparation system, electrolytic tank, rectifier, condensing device, washing system, drying oven and melting or casting equipment.
Information to confirm before buying
- What is the current gold purity and material form: jewelry scrap, crude gold, powder, filings, granules, anode plate or alloy?
- What final purity is required: 99%, 99.9%, 99.99% or 99.999%?
- What is the expected capacity per day or per batch?
- Does the workshop have acid fume treatment and environmental approval?
- Can the material be pressed or cast into anode plates, or should it be treated by aqua regia first?
- Can the project accept gold occupation in electrolyte and anode plates during electrolysis?
- Will the refined gold be sold as powder, melted into ingots, or cast into gold bars?
Related CDOCAST Pages
Useful equipment links for a complete refining workflow
FAQ
Gold refinery machine FAQ
What is the difference between aqua regia refining and gold electrolysis?
Aqua regia refining is a chemical dissolving and reduction process, usually used for low-purity gold and recovered gold-bearing material. Gold electrolysis uses anode dissolution and cathode deposition, and it normally requires high-grade feed around 22K or above before refining to Au99.99.
Which method should I choose for low-purity scrap gold?
Low-purity scrap gold is usually more suitable for aqua regia refining because the feed does not need to be made into anode plates first. However, the workshop must handle acid mist, NOx, chlorine, mist separation and waste gas treatment correctly.
Can a gold electrolysis system produce 99.99% gold?
Yes. A properly designed gold electrolysis system can produce Au99.99 gold, and under special process requirements it can also produce 99.999% purity gold. The feed should normally be 22K or above and prepared into anode plates.
Why is aqua regia often recommended first for gold recovery material?
Gold is expensive, and electrolysis requires gold to be pressed or cast into anode plates. The electrolyte also needs dissolved gold content before stable operation, so electrolysis occupies gold in both the anode plates and the electrolyte. For lower-grade gold recovery material, aqua regia treatment is often more practical before any high-purity electrolysis route.
How long does gold electrolysis usually take?
The electrolysis time is normally about 20-22 hours depending on material purity, current density, electrolyte condition and machine capacity.
Why does the electrolyte need to be replaced or treated?
After repeated electrolysis, impurity ions in the electrolyte can exceed the standard and affect cathode gold quality. The electrolyte should be replaced or treated to recover remaining gold and keep refining quality stable.
Do I need a smoke spray tower for a refinery workshop?
For chemical refining and gold dissolution processes, a smoke spray tower or waste gas treatment system is strongly recommended. It collects and treats acid gas before discharge, helping protect operators and meet local environmental requirements.
Can refined gold powder be directly melted into ingots?
Yes. After purification, washing and drying, refined gold powder or cathode gold can be melted in a gold melting machine and cast into ingots, gold bars or customer-required specifications.
What should I send before asking for a gold refinery machine quotation?
Please send the material form, current purity, target purity, expected capacity per day, available workshop space, local environmental requirements and final product form. These details help choose between aqua regia refining, gold electrolysis or a combined refinery line.
Project Support
Need help choosing a gold refinery machine?
Send your gold purity, material form, capacity and target purity. CDOCAST can recommend aqua regia refining, gold electrolysis or a combined refining-to-casting workflow based on your actual production requirement.