In the field of precious metal recycling, the purity of gold recovery
directly determines its economic value. Traditional pyrometallurgical
smelting can deal with bulk metals, but it is difficult to break through
the purification efficiency and precision of gold, silver and other
precious metals. Electrolytic refining technology by virtue of its 99.99%
or more ultra-high purity output rate, electronic waste, jewelry
processing waste liquid and other gold-containing materials
purification of the “gold standard”. In this paper, we will systematically
analyze the process principle of this technology, equipment innovation
and industrialization application scenarios.
Electrolytic refining: from crude gold to the
metamorphosis of 4N grade pure gold
The core of the electrolytic method of gold purification is the use of
electrochemical selective deposition principle. Crude gold is cast into
an anode plate and placed in a FRPP (reinforced polypropylene)
electrolyzer, which forms a circuit with a cathode plate of high-purity
gold. The electrolyte adopts the mixed system of hydrochloric acid
and gold chloride, and the reaction occurs under the drive of
direct current:
anode: Au (crude gold) → Au³⁺ + 3e-
cathode: Au³⁺ + 3e- → Au (high purity gold)
During the process, impurities such as silver and copper are retained
in the anode mud due to the difference in oxidation potentials.
During the process, impurities such as silver and copper are retained
in the anode mud due to the difference in oxidation potentials, while
gold ions migrate directionally to the cathode plate for deposition.
Purity increase is realized through three layers of precision control:
electrolyte optimization: free hydrochloric acid concentration is
precisely controlled at 5%-10% to inhibit the occurrence of side
reactions;
current density regulation: 200-300A/m² interval is dynamically
adjusted to avoid dendritic crystal growth;
anode slime interception: 300 mesh nylon cloth bag is used to
wrap the anode, and the interception rate of impurities is more than 99.5%.
Key equipment and technological
breakthroughs
1. FRPP electrolyzer: corrosion-resistant reaction hub
Composite material structure: three-layer reinforced polypropylene
sheet, lined with carbon fiber mesh, with a hydrochloric acid
corrosion-resistant service life of more than 10 years;
Intelligent temperature control system: built-in titanium alloy coils,
maintaining the electrolyte temperature at 45±2℃, reducing energy
consumption by 30%;
Modular design: flexible configuration of the single-tank volume
ranging from 0.5 m³ to 5 m³, suitable for small-volume Modular
design: flexible configuration from 0.5m³ to 5m³, suitable for small
batch precious metal recycling and industrial production line.
2. Cathode and anode system
Anode casting process: crude gold is smelted by vacuum induction
melting, and cast into 10mm-thick electrode plate, with porosity <0.3%;
Cathode activation treatment: titanium-based platinum-plated
cathode plate, with surface roughness ≤0.8μm, and the bonding
force of deposited gold layer is increased by 50%;
Dynamic adjustment of pole distance: real-time monitoring of pole
plate distance by laser rangefinder, with precision of ±0.1mm.
3. Closed-circuit recycling system
Electrolyte regeneration Module: Ion exchange resin adsorption of
copper and nickel impurities, solution reuse rate of more than 95%;
Exhaust gas treatment unit: three-stage spray tower + activated
carbon adsorption, chlorine gas emission concentration <1mg/m³;
Anode sludge recycling system: centrifugal separation - nitric acid
leaching process, silver, palladium and other by-product metals
recovery rate of 90%.
Process flow
Raw material pretreatment
Crude gold is dissolved by aqua regia, reduced and precipitated,
and made into crude gold plate with gold content ≥95% and
size error ≤2mm.
Electrolysis tank assembly
Cathode plate spacing is set at 80-100mm, electrolyte pH is
adjusted to 1.5-2.0, and circulating flow rate is 3m³/h.
Energized deposition
Initial current density is 180A/m², and it is gradually increased to
260A/m² after 48 hours, and the total cycle is 5-7 days. The total
cycle time is 5-7 days.
Cathode replacement
Replace the cathode when the thickness of gold deposited
reaches 3mm per kg, the residual rate is <0.5%.
Gold sludge stripping
High-pressure water jet flushing cathode plate, collect sponge
gold, purity ≥99.95%.
Melting and casting molding
High-frequency induction furnace 1500 ℃ melting, borax covered
with impurity removal, casting into 1kg/ ingot standard gold ingot,
purity 99.99%-99.999%.
Waste liquid regeneration
The electrolyte is filtered by activated carbon and dechlorinated by
electrodialysis, and the metal ion residue is <5ppm.
Industrialized application and economic benefits
1. Gold extraction from electronic waste
120-150g of gold can be extracted from each ton of waste CPU boards, which
reduces 40% of the cost of purification compared with the cyanide method.
In the treatment of cell phone motherboards, the gold recovery rate is
increased from 75% to 98%, and the purity is up to 4N level.
2. jewelry industry waste regeneration
electroplating waste liquid by electrolytic treatment, a single set of system
daily recovery of gold 200-500g;
smelting slag gold recovery rate of more than 99%, to avoid the loss of
several tons of precious metals each year.
3. Value-added mining tailings
Low-grade gold ore (1-3g/t) is directly purified by electrolysis, eliminating
the leaching-replacement process;
In the treatment of gold-containing sulphide ore, the removal rate of arsenic
and antimony impurities is increased to 99.9%.
Technology evolution
Future electrolysis gold extraction technology will show three major trends:
digital twin control: through the current density - purity prediction model,
real-time optimization of deposition parameters;
zero-emission process: the electrolyte full-cycle technology + waste heat
power generation system, to achieve zero wastewater and waste gas
emissions;
miniaturization equipment: containerized electrolysis device, to meet the
needs of jewelry workshops, laboratories and other small-scale scenarios.
Conclusion
Gold purification by electrolysis not only rewrites the precision standard of
precious metal recovery, but also reshapes the resource recycling system
in a green and efficient mode.