The hot gold water in the gold melting furnace is slowly injected into the mold and cooled into dark
red anode plates. When they are hoisted into the electrolysis tank filled with yellowish liquid, a
metamorphosis that determines the ultimate purity of gold quietly opens - this is the core site of modern
electrolytic gold refining, using the power of electric current to purify the crude gold containing impurities
to the ultimate realm of four 9s after the decimal point.
Current magic in the king's water
Unlike copper electrolysis, gold electrolysis takes place in a strongly corrosive medium:
Electrolyte Recipe
Chloroauric acid (HAuCl₄) solution becomes the gold carrier, and the hydrochloric acid concentration is precisely
controlled at 120-150 g/L. Trace amounts of platinum, palladium, and other precious metal impurities coexist in the
turquoise liquid in ionic form.
Polar Plate Secrets
The crude gold anode plate (containing 92%-95% gold) stands opposite to the pure titanium cathode plate. When
0.3-0.5V DC voltage is loaded, the anode gold atoms lose electrons and become Au³⁺ dissolved into the electrolyte,
which is then reduced to pure gold atoms at the cathode and deposited layer by layer.
Impurity gaming
silver ions and chloride ions combined into AgCl white flocculent deposited into the anode mud; platinum and palladium
and other potential close to the metal, by adding complexing agent to inhibit its deposition, and ultimately 99.98% of
the gold ions preferentially precipitated at the cathode.
Millimeter-scale pure gold growth technique
Cathodic deposition is a subtle art:
Temperature control: electrolyte constant temperature 45 ± 1 ℃, too large a temperature difference will lead to dendrite growth
Current density: maintain 80-100A/m² gold zone, too high to produce black oxide gold layer
Dynamic circulation: the solution is replaced 3 times per hour to prevent local ion concentration imbalance.
Cathode care: Pure titanium plate is sandblasted and roughened to ensure that the gold layer is firmly attached and does not fall off.
After 48 hours of growth cycle, the cathode surface is covered with 0.5mm thick pure gold foil with velvet-like texture.
Workers use a special plastic scraper to peel off the whole sheet, and the gold foil shows a unique rose gold color under
the light - a visual imprint of 99.99% high purity gold.
Treasure in the anode mud
The black sludge precipitated at the bottom of the tank is the real value rich mine:
Silver recovery: Nitric acid dissolves AgCl precipitation, electrolysis gets 99.95% pure silver
Platinum group capture: aqua regia secondary dissolution, ion exchange resin precise separation of platinum palladium rhodium
Rare Earth Enrichment: Residue extraction of scandium ytterbium and other strategic metals
12kg of platinum group metals can be recovered per ton of anode mud, which is worth more than gold itself.
Absolute safety of highly toxic system
Facing the double risk of cyanide and aqua regia, modern refineries build five-fold protection:
Totally enclosed electrolysis tank: titanium alloy tank with double-layer windows, negative pressure system to prevent vapor leakage.
Intelligent pH monitoring: sensors warn of hydrogen cyanide generation in real time and automatically inject lye to neutralize it.
Zero tailing discharge: three-stage countercurrent rinsing system, 99.98% precious metal recovery rate.
Emergency fusing mechanism: cut off the power supply within 0.1 second of current abnormality, preventing the generation
of explosive chlorine gas.
Robot inspection: corrosion-resistant robotic arm replaces manual sampling, remote monitoring by operators
Scale of value of pure gold
When gold ingots are embossed with “9999”, their journey has just begun:
Electronic grade gold wire: 1μm ultra-fine bonding wire, connecting chips and circuit boards.
Aerospace plating: 0.2mm gold foil wrapped around satellite components to reflect cosmic rays.
Medical application: radioactive gold particles precisely kill cancer cells.
Financial cornerstone: standard reserve in the vaults of central banks of all countries
In the dense acid mist of the electrolysis workshop, every micron of gold layer growing on the cathode plate is the ultimate
pursuit of purity. When the final casting of the gold ingot in the detector under the uniform halo of red gold, mankind's
worship of absolute purity at this moment reached its peak. From the purification of alluvial gold by ancient Egyptian pharaohs
to the modern nanoscale electronic gold plating, electrolytic refining has always been the ultimate footnote of gold civilization.
This metallic glow that has traveled through the millennia is still illuminating the future path of technology and wealth.