Gold stripping primarily employs chemical methods, using specific solutions to dissolve the gold layer from the metal substrate before purifying and recovering it. This approach is efficient and relatively low-cost, making it suitable for most gold-plated items.
Chemical stripping commonly utilizes cyanide solutions or acidic stripping agents. A combination of sodium cyanide and hydrogen peroxide effectively dissolves the gold layer; however, due to the extreme toxicity of cyanide, operations must be conducted using specialized ventilation equipment and protective gear. Acidic agents such as nitric acid or aqua regia (a mixture of hydrochloric and nitric acids) are also frequently used, though aqua regia generates toxic fumes, requiring strict control of operating conditions. Following the stripping process, the gold in the solution is recovered as pure gold through precipitation using reducing agents (such as ferrous sulfate or oxalic acid) or via electrolytic refining.
For small gold-plated items like electronic components, the electrolytic method is safer. The item serves as the anode in an electrolytic cell; a direct current causes the gold layer to dissolve and deposit onto the cathode plate, after which the deposit is scraped off and purified. This method results in minimal pollution but offers lower efficiency.
Thermal oxidation is suitable for gold-plated parts with metal substrates; high-temperature heating oxidizes the substrate, causing the non-oxidizing gold layer to peel away, though this process consumes significant energy and risks damaging the substrate. Mechanical stripping involves using sandpaper or a scraper to directly remove the gold layer; this is suitable only for items with thick gold plating, as recovery rates are low and the gold often becomes contaminated with base metal.
Regardless of the method used, operators must wear protective gear and handle chemicals in well-ventilated areas; waste solutions require neutralization and proper disposal. Performing these procedures in a home environment is not recommended due to the risks of poisoning or environmental contamination. Professional recycling facilities employ more efficient processes—such as solvent extraction or ion exchange—to achieve higher purity in gold recovery.
