Precious metal refining is a high-tech process that removes impurities to reach 99.95% purity and above — a prerequisite for industrial applications.
Refining fundamentals
Refining combines chemical and physical processes designed to remove impurities and obtain metals of exceptional purity.
Refining objectives
- Increase metal purity
- Remove harmful impurities
- Meet regulatory and market standards
Process principles
- Chemical separation
- Electrolytic purification
- Thermal treatment
Gold refining methods
Gold is one of the most demanded precious metals and requires specialised refining techniques to achieve high purity.
Miller process
Chlorination of molten gold to remove impurities.
Electrolysis
Electrolytic purification of gold up to 99.99% purity.
Wohlwill process
Dissolving gold in aqua regia followed by selective precipitation.
Silver refining
Silver needs specific refining approaches because it readily forms compounds with impurities.
Electrolytic method
Anodic dissolution
Silver anodes dissolve in the electrolyte.
Cathodic deposition
Pure silver plates out on the cathode.
Chemical methods
Cupellation
Oxidising base impurities at high temperature.
Acid dissolution
Dissolving feedstock in nitric acid.
Platinum-group metal refining
Platinum-group metals demand the most sophisticated refining technologies because of their chemical inertness and stable complexes.
Aqua regia dissolution
Initial dissolution of platinum-group metals in hydrochloric and nitric acid.
Selective precipitation
Step-by-step precipitation of individual metals with targeted reagents.
Ion-exchange polishing
Ion-exchange resins that remove residual impurities.
Hydrogen reduction
Reducing metal salts to pure metals in a hydrogen atmosphere.
Quality control
Modern refining requires rigorous control at every stage to comply with international quality benchmarks.
Spectral analysis
Determining metal composition and purity.
Assay testing
Traditional cupellation-based verification of metal content.
Certification
Issuing certificates of conformity.