Refining / Affinage
Also: Refining, Precious metal refining, Parting
Refining (affinage) refers to the industrial purification and processing of crude precious metals to commercially or investment-grade finenesses.
Refining (from the French affiner – to refine) is the technical heart of precious metal processing: it converts impure crude metal – such as doré bars directly from a mine or melted-down scrap gold – into commercially pure metal with a defined fineness. It is only through refining that precious metals become exchange-tradable and meet international standards such as the LBMA Good Delivery rules.
Where Does the Crude Metal Come From?
Refineries process two fundamentally different material streams:
- Primary crude metal – doré bars from gold mines (typically 70–95 % Au/Ag content), platinum ore concentrates or nickel slimes from which platinum-group metals are recovered.
- Secondary crude metal – scrap gold, scrap silver, dental gold alloys, electronic scrap (urban mining) and industrial returns from catalytic converter processing.
Common Processes at a Glance
| Process | Metal | Principle | Fineness achieved |
|---|---|---|---|
| Chlorination (Miller process) | Gold | Cl₂ gas displaces impurities | ~995 ‰ |
| Electrolysis (Wohlwill process) | Gold | Anodic dissolution, cathodic deposition | 999.9 ‰ |
| Electrolytic silver refining | Silver | Silver nitrate bath, cathode 999+ ‰ | 999 ‰ |
| Solvent extraction / ion exchange | Platinum-group metals | Selective precipitation from hydrochloric acid | 999.5 ‰ |
| Fire refining | Gold/Silver | Oxidising smelting, slag removal | 980–990 ‰ (preliminary stage) |
The Wohlwill Process (Gold, simplified)
Anode (crude gold, ~995 ‰)
→ Dissolution in HCl/HAuCl₄ electrolyte
→ Cathodic deposition as fine gold 999.9 ‰
The process is energy-intensive but yields the purest commercially produced gold and forms the basis for fine gold bars and bullion coins.
From the Refinery to the Tradable Bar
An accredited refinery – such as Heraeus, Umicore, PAMP Suisse or Argor-Heraeus – undergoes several quality assurance steps after refining:
- Sampling and assay: Precise determination of fineness before and after refining.
- Casting or minting: Refined metal is processed into cast or minted bars.
- Stamping: Manufacturer, weight, fineness and serial number are applied (hallmark).
- Certification: LBMA-listed refineries are subject to regular audits; their Good Delivery stamp is the global quality mark.
The melt value calculator can be used to quickly determine the metal value of an item before submitting it to a refinery – a useful guide when comparing buying offers.
Economic Significance
A region's refining capacity is an indicator of its position in the global precious metals market. Switzerland (Valcambi, Argor-Heraeus, PAMP Suisse) processes an estimated 70 % of the world's secondary gold stream. Germany is also an important location with Heraeus (Hanau) and C. Hafner (Pforzheim).
For private investors, refining is particularly relevant in scrap gold recycling: the buying price depends on fineness – knowing it makes for better negotiation. Keeping an eye on the current gold price as a reference at all times helps to assess offers realistically. The same applies to silver.
In Brief
Refining is the process that transforms raw or mixed precious metal into the exchange-tradable, standards-compliant metal that ends up in bars and coins. Without a functioning refining infrastructure, neither standardised investment products nor a liquid global market would be possible.