The primary, secondary, and tertiary processing of gold involves a series of steps to extract, refine, and further process gold from ore into usable forms. Here’s a breakdown of each stage:
1. Primary Processing (Extraction & Concentration)
This stage involves extracting gold from its ore and concentrating it for further refining.
# Key Steps:
– Mining: Gold is extracted from the earth through open-pit or underground mining.
– Crushing & Grinding: The ore is crushed into fine particles to liberate gold grains.
– Gravity Separation (Optional): Heavy gold particles may be separated using jigs or centrifuges.
– Froth Flotation (Optional): Chemicals are used to separate gold-bearing minerals from waste rock.
– Cyanidation (Most Common Method):
– The crushed ore is leached with a dilute cyanide solution (NaCN or KCN).
– Gold dissolves into the solution as gold cyanide complex [Au(CN)₂⁻].
– Activated carbon (CIP/CIL) or zinc precipitation (Merrill-Crowe) recovers gold from the solution.
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# Output:
– Gold-rich concentrate or precipitate (Dore bars with impurities like silver & copper).
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2. Secondary Processing (Refining)
This stage purifies the gold obtained from primary processing.
# Key Methods:
– Smelting:
– Dore bars are melted in a furnace with fluxes to remove impurities.
– Produces impure gold bullion (~90–95% purity).
– Electrolytic Refining (Wohlwill Process):
– Uses electrolysis with hydrochloric acid (HCl) and gold chloride (AuCl₃) solution.
– Produces high-purity gold (99.99% pure).
– Aqua Regia Refining (For Small-Scale):
– Dissolves impure gold in aqua regia (HNO₃ .jpg)
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# Output:
– High-purity gold bars, granules, or powder (99.5–99.99% pure).
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3. Tertiary Processing (Fabrication & End Use)
This stage transforms refined gold into final products.
# Key Processes:
– Alloying: Mixing pure gold with metals