Gold Processing: An Introduction

INTRODUCTION

Gold, with its minute presence in the Earth's crust (0.005g/t), is cherished not only for its scarcity but also for its lustrous color, tarnish resistance, and being the noblest metal. Its applications span across decoration, jewelry, electronics, space exploration, medicine, dentistry, and wealth protection.

GOLD EXTRACTION

Gold extraction involves a series of processes, including comminution, mineral processing, hydrometallurgical, and pyrometallurgical processes. The methods employed depend on the nature of the ore.

OCCURRENCE AND MINERALOGY

Gold occurs in nature through veins or placers. Veins, formed by hydrothermal fluid, create gold deposits embedded into rocks. Placers eroded gold from veins, resulting in free flakes, grains, or nuggets settling in riverbeds or seas.

GOLD EXTRACTION FLOWSHEETS

3.1 Gold Processing History

Historically, gold recovery required no chemical knowledge due to its native state. Techniques included amalgamation, chlorination, and cyanidation. Cyanide leaching is a predominant method today, owing to its effectiveness and low cost.

3.2 Factors Influencing Processing Selection

Various factors impact processing selection, such as mineralogy, metallurgical characteristics, geographical location, and economic and political conditions. Understanding these influences aids in determining the most effective and economical extraction method.

3.3 Typical Steps in Current Gold Processing Flowsheets

• Gravity Separation: Suitable for placer deposits with free gold blended with sand.
• Flotation: Improves sulfide-type gold ore grade; concentrates can be smelted or leached.
• Leach Pre-Treatment: Essential for refractory ores; includes chemical blanking, roasting, chlorination, bio-oxidation, pressure oxidation, chemical oxidation, and ultrafine grinding.

3.3.5 Gold Recovery from Leach Solution

Pregnant solutions obtained during leaching may contain gold, recoverable through processes like zinc cementation, activated carbon adsorption, ion exchange/solvent extraction, and electrowinning.

3.3.6 Amalgamation

Outdated and toxic, amalgamation relies on ore-mercury contact to form a gold-mercury amalgam, still used by artisanal miners in certain regions.

3.3.7 Smelting and 3.3.8 Refining

Smelting involves melting gold in a furnace, separating impurities. The final stage, refining, removes impurities from smelted products, producing gold bars with purity exceeding 99.9%.

CONCLUSION

Gold extraction involves a sophisticated interplay of geological, metallurgical, economic, and environmental factors. The evolution of extraction methods reflects advancements in technology, efficiency, and environmental considerations.

WORKS CITED

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