Gold Extraction by Carbon-in-Pulp (CIL) Process: From Adsorption to Smelting

Gold Extraction by Carbon-in-Pulp (CIL) Process: From Adsorption to Smelting

The Carbon-in-Pulp (CIL) process is one of the cyanidation methods for gold extraction, involving the cyanidation of gold-bearing materials and the adsorption of gold cyanide complexes. The CIL process is widely used and highly adaptable, suitable for both oxide and sulfide ores. It is particularly effective for gold-bearing oxide ores with high clay content, where conventional methods struggle with solid-liquid separation due to the difficulty in effectively separating the pregnant solution from solids. In such cases, the CIL process offers better technical and economic outcomes.

Historically, it was discovered that activated carbon could adsorb precious metals from solutions. Initially, gold was adsorbed from liquid solutions, and the gold-loaded carbon was then smelted to recover gold and silver. Later, the process evolved to directly adsorb gold from cyanide pulp using activated carbon, eliminating the need for solid-liquid separation. The gold-loaded carbon is then subjected to high-temperature, high-pressure desorption and electrolysis using sodium hydroxide, achieving satisfactory results. Activated carbon, after a period of use, can be reactivated and reused.

Gold-bearing materials undergo crushing and grinding operations to achieve an appropriate particle size, typically -200 mesh at 80-90%, while removing impurities such as wood chips. The material is then thickened and dewatered using thickeners to increase the pulp density to 40-42% before entering the leaching stage.

The cyanide pulp is fed into the agitation adsorption tanks, similar to conventional cyanidation, usually consisting of 5 to 8 double-impeller agitation leaching tanks. Lime and sodium cyanide are added to the tanks, and compressed air is introduced to facilitate leaching and adsorption.

In the adsorption tanks, charcoal screens and pulp lifters are installed to enable the counter-current flow of activated carbon and pulp. The activated carbon is extracted from the first adsorption tank and flows by gravity to the desorption and electrolysis operation for the desorption and electrolysis of activated carbon. Desorption and electrolysis methods include ambient temperature and pressure desorption, as well as high-temperature and high-pressure desorption. The final step is gold mud smelting, through which the glittering gold is obtained.