The carbon slurry gold extraction process is one of the methods for cyanide gold extraction. After the cyanide leaching of gold-containing materials is completed, the monovalent gold cyanide [KAu(CN)2] is used for carbon adsorption. It has long been found that activated carbon can adsorb precious metals from a solution, and initially only adsorbs gold from the supernatant, and smelts the gold-bearing charcoal to recover gold. Since the cyanide slurry needs to be separated by solid-liquid separation to obtain a clear liquid and the activated carbon cannot be returned, this method cannot be industrially competitive with the widely used zinc substitution method. Later, directly from the activated carbon adsorption of gold cyanide pulp, thus eliminating the need for solid-liquid separation operations; gold loaded activated carbon desorption mixture was neutralized with sodium hydroxide and sodium cyanide gold and silver, the process may return the activated charcoal used. Therefore, in recent years, the development of carbon slurry has become a new technology for gold extraction. China has built a production plant using the carbon slurry process in the Linghu gold mine in Henan Province and the Chiweigou gold mine in Jilin Province.
The carbon extraction process includes the main operations of raw material preparation and activated carbon regeneration. The process flow is shown in Figure 8-2.
(1) Preparation of raw materials The gold-containing materials are ground to a size suitable for cyanidation, generally less than 28 mesh, and impurities such as wood chips are removed, and the concentration of the leached pulp is preferably 45% to 50% by concentration and dehydration.
(2) Stirring leaching is the same as the conventional cyanidation method, and is generally 5 to 8 stirring tanks.
(3) Carbon adsorption cyanide slurry enters the agitation adsorption tank (carbon slurry tank). The Linghu gold mine in Henan Province is equipped with a format sieve and a slurry riser in the suction tank, which is used to realize the reverse flow of activated carbon and slurry, and adsorb the slurry. The dissolved gold, bridge screen can reduce the wear of activated carbon. At present, the sieve holes of the bridge screen are easily blocked by activated carbon, and are cleaned with compressed air.
(4) Desorption of gold-loaded carbon can be desorbed by four methods: 1 desorption of hot caustic sodium cyanide solution; 2 low concentration of caustic sodium cyanide solution plus alcohol desorption; 3 desorption by caustic sodium cyanide solution under heating and pressing conditions ; 4 high concentration of caustic sodium cyanide solution desorption.
(5) Electrodeposition method or conventional zinc powder replacement precipitation Gold-loaded gold charcoal desorption can obtain high-grade noble liquid containing gold up to 600 g/m3, and gold powder is obtained by electrowinning or zinc replacement method, and sent to smelt to obtain gold ingot.
(6) Regeneration of activated carbon The activated carbon after desorption is first acid washed with dilute sulfuric acid (nitric acid) to remove aggregates such as carbonates, and after several times of use, thermal activation is required to restore the adsorption activity of carbon.
The carbon slurry method is mainly applied to gold-bearing oxidized ore with high sludge content. Because the ore contains high mud and solid-liquid separation is difficult, the existing filter can not effectively separate the precious liquid and the slag, so the conventional cyanidation method cannot Get better technical and economic indicators. Practice has shown that the carbon slurry method has achieved good results in industrial production. The gold content of Linghu Gold Mine is about 8 g/ton, and the total recovery rate of gold is 93% to 94%.
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