Cyanidation method for gold extraction

Cyanidation is a chemical method that belongs to the category of hydrometallurgy and has been used for gold selection since the last century.

The cyanidation method uses a dilute solution of alkali metal or alkaline earth metal cyanide to leach precious metals such as gold and silver in the presence of air, and then replaces the dissolved gold and silver with zinc, or adsorbs them with ion exchange resin or activated carbon.

The traditional cyanidation method generally includes three processes: tank leaching, liquid-solid separation, and zinc replacement. With the gradual development of the cyanidation process, the leaching process has also been continuously improved and upgraded. At present, the tank leaching method has been gradually eliminated, and the heap leaching method is used to increase the processing capacity; the zinc replacement process is upgraded to adsorption with ion exchange resin or activated carbon. The specific methods can be divided into carbon-in-pulp method (CIP), carbon-in-leach method (CIL), resin-in-pulp method (RIP) and heap leaching method.

(1) Carbon-in-Pulp (CIP): In addition to cyanide leaching of the ore, a certain amount of activated carbon (about 20 g/t) needs to be added to the leaching slurry to adsorb gold from the cyanide slurry, and then the gold-loaded carbon is extracted from the slurry. After desorption, the gold-loaded carbon is used to recover gold from the gold-containing electrolyte by electrolysis. The characteristic of the carbon-in-pulp method is that the leaching, adsorption and desorption of gold-loaded carbon replace the leaching, washing and clarification operations of the conventional cyanide method. It has good adaptability to various types of minerals, high recovery rate of soluble gold and good economic benefits.

(2) Carbon-in-Pulp (CIL): It refers to a gold extraction method in which activated carbon adsorbs gold while cyanide leaching, that is, cyanide leaching and carbon adsorption are carried out in the same tank. The significant advantages of this method are low investment, small footprint and energy saving. Due to the simultaneous leaching and absorption, the gold dissolution rate is fast and the recovery rate of soluble gold is high. However, the disadvantages are short leaching time, large amount of carbon stored in the process (large amount of accumulated gold), and large amount of carbon wear. Therefore, carbon leaching is suitable for gold ores that are easy to leach and have low grade.

(3) Resin slurry method (RIP): Due to the disadvantages of activated carbon such as easy breakage, high temperature activation, and low adsorption rate, resin has more advantages than activated carbon in terms of adsorption speed and adsorption amount, and desorption is also easier. The RIP method greatly saves investment and operating costs.

(4) Heap leaching: This method is to transport the mined ore to a pre-prepared stockpile for heap building, or directly on the already stored waste rock or low-grade ore, and then spray or percolate the oxidized leaching solution to make the solution pass through the ore to produce percolation and leaching. The cyanide leaching solution of the heap leaching method needs to be repeatedly sprayed on the ore heap. After multiple cycles, the leaching solution is collected and then the gold is recovered by the above-mentioned activated carbon adsorption method, resin adsorption method or zinc powder replacement method.

The cyanide leaching method is very effective in extracting gold and silver from fine-grained gold ore. Although the cyanidation method has various advantages such as mature technology, high extraction rate, large output, strong adaptability to ores, low unit cost, simple process, easy operation, and can achieve in-situ gold production.