Cyanide heap leaching

Gold recovery Operation of carbon in leach, carbon in pulp, and heap leach circuits Recovery of gold from tailings dissolved in sodium cyanide... 

Hydrometallurgical methods are normally employed for recovery of gold from oxidized deposits (heap leach), low-grade sulphide ores (cyanidation, CIP, CIL) and refractory gold ores (autoclave, biological decomposition followed by cyanidation). 

Heap leaching, ie, spraying of sodium cyanide solution over roughly cmshed ores heaped on an impervious pad, has become the most economical way of recovering precious metal values from very low grade ores. Recoveries are lower, however, ca 70%, for heap leaching ca 85% for milling and cyanidization. 

There has also been some interest in heap leaching of low-quality refractory ores. This is a two-stage process, as bacterial leaching of the ore must be followed by leaching with alkaline cyanide to solubilize the gold. The heap must also be washed and neutralized before the cyanide leach can be applied (103). 

K. P. Galvin, M. D. Engel, and S. K. Nicol, "The Selective Ion Flotation of Gold Cyanide from a Heap Leach Mine Feed Liquor, Proceedings XVlll International Mineral Processing Congress, Sydney, Australia, Austr. IMM. 

Figure 6.2 shows a descriptive diagram of the heap-leaching process [69], The process sprays and alkaline cyanide solution over ore that has been stacked on an inclined, impermeable pad. Gold is dissolved in the solution by the following reaction and flows off the pad to a lined impoundment. 

Heap-leach operations are typically zero-discharge facilities [69]. A typical heap leach operation is shown in Figure 6.3. A weak cyanide solution is sprayed over the stacked ore and pregnant solution flows to a lined collection ditch, then to a pregnant solution pond, then to a recovery plant with carbon... 

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