![]() ![]() The operators of small properties are limited in processing technology to low-cost heap leaching or small-scale agitation cyanidation. Many of the precious metal resources are too small to warrant expenditure of large amounts of capital to recover the contained values. Concurrently, the Bureau of Mines has devised improved leaching technology for processing gold-silver ores. The increase in precious metals prices since 1975 has stimulated extensive exploration programs. The chemical refining method provides a viable technique for the smaller operator to produce high-purity gold without using pyrometallurgical refining methods. The gold precipitates ranged in fineness from 997 to 999 fine. The leaching-precipitation experiments recovered 99.9 pct of the gold. High-purity gold was precipitated from the aqua regia solution with oxalic acid, sulfurous acid, sodium bisulfite, and gaseous sulfur dioxide. The gold-bearing residue was leached in dilute aqua regia to solubilize the gold. The precipitates and cathodes were treated with dilute acid to solubilize the silver and/or base metals. The precious-metal-bearing steel wool cathodes contained 20.65 pct Au and 4.84 pct Ag. The zinc precipitates contained 14.40 pct Au and 0.35 pct Ag. Precious-metal-bearing zinc precipitates and steel wool cathodes are unrefined products from conventional cyanidation and heap leaching-cyanidation operations. We investigated chemical methods for producing high-purity gold from precious-metal-bearing zinc precipitates and steel wool cathodes.
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