During the past 30 yr, many techniques used by industry to recover gold and silver were pioneered and developed by the Bureau. In 1952, technology was developed to strip gold from granular activated carbon and allow the carbon to be reused. In 1969, the heap- leaching concept was applied to low-grade gold and silver ores and mine wastes. Heap leaching with carbon adsorption-desorption permits very low value material to be economically processed. In 1970, a hypochlorite oxidation treatment waskieveloped to increase the recovery of gold from carbonaceous gold ores by cyanidation. In the early 1950's, attempts were made to employ carbon-in-pulp technology to recover gold from ores, but the process was unprofitable. The Bureau and Homestake Mining Company jointly operated a carbon-in-pulp pilot plant, and the technology was used in full- scale production at the Homestake mine in 1972. In 1973, a rapid pressure-stripping method was developed to desorb gold and silver from carbon. An alcohol desorption method, developed in 1976, also decreased the carbon stripping time. These stripping methods are in commercial use. In 1979, an agglomeration pretreatment was developed that permitted clayey precious-metal ores to be heap- leached. Agglomeration-heap-leaching technology is being used by at least 30 operations, several of them major gold and silver mines.
Paper in Precious Metals: Min., Extrac., and Proc., Metall. Soc. AIME, 1984, PP. 387-395