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Recovery of Gold from Ores.
U S Pat 3 825 651 1974 Jul; :
Gold can be vaporized from any finely crushed ore, at 200 deg.-500 Deg. C as aufecl6, aualcl6, or augacl6, by heating the ore in a fluidized or static bed with cl2 and a promoter which can be fe, al, ga, or any compound thereof, preferably sulfide, that reacts readily with cl2 to form a trichloride. Usually 0.5-5 pct of the promoter by weight of ore is sufficient. The vapor is readily condensed to a brown powder by air-cooling, or can be dissolved in h2o, acid, or basic solutions, from which the gold can be recovered by any simple method. The results or numerous laboratory experiments with the method are reported, on ore containing 0.4 Oz au/ton, using 0.25 G each of various promoters mixed separately into 20-g ore batches, and heated in a 1-in-diam tube through which cl2 flowed at 50 cm3/mm (ed: should be min) for 1 h. The only promoters giving 92 pct or more au extraction as vapor at 200 deg. C were fes2, al2s3, and ga2s3. At 400 deg. C 99 pct extraction was attained with fes, fes2, cufes2, fecl3.6H2o + s, and al2s3, respectively, compared with 65 pct extraction with no promoter; but 98 pct was attained at that temperature with fe2o3 + s, and 97 pct with ga2s3.
U.S. Pat. 3,825,651; July 23, 1974; Chem. Abstr. 81:124,641B
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