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Recovery of Gold from Dilute Solutions.
U S Pat 3 635 697 1972 Jan; :
Gold recovery from ores by leaching is improved by replacing cyanide with malononitrile as a 0.05-0.25 Wt pct aqueous solution with lime at ph 10-12, and a 1.5-3 Ratio of solution to ore. The au is probably dissolved as negatively charged au[ch(cn)2]-. This can be recovered from the leach solution by sorption on the same anion exchange resin as was suggested for au(cn)2- in U.S. 3,317,313, and elution with a strong mineral acid then recovers the gold. The preferred resin is a poly(styrene-divinyl-benzene) matrix having quaternary ammonium strong-base exchange groups. A method is given for its preparation. The solution can be contacted by the resin in any convenient way, and the au is eluted from it with a 10 pct solution of an acid such as h2so4 more readily than when au(cn)2- was sorbed on the resin. When 2 kg of carbonaceous ore containing 0.25 Oz au/ton was slurried with 6 l h2o, 5 g malononitrile, 20 g lime, and 70 g or 200 ml of 20-40 mesh granules of the preferred resin, the ph was 11.5 and after stirring 24 h the resin separated by screening contained 80 pct of the au in the ore used. Complete elution was achieved with 10 pct h2so4 in a column having 0.25 In diameter. When the ore was leached with nacn as a complexing agent in the same way and the same recovery method was used, the extraction into the resin was 63 pct and the elution recovery only 5 pct of the au.
U.S. Pat. 3,635,697; Jan. 18, 1972; Chem. Abstr. 76:88,965W