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Separate Recovery of Silver and Gold from Cyanide Solutions.

Heinen-HJ; Peterson-DG; Lindstrom-RE
U S Pat 4 072 587 1978 Feb; :
Silver and gold are selectively recovered from cyanide solutions by addition of lime, and precipitation of the silver as sulfide by means of sodium sulfide, followed by electrowinning of gold from the filtrate. Thus, a semicontinuous test was conducted on a 2-lb charge of loaded activated carbon, containing 94 oz/ton au and 45 oz/ton ag and obtained from a commercial cyanidation plant employing carbon-in-pulp technology. The precious metals were stripped from the carbon with 1-pct naoh-0.1-Pct nacn-20 vol pct methanol at a ph of about 14 and a temperature of 80 deg c. Most of the silver was desorbed during treatment with 10 bed volumes of strip solution (15 liters), whereas the gold required a total of 20 bed volumes of strip solution. Each 5-l volume of enriched strip solution was agitated with 0.5 Lb of 98 percent-grade cao and 0.06 Lb of technical- grade na2s per troy ounce of silver (145 pct of theoretical na2s) for 1 h and then filtered. Successive 5-l increments of enriched strip solution showed ag content decreasing from 80 to 0.6, 39 to 0.6, 21 to 2.5, and 34 to 2.3 Ppm as a result of the sulfide precipitation. Gold content remained constant at 370, 190, 110, and 70, respectively, for the same four increments. The ag2s precipitates were combined and fire assayed for silver and gold. The precipitate analyzed 5,588 oz/ton ag and <0.005 Oz/ton au. The ag2s filtrates were electrolyzed to win the gold on a steel wool cathode and barren electrolyte was recycled to strip more gold. The gold cathode sponge was fire refined using a flux containing borax, soda ash,
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PAT 4,072,587
NIOSH Division
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U.S. Pat. 4,072,587, Feb. 7, 1978; Chem. Abstr. Not Found