When lean au ores can be treated profitably for au extraction, they are nearly always leached with a cyanide solution, which can be hazardous for cattle and game animals; and alphahydroxynitriles, as proposed in U.S. 2,829,045, can also hydrolyze to produce cyanide. Less hazardous leaching agents dissolving au, ag, cu, ni, CO, cd, and zn with higher extractions than are obtained by cyanide are aqueous solutions having a ph 7-8 and containing 0.01-1 Wt pct malononitrile, bromomalononitrile, or alkali cyanoform such as kc(cn)3. These compounds on hydrolysis produce stable carbanions instead of cn- or hcn. Any leach technique and any alakali to obtain the required ph, can be used. When a siliceous ore containing 0.4 Oz au/ton as very fine particles was ground to -100 mesh and agitated 24 h with 3x its weight of aqueous solution containing 0.05 Wt pct malononitrile, the au extraction was 95 pct at ph 8-12 with lime, and 5-10 pct at ph 6-7. A carbonaceous shale containing 0.24 Oz au/ton similarly leached with the same solvent and lime solution gave 58.5 pct extraction compared with 35 pct when nacn was used; and after grinding with kerosine to lessen the interference of carbonaceous matter, leaching with 0.1 Wt pct solutions of the same two solvents gave 91.8 pct and 75 pct extractions, respectively.
U.S. Pat 3,542,540; Nov. 24, 1970; Chem. Abstr. 74:33,805X