Leaching Gold-Silver Ores with Sodium Cyanide and Thiourea under Comparable Conditions

摘要

There is currently much interest in how extraction of gold and silver from ores with acidic thiourea solution compares with extraction using alkaline cyanide solution. Agitation leaching tests were performed by the Bureau of Mines on 14 precious metal ores using sodium cyanide (NaCN) and thiourea ((NH sub 2) sub 2 CS) as extractants. The objective was to compare the results of the two extractants. NaCN was used at a concentration of 2 g/L with and without H sub 2 O sub 2 as an oxidant. (NH sub 2) sub 2 CS was used at concentrations of 2 and 20 g/L, and the solution potential was controlled at 390 to 420 mV standard hydrogen electrode (Eh) with Fe sub 2(SO sub 4) sub 3. With both reagents at 2-g/L extractant levels, NaCN extracted more gold and silver than (NH sub 2) sub 2 CS from all of the ores. At 20 g/L (NH sub 2) sub 2 CS compared with 2 g/L NaCN, (NH sub 2) sub 2 CS extracted more gold than NaCN from two ores, the same amount from one ore, and more silver from one ore. NaCN extracted more gold than (NH sub 2) sub 2 CS from 10 ores and more silver from 4 ores.