Use of chloride–hypochlorite leachants to recover gold from tailing

This study evaluated the speciation of various gold and silver chloride species to determine their stability of gold and silver in a chloride solution. Optimum conditions were then chosen to leach a mine tailing containing gold and silver. If chlorinated sea water (approximately 0.5 M NaCl and pH5.5 and Eh of less than 1.00 V vs Ag–AgCl reference) was used for leaching, both gold and silver could not be fully extracted due to the formation of gold hydroxide and silver chloride. The pH is better kept below pH4 and the solution potential Eh is kept over 1.00 V to maintain gold in solution. An increase in sodium chloride concentration in the range 0.5–3 M will enhance the stability of gold chloride. However, within this range, more than 50% of silver still remains in solid AgCl form. Leaching of gold and silver using both stirred reactors and in static tests confirmed that maximum gold and silver extractions were governed by these constraints. Nevertheless, the gold and silver extractions reached 80% and 50% in reactor leaching. Static tests simulating the in-situ leaching of the tailing show lower extractions for both gold and silver, reaching 70% and 30%, respectively after at least 6 days.