: Leaching experiments of gold and silver from roasted concentrate were carried out using a chlorine-hypochlorite solution. The leaching rate of gold was 75% at 1.5:1 ratio of chlorine and hypochlorite and increased to 81% with adding 1 M NaCl. However, at 1% pulp density and at 65℃, the leaching rates of Au were close to 100%. XRD analysis identified quartz in the solid residues after digestion of roasted concentrate with aqua regia or chlorine-hypochloride leaching solution. This suggests that the gold may not be leached out of the quartz in aqua regia or chlorine-hypochlorite solution. In order to leach the gold from the quartz, the concentrate will have to be pre-treated through ultra-fine grinding or treated with stronger oxidative agents.

In order to dissolve Au, Ag, and other valuable metals from gold ore concentrate, raw gold concentrate was pre-treated by roasting and salt-roasting at 750℃. The roasted concentrate was treated with aqua regia digestion to dissolve the valuable metals and higher amount of Au, Ag, and valuable metals were extracted from the roasted concentrates than from the raw concentrate. Higher amount of these metals were also extracted from the salt-roasted concentrate than from the roasted concentrate. The results of the gold dissolution experiments showed that the gold dissolution was most efficient when particle size, roasting temperature, and the percentage of added salt in salt roasting were about 181∼127 µm, 750℃, and was 20.0%, respectively. The XRD analysis suggests that quartz and pyrite were not destroyed even through roasting at 750℃ and decomposition with aqua regia. However, through salt roasting, pyrite was completely decomposed, whereas quartz could not be destroyed through salt-roasting at 750℃ and aqua regia digestion. Accordingly, it was expected that the gold

: In order to optimize the gold leaching process from refractory sulfide concentrate, a chlorine-hypochlorite solution with varying concentrations and temperatures were applied to salt-roasted concentrate. The concentrate consisted of pyrite, chalcopyrite, and galena, which were turned into hematite through air-roasting at 750℃. Also these concentrates were changed into hematite and nantokite (CuCl)) through salt (NaCl)-roasting at 750℃. The results of the gold leaching experiments showed that the best gold leaching parameters were obtained when the hydrochloric acid-sodium hypochlorite mix was at a ratio of 1 : 2, the added concentration was 1.0 M concentration, the pulp density was 1.0%, and the leaching was done at a 60℃ leaching temperature. The leaching rate for gold was much greater in the roasted concentrate than in the raw concentrate. The leaching rate was greater in the salt-roasted concentrate than in the plain roasted concentrate too. From XRD analysis, quartz was found in the saltroasted concentrate and in the solid residue from the chlorine-hypochlorite leaching solution at 60℃.

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