Ammoniacal thiosulfate leaching of pressure oxidized sulfide gold concentrate with low reagent consumption

• Pressure oxidized gold concentrate is effectively leached.
• Low reagent concentrations are used.
• Low reagent consumption is obtained.

Ammoniacal thiosulfate leaching of pressure oxidized sulfide gold concentrate received from a gold mine is studied. The main chemical composition of the concentrate was Au 32 g/t, Ag 12 g/t, Fe 59%, S 21% and As 19%. The experimental variables studied were ammonia concentration, thiosulfate concentration, copper concentration, and temperature. The highest gold extraction (89%) was achieved with the following leaching solutions: 0.2 mol S2O3/L, 0.2 mol NH3/L, and 0.1 g Cu/L; and with the following conditions: solids, 30 m-%; pressure, 1 atm; continuous aeration (0.2 L/min); temperature, 30 °C; and leaching time, 6 h. Measured thiosulfate and copper concentrations after 6 h of leaching were 0.19 M and 0.08 g/L, respectively. The results from the leaching experiments showed that the pressure oxidized gold concentrate was effectively leached in an ammoniacal thiosulfate leaching solution with minimal reagent consumption. The study shows that the widely reported problem of high reagent consumption can be circumvented in leaching of pressure oxidized sulfide gold concentrate by the use of low reagent concentrations. The results indicate good premises for gold recovery by ion-exchange resins, since minimal thiosulfate consumption also ensures low polythionate concentration, which is an important issue in gold recovery with ion-exchange resins. The minimal reagent consumption also indicates that there are good possibilities to circulate the leaching solution for re-use in the leaching stage after gold recovery and solid–liquid separation.