Enhancing the effectiveness of copper and cyanide recovery in gold cyanidation: A new integrated membrane process

The industrial validated technology used in gold mining that deals with copper-gold ores is the SART process, which allows a viable treatment for these complex minerals. The clarification or thickening stage in this processing, in which copper precipitates are separated, has several challenges such as copper losses (as solids in the overflow or by re-dissolution due to the high residence time) and large size pieces of equipment due to the complex settling characteristics of the copper precipitates. In this regard, this study presents a change in the traditional process by replacing conventional equipment with membrane-based unit operations. This new integrated membrane process, called SuCy process, is based on metal sulfide precipitation, as the SART process, and comprises a sequence of stages including microfiltration to clarify the copper precipitates, gas-filled membrane absorption (GFMA) to produce a concentrated cyanide solution, and a final membrane ultrafiltration stage to clarify the gypsum generated in the neutralization of the treated solution. This study includes sequential tests for each membrane stage at laboratory scale, treating three synthetic cyanide solutions containing different contents of copper (1800 and 1000 mg/L), a mixture of copper and zinc (616 mg/L Cu and 316 mg/L Zn), and a real cyanide solution from a gold mine. Permeate flux for the microfiltration stage ranged from 0.1 L/m(2)s to 1.4 L/m(2)s, where the highest values were achieved for copper precipitates suspensions. The characteristics of zinc precipitates promoted a decrease in permeate flux. The HCN flux in the GFMA stage was higher than 0.9 mg/m(2)s, with cyanide recovery values higher than 98% at 60 min. The permeate flux for the ultrafiltration stage for gypsum clarification was higher than 0.25 L/m(2)s for all synthetic solutions tested, with a severe decline by one order of magnitude for the real solution due to its high sulfate content. These results were compared with the SART process, both at laboratory scale, including process design and economic estimation, showing a plant size reduction up to 90% for the SuCy process with respect to the SART process, in addition to decreasing the capital cost by over 25% and keeping the operational costs under similar evaluation conditions. Thus, the integrated membrane process proposed here could be a promising alternative for the conventional SART process, enhancing the clarification effectiveness and reducing equipment size requirements and capital costs.