An evaluation of pretreatments to increase gold recovery from a refractory ore containing arsenopyrite and pyrrhotite

The effect of three ore pretreatments on gold recoveries fr om an ore in which the gold existed in solid solution in an arsenopyrite matrix, as well as being encapsulated in a pyrrhotite phase, was examined The three pretreatments evaluated included fine grinding, pyrolysis-roast (Pyrox), and an oxidative pressure acid leach (PAL). It was found that untreated ores did not yield high gold recoveries even when a fine grind (<45 mu m) was employed, while oxidative treatments led to a significant improvement of recoveries. The Pyrex pretreatment was found to decompose the sulfide matrix of the ore to a greater extent than a 3 hour PAL treatment. However, the PAL process produced a slightly better gold recovery of 79% compared to the Pyrex recovery of 75%, and both of these were greater than the 55-60% recoveries achieved with the untreated ore. Furthermore, the depletion of dissolved oxygen levels observed during cyanide leaching were significantly reduced by the two oxidative treatments, compared to the untreated ores. PAL war; found to benefit over the Pyrex pretreatment by affording a solid product, which effectively "locked" the arsenic component of the mineral from being recovered in solution. The PAL process required more lime for neutralization of acid produced from the decomposition reaction. (C) 1999 Elsevier Science Ltd. All rights reserved.