Chloride Leaching of Mineral Sulfides: Alternative Route for the Treatment of Refractory Gold Ores

摘要

In refractory gold ores, the valuable metal is usually found occluded in mineral sulfides, mainly in pyrite or arsenopyrite. For an efficient gold recovery, it is first necessary to break down the sulfide matrix by partial oxidation pretreatments, which is currently done either by roasting, pressure leaching, or bioleaching. Gold is subsequently dissolved by cyanidation in alkaline conditions. In this context, the chloride leaching with cupric ions is an interesting alternative process to leach refractory ores, as it allows simultaneously to dissolve the sulfide matrix and the contained gold in only one oxidative leaching step in acidic conditions. Cupric ion in high chloride concentration enables to establish a high oxidative potential in solution, which can oxidize both the sulfides and gold. Also, this ion is considered as a self-propagating oxidant in the leaching process. In this work, the kinetics of leaching of pyrite in cupric chloride solutions was investigated. Experiments were carried out in 1 L solution of 4.0 M NaCl for 250 hours. The effect of temperature was evaluated by experiments at 45, 60 and 75 °C using a solution with 0.05 M Cu (II). The effect of cupric concentration was evaluated by experiments with 0.05, 0.25 and 0.50 M Cu (II) at 60 °C. The leaching experiments results showed that this process is governed by an electrochemical mechanism. The increase in temperature and cupric concentration improved the pyrite dissolution. The calculated activation energy was 72.037 kJ/mole and the exponent on the Cu (II) was 0.231. The general rate kinetic equation proposed is -r_(FeS_2) = k_(FeS_2)[_(FeS_2)][Cu(II)]~(0.231). Based on the shrinking core model, the mathematical expressions predict the pyrite conversion as a function of the known temperature, cupric concentration and time. The model predictions agreed well with the experimental data over the range of conditions tested.