The selective chlorination of nickel and copper from low-grade nickel-copper sulfide-oxide ore: Mechanism and kinetics

Abstract

On account of the complex occurrence of valuable metals in a large amount of low-grade nickel sulfide ore, obstacles have been caused by using the existing metallurgical method. Therefore, we are reporting a new selective chlorination roasting and water leaching process to treat complex nickel sulfide ore. Anhydrous aluminum chloride was firstly used as the solid chlorination agent to sulfide ore. The chlorination mechanism for metals in nickel-copper sulfide ore were determined by thermodynamic calculation and experiment. The thermodynamic analysis showed that the predominant matter contributing to the chlorination of talc, lizardite, and magnetite were AlCl3 (both solid or gas) and the generated HCl, however, the chlorination of metal sulfide (pentlandite, chalcopyrite, and pyrite) were mostly contributed by the generated Cl2. The effect of roasting temperature, the roasting time, the mass ratio of AlCl3 to the ore, the content of O2 in the roasting atmosphere and the particle size of ore were investigated. The orthogonal experiments results showed that the optimal conditions of the chlorination roasting process were the roasting time of 3 h, the roasting temperature of 450 °C, the mass ratio of AlCl3 to ore of 1.5:1, the content of O2 of 20%, and particle size of the ore of 96–80 μm, under this condition, an extraction rate of nickel, copper, iron, and magnesium of 91.6%, 88.5%, 28.4%, and 16.4% was obtained. The chlorination mechanism is that, in the chlorination roasting process, nickel and copper were transferred into their corresponding metal chlorides, while most of the iron and magnesium were transferred into ferric oxide and magnesia-alumina silicates, respectively. TAK (thermal analytic kinetics) were used to clarify the chlorination kinetics, the results showed that the apparent activation energy calculated from DSC data was 70.4 kJ·mol−1, while calculated from TG data was 86.5 kJ·mol−1 (average) by using the FWO method, one of the most probable mechanism function of the chlorination process was G(α)=0.8701[1-(1-α)0.8701] (integral form) and f(α)=(1-α)1.8701 (differential form). The chlorination selectivity for metals could give guidance to the extraction of metals (especially for valuable metals) either in nickel sulfide ore or other minerals with a complex metal occurrence.