Influence of phase and microstructure on the rate of hydrochloric acid leaching in pretreated Panzhihua ilmenite

The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate ofPanzhihua ilmenite. The as-pretreated ilmenite was leached with 20% HCI at 105 ℃, The leaching process was controlled by the phases and microstructures that evolved during the pretreatment processes. The leaching kinetics of pure hematite, ilmenite and pseudobrookite were characterized to clarify the phase effect on the iron-leaching rate; the rate of iron leaching occurs in the following order in the HCI solution： hematite （ferric iron） 〉 ilmenite （ferrous iron） 〉〉 pseudobrookite （ferric iron）. Therefore, the often-cited notion that ferrous iron dissolves faster in HCl solutions than ferric iron when explaining the pretreatment effects is inaccurate. Moreover, the oxidation pretreatment （at 600-1000 ℃ for 4 h） cannot destroy the dense structure of the Panzhihua ilmenite. Therefore, the influence exerted by the oxidation on the leaching process is primarily determined by the phase change; oxidation at 600 and 700℃ slightly increased the rate of iron leaching because the ilmenite was transformed into hematite, while the oxidation at 900-1000℃ significantly reduced the rate of iron leaching because a pseudobrookite phase formed. The reduction effect was subsequently investigated; the as-oxidized ilmenite was reduced under H2 at 750 ℃ for 30 min. The reduction significantly accelerated the rate of subsequent iron leaching such that nearly all of the iron had dissolved after leaching for 2 h in 20% HCl at 105 ℃. This enhanced iron-leaching rate is mainly attributed to the cracks and holes that formed during the reduction process.

Extraction of copper,zinc and cadmium from copper–cadmium-bearing slag by oxidative acid leaching process

An intensified oxidative acid leaching of copper–cadmium-bearing slag featuring using high-efficient oxygen carrier, such as activated carbon, was investigated to achieve high leaching rate of valuable metals. The effects of leaching variables, including agitation rate, sulfuric acid concentration, temperature, slag particle size, activated carbon and cupric ion concentration, were examined. It is found that leaching rates of cadmium and zinc both exceed 99 % in a very short time, but for copper, leaching rate of 99 % is achieved under the optimized leaching parameters, which are agitation rate of 100 r·min^(-1), sulfuric acid concentration of 15 wt%, leaching temperature of 80 ℃, slag particle size of 48–75 lm, activated carbon concentration of 3 g·L^(-1),liquid-to-solid ratio of 4:1, oxygen flow rate of 0.16 L·min^(-1),and leaching time of 60 min. The macro-leaching kinetics of copper metal was analyzed, and it is concluded that the inner diffusion is the controlling step, with apparent activation energy of 18.6 kJ·mol^(-1). The leaching solution with pH value of 2–4 can be designed to selectively extract valuable metals without neutralization, and the leaching residue can be treated by prevailing Pb smelting process.