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A direct hydrometallurgical route for nickel and molybdenum extraction from a nickel–molybdenum (Ni–Mo) ore using pressure acid leaching was studied. The nickel and molybdenum were extracted by acid leaching under oxygen pressure. Compared with traditional roasting methods, this hydrometallurgical method eliminates SO2 and As2O3 emission (the Ni–Mo ore containing 15%–25% S). Compared with existing alkali leaching recovery of molybdenum process, almost all the nickel and considerable molybdenum were extracted in the acid leaching process. Under oxygen pressure conditions, almost all the nickel and a substantial part of the molybdenum were dissolved into the acid leaching liquor and the other part of the molybdenum was left in the acid leach residue. The acid leach residue was further leached under alkaline (NaOH) conditions. Under optimal experimental conditions, the extraction rates nickel and molybdenum reached 97% and 96%, respectively.

Direct flotation of zinc oxide ore is characterized by poor recovery of only around 50% of zinc. Hydrothermal sulfidation of hemimorphite with elemental sulfur resulted in the formation of stable metal sulfide compounds that would enhance zinc recovery by flotation process. The variables considered in the study were sulfur dosage, temperature, time, stirring speed and particle size. Temperature was the most important factor. The experimental data indicated that under the hydrothermal conditions with sulfur dosage 1.2, temperature 220 °C, time 180 min, agitation speed 500rpm and particle size74-106μm, and 73% hemimorphite conversion fraction was achieved.

A hydrometallurgical process was used for selectively extraction of valuable metals from zinc plant residues. The process includes the following two steps. (1) The zinc plant residue is treated by sulfuric acid atmospheric leaching process with KMnO4 as oxidatant to selectively dissolve zinc while leaving most (above 98 pct) of indium and germandium in the iron residues. (2) The iron residues are treated by acidic atmospheric leaching process with NaClO3 as oxidant to dissolve indium and germanium. The valuable metals of indium and germanium in the second leaching solution can be reclaimed by further treatment. The optimum operating parameters of the first stage and the second stage were established by conditional tests. The experimental data indicated that under the conditions employed the zinc extraction in the first stage was above 95%, and the leaching percentage of indium and germanium in the second stage reached 91.6% and 90.7%, respectively.

Hydrothermal sulfidation of pure white lead with elemental sulfur has been studied in the present paper. The variables considered in the study were temperature, time, particle size and elemental sulfur fraction in the reacting mixture. Temperature and time were the most two important factors, with an increase in temperature and holding time the sulfidation extent of lead improved greatly and the constituent of products changed a lot. At temperatures above 140°C, PbS and PbSO4 were the only stable reaction products in the sulfidation of white lead. The experimental data indicated that under the hydrothermal conditions with a particle size of -58+48 μm and sulfur fraction in reacting mixture of 8% at 140 °C for 90 min, and 86% of lead sulfidation extent was achieved.