Leaching of oxidized zinc ores in various media

The leaching of various oxidized zinc ores in different solvents has been studied in laboratory tests by agitation leaching and in some cases by percolation leaching. Some tests have also been carried out on synthetic zinc compounds.The comparison of the leaching of four different Belgian ores in sulfuric acid, sulfurous acid, ammonium hydroxide and sodium hydroxide, shows that the better results are obtained with sulfuric acid and with caustic soda when the concentration of the latter is high enough. All the ores respond very well to leaching except one which is very rich in iron and can be processed only with concentrated caustic soda. Mineralogical studies have shown that smithsonite is completely leached but that hemimorphite is refractory to leaching in any solvent studied.The leaching in alkaline media (ammonia, caustic soda, diethylenetriamine) has been studied on five different ores. It is confirmed that hemimorphite is difficult to dissolve. Good results are obtained only with caustic soda at high temperature. In ammoniacal solutions, the presence of ammonium carbonate enhances the leaching of hemimorphite but decreases the leaching of smithsonite. The optimum concentration of diethylenetriamine is 250 g/l.Caustic soda leaching tests were carried out on pure compounds and showed that ZnO, Zn(OH)₂, PbO, PbCO₃ and 2PbCO₃βPb(OH)₂ dissolve very rapidly and completely, that the leaching of Zn₂SiO₄ is controlled by kinetics and that the leaching of ZnS, PbS and PbSiO₄ is very poor, their solubility product being very quickly attained.The percolation leaching by sulfuric acid has been tested on Belgian ores and the good results obtained support the idea that this kind of ore could be successfully treated in this way.