Recovery of zinc from a low-grade zinc oxide ore with high silicon by sulfuric acid curing and water leaching

Abstract

A low-grade zinc oxide ore with high silicon was cured by sulfuric acid in a water-starved system and then leached in water. Thermodynamics of the curing process was analyzed according to the phase stability diagram for the systems of Zn-S-O-H and Si-O-H. It was indicated that the extraction of zinc and the dissolution of silica were influenced by the water content in samples during cured. Under optimal conditions, the extraction percentage of zinc was 99.22% and dissolution of silica was as low as 0.56%. XRD examination of the samples demonstrated that all the zinc-bearing minerals were transformed into ZnSO4·H2O while combined silica and iron were changed to quartz and rhomboclase (FeH (SO4)2·H2O) after acid curing, respectively. The major phases presented in the water leaching residues were SiO2, CaSO4 and PbSO4. SEM analyses showed that the samples had considerable changes in morphology and particle size after cured and leached. With acid curing and water leaching for the zinc ores, the zinc in hemimorphite was well separated from silica and the silicic gel could be effectively avoided in leaching process.