Mohammad Taghi Kiani - PhD of Chemistry, Zanjan University, Angouran mine lab,
Rahmat Samiei - Supervisor of Angouran mine lab
Mohsen Pourjafari - MSc of Chemistry, Zanjan University, Angouran mine lab
Mehrdad Tahamtan - Project Manager of Madan Zamin Co, Angouran mine

The leaching of various oxidized zinc ores in sodium hydroxide solvent 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 a few different Angouran ores in sodium hydroxide shows that the better results are obtained 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. It is confirmed that hemimorphite is difficult to dissolve. Good results are obtained only with caustic soda at high temperature. The optimum concentration of caustic soda is 240 g/L. Caustic soda leaching tests were carried out on pure compounds and showed that ZnO, Zn(OH)2, PbO and PbCO3 dissolve very rapidly and completely, that the leaching of Zn2SiO4 is controlled by kinetics and that the leaching of ZnS and PbS is very poor.

caustic soda, oxidized zinc, Angouran mine