Hydrometallurgical Processes Development for Zinc Oxide Production from Waelz Oxide

This study is focused on the development of a hydrometallurgical process which allows the zinc recovery from Waelz oxide (WO). This process is aimed to zinc oxide production. So, it must allow the production of a widely used compound, mainly in tyre and ceramics production processes, from industrial residues such as EAF dusts considered as Toxic and Hazardous Wastes (THWs), from which the WO is generated [1]. Although some studies have been previously published describing zinc oxide hydrometallurgical production processes, none of them used a raw material with similar characteristics to the WO ones. The developed process consists of a series of initial stages in which an appropriate liquor is prepared through lixiviation and purifying steps, and some final stages where the zinc ion present in the liquor is precipitated as zinc hydroxide and calcined to obtain zinc oxide. Two different acids were studied as lixiviation agents, hydrochloric and sulphuric acid liquors, obtaining in both cases zinc lixiviation yields higher than 85%. After the purifying stages, the metallic zinc impurities concentration in the liquor was lower than 85 ppm in the case of hydrochloric acid liquors and lower than 47 ppm in the case of sulphuric acid liquors. The zinc hydroxide precipitated from the purified liquor was calcined obtaining a zinc oxide whose purity was higher than 99.99% in the case of hydrochloric liquors and lower than 20% when sulphuric liquors were used.