Research on recovery/purification of ZnO from the Waelz oxide by NH4Cl leaching-CaO precipitation method

Abstract

Zinc recovery from secondary sources has become a key issue for sustainable development of zinc metallurgy with the shortage of zinc concentrate supply. As the main intermediate product of the Waelz process, Waelz-fume has always been the focus of research. In this paper, a new hydrometallurgical process to recovery ZnO from Waelz oxides is developed. The main steps include leaching Waelz oxide with NH4Cl solution, purifying the leachate by zinc cementation, and precipitating zinc as ZnO by CaO addition. The zinc extraction can reach 87.9 % through NH4Cl leaching, and more than 99.0 % of Pb and Cd are from the leaching solution removed by the zinc cementation. Under optimal precipitation conditions, 96.6 % of the zinc in the leachate is precipitated as ZnO with high purity. The preliminary estimation shows that the process provides a cost-effective and environmentally feasible scheme for high purity ZnO preparation from Waelz oxide.