Thermodynamics and phase transformations in the recovery of zinc from willemite

• Published in: International journal of minerals, metallurgy and materials Vol. 25; no. 12; pp. 1373 - 1379
• Main Authors: Chen, Feng, Chen, Wei, Guo, Yu-feng, Wang, Shuai, Zheng, Fu-qiang, Jiang, Tao, Xie, Ze-qiang, Yang, Ling-zhi
• Format: Journal Article
• Language: English
• Published: Beijing University of Science and Technology Beijing 01.12.2018; Springer Nature B.V; School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China
• Subjects: Ammonia; Ammonia pressure leaching; Ammonium chloride; Calcification; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Corrosion and Coatings; Extractive metallurgy; Glass; Leaching; Materials Science; Metallic Materials; Natural Materials; Phase transitions; Recovery; Roasting; Surfaces and Interfaces; Thermodynamics; Thin Films; Tribology; Zinc oxide; Zinc oxides; Zinc silicates; thermodynamics; willemite; zinc residues; calcified-roasting; mineralogical phase conversion
• DOI: 10.1007/s12613-018-1691-7
• ISSN: 1674-4799

Willemite is a common component of zinc and lead metallurgical slags that, in the absence of effective utilization methods, cause serious environmental problems. To solve this problem and increase zinc recovery, we proposed a novel extraction method of zinc from willemite by calcified roasting followed by leaching in NH 4 Cl–NH 3 ·H 2 O solution. The thermodynamics and phase conversion of Zn 2 SiO 4 to zinc oxide (ZnO) during calcified roasting with CaO were investigated. The mechanism of mineralogical phase conversion and the effects of the CaO-to-Zn 2 SiO 4 mole ratio ( n (CaO)/ n (Zn 2 SiO 4 )), roasting temperature, and the roasting time on zinc-bearing phase conversion were experimentally investigated. The results show that Zn 2 SiO 4 was first converted to Ca 2 ZnSi 2 O 7 and then to ZnO. The critical step in extracting zinc from willemite is the conversion of Zn 2 SiO 4 to ZnO. The zinc percent leached in the ammonia leaching system rapidly increased because of the gradual complete phase conversion from willemite to ZnO via the calcified roasting process.