Thermodynamics and phase transformations in the recovery of zinc from willemite
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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 NH4Cl–NH3·H2O solution. The thermodynamics and phase conversion of Zn2SiO4 to zinc oxide (ZnO) during calcified roasting with CaO were investigated. The mechanism of mineralogical phase conversion and the effects of the CaO-to-Zn2SiO4 mole ratio (n(CaO)/n(Zn2SiO4)), roasting temperature, and the roasting time on zinc-bearing phase conversion were experimentally investigated. The results show that Zn2SiO4 was first converted to Ca2ZnSi2O7 and then to ZnO. The critical step in extracting zinc from willemite is the conversion of Zn2SiO4 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.
Keywordswillemite zinc residues calcified-roasting thermodynamics mineralogical phase conversion
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This work was financially supported by National Program on Key Basic Research Project of China (973 Program, No. 2014CB643403) and the Postdoctoral Foundation of Central South University.
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