Enhanced recovery of zinc and lead by slag composition optimization in rotary kiln
(1. School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China;
2. State Key Laboratory of Comprehensive Utilization of Low Grade Refractory Gold Ores, Zijin Mining Group Co., Ltd., Shanghang 364200, China;
3. Zijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, China)
2. State Key Laboratory of Comprehensive Utilization of Low Grade Refractory Gold Ores, Zijin Mining Group Co., Ltd., Shanghang 364200, China;
3. Zijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, China)
Abstract: High-efficiency recovery of Zn and Pb from silicon-rich zinc leaching residues is realized in a rotary kiln. Characterizations by means of XRD, SEM, EDS and ICP reveal that the leaching residue contains 12.4 wt.% SiO2, 16.1 wt.% Zn, and 7.4 wt.% Pb. Thermodynamic analysis shows that metallic vapor of Zn and Pb can be easily generated from the zinc leaching residue at 1150-1250 °C inside the rotary kiln. Viscosities and melting points of 13 slag compositions were analyzed and three slag compositions (47wt.%SiO2-23wt.%CaO-30wt.%FeO, 40wt.%SiO2- 28wt.%CaO-32wt.%FeO, and 40wt.%SiO2-30wt.%CaO-30wt.%FeO) possessed the desirable physical properties, with the melting point and viscosity in the range of 1150-1280 °C and 0.2-0.5 Pa·s, respectively. The industrial tests show that adopting the optimized slag composition can contribute to very high recovery rates of Zn and Pb (97.3% for Zn and 94.5% for Pb), corresponding to slags with very low average contents of Zn and Pb (0.51 wt.% Zn and 0.45 wt.% Pb). The National-Standard leaching tests of the water-quenched slags result in 1.82 mg/L Zn, ~0.01 mg/L Cu, 0.0004 mg/L As, ~0.01 mg/L Cd, 0.08 mg/L Pb, and ~0.02 mg/L Hg in the leachate, verifying the detoxification of the zinc leaching residue at the same time.
Key words: zinc leaching residues; metals recovery; rotary kiln; slag composition optimization; detoxification