Sulfidation and Sulfur Fixation of Jarosite Residues During Reduction Roasting
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is widely applied in the battery and electroplate industries and is mainly produced from zinc sulfide concentrates through a roasting-leaching-purifying-electrowinning process.[1–3] The objective of the roasting is to convert zinc sulfide into zinc oxide that can be leached out in the subsequent leaching process.[4] However, iron impurity contained in zinc sulfide concentrates can react with zinc oxide to form zinc ferrite during the roasting process.[5–7] Zinc ferrite has a stable tetrahedral structure and cannot be dissolved in dilute sulfuric acid solution. Therefore, the formation of zinc ferrite results in a low zinc leaching rate and considerable amounts of leaching residues containing zinc. The stockpiling of the residues causes not only a potential environmental risk but also a waste of metal resources.[8–10] In order to solve this problem, the zinc leaching residues are generally subjected to a leaching with hot and concentrated sulfuric acid instead of dilute sulfuric acid to destroy the zinc ferrite structure, thereby decreasing the amount of zinc leaching residue and improving the zinc leaching rate up to 95 pct.[11–13]
BO ZHANG, LIN ZHU, WEI LIU, JUNWEI HAN, FEN JIAO, and WENQING QIN are with the School of Minerals Processing and Bioengineering and also with the Key Laboratory of Hunan Province for Clean and Efficient Utilization of Strategic Calcium-containing Mineral Resources, Central South University, Changsha 410083, P.R. China. Contact emails: [email protected] and [email protected] Bo Zhang and Lin Zhu contributed equally to this work. Manuscript submitted August 29, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
However, more than 80 pct of iron is also dissolved in the leachate simultaneously, and it must be removed from the leaching solution prior to purification and electrolysis processes.[14,15] In this regard, the jarosite method was developed as one of the most effective commercial processes for removing iron from the solution by precipitating it as an easily filterable crystalline residue.[16] This technology successfully solves the problems of low zinc leaching rate and waste of zinc resource, but a huge quantity of jarosite residues, which have never found any application and require further disposal, are generated.[17] In the production process of jarosite, iron is precipitated into a basic iron sulfate complex in hot acid leaching solution in the presence of alkali or ammonium ions.[18–21] The formation process can be expressed as the following equation: 3Fe2 ðSO4 Þ3 þ X2 SO4 þ 12H2 O ¼ 2XFe3 ðSO4 Þ2 ðOH)6 þ 6H2 SO4
½1
where X represents any of the ions (K+, Na+, NH4+, H3O+, Ag+, or 1/2Pb2+). However, metal impurities, such as Zn, Co, and Cd, can replace Fe into the crystal lattice of jarosite, resulting in the loss of some heavy metals.[22–25] In China, more than one million tons of jarosite residues are produced and dumped every year. The unreasonable disposal of jarosite residues will cause a potential environmental risk and waste of valuable metals.[26,27] In recent decades, n
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