Synthesis, Thermodynamic, and Kinetics of Rubidium Jarosite Decomposition in Calcium Hydroxide Solutions
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JAROSITE-TYPE compounds are hydrous sulfate minerals containing alkalis and ferric ions, MFe3 (SO4)2(OH)6, where M can be H3O+, Na+, K+, Rb+, Ag+, NH4+, Tl+, ½ Pb2+, or ½ Hg2+. Jarosite-type compounds are formed by the natural in situ oxidation of pyritic ores that replace the original iron sulfides and iron oxides, leading to enriched gold, silver, lead, selenium, and bismuth, among others.[1] The interest in jarosites is based on its ability to eliminate or diminish the iron content of the acid leach solution produced in zinc hydrometallurgical processing with relatively low losses in the liquid wastes of divalent metals such as Zn2+, Cd2+, Cu2+, or Co2+. However, ensuring low losses of valuable metals, proper physicochemical properties, and an environmental stability of these compounds demands a careful study of the conditions under which they are formed. MIGUEL PEREZ-LABRA, MARTIN REYES-PEREZ, and ELEAZAR SALINAS-RODRIGUEZ, Professors, are with the Academic Area of Earth Science and Materials, Mineral de la Reforma, Hidalgo, C.P. 42184, Mexico, Mexico. Contact e-mail: Miguelabra@ hotmail.com ANTONIO ROMERO-SERRANO, Professor, is with the Metallurgy and Materials Department, ESIQIE-IPN, UPALM, Lindavista, C.P. 07738, Mexico, Mexico. ERIKA O. AVILA-DAVILA, Professor, is with the Instituto Tecnolo´gico de Pachuca, Pachuca Hidalgo, C.P. 42080, Mexico, Mexico. Manuscript submitted June 21, 2011. Article published online March 31, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
Previous works[2,3] have reported the synthesis of potassium jarosite KFe3(SO4)2(OH)6, natrojarosite NaFe3(SO4)2(OH)6, and hydronium jarosite (H3O)Fe3 (SO4)2(OH)6 by the dissolution of ferric sulfate solutions and sulfate alkali in deionized water and heating at a temperature close to their boiling point. The structure of jarosite KFe3(SO4)2(OH)6 and alunite KAl3(SO4)2(OH)6 was investigated by Hendricks.[4] Brophy and Sheridan[5] reported a K-Na-H3O jarosite solid solution. Lengauer et al.[6] studied the incorporation of trivalent and hexavalent chromium into a jarosite structure KCr3(SO4)2(OH)6, whereas Dutrizac et al.[7–9] investigated the incorporation of mercury, cadmium, and gallium. The thallium jarosite was synthesized by Dutrizac and Kaiman[10] by heating thallium sulfate and ferric sulfate solutions at 368 K (95 °C). The product was characterized by X-ray diffraction (XRD), chemical analysis, and thermal methods. Fairchild[11] has also synthesized silver jarosite by heating solutions of ferric sulfate, sulfuric acid, and silver sulfate at 383 K and 473 K (110 °C and 200 °C) in pressurized reactors. May et al.[12] synthesized pure silver jarosite and used XRD and thermal analysis techniques for characterization. Rubidium jarosite was synthesized successfully for the first time by Fairchild.[11] In this work, a solution of impure rubidium ferric sulfate was heated at a temperature between 438 K and 453 K (165 °C and 180 °C) in a pressurized reactor. The phase obtained was not well defined structurally. Dutrizac and Kaiman[10] synthesized p
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