Production of magnetite from sodiumjarosite under reducing hydrothermal conditions. The reduction of Fe-III to Fe-II with cellulose

Jarosite is a waste product, of zinc industries using the hydrometallurgica l processing route to remove iron from the pregnant solution, generally by the addition of ammonium sulfate. Its formula is (MFE3(SO4)(2)(OH)(6)), in which M represents cations like NH4+, Na+, K+, H3O+, 1/2 Pb2+. The jarosite is usually stored in lined ponds near the factory, since recycling is stil l not an economically feasible option. A promising recycle technique is red uction of industrial jarosite with sewage sludge under hydrothermal conditi ons in an autoclave in the presence of a suitable neutralizing agent. The r esulting liquid, containing most of the sulfur species, is separated from t he solid, containing the metals. Under appropriate conditions iron is mainl y precipitated as magnetite. This paper describes the production of magnetite out of sodium jarosite, st arting from pure chemicals. MgO was used as a neutralizing agent, pure, aci d washed cellulose as a reducing agent. Na-jarosite was produced in the lab oratory. The aim of this study was to find the optimal ratio of jarosite/ce llulose/MgO and to describe the reaction pathway. Several reactions were ca rried out in an autoclave at 250 degrees C and one hour retention time. Aft er quenching and solid/liquid separation, the solids were analyzed by XRD a nd ICP-AES. The liquids were characterized by ICP-AES and spectrometric tec hniques. In-situ filtration was performed during the tests, providing addit ional information on the reaction pathway. The optimal ratio for the produc tion of magnetite out of jarosite was 100 g/L Na-jarosite, 30 g/L cellulose and 20 g/L MgO. The jarosite was first converted to goethite, which was re crystallized to magnetite. (C) 2000 Published by Elsevier Science Ltd on be half of the Canadian Institute of Mining and Metallurgy. All rights reserve d.