Effect of Specific Surface Area of a Mechanically Activated Chalcopyrite on Its Rate of Leaching in Sulfuric Acid-Ferric
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CHALCOPYRITE (CuFeS2) is the most abundant copper-bearing mineral. The current method of treating chalcopyrite concentrates involves smelting and refining. Large volumes of sulfur dioxide emitted into the atmosphere from this type of treatment cause serious pollution problems. Hydrometallurgical processing is believed to be a capable method of solving such environmental problems.[1] Direct hydrometallurgical treatment of chalcopyrite is performed most frequently by oxidative leaching with low-cost ferric sulfate oxidant which allows for possible regeneration of the oxidizing agent. The reaction of chalcopyrite with ferric sulfate in acid medium is governed by the following equation: CuFeS2 þ 2Fe2 ðSO4 Þ3 ! CuSO4 þ 5FeSO4 þ 2S: ½1 There has been disagreement over the factors influencing the leaching rate of chalcopyrite.[2] Nevertheless, it is well known that the reaction [1] has a slow kinetics, and its rate decreases with time. This phenomenon has been ascribed to the formation of a passivating layer during the leaching course under oxidizing conditions. The protective layer so formed inhibits further reaction. Many previous studies suggested that this layer is
M.SH. BAFGHI, Associate Professor, and A. ZAKERI, Professor Assistant, are with the School of Materials Engineering and Metallurgy, Iran University of Science and Technology, 16846, Tehran, Islamic Republic of Iran. Contact e-mail: [email protected] A.H. EMAMI, Professor Assistant, is with the School of Materials Engineering, Islamic Azad University, Branch of Najafabad, Najafabad, Islamic Republic of Iran. Manuscript submitted July 21, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
composed of nonporous sulfur. On the basis of the results of electrochemical experiments, it has been proposed that passivation is caused by an amorphous nonstoichiometric sulfide.[3] On the other hand, the more chemically stable the sulfide layer, the more difficult the leaching process is. Hence, to overcome this obstacle, chemical stability of the protective film has to be modified by a suitable preleaching treatment. Mechanical activation of the ore by intensive milling is a relatively simple method for this purpose.[4] The effect of mechanical activation of some minerals as a preleaching treatment has been investigated by Hu et al.[5] and Yang et al.[6] Although milling exerts an additional cost because of its high energy consumption, it should be noted that milling is a compulsory step for the preparation of ores.[7] Almost all mineral processing plants use a milling step for size reduction of the particles prior to physical and chemical processing. Continuation of milling beyond that limit required for size reduction, leads to the mechanical activation.[8] To be able to have a convincible judgment about the overall process cost, it is essential to find out whether the energy cost of milling exceeds the energy saving resulted from reducing the temperature and pressure levels of the subsequent leaching steps.[7] Research results reported in the literature show that ultra fine
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