Investigation of Leaching Kinetics of Copper from Malachite Ore in Ammonium Nitrate Solutions
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IN the literature, oxide and sulfide copper ores mainly are known as azurite, malachite, tenorite, chrysocolla, brochantite, enargite, chalcopyrite, chalcocite, covellite, and bornite.[1] The production of metallic copper from these ores is carried out by pyrometallurgical and hydrometallurgical methods.[2] Pyrometallurgical methods are generally applied to the relatively high-grade sulfide copper ores. Increasingly, the lowgrade copper ores and secondary sources containing copper are being used for the production of copper because of depletion of high-grade copper ores at the present time.[3] Pyrometallurgical methods are not normally suitable for the processing of low-grade ores. Instead, hydrometallurgical methods are usually preferred for the recovery of copper from these kinds of ores. Leaching is the term applied to the process of recovering a metal from the metal source by a solvent or lixiviant, and it is typically the first step of any hydrometallurgical process.[4] In the leaching process, strong acids, such as HCl, HNO3, and H2SO4, are commonly used as the leaching reagents.[5] Sulfuric acid is the preferred lixiviant in the leaching of the oxidized copper ores, such as azurite, malachite, tenorite, and chrysocolla.[2,6] However, during the leaching of ores, AHMET EKMEKYAPAR and ASIM KU¨NKU¨L, Professors, and _ _ DEMIRKIRAN, _ NIZAMETT IN Assistant Professor, are with the Chemical Engineering Department, Faculty of Engineering, Inonu University, Malatya 44280, Turkey. Contact e-mail: nizamettin. _ [email protected] EVRIM AKTAS, Chemical Engineer, is with the Malatya Sugar Factory, Malatya 44080, Turkey. Manuscript submitted September 22, 2011. Article published online Apirl 26, 2012. 764—VOLUME 43B, AUGUST 2012
other metals in ore matrix are also dissolved along with the copper. These undesired impurities cause some problems in further processing of the leaching solution, such as the electrowinning of copper.[7] In addition, the impurities in the ore can cause a high consumption of acid. For these reasons, the use of solutions more basic than sulfuric acid can be attractive in the leaching of oxidized copper ores. For example, ammoniacal leaching systems have some advantages over acid leaching systems. In the ammoniacal leaching system, the dissolution of ore can be carried out at mildly acidic or basic conditions. Second, ammonia can be recovered by evaporation. Furthermore, some metals, which pass into the solution during the leaching process, precipitate because of the higher pH of solutions containing ammonia. Ammonia also forms stable complexes with copper ions, which can lead to an increase in the leaching rate from the ore. Thus, ammonia allows for selective extraction of the copper from ore, leaving the undesired components in the residue.[7–9] As a result, at the end of the leaching process, a high purity solution can be obtained for the electrolytic recovery of copper. The leaching and kinetics of malachite, which is an oxidized copper ore, in ammonia-containing solutions has been investiga
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