Kinetics of Copper Removal from Sulfidized Molybdenite Concentrates by Pressure Leaching
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MOLYBDENITE concentrates produced from porphyry copper deposits always contain copper as an impurity in variable quantities depending on the efficiency of the differential flotation processes. Therefore, to produce a high-grade molybdenite concentrate, a chemical purification method is normally practiced. There are various hydrometallurgical processes proposed for the purification of molybdenite and some of them, such as the ferric chloride leaching and sodium cyanide leaching, have been used by the industry.[1,2] The ferric chloride leaching process was developed for the removal of copper, lead, and calcium from molybdenite concentrates, and modified versions of this process are currently in use, e.g., Andina mine in Chile. The original process used a concentrated brine solution constituted of 30 pct CaCl2, 10 pct FeCl3, and 2.1 pct CuCl2 as highly corrosive leaching solution at 383 K (110 C). The sodium cyanide leaching process was used to remove copper and gold from molybdenite concentrates in Chuquicamata, Utah Copper, and San Manuel,[2] and hydrochloric acid leaching was also used to remove lead and bismuth from molybdenite concentrates.[1,3] One of the major disadvantages of cyanide RAFAEL PADILLA and MARIA C. RUIZ, Professors, are with the Department of Metallurgical Engineering, University of Concepcio´n, Edmundo Larenas 285, Concepcio´n, Chile. Contact e-mail: [email protected] CRISTIAN OPAZO, Student, is with the Department of Chemical Engineering, University of Concepcio´n, Concepcio´n, Chile. Manuscript submitted February 5, 2014. Article published online August 26, 2014. 30—VOLUME 46B, FEBRUARY 2015
leaching is the low dissolution of chalcopyrite in this medium, which definitely deters the application of this process to Chilean molybdenite concentrates. Ruiz and Padilla[4] studied the removal of copper from molybdenite concentrates by leaching in sodium dichromate solutions. It was reported that leaching in 0.3 M H2SO4 and 0.12 M sodium dichromate solution at 373 K (100 C) for 5400 seconds could dissolve 95 pct of copper with little dissolution of molybdenum. However, the presence of chromium in the solutions is inconvenient from the environmental point of view. Other chemical processes investigated include the hot acid baked treatment of molybdenite concentrate.[5] The process consisted of mixing sulfuric acid of 93 pct H2SO4 with molybdenite concentrate in a 1:1 ratio at 433 K to 463 K (160 C to 190 C) for about 7200 seconds. The hot baked pulp was after leached in water to remove the copper as a soluble copper sulfate. However, the operational variables and materials selection for the reactor were deterrents for the success of a continuous operation. Recently, bioleaching studies were also conducted by Romano et al.[6] for removal of chalcopyritic copper from molybdenite concentrates. Using mesophilic microorganisms, these investigators claimed that 50 pct of copper was dissolved with less than 1 pct of molybdenum dissolution. In the same line of work, Askari Zamani et al.[7] using a native microorgan
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