Characterization of Raw and Decopperized Anode Slimes from a Chilean Refinery
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RODUCTION
MOST copper production around the world is based on pyrometallurgical methods, through which copper anodes must be electrorefined to meet market requirements in terms of impurities, and products of electrorefining are copper cathodes with 99.99 pct purity. Copper anodes contain selenium (Se), tellurium (Te), lead (Pb), arsenic (As), antimony (Sb), iron (Fe), bismuth (Bi), silver (Ag), and gold (Au), as shown in Table I.[1] During electrolysis, copper from the anode is deposited onto the cathode. However, other impurities are released from the anode without being deposited onto the cathode. Some dissolve and are concentrated in the electrolyte, while others form a mud at the bottom of the cell. The latter is termed raw anode slime, which is collected from the bottom of the electrolytic cell for subsequent treatment. The slime has a high commercial value due to the presence of elements such as Au, Ag, Se, Te, and PGM. The composition of anode slimes
EVELYN MELO AGUILERA, Ph.D. Student, and TEO´FILO GRABER SEGUEL, Academic (Professor), are with the Department of Chemical Engineering, Universidad de Antofagasta, Av. Universidad de Antofagasta 02800, Antofagasta, Chile Contact e-mail: [email protected] MARI´A CECILIA HERNA´NDEZ VERA, Academic (Professor), is with the Department Metallurgical and Mines Engineering, Universidad Cato´lica del Norte, Av. Angamos 0610, Antofagasta, Chile. JOAN VIN˜ALS, Academic (Professor), was with the Department of Materials Science and Metallurgical Engineering, Universidad de Barcelona, Martı´ i Franque´s 1, 08028, Barcelona, Spain. Joan Vin˜als—Deceased. Manuscript submitted July 24, 2013. Article published online December 31, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
varies between refineries, depending on the impurities present in the anode. The traditional treatment of slimes is through pyrometallurgy, which consists of stages of fusion, conversion, and refining through which an anode of metal dore´ is obtained.[2,3] In the last decade, studies of hydrometallurgic alternatives have been carried out using different lixiviant mediums, which can fully or partially replace the traditional process.[3–5] The acid lixiviation of slime in a chloride medium is currently being used at an industrial level in refineries in Naoshima[4] and Rı´ o Tinto.[6] The use of acid lixiviation to dissolve copper is considered a first step in all treatments, with decopperized slime as the product
II.
EXPERIMENTAL
Two samples of anode slime, one raw and the other decopperized by means of agitated leaching with air injection, were provided by a Chilean refinery, in 2010. These slimes are materials composited during the above period. The decopperized slime is not the product of the raw anode slime analyzed in the present document. The samples were washed three times with distilled water, in order to remove all impregnated soluble copper, and dried at 343 K (70 °C) for subsequent characterization by chemical analysis (AA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with dispersive X-ray e
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