Mineralogical characterization of a copper anode and the anode slimes from the la caridad copper refinery of mexicana de
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I. INTRODUCTION
THE La Caridad Copper Refinery, located in Nacozari in the state of Sonora, Mexico, is owned by Mexicana de Cobre, which is part of Grupo Mexico. The refinery began operations in July of 1997 with an initial cathode capacity of 180,000 t/y and reached its expanded capacity of 300,000 t/y in May of 1998.[1,2] It treats copper anodes produced from its own copper sulfide concentrates originating from the La Caridad and Cananea mines. The anodes are cast at the La Caridad metallurgical complex using conventional molds. Barite is used as the mold wash during anode casting. An anode preparation machine is employed, and the anode dimensions are 940 (width) 957 (length) 45 mm; the anode weight is approximately 342 (337 to 358) kg. The La Caridad refinery has adopted the Kidd permanent stainless steel cathode technology. The anodes are refined at 280 to 289 A/m2 current density and at 63 °C to 65 °C in an electrolyte containing 45 g/L Cu, 180 g/L H2SO4, and 14 g/L As. The operation employs a 20-day anode cycle, with two 10-day cathode cycles. The amount of anode scrap is approximately 16 pct of the anode mass; the slimes fall is approximately 4.8 kg/t of anode. The anodes contain high levels of impurities. The average anode analysis is as follows: 650 ppm Ag, 2080 ppm As, 670 ppm Sb, 215 ppm Bi, 825 ppm Pb, 130 ppm Fe, 75 ppm S, 15 ppm Zn, 245 ppm Se, 40 ppm Te, 205 ppm Ni, and 1440 ppm O. Lead is added to the anodes to control bismuth; the lead content of the anodes is presently conT.T. CHEN and J.E. DUTRIZAC, Research Scientists, are with the Mining and Mineral Sciences Laboratories, CANMET, Natural Resources Canada, Ottawa, ON, Canada K1A OG1. Contact e-mail: [email protected] Manuscript submitted February 11, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
trolled at 1200 ppm. Antimony in the electrolyte is controlled by arsenic, and efforts are made to maintain the level of arsenic at 12 g/L through controlled bleeding of the electrolyte. The anodes have relatively low Ni, Se, and Te contents; however, they have higher S, Fe, and Zn contents relative to most North American copper anodes.[3] The anodes typically contain high levels of Pb, As, Sb, and Bi; arsenic contents ranging from 800 to 3000 ppm, Pb contents varying from 500 to 1200 ppm, and antimony contents as high as 1000 ppm are observed. The composition of the anode slimes is variable; the average well-washed slimes contain approximately 17 pct Ag, 5 pct Se, 3 pct As, 12 pct Sb, 3 pct Bi, and 18 pct Pb. The slimes are collected, filtered, repulped with water at 45 pct solids, and then fed to an autoclave to dissolve copper at 100 °C to 110 °C under an oxygen partial pressure of 6 bars. After leaching, the autoclave is discharged to a flash tank; the slurry is then filtered and the slimes are air dried. The slimes are subsequently transported to the precious-metals refinery to recover the valuable metals. It is sometimes concluded in commercial copper electrorefining operations that high Pb contents in the copper anodes reduce the As, S
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