Leaching of Chalcopyrite with Sodium Hypochlorite
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HYPOCHLOROUS acid (HClO) has been recognized as a strong oxidizing reagent to leach sulfide minerals. Ikiz et al.[1] investigated the leaching of a lowgrade chalcopyrite ore (3 pct Cu) with hypochlorous acid. They found that the leaching rate was fast enough to yield 40 pct to 80 pct conversions in 15-minute periods. The optimum conditions were an initial pH of 5, hypochlorous acid of 0.2 N, a solid dosage of 4 g/L, and room temperature. They also found that the leaching rate was controlled by diffusion through the product layer with an activation energy of 19.88 kJ/mol. Similar results were observed by Colak et al.[2] in a study where chalcopyrite was leached in a solution saturated with chlorine gas. The leaching rate was also fast enough to yield nearly complete conversion in 90 minutes at 10 °C. The leaching rate was controlled by diffusion through the product layer. Cho[3] found that the leaching of 65 9 100 mesh-sized particles of chalcopyrite at 0.23 molar hypochlorous acid and room temperature achieved about 90 pct conversion in 1 hour. The reagent consumption ratio—defined as the number of moles of hypochlorous acid consumed to leach 1 mole of chalcopyrite—was between 6.1 and 7.2. Vinals et al.[4] investigated the conversion of Cu3AsS4 (enargite) into copper oxide with OCl– (hypochlorite). They found that the conversion rate was fast enough to RAVINDER K. GARLAPALLI, Graduate Research Assistant, EUNG HA CHO and RAY Y.K. YANG, Professors, are with the Department of Chemical Engineering, West Virginia University, P.O. Box 6102, Morgantown, WV 26506. Contact e-mail: eung.cho@ mail.wvu.edu Manuscript submitted May 28, 2009. Article published online December 24, 2009. 308—VOLUME 41B, APRIL 2010
yield near completion at 60 °C, 0.27 molar hypochlorite, 0.03 molar OH–, and 1 hour of reaction time. The reaction orders with respect to the concentrations of hypochlorite and OH– were 0.5, which is consistent with general electrochemical control. They also found that the conversion rate was controlled by a chemical reaction with an activation energy of 58 kJ/mol. Garlapalli et al.[5] conducted a preliminary study on the leaching of chalcopyrite with hypochlorite in two stages; in the first stage, chalcopyrite was converted to CuO (cupric oxide) with hypochlorite, which subsequently was dissolved in an acid solution in the second stage. They found that the conversion rate was fast enough to yield 71 pct at 0.5 molar hypochlorite, 55 °C, pH 13, 1 g/500 ml solid dosage, and 1 hour of reaction time. The hypochlorite consumption ratio increased as the conversion increased, and the initial concentration of the reagent also increased. The consumption ratio reached 65 under the same conditions mentioned while its stoichiometric ratio was 8.5. Hypochlorous acid and hypochlorite are both chlorine derivatives, which are predominant in concentrations between pH ranges of 4 and 7 as well as above 8, respectively, under normal conditions. Some advantages may be found in the leaching and subsequent processes of chalcopyrite with hypochlo
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