Kinetics of Pressure Dissolution of Enargite in Sulfate-Oxygen Media
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TRODUCTION
THE hydrometallurgical methods for extracting copper from concentrates are viable alternative processes especially when the concentrates contain appreciable amounts of toxic elements such as arsenic. In Chilean copper concentrates, arsenic is present mainly in the form of enargite (Cu3AsS4), which is associated with most of the copper sulfides. When the enargite content in copper concentrates is relatively low, the concentrates are treated by conventional smelting-converting pyrometallurgical methods. However, if the concentrates contain appreciable amounts of enargite, the copper production by direct smelting and converting of the concentrate is problematical, because most of the arsenic reports to the gas phase increasing the risk of environmental pollution. In addition, the fraction of arsenic retained in the condensed metal phase leads to a deteriorated quality of the final metal product.[1–3] Thus, an additional step of pretreatment, such as roasting, may be required to eliminate arsenic from the concentrate prior to smelting when the arsenic content is over 2 pct.[3] The natural alternative method to process copper concentrates with high enargite content is leaching. In particular, sulfuric acid leaching has always been considered as a viable process when direct smelting of R. PADILLA and M.C. RUIZ, Professors, Department of Metallurgical Engineering, and C.A. RIVAS, Student, Department of Chemical Engineering, are with the University of Concepcio´n, Concepcio´n, Chile. Contact e-mail: [email protected] Manuscript submitted January 29, 2008. Article published online June 13, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
the concentrate is not technically feasible. The advantage of sulfuric acid leaching is that the pregnant solutions can be integrated to current solvent extraction and electrowinning operations. However, for a leaching process of copper concentrates to be effective, it is necessary to understand the leaching behavior not only of copper sulfides but also of the toxic impurities such as enargite present in the concentrate. In this framework, the present work is a kinetic study of the pressure leaching of enargite in sulfuric acid–oxygen media. Recently, Lattanzi et al.[4] and Filippou et al.[5] reviewed the oxidation of enargite in various leaching media. Here, we briefly review the pertinent data on the aqueous oxidation of enargite in acidic solutions. In 1952, Koch and Grasselly[6] studied the dissolution of enargite and enargite-pyrite mixtures in acidic ferric sulfate solutions. Their results indicated a very slow dissolution of enargite in this media and slightly accelerated dissolution in the presence of pyrite. Later in 1972, Dutrizac and MacDonald[7] studied the leaching kinetics of synthetic enargite discs in sulfuric acid-ferric sulfate solutions in the temperature range 60 C to 95 C. They also concluded that enargite dissolution was very slow in this leaching media and it occurred with linear kinetics. The sulfide sulfur was oxidized mainly to elemental sulfur, and the coppe
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