Leaching of CuFeS 2 by aqueous FeCl 3 , HCl, and NaCl: Effects of solution composition and limited oxidant

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I.

INTRODUCTION

CHALCOPYRITE is both the most abundant copper sulfide and the most refractory. Much work has been done on the leaching of chalcopyrite by ferric chloride ~-j3 since Sullivan recognized the value of ferric chloride as a possible lixiviant over fifty years ago. In this early work, it was found that for equal ferric concentrations, FeC13 leaching was considerably faster than Fe2(SO4)3 leaching.~ More recently, a number of investigators have reported the activation energy for FeC13 leaching (e.g., References 6, 8, and 10). The effect of the ferric chloride concentration on the leaching rate has been studied 9'~~ and the role of the total chloride concentration has been discussed.8 The influence of FeC12 on FeC13 leaching has also been considered. 5'6~13Except for some of the work by Haver and Wong, 3'~ these later studies were conducted at constant oxidant concentrations. Haver and Wong, however, chose conditions such that the Fe(III) and Cu(II) concentrations were very low at the termination of the experiments. Simultaneously, the Cu(1) concentrations were high. Cupric leaching systems 14-17 have not received as much attention but, as discussed below, the two systems are closely linked. The following reactions are generally accepted as representing the leaching of chalcopyrite in FeCI3 and CuC12: CuFeS2 + 4Fe(III)--~ Cu(II) + 5Fe(II) + 2S ~

[1]

CuFeS2 + 3Cu(II) ~ 4Cu(I) + Fe(II) + 2S ~

[2]

Cu(II), one of the products of Eq. [I], can itself leach the mineral. M. L. O'MALLEY, Graduate Student, and K. C. LIDDELL, Associate Professor, are with the Department of Chemical Engineering, Washington State University, Pullman, WA 99164-2710. Manuscript submitted June 30, 1986.

METALLURGICALTRANSACTIONS B

Further complicating this situation is the redox reaction between aqueous copper and iron Fe s+ + Cu + = Fe 2+ + Cu z+

[31

Because of this reaction, the concentrations of ferric and cupric ion cannot be varied independently. In Eq. [3], Fe 2+ and Cu 2+ are strongly favored thermodynamically. ~8 The ability of each of the metal valences to complex with chloride ion must also be considered. Univalent copper complexes very strongly with chloride; complexation by divalent copper and by di- and trivalent iron is less pronounced. One effect of the simultaneous redox and complexation equilibria is that the Cu(I)/Cu(II) ratio is strongly dependent on the chloride concentration. 18High Cu(I) concentrations are possible only in solutions with high ligand concentrations and are favored by low concentrations of Fe(III). To investigate in detail the formation of Cu(I) during FeCI3 leaching of chalcopyrite, batch leaching experiments were undertaken in which the reaction was allowed to proceed until there were no further concentration changes. The initial oxidant (Fe(III) in this work) was the limiting reagent. A method was developed to analyze the leach liquor for Cu(II) and Fe(III); 2~ total Fe and total Cu concentrations were also determined. In selected experiments, the potential of solution samples was also dete