Mineralogical characterization of a copper anode and the anode slimes from the la caridad copper refinery of mexicana de cobre

Abstract

A detailed mineralogical study was carried out to characterize a copper anode, the anode-face slimes, the slimes on the bottom of the refining cell, and the autoclave-leached slimes from the La Caridad refinery of Mexicana de Cobre. The objective was to identify possible Pb-Sb-Bi and As-Sb-Bi interactions that could control the Sb and Bi concentrations of the electrolyte. Although some Pb, As, Sb, and Bi can be found in solid solution in the copper crystals of the anode, these elements are mostly present as Cu-Pb-As oxide and Cu-Pb-As-Sb-Bi oxide inclusions at the grain boundaries. During electrorefining, the Pb, As, Sb, and Bi in solid solution dissolve. Part of the Pb, As, Sb, and Bi in the oxide inclusions also dissolves, but part reacts in situ to form PbSO₄ and Pb₅(AsO₄)₃(OH,Cl). Some of the dissolved elements reprecipitate as PbSO₄, SbAsO₄, Sb-As oxide, Sb-As-Bi oxide, Pb₅(AsO₄)₃(OH,Cl), and an oxidate phase of mainly Cu-Ag-AsO₄-SO₄ composition. Thus, high As contents facilitate the precipitation of Sb and Bi from the electrolyte. Although Pb-Sb oxide and Pb-Bi oxide species were only rarely detected, a high Pb content in the anode may retard the dissolution of the Cu-Pb-As-Sb-Bi oxide inclusions, thereby retaining some Sb and Bi in the raw anode slimes. Autoclave leaching dissolves part of As, Sb, and Bi, but the SbAsO₄ and Sb-As-Bi oxide species remain in the leach residue. The Pb is converted almost entirely to PbSO₄, which is present as subhedral crystals in the autoclave leach residue.