The Effects of Chalcopyrite Trace Elements on Resistivity

Abstract

This paper presents preliminary data toward resolving some of the wild inconsistencies observed in the leaching behavior of chalcopyrite (CuFeS2), a common copper ore mineral notorious for variable but generally poor recovery in hydrometallurgy. Ongoing research has found major inconsistencies in activation energy, dissolution mechanisms, and other leaching phenomena, even for chalcopyrites leached in the same solution. One current hypothesis for this variability is the semiconducting properties of chalcopyrite, which are thought to vary as a function of their composition. Crystallographic defects, impurities such as Zn, Ag, Ni, and Se, and major-element ratios are all thought to influence the semiconducting properties of chalcopyrite, like charge carrier type, density, and resistivity, thus accelerating or restricting dissolution. If the true determinant of these properties in natural chalcopyrite is better known, then industry can increase recovery by tailored processing strategies. However, the literature contains few measurements of semiconducting properties for natural samples, and even fewer correlated with sample composition. In this research, the trace element compositions of 14 high-grade natural chalcopyrite samples from several deposit types are measured for resistivity. Results suggest that individual trace elements have little to do with the resistivity of chalcopyrite. The highest correlations are with Co, Ga, Ag, and Se, but top out at R2 = 0.45 (Co). Modest correlations also emerge when the trace elements are grouped by substitution of crystallographic site. The strongest correlations are with the combined substitution of As, Se, and Te into the S site (0.3 < R2 < 0.4). While experiments to understand the connections between sulfur deficiency, trace element substitution, and leaching have not been done, tentative conclusions from sulfur-deficient (Cu-oversaturated) chalcopyrite samples show an increase in dissolution rate. These preliminary results suggest that the semiconducting properties of chalcopyrite emerge from a complex mix of factors, including deposit type, and are only partly related to trace element composition. They also indicate the potential limitations of attempts to understand chalcopyrite leaching phenomena with single-element approaches. Further work will focus on testing more chalcopyrite samples from constrained deposit types to improve the consistency of data.