The effect of silver on the acidic ferric sulfate leaching of primary copper sulfides under recycle solution conditions observed in heap leaching. Part 4: Semiconductor behaviour

Abstract

The semiconductor properties of chalcopyrite during leaching in sulfate solutions in the presence of silver have been investigated. A combination of Mott-Schottky plots and potentiodynamic polarisation was used to determine the transformations of the chalcopyrite surface as the potential was changed between +200 mV (SHE) and 1200 mV (SHE). The tests were carried out at 25 °C and 50 °C. The solutions used were 0.2 M and 0.5 M H2SO4 in the presence of 100 ppm Ag+ and then in the absence of Ag+. The semiconductor behaviour of chalcopyrite was different depending on the presence or absence of Ag. At 25 °C, two surface layers formed between 500 mV (SHE) and 1000 mV (SHE) in both the 0.2 M and 0.5 M acid solutions. The presence of Ag in both these solutions shifted the potentials at which the surface phases formed to more positive potentials. In the presence of Ag at 50 °C, there was formation of successive surface layers at potentials between 850 mV (SHE) and 1000 mV (SHE). It was concluded that Ag had a significant influence on the semiconductor properties of the chalcopyrite surface. The Ag present on the surface as metallic Ag acts as surface states and provides a path for electrons to tunnel or hop from the valence band to the conduction band.