Patterned Copper Sulfide Thin Films: a Method for Studying Leaching Behaviour

Abstract

An experimental study on copper leaching from Cu1.85S thin films is presented, wherein copper extraction is quantitatively evaluated by changes in film thickness measured by white light interferometric profilometry. Changes in the film morphology and elemental composition, as assessed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, are used to confirm that the loss in film thickness is due to changes in the copper content and that the resultant film species is consistent with the mechanism of copper dissolution. The Cu1.85S thin films were synthesized by chemical bath deposition. The leaching behaviour of copper from the films was investigated in acidic ferric sulfate media at pHs 1, 2, and 3, and pH 1 at redox potentials of ~350–650 mV versus Ag/AgCl in 3 M KCl. The changes in the film thickness and copper sulfur ratio were shown to reflect copper dissolution behaviour from chalcocite. Leaching of the Cu1.85S films demonstrated a greater decrease in film thickness as pH decreased. In addition comparison of the order of reaction as a function of proton concentration in non-oxidative dissolution of Cu1.85S (0.06) and as a function of iron(iii) concentration in ferric oxidation of Cu1.85S (0.40) shows that the proton dissolution reaction is negligible. Leaching of the Cu1.85S films at redox potentials of up to ~476.4 mV versus Ag/AgCl in 3 M KCl produced covellite and demonstrated greater decreases in film thickness with increases in the redox potential. Leaching of the films above ~476.4 mV resulted in the formation of spionkopite and demonstrated a much lesser decrease in film thickness. These results are consistent with Eh-pH diagrams for the Cu–S–H2O system.