Disulfide disproportionation and CdS formation upon cadmium sorption on FeS2

Adsorption reactions are important for understanding the distribution of ions between aqueous and solid phases; they govern solution concentrations, bioavailability, and mobility of ions in the environment. Iron disulfide is a sorbent of cadmium in reduced systems but sorption on sulfides is not well understood. The purpose of this research is to determine the surface structures and products of cadmium sorbed on amorphous FeS2. Raman spectroscopy, x-ray diffraction, electron microscopy, and scanning tunneling microscopy were used to study the disulfide surface. The FeS2 undergoes surface reconstruction and disproportionation during cadmium sorption, which leads to discrete zones of elemental sulfur, cadmium sulfide, and iron hydroxide. Therefore, simple surface complexation is not the predominant mechanism of sorption. Disproportionation may provide a mechanism for the surface to reorganize and for isolated crystalline cadmium sulfide domains to develop. Cadmium surface precipitates are very stable and their formation may be a significant means of attenuating this hazardous element. Thus, it appears that FeS2 may be an important sorbent of cadmium in natural environments. Copyright (C) 2000 Elsevier Science Ltd.