A DFT study on mechanisms of indium adsorption on sphalerite (100), (110), and (111) surfaces: Implications for critical metal mineralization

The genesis model of indium-bearing sphalerite derived from the DFT study of indium adsorption in the sphalerite (100), (110) and (111) surfaces. • Adsorption analysis of indium onto the sphalerite (100), (110) and (111) surfaces. • The (111) surface is the most favorable for indium adsorption. • Cu + significantly promotes the enrichment of indium on the sphalerite surface. • The surface chemical reaction of sphalerite triggers its indium enrichment. As an important critical metal, indium (In) enters sphalerite through isomorphous substitution of Zn. Regarding crystallography and chemical kinetics, In adsorption in sphalerite surfaces is a key factor controlling its occurrence in sphalerite, because this is a prerequisite for triggering the substitution process. Nevertheless, mechanisms of In adsorption on sphalerite surfaces remain ambiguous, which hinders our understanding of the physicochemical conditions for forming In-bearing sphalerite. Thus, we employed the first-principles calculations method based on density functional theory to investigate the structural characteristics of the three primary sphalerite surfaces, namely (100), (110), and (111), under In adsorption. As an illustrating purpose, we addressed the substitution process of In 3+ + Cu + → 2Zn 2+ , one of the most common and important substitution mechanisms for forming In-bearing sphalerite in natural mineralization. We calculated the adsorption energy and electronic structure of In 3+ and In 3+ –Cu + adsorption in the sphalerite (100), (110), and (111) surfaces, respectively. The results suggest that the (111) surface is notably the most conducive to In entering sphalerite, attributed to the low adsorption energy for both In 3+ and In 3+ –Cu + onto it. Cu + enhances In 3+ adsorption on the sphalerite surfaces since it significantly reduces the adsorption energy. The considerable differences in the electronic structures of the three sphalerite surfaces restrict the charge transfer between In 3+ and other atoms present, ultimately controlling their In adsorption behaviors. This analysis sheds light on the variations in the In 3+ adsorption processes on the sphalerite (100), (110), and (111) surfaces at an atomic level. It offers a deep understanding of the mechanisms driving the formation of In-bearing sphalerite, especially in the context of critical metal mineralization.