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

Abstract

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 absorption in 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 In³⁺ + Cu⁺ → 2Zn²⁺, 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 In³⁺ and In³⁺–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 In³⁺ and In³⁺–Cu⁺ onto it. Cu⁺ enhances In³⁺ adsorption in the sphalerite surfaces due to it significantly reduces the adsorption energy. The considerable differences in the electronic structures of the three sphalerite surfaces restrict the charge transfer between In³⁺ and other atoms present, ultimately controlling their In adsorption behaviors. This analysis sheds light on the variations in the In³⁺ 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.