Evaluation of adsorption differences of DL-cysteine on sphalerite surfaces with different degrees of iron substitution: Experimental and DFT studies

Abstract

Conventional flotation processes often employ cyanide as a depressant for sphalerite, posing environmental concerns. This study investigates the adsorption of 2-Amino-3-mercaptopropionic acid (also known as DL-Cysteine) on sphalerite surfaces with varying degrees of Fe substitution using density functional theory calculations. The focus encompasses electronic properties, charge transfer, and orbital coordination. The potential of DL-cysteine as a sphalerite depressant was assessed and subsequently confirmed experimentally. Our findings indicate that Fe substitution increases the acidity of the mineral surface, thereby enhancing its reactivity to readily interact with the S, O, and N atoms abundant in lone-pair electrons. The Fe-substituted sphalerite surface primarily adsorbs DL-cysteine through interactions with -SH and –NH2 groups on Fe ions, in contrast to those on Zn ions. Analyses of the partial density of states and charge transfer confirm the spatial and orbital compatibility in the system. Moreover, micro-flotation tests, contact angle measurements, and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy substantiate that DL-cysteine efficaciously adsorbs onto marmatite surfaces, thereby reducing their hydrophobicity. On the contrary, the adsorption strength of sodium diethyldithiocarbamate on the mineral surface is significantly weaker. Overall, the potent adsorption capability of DL-cysteine makes it a viable, eco-friendly depressant alternative for marmatite.