Flotation separation of molybdenite from sphalerite using dl-cysteine as a depressant and insight into its selective adsorption mechanism

Abstract

dl-cysteine (DLC) was investigated as an eco-friendly and nontoxic sphalerite depressant in the flotation separation of molybdenite from sphalerite. Micro-flotation tests were carried out to study the flotation performance of sphalerite and molybdenite treated by DLC, and the selective depression mechanism of DLC on sphalerite was systematically explored using various characterizations. Flotation experiments indicated that DLC can selectively depress sphalerite in a wide range of pH, and its effect on the floatability of molybdenite was negligible. Zeta potential, Fourier infrared, and adsorption density analyses indicated that DLC was more inclined to be adsorbed on the sphalerite surface than on the molybdenite surface. The pre-adsorbed of DLC further hindered the subsequent adsorption of butyl xanthate on the sphalerite surface. X-ray photoelectron spectroscopy illustrated that DLC coordinated with Zn atom via its SH or/and NH2 groups, thus inducing the sphalerite surface hydrophilic. The first-principle periodic calculation further demonstrated that DLC would prefer to be adsorbed on sphalerite (110) surface via its NH2 group because of the more negative adsorption energy of NH2 group complexed with unsaturated Zn atom. Overall, this study serves as a theoretical guidance for using DLC as an effective sphalerite depressant for the flotation separation of sphalerite from molybdenite.