Evaluation of l-cysteine as an eco-friendly depressant for the selective separation of MoS2 from PbS by flotation

Abstract

Herein, we employed a range of instrumental techniques to investigate the performance of l-cysteine as a biodegradable and selective depressant in the flotation separation of molybdenite (MoS2) from galena (PbS), demonstrating that this amino acid exhibited a superior depressing efficiency toward PbS and enabled the separation of the above minerals under alkaline conditions. In the presence of l-cysteine, the zeta potentials of PbS shifted to more negative values, which was indicative of chemisorption. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements indicated that the above chemisorption involved the formation of a five-membered chelate ring via coordination of Pb by S (–SH) and N (–NH2) atoms, as was further confirmed by time-of-flight secondary ion mass spectrometry measurements. Moreover, the detection of l-cysteine dimer on the surface of PbS was ascribed to the occurrence of oxidation processes. The predicted adsorption modes suggested an appreciable extent of surface interaction between l-cysteine and PbS, whereas density functional theory calculations demonstrated that the interaction between l-cysteine and the PbS (100) slab corresponds to both physical and chemical adsorption.