Evaluation of the effects of L-cysteine addition on the bioleaching of zinc and cadmium from sphalerite flotation concentrate

Abstract

The primary zinc ore in the world is sphalerite, and roasting-leaching-electrowinning (RLE) is the most typical method of processing. This method has different disadvantages, and bioleaching is an alternative and eco-friendly method for sphalerite treatment. The major drawback of bioleaching is its slow kinetics. In this study, an evaluation of the effects of L-cysteine addition on the bioleaching of zinc and cadmium from a concentrate of sphalerite was investigated in the presence of mixed cultures of mesophilic and moderately thermophilic microorganisms. The results showed that L-cysteine addition increased the dissolution rates of zinc and cadmium while reducing them at higher concentrations. The optimal conditions were achieved by using 0.1 g/L of L-cysteine in mesophilic cultures with zinc recovery of 73.92% and cadmium recovery of 81.45%, respectively. Similarly, zinc recovery was 92.54% in thermophilic cultures, while cadmium recovery was 88.66%. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analyses have detected the formation of jarosite and elemental sulfur on sphalerite surfaces in mesophilic conditions, as well as ammoniojarosite and elemental sulfur in moderately thermophilic conditions. Fourier transform infrared (FTIR) spectroscopy was employed to identify molecular structures and functional groups on the surface of bioleached residues in mesophilic and moderately thermophilic conditions. To assess the environmental risk of residues, a combination of synthetic precipitation leaching procedure (SPLP) and toxicology characteristic leaching procedure (TCLP) methods were used.