Enhanced oxidative bioleaching of Cd-bearing ZnS concentrate in moderately thermophilic conditioning, comparing additives effects at high pulp density

The study aimed to enhance the dissolution rates of zinc (Zn) and cadmium (Cd) in sphalerite concentrates through bioleaching using moderately thermophilic bacteria. The research explored the impact of various additives, such as silver ions (Ag + ), L -cysteine, pyrite, elemental sulfur, and ferrous sulfate, on the efficiency of bioleaching. The findings revealed that pyrite had the most significant effect on Zn and Cd dissolution rates, followed by L -cysteine and Ag + . Through a five-test design, the study optimized pyrite and L -cysteine concentrations at 12% pulp density and observed that 15 wt% pyrite and 0.5 g/L L -cysteine significantly improved dissolution rates. The maximum dissolution rates of 91.7% for Zn and 72.8% for Cd were achieved with 15 wt% pyrite after 60 days. Similarly, L -cysteine at 0.5 g/L enhanced Zn and Cd dissolution to 84.73% and 71.05%, respectively. Ultimately, field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) techniques were employed to examine the surface characteristics of the bioleached residues.