Bioleaching of zinc from gold ores using Acidithiobacillus ferrooxidans

The present work investigated microbial leaching of zinc from ore using Acidithiobacillus ferrooxidans (ATCC 14859). The ore samples, consisted of 13wt% zinc, were obtained from a gold mine in north-eastern Thailand. A shake flask study was performed on the ore samples using a rotary shaker under the following fixed conditions (250 r·min⁻¹, 30°C for 16 d). The influence of various conditions, namely medium type (with and without iron), particle ore size (<20, 20-40, 40-60, 60-100, and >100 mesh), ore density (20 kg·m⁻³, 50 kg·m⁻³, and 100 kg·m⁻³), and pH of the medium (2, 2.5, 2.8, and 3), were investigated. The microbial leaching was assessed by determining the concentration of zinc in the medium and compared with the initial sample concentration. The results show that Acidithiobacillus ferrooxidans can successfully leach zinc by as much as 6 times compared with the control experiment (without Acidithiobacillus ferrooxidans ferrooxidans). The maximum efficiency (92.3%) for microbial leaching is obtained in iron-containing medium, 20-40 mesh ore sizes, 20 kg·m⁻³ ore density at pH 2.8, and the zinc content is found in the medium at about 120 mg·L⁻¹.