Microbial Leaching of Zinc from Low Grade Ore

Abstract

The present work investigates microbial leaching of zinc from low grade ore using Acidithiobacillus ferrooxidans (ATCC 14859). The initial low grade ore samples were collected from north-eastern Thailand, (Thongkum Mine, Amphoe Muang, Loei Province), and consisted of 13 % of initial zinc or 130 g kg-1. The experiments were undertaken at the shaken flask scale under controlled conditions of shaking speed 250 rpm, temperature 30 o C, time 16 days and 4 factors were varied; type of medium (0 k and 9 k medium), particle ore size (<20, 20-40, 40-60, 60-100 mesh and >100 mesh), percentage of ore density (2%, 5% and 10%) and the initial pH of the medium (2, 2.5, 2.8 and 3). The microbial leaching was assessed by determining the concentration of zinc in the medium and comparing it with the initial sample concentration. The results show that A. ferrooxidans can successfully leach zinc by as much as 6 times compared with the control experiment (without addition of A. ferrooxidans). The maximum efficiency (92.3%) for microbial leaching was obtained in 9 K medium, 20-40 mesh ore sizes, 2% ore density at pH 2.8 and the zinc content was found in the medium to be about 120 mg l-1.