The influence of micro-cracks on copper extraction by bioleaching

Abstract

Micro-cracks produced in the crushing stage could improve the permeability and diffusion of leaching solution within the ore particles, which would favor for the leaching process. However, its influence on the extraction of copper by bioleaching has rarely been studied. In this work, we reported the enhancement effect of micro-cracks on the bioleaching of low-grade copper sulphide ore. Jaw crusher and high-pressure grinding rolls were adopted to prepare ore samples of the same size fraction but with different number of micro-cracks in the ore particles. Statistical data, scanning electron microscope (SEM) and stereomicroscopy (SM) images clearly showed that high-pressure grinding rolls could generate more and larger micro-cracks than the same produced by jaw crusher. Subsamples from the −0.9 mm and 3–6 mm size fractions were utilized for shake flask and column bioleaching experiments, respectively. The earlier change in pH and higher oxidation-reduction potential (Eh) indicated that more micro-cracks were beneficial for the growth of bacteria, which then enhanced the bioleaching efficiency of copper. In the shake flask experiments, the copper extraction efficiency was increased from 87.4% to 94.3% on the 30th day at 40 °C and 150 rpm. Similarly, in the column experiment with the ore sample prepared by high-pressure grinding rolls, an approximately 12.2% improvement of bioleaching efficiency was observed as compared to the system with the ore sample prepared by jaw crusher. These results demonstrated that creating micro-cracks could be crucial for heap bioleaching of low-grade copper sulphide ores.