Effect of X-Ray µCT Scanning on the Growth and Activity of Microorganisms in a Heap Bioleaching System

Abstract

In heap bioleaching, a process in which microorganisms are required for the regeneration of leach reagents and control of reaction products, inaccessibility of non-surface mineral grains is a key cause of low recovery and long extraction times. High resolution, non-destructive 3D X-ray micro-computed tomography (μCT) is an imaging technique that has been successfully demonstrated for the study of abiotic leaching of non-surface minerals. For this technique to be applied to biotic leaching, it is required that the iron and sulphur oxidizing abilities of the microorganisms are not affected by the irradiation experienced. In the current study, the feasibility of investigating biotic leaching by X-ray μCT is explored by examining the relative energies required to achieve the high image resolution needed for mineral grain mapping while avoiding microbial deactivation. A mixed mesophilic and moderately thermophilic culture in solution was used and exposed to various X-ray energy doses. Direct microscopic cell counting and redox potential were measured to quantify the microbial activity and growth. The results showed that exposure to X-ray does not affect microbial activity at 35-90 kV, 200-280 μA and a distance of 7.2 cm between energy source and sample, however, it has an influence at 120 and 150 kV. This indicates that while X-ray μCT does influence the microbial cultures, it can be used for bioleaching studies at lower energy doses.