Influence of X-ray μ-Computed Tomography on the microbial activity of a mixed thermophilic and mesophilic bioleaching culture colonising a mineral surface

Abstract

X-ray micro-Computed Tomography (X-ray μCT) allows for non-invasive 3D investigations of heap leaching processes. It permits study of mineral liberation, pore network structure in particles or beds, and bioleaching of non-surface mineral grains. A premise for bioleaching studies integrating X-ray μCT is that the metabolic activity of microorganisms is not affected by X-ray energy doses. This study therefore evaluates the compatibility of bioleaching microorganisms with X-ray energy exposure. The X-ray effect on a mixed thermophilic culture suspended in solution was assessed using imaging conditions of 35–150 kV, 200–280 μA and 1–2 hours. Microorganisms were unaffected between 35–90 kV and 200–280 μA while there was some detrimental effect at 120 and 150 kV. The X-ray influence on a mixed mesophilic culture colonising a mineral surface was investigated at 90 kV and 225 μA for a 1 h exposure time. The system was monitored before and after exposure through measurement of: redox potential of the effluent solution, microbial cell concentration, heat output from the colonised surface using isothermal microcalorimetry (IMC), and cell attachment on the ore surface using scanning electron microscopy (SEM). The redox and cell concentration measurements showed insignificant differences between exposed and unexposed samples. Equivalent heat generation and good colonization of the mineral surface was demonstrated, confirming continued microbial activity post exposure, hence recommending its use in support of bioleaching studies.