Macroparticle-enhanced bioleaching of uranium using Aspergillus niger

Abstract

Fungal leaching is a promising method for uranium extraction from its low-grade ores. Nevertheless, an efficient leaching process needs to be developed. Herein, we proposed a macroparticle-enhanced method by which millimetre-sized inert particles were added to a culture medium for a two-step fungal leaching process. The impact of the addition of glass bead macroparticles on Aspergillus niger morphology and subsequent uranium extraction were investigated. Pellet-type morphology was found to be favorable to uranium extraction, and bio-ore pellets with 4–5 mm diameters showed a high leaching efficiency. However, the morphology of A. niger was driven toward dispersed mycelia and uranium extraction decreased at 210 rpm. The maximum uranium extraction of 75.5% was achieved with glass beads (40 g/L, 0.5 mm) at 180 rpm, an increase of approximately 10% compared to the control without glass beads. Analyses of organic acids by ion chromatograph showed that at these conditions, the amount of citric acid and oxalic acid consumed for uranium dissolution was the greatest. The three dimensional (3D) structures of bio-ore pellets were characterized by nano-computed tomography (nano-CT), and they presented different structures under the conditions with and without glass beads. The effect of stress energy (SE) induced by the glass beads was evaluated by a mathematical model, which revealed that the proper amount of energy input would contribute to increased uranium extraction.