Bioleaching of vanadium from stone coal vanadium ore by Bacillus mucilaginosus: influencing factors and bioleaching mechanism

Vanadium and its derivatives are used in a wide range of industries including steel, metallurgy, pharmaceuticals and aerospace engineering, etc. The reserves of stone coal resources are huge but the grade is low in China. Therefore, the effective extraction and efficient recovery of metal vanadium from stone coal is an important way to realize the efficient resource utilization of stone coal vanadium ore. In this thesis, Bacillus mucilaginosus was selected as the leaching strain and  vanadium leaching reached 35.5% after 20 d of bioleaching under the optimized operating conditions. The cumulative leaching rate of vanadium in the contact group reached 35.5%, which was higher than 9.3% in the non-contact group. The metabolites of B. mucilaginosus, such as oxalic acid, tartaric acid, citric acid, and malic acid played a dominant role in the bioleaching process, contributing 73.2% of the vanadium leaching rate. Interestingly, during the leaching process, the presence of stone coal stimulated the expression of carbonic anhydrase in the bacterial cells and the enzyme activity increased by 4.4442 U. The enzyme activity positively promoted the production of metabolite organic acids, and the total organic acid content increased by 39.31 mg/L, resulting in a decrease of 2.35 in the pH of the leaching system, which favored the leaching of vanadium in stone coal. Atomic force microscopy analysis illustrated the bacterial leaching action led to a deepening of the corrosion on the surface of the stone coal, even exceeding 10 nm. Our study provides a clear strategy to explore the bioleaching mechanism from the perspective of microbial enzyme activity and metabolite which appears very promising for the exploration the bioleaching mechanism.