Insights into formation and dissolution mechanism of bio-ore pellets in the one-step uranium leaching process by Aspergillus niger

• Secretion of organic acids changed the electrostatic property of the particles. • Electrostatic attraction force among ore particles promoted particles’ aggregation. • Hyphae and metabolites of A. niger could erode the surface of ore particles. • Globular bio-ore pellets were beneficial to uranium dissolution. In the one-step bioleaching process of uranium by Aspergillus niger , the formation mechanism and uranium bioleaching model of bio-ore pellets were explored and proposed. The results showed that the formation of bio-ore pellets could be divided into three phases. In the adaptive-growth phase, a small number of ore particles were adsorbed by mycelia to form flake mycelia with a diameter of 1–2 mm. In the rapid-growth phase, ore particles began to gather and form stable bio-ore pellets (diameter reaching 4.98 mm) owing to the force of electrostatic attraction, secretion of organic acids, and EPS adhesion. In the stationary growth phase, the bio-ore pellets have been stably formed (Zeta potential stable at approx. ±2.5 mV), the oxalic acid, citric acid, and tartaric acid secreted by A. niger accumulated and reached a peak of 7625 mg/L, and the uranium recovery achieved a peak of 79.6%. Furthermore, the atomic force microscope (AFM) scanning results indicated that the hyphae and metabolites of A. niger could erode the surface of ore particles. Finally, a uranium dissolution model of the bio-ore pellets was established. It indicates that the globular bio-ore pellets were beneficial to uranium dissolution under the double effects of mycelial mechanical damage and organic acid corrosion.