Study On Macroparticle-enhanceed Bioleaching Of Uranium By Aspergillus Niger

Fungal leaching has been considered a novel,cost-effective and eco-friendly bioleaching method,in which target metals were released from its minerals by organic acids produced by fungus.The weak acidity of organic acids leads to a relatively low recovery of metals,so enhanced leaching technologies need to be developed to improve leaching efficiency.In this study,a macroparticle-enhanced fungal leaching was presented,and using glass beads and ceramic particles as macroparticles the enhancement of uranium leaching from carbonaceous-siliceous-argillaceous type uranium ore by Aspergillus niger(A.niger)was investigated.The main achievments are summed as follows:(1)One-step macroparticle-enhanced uranium bioleaching experiments with A.niger were carried out to examine the effects of glass beads and ceramic particles on uranium recovery,and verify the potential for uranium improvement.The results showed that the suitable particle size and concentration and shaker speed can enhance uranium leaching.Under the conditions of 2% pulp density and 150 rpm,addition of 1 mm diameter ceramic particles at a concentration of 50 g/L gave 71.11% uranium extrction,which increased by 6.19% compared to the controll without ceramic particles;by addition of 1 mm diameter glass beads with a concentration of 20 g/L the uranium extrction of 76.04% was achieved,increasing by 11.12% in contrast to the control.(2)Two-step macroparticle-enhanced uranium bioleaching experiments with A.niger were carried out to examine the effects of glass bead particle size and concentration,and shaker speed on the biomass and morphological characteristics of A.niger,and uranium recovery were examined.The results showed that the cell dry weight of A.niger had a decrease trend as the shaker speed and glass bead particle size increased.It was observed that bio-ore pellets were formed by mycelia wrapping uranium ore particles at 150 rpm and 180 rpm in the presence of glass beads;the morphology of A.niger switched toward clumps or disperse mycelia at 210 rpm.At a pulp density of 4%,the maximum uranium recovery of 75.49% was achieved with 0.5 mm glass beads at 40 g/L,which increased by 9.82% against the control.(3)Stress energy(SE)was introduced referring to a mechanical stress model for a ball to characterize the energy induced by glass beads,and the relationships between SE and the CDW of A.niger,the diameter of the bio-ore pellet and the uranium extraction were analyzed.The results showed the change of SE can be divided into two stages: SE increases gently when the diameter of glass beads is in the range of 0.5-1mm(stage I);SE increases sharply after the diameter of glass beads increases to 2 mm(stage?).At different stages of SE,the CDW of A.niger,the diameter of the bio-ore pellets and the uranium extraction demonstrated different trends.The critical SE at 150 rpm,180 rpm,and 210 rpm are respectively 0.631 ?J,0.910 ?J,and 1.24 ?J.The high SE input generates inhibitory effect on A.niger growth,change in morphologies of A.niger,and decreased uranium extraction.