High-efficiency removal of rare earth elements from acid mine drainage by microbially induced carbonate precipitation process

Microbially induced carbonate precipitation (MICP) is an emerging bioremediation technology commonly used for the removal of metal elements from water. The feasibility of using this technological process to remove rare earth elements (REEs) from acid mine drainage (AMD) is investigated in this study. The indigenous ureolytic bacterial consortium UBC (95.29 % of Lysinibacillus, 2.7 % of Citrobacter, and 1.7 % of Pseudomonas) was successfully obtained from AMD sludge by targeted acclimation (four acclimation transfers) and a ureolytic bacterium strain U1 (Lysinibacillus fusiformis) was isolated from UBC. U1 can tolerate pH of 4, whereas UBC can tolerate pH as low as 3 by altering the community structure. The interaction between ureolytic bacteria and REEs was then studied using strain U1. U1 can tolerate up to 100 mg L-1 of REEs. Light REEs La, Ce, and Nd showed significant hormesis effect on bacterial growth. REEs precipitation experiments showed that REEs were removed by bacterial adsorption and accumulation, as well as by co-precipitation with calcite. The presence of Ca2+ significantly enhanced the removal of REEs. Finally, the performance of UBC in synthetic AMD solution was explored. The results showed that UBC can tolerate the AMD environment and maintain its functionality. It entered the logarithmic growth phase after 16 h and removed >99.9 % of REEs within 32 h. Other metal ions were also removed to varying extents. This study demonstrates that MICP is capable of effectively removing REEs from AMD, thereby expanding its application, and providing a promising approach for the resource recovery of AMD.