Coupling effect of phytic acid and chlorite on uranium removal by Shewanella putrefaciens under simulated natural environment

Understanding the transport and transformation of uranium species in surface and underground water environments, including biological migration, is a critical issue in nuclear environmental research. While it is known that uranium is primarily immobilized through reduction and mineralization with clay minerals and microorganisms, the coupled processes involving these motifs and their molecular mechanisms under multiple environmental factors remain elusive. In this work, using phytic acid (denoted as IP₆ hereinafter) as a typical organic ligand and chlorite (a layered hydrous aluminum silicate with Mg²⁺, Fe²⁺, etc.) as a typical inorganic clay mineral, we investigate the immobilization of UO₂²⁺ [abbreviated as U(VI) here in after] by S. putrefaciens under simulated natural aerobic conditions. The experimental results show that in aerobic environment, the reduction of uranium by S. putrefaciens is inhibited, and only mineralized products are observed. In the chlorite-U(VI) system, UO₂²⁺ enters the chlorite interlayer due to internal channel restriction effects and becomes more firmly fixed over time. When there are decomposed S. putrefaciens, UO₂²⁺ is fixed by its stronger binding sites and adsorbed on the surface of chlorite. After adding phytic acid, the process of uranium biomineralization by S. putrefaciens is blocked. In the simulated aerobic four component system, some Fe²⁺ and Mg²⁺ ions dissolve from the chlorite and replace the UO₂²⁺ adsorbed by IP₆. The released UO₂²⁺ combines with the decomposing S. putrefaciens, and the complex deposits on the surface of the chlorite. At low pH values (pH<5.5), IP₆ dissolves the metal ions of the chlorite and reduces their coupling with uranium coordination. Quantum-chemical methods are utilized to understand the experimental results at the molecular level and to provide an analysis of the interlayer structure of uranium in clay minerals. This study delves into the migration and fixation mechanisms of uranium in complex aerobic water environments, providing a theoretical basis for in-situ remediation of uranium contaminated water environments and understanding the biogeochemical behavior of nuclides in aquatic ecological environments.