Experimental and computational study on the inhibitory effect of phytic acid on U(VI) biomineralization by Shewanella putrefaciens

Uranyl (UO22+) species with hexavalent U(VI) oxidation state is the most ubiquitous form of uranium in natural minerals, underground water, contaminated soils, and ocean. Interplay between bioorganic molecules and U(VI) is rather complicated due to its various complex configurations and reaction networks. In this study, the widely present phytic acid (IP6) is selected as a model organic molecule together with the bacteria Shewanella putrefaciens (S. putrefaciens, existing mainly in marine environments) to explore its role on U(VI) biomineralization. We found that phytic acid had a clear inhibition effect on the U(VI) removal of S. putrefaciens, with the absorption capacity dropped from 382.77 mg/g to 102.45 mg/g. Further Dialysis experiment suggested that phytic acid tended to chelate with U(VI) to form colloid polymer. Quantum-theoretical modeling confirmed that phytic acid bond strongly with uranyl ions, while calcium and magnesium ions could bind with phytic acid as well via ionic bonding, thus relieving the inhibition effect of phytic acid in the solution through breaking the hydrogen bonding network. XRD and SEM-EDS results showed that phytic acid could hinder the formation of mineralized body (Metanatroautunite [Na(UO2)(PO4)·3H2O]) and prefer to form amorphous material. Further FTIR and XPS data illustrated that the bacteria mainly interacted with U(VI) through phosphorous functional groups. This study presents detailed information for colloid formation between phytic acid and U(VI) as well as the critical role of Ca2+ and Mg2+ ions on the matrix of S. putrefaciens bacteria, combining with molecular-level microscopic understanding on the chemical behavior of U(VI) in the presence of inorganic and organic ions in soil and water.