Study of the Interaction of Eu 3+ with Microbiologically Induced Calcium Carbonate Precipitates using TRLFS

The microbial induced biomineralization of calcium carbonate using the ureolytic bacterium Sporosarcina pasteurii in the presence of trivalent europium, a substitute for trivalent actinides, was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and a variety of physicochemical techniques. Results showed that the bacterial-driven hydrolysis of urea provides favorable conditions for CaCO precipitation and Eu uptake due to subsequent increases in NH and pH in the local environment. Precipitate morphologies were characteristic of biogenically formed CaCO and consistent with the respective mineral phase compositions. The formation of vaterite with some calcite was observed after 1 day, calcite with some vaterite after 1 week, and pure calcite after 2 weeks. The presence of organic material associated with the mineral was also identified and quantified. TRLFS was used to track the interaction and speciation of Eu as a molecular probe with the mineral as a function of time. Initially, Eu is incorporated into the vaterite phase, while during CaCO phase transformation Eu speciation changes resulting in several species incorporated in the calcite phase either substituting at the Ca site or in a previously unidentified, low-symmetry site. Comparison of the biogenic precipitates to an abiotic sample shows mineral origin can affect Eu speciation within the mineral.