Processes Driven by Iron Reducing Bacteria on Technetium Immobilization

In this work, we have studied the influence of Desulfitobacterium sp. G1-2 on Tc mobility. It is a novel isolate extracted from FEBEX bentonite. The Desulfitobacterium genus utilizes different forms of ferric iron (e.g. Fe^IIICl₂, Fe^III citrate) as electron acceptor for the external electron transfer of the anaerobic respiratory chain. In the first step, Desulfitobacterium sp. G1-2 was grown in a liquid medium in presence of Fe^III citrate. The bacterial growth was followed by cell counting, and the consumption of Fe^III and production of Fe^II was analyzed by ferrozine assay. During the growth of the bacteria, the formation of a white precipitate was observed. Raman microscopy and X-ray diffraction confirmed the identity of the precipitate as vivianite (Fe^II₃(PO₄)₂.8H₂O). In the second step, the biogenic vivianite was extracted and isolated, to study its interaction with Tc as a function of time, pH, ionic strength, and Tc concentration. Sorption experiments were performed to study the yield of Tc retention by biogenic vivianite. In addition, microscopic and spectroscopic methods (Raman microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy) were used to determine the molecular environment of Tc in the solid. It was shown that Tc immobilization by biogenic vivianite is due to the reduction of Tc^VII to Tc^IV and it is dependent on time, and pH. The Tc activity in solution decreased with more basic environments, reaching the lowest value at pH 11. It was also observed, that at pHeq ≅ 8.5, Tc removal from the aqueous phase in presence of biogenic vivianite reached 94% after seven days of interaction