Speciation-Dependent Kinetics of Uranium(VI) Bioreduction

pH‐dependent speciation and hydrogen (H2) control U(VI) respiration by Desulfovibrio vulgaris

“…Cytochrome c3 has a mid-point redox potential near −300 mV versus SHE (standard hydrogen electrode) at 25°C (Niki et al, 1984), while the U(VI)-U(IV) couple has a mid-point potential of +334 mV versus SHE of dissolved inorganic carbon (DIC) and with a wide range of pH is of paramount importance for understanding microbial reduction of U(VI), since different U(VI) species could have different susceptibilities of being reduced based on their bioavailability. A decrease in U(VI) reduction rate with increasing DIC concentration, along with sensitivity towards pH, has been well documented in the literature (Belli et al, 2015;Bernhard, Geipel, Brendler, & Nitsche, 1998;Brooks et al, 2003;Croteau, Fuller, Cain, Campbell, & Aiken, 2016;Drobot et al, 2015;Guillauont et al, 2003;Jones et al, 2015;Sheng & Fein, 2014;Ulrich et al, 2011).…”

“…Carbonate is a key ligand in natural environments, and it influences the speciation of uranium (Clark, Hobart, & Neu, 1995;Langmuir, 1978;Stumm & Morgan, 1996), along with being an important pH buffer. Although U(VI) speciation and bioavailability of U(VI) in its different complexes have been studied for decades in isolation (Belli, DiChristina, Cappellen, & Taillefert, 2015;Brooks et al, 2003;Murphy & Shock, 1999;Stewart, Amos, Nico, & Fendorf, 2011;Sheng & Fein, 2014;Ulrich, Veeramani, Latmani, & Giammar, 2011), the connections between aqueous uranyl speciation, and electron partitioning between respiration & fermentation during U(VI) bioreduction were seldom studied. In sulfate-reducing conditions, the availability of the electron acceptor affects how electrons from the electron donor (lactate in our case) are distributed among fermentation and respiration end products.…”

Uranium Bioreduction and Biomineralization

“…For example, U(VI) reduction was fastest for U(VI) hydroxide and U(VI) organic complexes, 24 times faster than the reduction of U(VI)-carbonate complexes, and 735 times faster than the reduction of CaU(VI)-carbonate complexes (Ulrich et al, 2011). More U(VI) 14 reduction was achieved in the presence of bicarbonate, which facilitates HUP dissolution, while less bioreduction was observed with phosphate (Rui et al, 2013).…”

“…Aluminum oxides are less likely to be involved in the removal of uranium at pH values greater than 4.0 in the presence of iron oxides (Zheng et al, 2003). In contrast, U(VI) reduction rates increased with increasing dissolved inorganic carbon (DIC) and Ca 2+ concentration (Ulrich et al, 2011). Humic substances such as humic acids and fulvic acids have been demonstrated to be beneficial for U(VI) reduction.…”

“…At higher pH, redox potential becomes more negative resulting in slower U(VI) reduction. For example, a relatively minor change in pH from 6.3 to 6.8 could significantly slow down the rate of microbial U(VI) reduction, with the lowest rate being found at pH 8 (Ulrich et al, 2011). Brooks et al (2003) concluded that the redox potential is the main factor responsible for the slow reduction of CaU(VI)-carbonate complexes.…”