Pb-Bearing Ferrihydrite Bioreduction and Secondary-Mineral Precipitation during Fe Redox Cycling

Abstract

The significant accumulation of Pb from anthropogenic activities threatens environmental ecosystems. In the environment, iron oxides are one of the main carriers of Pb. Thus, the redox cycling of iron oxides, which is due to biotic and abiotic pathways, and which leads to their dissolution or transformation, controls the fate of Pb. However, a knowledge gap exists on the bioreduction in Pb-bearing ferrihydrites, secondary-mineral precipitation, and Pb partitioning during the bioreduction/oxidation/bioreduction cycle. In this study, Pb-bearing ferrihydrite (Fh_Pb) with various Pb/(Fe+Pb) molar ratios (i.e., 0, 2, and 5%) were incubated with the iron-reducing bacterium Shewanella oneidensis MR-1 for 7 days, oxidized for 7 days (atmospheric O2), and bioreduced a second time for 7 days. Pb doping led to a drop in the rate and the extent of the reduction. Lepidocrocite (23–56%) and goethite (44–77%) formed during the first reduction period. Magnetite (72–84%) formed during the second reduction. The extremely-low-dissolved and bioavailable Pb concentrations were measured during the redox cycles, which indicates that the Pb significantly sorbed onto the minerals that were formed. Overall, this study highlights the influence of Pb and redox cycling on the bioreduction of Pb-bearing iron oxides, as well as on the nature of the secondary minerals that are formed.

The role of starch in nano-magnetite formation: A spectrometric and structural investigation

“…The value obtained for the starch free material (CP-R0) is lower than the theoretical value of the bulk magnetite (92 emu g -1 (Han et al, 1994)). Previous reports on Fe3O4 NP (Amir et al, 2016;Byrne et al, 2013;Daou et al, 2008Daou et al, , 2006Kotsikau et al, 2018;Meite et al, 2022bMeite et al, , 2022aZegeye et al, 2021) indicated that Ms decreases with particle size (see inset of Fig 6). Our results on CP-R0, as well as on OP-R0 (Ms = 89.1 emu g -1 for 67 nm particles), are fully consistent with the reported trend.…”