Retention of Iodide by Bacteriogenic Iron Oxides

Abstract

This study was performed to determine the ability of wetland bacteriogenic iron oxides (BIOS) to immobilize iodide in contaminated groundwater systems near Chalk River, Canada. The sorption of iodide onto synthetic hydrous ferric oxide (HFO) and BIOS was investigated using an autotitrator and an I − ion-selective electrode to generate high-resolution anion sorption data over a pH range of 2.5 to 9. The effect of strontium sorption in the presence of I − was also investigated to determine its effect on iodide retention as it is also a common contaminant near Chalk River. Both HFO and BIOS correspond to 2-line ferrihydrite with surface areas of 227.7 m 2 g −1 and 92.52 m 2 g −1 , respectively. Sorption of I − was found to be pH dependent for both HFO and BIOS and was most strongly immobilized at pH 2.5. The pH at which 50% of the I − was bound to HFO occurred at pH 4.0, whereas BIOS maintained 50% sorption to pH 9. Field data also indicated a 54% decrease for iodine and 75% for 129 I in waters passing over in-situ BIOS at circumneutral pH. Iodide sorption to HFO is best explained by homogeneous functional groups, whereas sorption of I − to BIOS is best explained by heterogeneous functional groups, due to the presence of bacterial functional groups with pKa values that extend to 9.0. The presence of Sr 2+ decreased iodide sorption on HFO by 10-20%, but had no effect on BIOS due to its surface functional groups being reactive over the pH range investigated in this study. These results imply that BIOS is a useful sorbent for natural retention of I − from groundwater and that the amount of organic material present in iron oxides is an important factor when considering remediation strategies for radionuclides in groundwater.

A comparison of Fe(III) reduction rates between fresh and aged biogenic iron oxides (BIOS) by Shewanella putrefaciens CN32

“…Accordingly, surface area could be used as a predictor of the potential iron reduction rate whereby an increase in mineral surface area tends to promote the bacterial iron reduction and vice versa (Roden and Zachara, 1996;Roden, 2003). BET analysis determined a surface area of 80 ± 9 and 150 ± 30 m 2 /g for aged BIOS from sites CR-01 and CR-02, respectively, while the surface area of fresh BIOS was previously determined to be~90 m 2 /g (Kennedy et al, 2011). In contrast to BIOS, the surface area of synthetic ferrihydrite varies between 200 and 700 m 2 /g (Cornell and Schwertmann, 2003).…”

Hydrodynamic Shear-Induced Densification of Bacteriogenic Iron Oxides: Mechanisms and Implications

“…Final suspension volumes tended to decrease at the end of each settling trial with concomitant increases in the aggregate solids volume fractions φ agg , which relates V BIOS (constant across cycles) to V ∞ , and decreases in the swelling ratio Q. Both trends are expected based on each parameter's relationship to V ∞ by Equations (11) and (12). The highest change in modelled V agg estimates between cycles was observed in sample OC-01, when an exposure time of 60 s to shaking at 2.69 s -1 led to a total decrease in suspension volume of 22.7 mL (58% of the total sample volume), from V ∞(A) = 30.1 mL to V ∞(B) = 7.83 mL.…”

“…These bacterial-mineral aggregates function as focal points for interactions between the geosphere and biosphere and have been the subject of ongoing research, especially those formed in conjunction with iron oxyhydroxides; these appear in the literature variously as bacteriogenic iron oxides (BIOS) [3,4], cell-Fe(III) mineral aggregates [5], Fe cell-mineral aggregates [6,7], Fe flocs [8], and ferrihydrite-bacteria composites [2]. While diverse in name, these materials all possess the same geochemically significant characteristics: wide distribution in soils, sediments, and surface and subsurface aqueous systems [9,10]; unique surface reactivity properties and high sorbent affinity for various compounds including trace contaminants [11,12]; a tendency to accumulate into large-scale flocculent microbial mats and biofilms associated with physical and chemical gradients, such as light and nutrient fluxes [13,14]; and an internal organic-mineral fibrillar architecture that mirrors the highly porous, hydrated meshwork structure of hydrogels [5,15,16].…”

Iodine in major Danish aquifers

“…Mobility of Iand IO 3 is concentration dependent: At ambient concentrations, inorganic iodine is immobilized due to covalent bonding with natural organic matter (Zhang et al 2011). At neutral pH, the retention of iodine is low because of the negative charges of the sediments (Kennedy et al 2011). Thus, generation of high-iodine groundwater is promoted by alkaline conditions, which are enhancing the desorption of iodine from clay minerals and iron oxyhydroxides (Li et al 2013).…”

“…Thus, generation of high-iodine groundwater is promoted by alkaline conditions, which are enhancing the desorption of iodine from clay minerals and iron oxyhydroxides (Li et al 2013). However, sorption experiment shows that if a bacteriogenic iron oxides (ferrihydrite precipitates and bacterial structures) are present, Isorption of about 50% is maintained over the pH range of natural waters (Kennedy et al 2011). Reducing conditions are also favorable for iodine enrichment in groundwater (Li et al 2013).…”