Effects of Calcium on Arsenate Adsorption and Arsenate/Iron Bioreduction of Ferrihydrite in Stimulated Groundwater

Abstract

The reduction and transformation of arsenic-bearing ferrihydrite by arsenate-iron reducing bacteria is one of the main sources of arsenic enrichment in groundwater. During this process the coexistence cations may have a considerable effect. However, the ionic radius of calcium is larger than that of iron and shows a low affinity for ferrihydrite, and the effect of coexisting calcium on the migration and release of arsenic in arsenic-bearing ferrihydrite remains unclear. This study mainly explored the influence of adsorbed Ca2+ on strain JH012-1-mediated migration and release of arsenate in a simulated groundwater environment, in which 3 mM ferrihydrite and pH 7.5. Ca2+ were pre-absorbed on As(V)-containing ferrihydrite with a As:Fe ratio of 0.2. Solid samples were analyzed by X-ray diffraction (XRD), scanning electron microscopic (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results show that calcium and arsenate can synergistically adsorb on ferrihydrite due to the electrostatic interactions, and the adsorbed Ca2+ mainly exists on the surface through the outer-sphere complex. Adsorbed Ca2+ entering the stimulated groundwater was easily disturbed and led to an extra release of 3.5 mg/L arsenic in the early stage. Moreover, adsorbed Ca2+ inhibited biogenic ferrous ions from accumulating on ferrihydrite. As a result, only 12.30% Fe(II) existed in the solid phase, whereas 29.35% existed without Ca2+ adsorption. Thus, the generation of parasymplesite was inhibited, which is not conducive to the immobilization of arsenic in groundwater.

Polycaprolactone-Modified Biochar Supported Nanoscale Zero-Valent Iron Coupling with Shewanella putrefaciens CN32 for 1,1,1-Trichloroethane Removal from Simulated Groundwater: Synthesis, Optimization, and Mechanism

“…A certain amount of nZVI@PBC was added into a 100-mL serum bottle in a glove box filled with N 2 . Then, 78.4 mL of simulated groundwater with a certain concentration of 1,1,1-TCA (the preparation method was described previously [ 44 ] and 1.6 mL of bacterial suspension (OD600 = 1.0) were added. Subsequently, the bottles were capped with rubber stoppers and sealed with aluminium crimps.…”

<i>In-situ</i> Stability and Remediation of Typical Antimony (Sb) Tailings by Combined Solid Waste in Southwest China

“…Compared with treatment groups 2 and 4, the contents of weak acid extraction state As and Sb in treatment groups 3 and 5 decreases in Qing Long, indicating that the stabilization effects of As and Sb were improved by drying sludge and rice husk ash. This is because organic matter contain large numbers of adsorption sites and functional groups such as hydroxyl, carboxyl and aromatic groups, which can be coordinated with heavy metals [37,38] to control and influence the occurrence state of heavy metals. Compared with treatment group 1, the weak acid extraction state As content in Qing Long at treatment group 2 increases slightly, which may be related to the As content in the dry sludge.…”

“…In treatment groups 1, 2 and 4, it is found that the content of weak acid extraction state As in Qing Long increased. This may be caused by the precipitation of Fe(II) and the inhibition of the formation of ferrous arsenate minerals [38]. The interaction of As, Sb and iron oxides reduced the mobility of Sb and increased the mobility of As in soil to a small extent [29].…”

Could the presence of ferrihydrite identified in a riverbed impacted by mining leachates be linked to the reduction in the Heavy Metals Contamination Index?

“…Ferrihydrite formation occurs through oxidereduction reactions mediated by various microorganisms (Thomas Arrigo et al, 2019;Scheinost et al, 2001), or by the hydroxylation of Fe (Schulz et al, 2022). Moreover, it is considered a metastable mineral, as it can spontaneously transform into crystalline iron oxides, thereby influencing the adsorption/desorption processes of PTEs (Chen et al, 2022;Shi et al, 2021;Scheinost et al, 2001). These characteristics render ferrihydrite one of the most promising absorbents across different environmental matrices, given its high efficiency in capturing elements such as As (18.38 mg/g), Cr (41.47 mg/g), Pb (34.32 mg/g), Cd (18.18 mg/g), and Cu (14.39 mg/g) (Mao et al, 2022;Tian et al, 2022;Zhang et al, 2022;Meng et al, 2019;Meng et al, 2014), alongside its widespread occurrence in natural environments.…”