Arsenic Sorption onto Soils Enriched in Mn and Fe Minerals

Abstract

The As sorption capacity of a natural Mn and Fe mineral-containing sample from the Iron Quadrangle province, Brazil, was investigated. A detailed mineralogical identification was obtained by combining X-ray diffraction analyses (with Rietveld refinement), X-ray fluorescence spectroscopy, optical microscopy, and scanning electron microscopy coupled with X-ray energy dispersive spectrometry-EDS. The oxidation state of the adsorbed As species was determined by X-ray absorption near edge structure spectroscopy. The results demonstrate that the presence of naturally occurring Mn oxides promotes the effective oxidation of As (III) to As(V). Also, the Mn minerals show a significant uptake of both the trivalent and pentavalent As species. This study demonstrates that the combined influences of As(III) depletion by oxidation and adsorption on a natural oxide sample consisting of Mn minerals and Fe oxides may effectively contribute to the reduction the As concentration in waters.

Arsenate uptake and arsenite simultaneous sorption and oxidation by Fe–Mn binary oxides: Influence of Mn/Fe ratio, pH, Ca2+, and humic acid

“…Deschamps and coworkers have observed that Mn and Fe enriched minerals could oxidize arsenite to arsenate and reacted better in arsenite uptake than that of arsenate [4,19]. In our previous studies [20,21], we encountered similar phenomena when a synthetic Fe-Mn binary oxide was used to adsorb both arsenate and arsenite from water.…”

“…The presence of arsenic at elevated concentrations in natural environments (soils, sediments, and waters) is attributable to both natural processes and anthropogenic activities [3]. The toxicity, mobility, and bioavailability of arsenic are highly dependent on its oxidation state and chemical speciation [4]. In natural environments, arsenic is primarily present in inorganic forms and exists in two predominant species, arsenate [As(V)] and arsenite [As(III)].…”

“…Previous studies on As sorption onto samples containing both Fe and Mn oxides are relatively few [4,[19][20][21] and limited to one natural sample or a synthetic Fe-Mn binary oxide with a fixed Fe/Mn ratio. It is known that the ratios of Mn/Fe in Fe-Mn binary oxides vary largely in natural environments [22], and Fe-Mn binary oxides with different Mn/Fe ratios may differ greatly in arsenic uptake.…”

Arsenic and Mercury mobility in brazilian sediments from the São Francisco River Basin

“…Recent data show that As mobility is reduced by high iron concentration. [32][33][34] Therefore, it can be presumed that the highest As concentrations obtained correspond to low mobility due to the iron oxide concentration in the soil.Mercury forms less labile compounds with iron oxides and mainly with sulfur. Hg and sulfur are soft ligands and can form inner-sphere compounds.…”

Characterization and Neutralization of Arsenical-Based WWII Era Chemical Munition Fills

“…The arsenate concentrations suggest mineralization rates of up to 10% (1:50 loading, 100 'C, 6-hr reaction), but these might be underestimates due to sorption of arsenate on the solids (MnO 2 and iron oxides) generated during the reaction. 93 These analyses were performed on filtered neutralent, without a caustic extraction as performed in later analyses (Section 3.7.3). The decrease in soluble arsenate during the 1:25 loading experiment conducted at 100 'C is, most likely, due to the enhanced formation of MnO 2 observed to take place during this experiment.…”