Arsenic speciation, oxidation and immobilization in an unsaturated soil in the presence of green synthesized iron oxide nanoparticles and humic acid

• Published in: Chemosphere (Oxford) Vol. 311; p. 137198
• Main Authors: Guo, Shurui, Jiang, Mingqin, Lin, Jiajiang, Khan, Nasreen Islam, Owens, Gary, Chen, Zuliang
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-01-2023
• Subjects: Arsenic; Humic acid; Iron oxide nanoparticles; Oxidation; Speciation; Oxidation; Arsenic; Iron oxide nanoparticles; Humic acid; Speciation
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.137198

While the availability of arsenic (As) in soil is well known to be highly correlated with the presence of iron (Fe) oxides and humic acid (HA) in the soil, the relationship between Fe oxides and HA and As species in the soil is less well understood. In this study, As speciation in an unsaturated soil in the presence of external HA and green synthesized Fe oxide nanoparticles (FeNPs) showed that As(V) was mainly distributed to the specifically-bound (F2), amorphous and poorly-crystalline hydrous oxides of Fe, Al (F3) and the well-crystallized hydrous oxides of Fe and Al (F4). While As(III). This was the major component in unsaturated soil, and was mainly distributed to F4 and the residual fraction (F5). As bound to F3 and F5 was most sensitive to the addition of HA and FeNPs, while HA/FeNPs treatment increased the F3-bound As(V); however, it decreased the F5-bound As(III). Nonetheless the effect of HA on As is completely different to the HA/FeNPs treatment. The increase of As(V) in F3 resulted from F5-bound As(III) oxidation when treated by HA/FeNPs. Cyclic voltammetry confirmed that HA and Fe3+/Fe2+ redox enhanced As(III) oxidation, while FTIR revealed that HA-bound As(III) was the least available fraction in the soil. Finally, a mechanism involving a combination of HA and FeNPs was proposed for explaining the redistribution of As species in the soil.
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•Co-influence of Fe and HA on As in soil was observed.•The As distribution in soil depended greatly on its species.•Adding FeNPs and HA impacted As species by redox reactions.•The redistribution of As species in soil was proposed.