Abstract

A study was carried out to evaluate how the adsorption process of arsenate on hematite is influenced by the presence of thiosulfate ion. The competition in sorption between the two anions was examined in relation to potential use of thiosulfate as an additive for phytoextraction in arsenic contaminated soils. Results obtained from sorption isotherms can be described according to the Langmuir equation which allows, by comparing adsorption maxima, a quantitative evaluation of the effect of increasing concentration of thiosulfate on arsenate adsorption. Due to the competition between the two anions for available sites on hematite, arsenic sorption decreased at increasing thiosulfate concentration. The negligible effect of ionic strength on the sorption process, strongly suggests that thiosulfate can substitute arsenate ions in the inner sphere complexes on the surface of hematite. The interpretation of the As adsorption process on hematite in terms of distribution coefficient (K_d) shows that thiosulfate ions competing for sorption on the same surface may significantly reduce the arsenate adsorption and enhance the release of arsenic in the liquid phase of soil. Results have a direct influence on the applicability of phytoextraction in arsenic contaminated soils since plants can uptake arsenic only from the liquid phase. The obtained results can explain the increase in As concentration in plants, reported in a recent paper in which the addition of thiosulfate was shown to promote As phytoavailability.

Keywords:

Anion adsorption, arsenic bioavailability, distribution coefficient, ion oxides, Langmuir equation, phytoremediation,

References

Competing interests

The authors have no competing interests.

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