Enhanced arsenite immobilization via ternary layered double hydroxides and application to paddy soil remediation

Abstract

A ternary CaMgFe-LDH was developed for the immobilization of aqueous arsenic from capillary water in paddy soils, with an outstanding removal performance for aqueous arsenite (As(III)). In an As(III) solution, the ternary LDH achieved a removal capacity for arsenite of approximately 16 mg g⁻¹ after 5 h, with a low equilibrium concentration of As(III) (0.048 mg L⁻¹). The As(III) removal capacity of LDH was studied with the different Ca/Mg molar ratios in LDH, which demonstrated that ternary LDHs with a higher Ca content can remove As(III) more effectively and rapidly. Accordingly, the ternary LDH material was used in the immobilization of total arsenic from a paddy soil system, achieving a removal efficiency for As(III) of 47% and a total As concentration of 346 μg L⁻¹ in capillary water after 40 days. Compared to that of the binary Mg–Fe LDH, the As removal performance of the ternary LDH was higher, which was attributed to the As precipitation with Ca in the first 20 days during the experiment. This, along with the efficient adsorption of As on the residual Mg–Fe-LDH framework, was responsible for the low concentration of As. Therefore, our study proposes a promising approach to the remediation of arsenic-contaminated paddy soils.