Sulfur-doped Fe–Cu–La trimetallic oxides as a novel magnetic adsorbent for efficient removal of As(iii) and As(v) from aqueous solution

Abstract

Sulfur-doped Fe–Cu–La trimetallic oxides (S-FeCuLaO) were synthesized by a coprecipitation method and applied as a novel magnetic adsorbent for the removal of As(III) and As(V) in water. Batch experimental results demonstrated that the material exhibited excellent adsorption properties for both As(III) and As(V) in a wide pH range and the maximum adsorption capacities of S-FeCuLaO at initial pH 6.0 were 181 mg g⁻¹ for As(III) and 250 mg g⁻¹ for As(V), respectively. Both As(III) and As(V) (10 mg L⁻¹) were completely removed by the regenerated adsorbent after the third cycle. Furthermore, the residual As(III) concentration in well water containing 1 mg L⁻¹ As(III) decreased to below 10 μg L⁻¹ after adsorption for 8 h. The adsorption process complied with the Langmuir isothermal model and the pseudo-second-order kinetic model. Among the five coexisting ions investigated (Cl⁻, NO₃⁻, SO₄²⁻, CO₃²⁻ and PO₄³⁻), only PO₄³⁻ could significantly inhibit the adsorption of As(III) and As(V) by competing for active adsorption sites. The removal mechanism of arsenic was proposed as (1) the oxidization of As(III) to As(V) by superoxide radicals (O₂˙⁻) produced between Cu(I) and the dissolved O₂ and (2) the adsorption of As(V) through electrostatic attraction and the further formation of inner-sphere complexes via ligand exchange. Thus, S-FeCuLaO could be used as an attractive material for arsenic removal from wastewater and groundwater.