Behavior and Mechanisms of Simultaneous Removal of Pb(Ii), Cd(Ii) and As(Iii) by Magnetite-Modified Attapulgite

Abstract

The coexistence of lead (Pb(II)), cadmium (Cd(II)), and arsenic (As(III)) remains an ongoing environmental challenge. In this study, magnetite (MG) modified attapulgite (ATP) materials (ATP@MG) with varying MG/ATP mass ratios were synthesized via the co-precipitation. The MG particles was incorporated onto the ATP surface, and ATP@MG-0.5 (MG/ATP=0.5) revealed the best adsorption properties. The maximum adsorption capacities of Pb(II), Cd(II), and As(III) reaching up to 194.90, 47.58 and 41.73 mg/g, respectively. In mono-component system, the adsorption isotherm of Pb(II) and Cd(II) conformed to Redlich-Peterson models, while the As(III) was consistent with Freundlich models. The adsorption kinetics were in line with Elovich models. Furthermore, the strong acid condition (pH≤2) and Ca2+, PO43- could affect the adsorption capacity of ATP@MG-0.5. In the multiple system, significant mutual restrictions existed between Cd(II) and Pb(II). The affinity order of ATP@MG-0.5 for metal(loid)s was observed to be Pb(II)>As(III)>Cd(II). The characterization results explicated the related mechanisms, including electrostatic attraction, surface complexation, precipitation and redox.

Keywords: Attapulgite, Adsorption affinity, adsorption mechanism, Complex heavy metal(loid)s, Magnetite