Evaluation of zeolite-supported microscale zero-valent iron as a potential adsorbent for Cd2+ and Pb2+ removal in permeable reactive barriers

Abstract

A new composite adsorbent, zeolite-supported microscale zero-valent iron (Z-mZVI) was evaluated as a potential adsorbent for the removal of Cd²⁺ and Pb²⁺ from aqueous solution using batch and column experiments. Adsorption isotherms were well fitted by Langmuir model, and the maximum adsorption capacity was 63.14 mg/g for Cd²⁺ and 154.61 mg/g for Pb²⁺, respectively. Both adsorption processes followed the pseudo-second-order model which indicated that the rate-limiting step for different initial concentration was dominated by chemical adsorption process. The coexistence of Cd²⁺ and Pb²⁺ caused the reduction of Cd²⁺ removal efficiency, but not for Pb²⁺. Z-mZVI has a high removal capacity for Cd²⁺ and Pb²⁺ over a wide pH range (3.0-6.8) as well as in the presence of competitive Ca²⁺ or Mg²⁺ ions (<2 mmol/L). Moreover, Z-mZVI shows a high immobilization capacity for the adsorbed Cd²⁺ and Pb²⁺ products, even at the acid solution (pH = 3.95). Column experiment confirmed that Z-mZVI could simultaneously remove Cd²⁺ and Pb²⁺ from solution efficiently. Thomas model can simulate the equilibrium adsorption capacity of Cd²⁺ and Pb²⁺ of the Z-mZVI column well. This study demonstrates that Z-mZVI is an efficient and promising reactive material in permeable reactive barriers for Cd²⁺ and Pb²⁺ removal from aqueous solution.

Keywords: Adsorption capacity; Heavy metal removal; Thomas model; Zeolite-supported microscale zero-valent iron (Z-mZVI).