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

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.