Evaluation of zeolite-supported microscale zero-valent iron as a potential adsorbent for Cd and Pb 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 Cd and Pb 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 Cd and 154.61 mg/g for Pb, 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 Cd and Pb caused the reduction of Cd removal efficiency, but not for Pb. Z-mZVI has a high removal capacity for Cd and Pb over a wide pH range (3.0-6.8) as well as in the presence of competitive Ca or Mg ions (<2 mmol/L). Moreover, Z-mZVI shows a high immobilization capacity for the adsorbed Cd and Pb products, even at the acid solution (pH = 3.95). Column experiment confirmed that Z-mZVI could simultaneously remove Cd and Pb from solution efficiently. Thomas model can simulate the equilibrium adsorption capacity of Cd and Pb of the Z-mZVI column well. This study demonstrates that Z-mZVI is an efficient and promising reactive material in permeable reactive barriers for Cd and Pb removal from aqueous solution.