The surface reaction between zero-valent iron and Cr(Ⅵ)makes the utilization rate of Fe0-permeable reactive barrier(PRB)very low.In order to resolve this problem

sodium alginate(SA)was used to coat cast iron(SAC)and copper-iron bimetallic particles(SAB)

and they were tested in treating chromium-polluted groundwater.The results show that SAB is the best.Adsorption capacity of SA to Cr(Ⅵ)is small

chemisorptions of copper-iron bimetallic particles in SAB plays main role.As indicated by FEI and XPS

pore structures were created by cross-linking of SA with Ca2+

which not only provided a lot of attaching points for bimetallic particles

but also diffusion path for Cr(Ⅵ)to enter interior of copper-iron bimetallic particles.The results of XPS also indicate that variation of copper valence was used for transfer of electrons from reaction of Cr(Ⅵ)by Fe0 and the role of copper is as if a catalyst.Under neutral condition

the removal process of Cr(Ⅵ)by SAB follows the pseudo first-order kinetics.The rate constant k increase with increasing copper loading(for SAB)and copper-iron bimetal amount(for SAB2)

and decrease with Cr(Ⅵ)concentration(for SAB2).The rate constant is higher and removal capacity greater for SAB than for cast iron powder.Using SAB as the PRB is feasible for remediation of chromium contaminated groundwater.