Effects of chloride ion on hexavalent chromium removal by scrap iron

Abstract：Iron permeable reactive barriers are an effective remediation of groundwater contaminated with hexavalent chromium.In the process of groundwater treatment, effect of coexist chloride ion on performance of the granular iron media is a main factor for the long-term performance.In the study, batch tests, column experiments and corrosion potential measurement were done to determine the effect of chloride ion on hexavalent chromium reduction by granular iron.When chloride ion concentrations ranging from 0 to 500 mg/L, the surface area normalized rate coefficients (kSA) increased from 7.76 10-4Lmin-1m-2 to 8.68×10-4Lmin-1m-2, 8.35×10-4Lmin-1m-2 and 1.38×10-3Lmin-1m-2.The half-lives decreased from 8min to 4.53min.With enhancement being unconspicuous when chloride ion concentration was lower than 300 mg/L, the increase in iron reactivity was strong when chloride ion concentration was higher than 500 mg/L.Results from column experiments show that the presence of 1 000 mg/L chloride ion decrease iron corrosion potential and promote removal of the passivating oxide layer and pitting corrosion of the iron, which can sustain and increase granular iron reactivity.When chloride iron concentrarion was higher than 300 mg/L, enhancement on iron reactivity and depletion of iron material should be taken into account in iron PRB design for chromate contaminated groundwater.

Keyword：chloride ion;hexavalent chromium;scrap iron;