Effect Of Humic Acid And Nitrate On Chromium(Ⅵ) Removel By Iron In Groundwater

Our country has serious Cr(Ⅵ) pollution of groundwater in many regions.Cr(Ⅵ) is teratogenic, carcinogenic, mutagenic and hazardous to human health. Humic acid(HA) and NO3- exist in groundwater widely and have effect to the restoration of polluted groundwater. But less research foccus on the effect of HA and NO3- to the removal of Cr(Ⅵ) by iron permeable reactive barrier(PRB) and the mechanism is undefined. Therefore, this paper use batch experiments and column experiments to study the effect of HA and NO3- on the removal of Cr(Ⅵ) by iron. The main results are as follows:Study on the effect of HA indicated that:Because of the redox reaction of scrap iron remove Cr (Ⅵ) happened on the surface of the iron filings, the more scrap iron, the greater concentration of surface area is and beneficial to the reaction. When the concentration of HA was 10mg/L, iron filings was 20g/L and Cr(Ⅵ) was 10mg/L HA promote the reduction of Cr(Ⅵ) observably. As the HA concentration increased from 10mg/L to 98mg/L the removal rate was increased. The process of iron filings removed Cr (VI) matched pseudo first order kinetics when HA existed. Reaction rate was reduced with the increased of pH. Adsorption experiments of HA on the the iron filings and scanning electron microscope indicated HA and Cr (Ⅵ) formed a relatively larger HA-Cr (Ⅵ) complex which is more likely to be adsorbed onto the surface of iron and promote the reaction.Study on the effect of NO3- indicated that:Batch experiments indicated that when the concentration of NO3-N was 50mg/L, iron filings was 20g/L and Cr(Ⅵ) was 10mg/L NO3- promoted the removal of Cr (Ⅵ) by iron. The process of iron filings removed Cr (Ⅵ) matched pseudo first order kinetics when HA existed.Column experiments showed that the existence of NO3- enhanced the capability of iron column remove Cr(Ⅵ). The effect of NO3- to the removal of Cr(Ⅵ) by iron divided into three stages. In the first stage, NO3- competed the reaction sites and inhibited the Cr(VI) reduction slightly. The reduction of Cr(VI) in the column matched the pseudo first order kinetics. In the second stage, NO3- caused the integral synchronous passivation and produced Fe3O4 so as to enhence the ability of iron filings remove Cr(VI). In the third stage, the column produced nitrobacteria and passivated thoroughly.