| Laboratory experiments and theoretical modeling studies were performed to investigate the mechanisms of Cr(Ⅵ) removal from deoxygenated simulated groundwater using nanoscale zero-valent iron,and to evaluate influencing factors and kinetics based on zeta potential,redox potential,ferrous concentrations,and the pe-pH diagram of Fe-Cr-H2O system. Experimental results demonstrate that the removal efficiency of Cr(Ⅵ) decreases with the increasing Cr(Ⅵ)/Fe mass ratio. When the Cr(Ⅵ)/Fe mass ratios are 0.025,0.050,0.075,and 0.100,the corresponding Cr(Ⅵ) removal rates are 100.0%,85.6%,72.7% and 39.6%,respectively. The Cr(Ⅵ) removal is favorable at acidic pH with fixed Cr(Ⅵ)/Fe mass ratio of 0.100. When pH are 3.0，5.0，7.0，9.0 and 11.0,the Cr(Ⅵ) removal rates are 73.4%，57.6%，39.6%，44.1%,and 41.2%,accordingly. The Cr(Ⅵ) removal follows the pseudo second-order kinetics. When pH is 7.0 and Cr(Ⅵ)/nZVI mass ratio is 0.025,the rate of Cr(Ⅵ) removal is the highest with rate constant at 9.76×10-3g·(mg·min)-1. The conversion from Cr2O2-7 to Cr3+ should be instantaneous when Cr2O2-7 is absorbed on the surface of Fe. The Cr(Ⅵ) was reduced to Cr(Ⅲ),which was subsequently incorporated into the FeOOH shell and formed a Cr-Fe film. The film once formed could further inhibit the electron transfer between Cr2O2-7 and Fe. Then Cr(V) removal was primary controlled by the adsorption process. |
