Studies On The Process And The Mechanism Of As(Ⅲ) Removal From Water By Zero-valent Iron

High levels of arsenic is naturally present in groundwater around the world. At the same time, Arsenic pollution of groundwater caused by some industrial producing processes happened frequently. Therefore, the new effective technology urgently need to control and remedy arsenic pollution. Fe0-Permeable Reactive Barriar (Fe0-PRB) is regarded as one of the most potential tecnolgy for asenic removal. But, the present reports were rarely studied on the effect of reaction and operational conditions on As(Ⅲ) removal from water by zero-valent iron systemically. And the results had more differences because of heaving no compare on the reactivity of materials. Moreover, the loss in activity of Fe0 was the main existing problem of traditional Fe0-PRB. Based on these problems, this paper investigated the reaction rate, influencing factors, the mechanism of reaction, improving measures. The results obtained were as follows:1.Higher shaking speed. smaller particle size, lower solution pH, air atmosphere and higher concentration of electrolytes of Cl- could significantly promote the removal of As(Ⅲ). The rate constant of As(Ⅲ) removal on Fe0 is 0.0921 L·m-2·h-1 and the density dependent is kSA= 0.0921ρa+0.0001.2. The reactivity and mechanism of As(Ⅲ) removal on Fe0 was conducted by testing iron dissolution rate in system of EDTA/Fe0/H2O(EDTA-Fe), scanning of TAFEL, and Electrochemical Impedance (EIS). The results are as follows:1). The forced corrosion rate in As(Ⅲ) removal on Fe0 could be characterised by EDTA-Fe; The corrosion time eigenvalue-τEDTA had high correlation with the time of As(Ⅲ) removal; R2 being higher than 0.98;2).The intrinsic rate of corrosion in As(Ⅲ) removal on Fe0 could be characterised by TAFEL; The corrosion currents in different reaction or operational conditions were significantly correlated with As(Ⅲ) removal efficiency. 3). The EIS spectroscopy fitting results showed electron transfer resistance (Rct) on Fe0 in As(Ⅲ) removal; At the same initial As(Ⅲ) concentration, the Rct in nitrogen environment was higher than it in air environment, which showed that the film in nitrogen environment was much compacter and has more mass transfer resistance than it in air environment; Under the same air conditions, the Rct increased with the initial As(Ⅲ) concentration, which mains corrosion restrained effect occurd on As(Ⅲ) removal.3. The results showed that active carbon with diferent species or ratios had no obvious effect on As(Ⅲ) removal; Fe0/manganese mineral with high rotate speed had slightly higher effect on As(Ⅲ) removal than Fe0 only. Compared of the long-term dynamic tests in Fe0, Fe0/AC, and Fe0/manganese mineral, the effect ranking is Fe0/manganese mineral> Fe0/AC> Fe0. The performance of Fe0 and Fe0/AC were greatly influenced by the quickly corrosion in long-term dynamic tests.