The Effect Of Humic Acids On Zero Value Iron(ZVI) Reduction Of Cr(VI) In Contamintated Water

Enter the 21 centuries, along with the increase of the population and the fastdevelopment of the national economy, our country faces the crisis of water amountand water quality, the water quality crisis is more serious in the meantime. Regardlessthe surface water or the groundwater, pollution of the water quality in our countrypollutes is very serious. Hexvalent chromium is extensively applied in leather, drygoods production, printing and dyeing, dye, chromeplate industry, is a commoncontamination.Zero-valent Iron (Fe⁰, Zâ…¥), for its low cost, high reduction potential, and fastchemical reaction rate, has become one of the most effective reactive materials forin-situ remediation of groundwater. But groudwater may contain many substances,such as humic acid and hardness ions, will have effect to the application of hexvalentchromium removal by Fe⁰. In the present paper, the effect of humic acid or calcium,magnesium to the removal efficiency of hexvalent chromium (Cr(â…¥)) by iron fillingsor iron nanoparticles is researched.This paper investigated the major influence factors to the removal of hexvalentchromium by Fe⁰, kinetics of hexvalent chromium reduction by Fe⁰ was alsoestablished in the presence of humic acid. The adsorption of humic acid on thesurface of Fe⁰ was analyzed, mechanism of the inhibition of humic acid to thechromium removal by Fe⁰ was also discussed. We also carried out the effect ofhardness irons to the chromium removal by Fe⁰. Results indicate:1. Because the reaction of chromium removal by Fe⁰ is a surface reaction, so thesmaller the Fe⁰ particles, the higher the surface area, the faster the reaction rate.2. Humic acid has some effects to the chromium removal by Fe⁰, as the humicacid concentration increased, the remove rate was decreased, but was very close toeach other in a certain range, and probabily HA is acting as an electron mediator toenhance the reaction. When the HA concentration increased to 80mg/L, inhibition isobvious relatively. Kinetics analysis indicated that the chromium removal reaction is apseudo-first-order reaction in the presence of humic acid. The reaction rate constantk_obs increases with the decrease of initial pH and the increasing temperature.3. Because of the large surface area, the Cr(â…¥) reduction rate by Fe⁰nanoparticles was faster. Inhibition was more obvious when Cr(â…¥) was reducted byFe nanoparticles, and with the larger HA concentration, the larger inhibition. 4. Starch-stabilized Fe⁰ nanoparticles conduce to keep the disperse of Fe⁰nanoparticles, so appropriate starch adding will accelerate the removal rate by Fe⁰nanoparticles and eliminate the inhibition effect by humic acid.5. Through the adsorption experiment and TEM analyse, we know the inhibitioneffect of Cr(â…¥) removal rate by Fe⁰ nanoparticles by humic acid is because of theadsorption on Fe⁰ surface sites. Because of the large surface area, the adsorptionamount is 6.6 times to the iron fillings.6. We also discussed the effect of other ions in actual groundwater(calcium,magnesium and carbonate ) to the Cr(â…¥) removal rate by Fe⁰ elementary. Ca²⁺, Mg²⁺will accelerate the reaction, Ca²⁺ and HCO₃^- made the Cr(â…¥) removal efficiency drop16.5% when they exist at one time.