Effects And Mechanisms For Fe/Ti Modification Of Activated Carbon And Its Arsenic Removal From Water

Arsenic is a priority pollutant to be controlled in China. With the development of socio-economy and industry, many countries around the world are facing serious arsenic contamination. Investigating the remediation technology for removing arsenic from groundwater and its mechanism is of great significance in protecting ecological environment, enhancing the people’s health standard and constructing a harmonious society. The aim of this project is to establish fast, convenient, economical, efficient and safe technologies which use modified activated carbon as the main material to remove arsenic from water. Different kinds of activated carbon and modification reagents were selected and studied to prepare a kind of metals or metal oxides doped activated carbon which removed arsenic from water effectively. On this foundation, modern instruments including automatic specific surface and microporous analyzer, X-ray fluorescence ectrometer, scanning electron microscope, fourier transform infrared spectrometer, and X-ray diffractometer were used to characterize the metals or metal oxides doped activated carbon in effects and mechanisms in removing arsenic from water. At last, the modified activated carbon was filled in adsorption column to carry out small laboratory experiments and in situ pilot experiments to confirm the practical effects. The main results were as follows:1. Fe/Ti doped activated carbon improved the effects of arsenic removal efficiently. Modification of10-30mesh coal grain activated carbon with solution of0.025mol/L FeSO4and0.20mol/L TiCl4achieved the greatest percentages of arsenic removing. Experiments showed that the arsenic removal percentage in solution of arsenic200μg/L in1.5h by10g/L Fe/Ti doped activated carbon was about90%, which was70%higher than the non-modified activated carbon. In normal water quality conditions, arsenic will not be desorbed from the Fe/Ti doped activated carbon.2. Modern instruments were used to characterize Fe/Ti doped activated carbon, and the results showed that modified activated carbon exhibited the higher contents of titanium and iron, the smoother microporous surface structure, the finer average bore diameter, and the larger specific surface area. Because of introducing titanium and iron to the activated carbon, there were new Fe-O and Ti-O bonds formed around the modified carbon. XRD analysis indicated that Fe/Ti doped activated carbon were noncrystalline, and no new crystal was formed.3.The influcing factors including temperature, pH value, adsorption time, accompanying ions (K+, Mg2+, Ca2+, Cl-, SO42-, NO3-, Fe3+, SiO32-, H2PO4-) were investigated in arsenic removing from water by Fe/Ti doped activated carbon. The results showed that the arsenic removing from water by Fe/Ti doped activated carbon were not affected at temperature of10℃to40℃, the pH value of4to10. Althrough accompanying ions of K+, Mg2+, Ca2+, Cl-, SO42, NO3-had no effects on the percentages of arsenic removing, the accompanying ions of Fe3+, SiO32-and H2PO4-restrained significantly the arsenic removing of modified activated carbon. Freundlich and Langmuir equations well fit the As(V) and As(III) adsorption behavior of Fe/Ti doped activated carbon. The maxium adsorption amount of As(V) and As(III) was calculated from Langmuir adsorption isotherm equation were2.542mg/g and2.285mg/g respectively. The optimium condition for arsenic adsorption by Fe/Ti doped activated carbon in solution of arsenic200μg/L and addition of10g/L were natural light, pH value7, the adsorption time of1.5h, and the temperature is25℃, as well as without the accompanying ions of Fe3+SiO32-and H2PO4-.4. Studying on the mechanisms showed that the arsenic absorption was mainly the specific adsorption with coordination. In the light condition, no protonous As-0bonds were formed on Fe-O and Ti-O bonds on Fe/Ti doped activated carbon translated, and in the dark condition, Fe-O-As and Ti-O-As bonds through double coordination complexation were formed. And there was no new crystals produced after adsorption possessions, indicaton that the arsenic didn’t go into the crystal lattice of the Fe/Ti doped activated carbon.5. Lab experiments and in situ pilot experiments on arsenic removal by Fe/Ti doped activated carbon showed that the water treatment capacity decreased with the increasing flow rate of arsenic polluted water. Based on10μg/L of sanitary standard for drinking water (GB5749-2006), treated water of1kg Fe/Ti doped activated carbon at water flow rate of2mL/min and6mL/min of water containing arsenic200μg/L was332L and276L respectively. In the situ pilot experiments of groundwater remediation, with arsenic concentration of394μg/L, and the flow rate of0.5L/min, the water treatment capacity of the adsorption column contained5kg Fe/Ti doped activated carbon was44L/kg. The arsenic concentration of yield water was below40μg/L when the volume of the yield water was460L.