Study On Adsorption Of Arsenic By Diatomite Coated Iron Oxide

Purposes and aims Economically efficient methods for removing arsenic fromthe drinking water supply are urgently needed in many parts of the world. Iron oxidesare known to have a strong affinity for arsenic in water. However, they are commonlypresent in the forms of fine powder or floc, which limits their utility in watertreatment. In this study, a novel granular adsorbent, diatomite coated iron oxide, wasdeveloped and examined for its adsorption of arsenic from water. Simultaneouscontrasted some commercial iron oxide type ion exchange resin to determine itsquality.The diatomite was used as the iron oxide support. The diatomite was firstacidified and dried and then coated with iron oxide up to several times. The preparedabsorbent samples were characterized for their morphology, composition, elementalcontent, and crystal properties by various instruments. Experiments of equilibriumand kinetic adsorption of As(III) and As(V) on absorbent were conducted using0.1Land2L polyethylene bottles, respectively, at different pH and temperatures.According to the result of the experiment, the absorbent greatly improves theadsorption of As for water by absorbent as compared to using raw diatomite. Thisimprovement was attributed to increases in both surface affinity and surface area ofthe absorbent. The surface area of the absorbent increased to an optimal value.However, as the absorbent surface area (93m2/g) was only45%higher than that ofraw diatomite (51m2/g), the enhanced As adsorption resulted primarily from theenhanced association of negatively charged As ions with the partial positive surfacecharge of the iron oxide.In As(III) and As(V) adsorption, the absorbent after48hours to reach adsorptionequilibrium, but also presents different adsorption in the process of adsorptionbehavior. The absorbent for As(III) adsorption amount (about16mg/g) is in view ofthe As(V) adsorption amount (about6mg/g)2-3times, and commercial adsorbentadsorption ability, to the contrary. Considering the cost and need for oxidationpretreatment, the absorbent still has certain advantages. The pH value on theabsorption of As also presents the different results. When the absorbent adsorb As(III)at pH=4-8, can keep the higher adsorption capacity, whereas when pH<4or pH>8presents the downward trend, investigate its effects should be As(III) in water to formas the pH changes leading to the electrostatic force change caused in the process ofadsorption quantity increases after the first reduce. When the absorbent adsorb As(V),adsorption capacity decreased with increasing pH value, the assumption to followhigher pH, As(V) form changes increase the amount of negative charge in the water,at the same time, the negative charge on the surface of the diatomite increases theelectrostatic repulsion increases resulting in adsorption capacity decreased. With theincrease of pH Temperature on the modification of diatomite arsenic adsorption oftwo valence also have an impact, and decreased as the temperature increases adsorption. Again to verify the arsenic adsorption process of exothermic reaction, sothe adsorption decreased with temperature increase.The research results show that the absorbent has good adsorption capacity forarsenic. At the same time, the modified diatomite for arsenic adsorption process canbe better fitting by isothermal adsorption. In conclusion, modification of diatomite infuture research and application of water treatment has certain potential.