Preparation Of Adsorbents Removal Of Trace Arsenic And Arsenic Removal Performance

As the development of metallurgy and chemical industry and the growing demand of arsenicproducts, arsenic pollution has become one of the highlighted environmental problems. In manyparts of the world it was commonly found excessive amounts of arsenic in the drinking water. Sopeople had a further understanding on the severity of arsenic pollution and our country alsoreduced the concentration of arsenic from0.05mg/L to0.01mg/L in "Standard for DrinkingWater Quality"（GB5749-2006）.Recently，the methods of treating arsenic water include precipitation, ion exchange method,oxidation method and biological method, etc., but all of these methods have their defects fortreating water containing low concentration of As（Ⅲ）. Based on the characteristics of cheap, easygained, large capacity of adsorption and less secondary pollution of biological waste materials,spent grain were used as raw material for adsorbent preparation. DMol3module of MaterialsStudio5.5program was used to calculate and analyze the combining ability between As（Ⅲ） andfunctional groups. Furthermore, the energies of the frontier molecular orbital were calculated toprovide the theoretical basis of preparing adsorbent.Using spent grains modified by PAM/methanol to adsorb As（Ⅲ） has broken through thetechnical bottleneck that only under the condition of oxidating As（Ⅲ） to As（Ⅴ） can the purifiedwater treated by traditional technology. The optimum conditions which can reduce theconcentration of As（Ⅲ） to reach0.01mg/L in "Standard for Drinking Water Quality"（GB5749-2006） were biosorbent dosage3g/L, pH5, biosorption time2h.The effects of representative coexisting anions and cations in the water on adsorption ofAs（Ⅲ） by modified spent grains were studied. The experiment results showed that adding Cd2+and Fe³⁺can promote the adsorption on As（Ⅲ）, while the existing of F-, SO2-3-4and PO4inhibitthe adsorption. After treating onelevel water source of Ganzhou, the modified spent grains wasproved as a economical and effective adsorbent.The kinetics study on As（Ⅲ） biosorption onto modified grains showed that the experimentalresults were better fitted McKay second-order equation than that of Lagergren first-orderequation. The biosorption process of As（Ⅲ） by modified spent grains had a good relevance toFreundlich equation with the value of n within10which indicated that the adsorption processoccur easily. The negative value of enthalpy change△H showed the adsorption process wasexothermic reaction. The negative value of Gibbs free energy△G also illustrated the adsorptionprocess occur spontaneously.Desorption and leaching toxicity of spent adsorbent were studied. It was found that thedesorption effect of alkaline solution was better than that of acid solution. Based on the results of leaching toxicity experiment, spent grains after adsorpting can directly landfilled.The experimental results showed that PAM modified grains had better removal on As（Ⅲ）than that of methanol modified grains, which also coincide the results of the energies of thefrontier molecular orbital between As（Ⅲ） and functional groups. Through the Fourier TransformInfrared Spectrum （FTIR） analysis of spent grains can be known that the active of amide groupsat the surface of modified spent grains have been strengthened. Arsenic groups have beenappeared after As（Ⅲ） adsorpted from the water. The results of Electron Microscope Scanningalso showed that the pores of modified spent grain became bigger. The study of EnergyDispersive Spectrometer （EDS） indicated that PAM modified spent grains appear arsenic peaksafter As（Ⅲ） adsorption.