| Adsorption is the most widely used technology for arsenic removal in water treatment due to its inherent merits,including cost-effectiveness,high efficiency and ease of implementation.In recent years,titanium-based adsorbents have drawn tremendous attention owing to their stable property,low toxicity,and high affinity for arsenic.The titanium xerogel material(TAX)prepared by the sol-gel method has a high adsorption capacity(254 mg/g)for As（Ⅲ）,is less affected by coexisting ions,and holds great promise for application.However,the material presents some shortcomings: low adsorption rate and huge hydraulic loss of fixed bed,which limit its practical application.In order to solve the above problems,the supported titanium xerogel adsorbent TAX@D201 was developed by carrier screening and optimization of synthesis conditions.Its adsorption performance and practical application feasibility for As（Ⅲ）were extensively investigated.The specific research contents and conclusions are as follows:(1)A variety of typical carriers are employed in sol-gel-impregnation process as the support for TAX respectively,including activated carbon,sponges,hydrogels and resins.By comparing the titanium content,immobilization of TAX,adsorption capacity and adsorption rate,it is determined that the strong basic anion macroporous resin D201 is the most suitable carrier for loading TAX.TAX@D201 contains up to 5% of titanium,which is 4 times that of TAX@AC.Additionally,TAX@D201 will not leak TAX powder during static adsorption,making it sustainable and durable for application.Most importantly,adsorption rate constant and adsorption capacity of TAX@D201 for As（Ⅲ）are 4.8 times and 7 times that of TAX respectively.(2)The synthesis scheme of TAX@D201 was further optimized in terms of the selection of titanium source,the order of sample addition,the molar ratio of Ti to acetylacetone(AA),and the drying method.The physical and chemical characteristics of TAX@D201 were thoroughly investigated with the help of scanning electron microscopy,transmission electron microscopy,potentiometric titration and other characterization methods.The optimized Ti-OH active site concentration of TAX@D201 is 4 times that of TAX.Different kinetic and isotherm models were used to evaluate the adsorption performance of TAX@D201,and the correlation coefficient(R2)was compared to select a suitable fitting model.By fitting the kinetic data of TAX@D201 into pseudo-second-order(PSO)model,the initial adsorption rate of TAX@D201 was shown to be 3.70 mg/(g·min),which is nearly 20 times higher than TAX(0.18 mg/(g·min)).Freundlich model was used to fit the adsorption isotherm of TAX@D201 for As（Ⅲ）,and the maximum adsorption capacity was about 534 mg/g(normalized to unit mass Ti).(3)The practical application potential of TAX@D201 to adsorb As（Ⅲ）was evaluated.First,the effects of solution p H,coexisting anions and humic acid on the adsorption performance were investigated through batch adsorption experiments.In the range of p H 3.0-11.0,the adsorption capacity of TAX@D201 on As（Ⅲ）is almost not affected by p H.Common coexisting anions Cl-,SO42-,HCO3-(<1000 mg/L)and humic acid(<10 mg/L)have negligible effects on the adsorption of As（Ⅲ）by TAX.Secondly,to mimic real application environments and for a comparison with iron-loaded resin,laboratory simulated groundwater and actual arsenic-containing groundwater in Shanxi were treated with fixed-bed adsorption experiments.The TAX@D201 packed column can effectively reduce the As（Ⅲ）concentration in the groundwater of Shanxi from 200μg/L to less than 10 μg/L,and the effective treatment bed volume reaches 560 BV,which is 2.8 times of that of the iron-loaded resin material(199 BV)with the same metal loaded.The research results highlight that loading the TAX on the macroporous resin D201 is an effective way to improve the adsorption capacity and adsorption rate of TAX,which opened a new avenue for titanium-based adsorbents to be used in the treatment of As（Ⅲ）polluted water. |
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