| Groundwater containing arsenic has become a serious global problem,which shows significant hazards on human health and environment.Inorganic arsenic is mainly in the form of arsenite and arsenate,in which arsenite is more toxic and stable in solution.Among the As（Ⅲ）removal technologies,coagulation is widely used in water and wastewater treatment due to its simple operation,low cost and high removal efficiency of pollutants.Titanium salt is a kind of coagulant with non-toxicity,and the coagulated flocs can be recycled for TiO2 catalyst.The removal efficiency on As（Ⅲ）was reported to be higher than the convential Fe and Al coagulants.However,its application in As（Ⅲ）had two main problems:（1）the coagulation process was hard to be regulated due to the rapid hydrolysis of Ti4+,and（2）the effluent pH tended to decrease too much.Therefore,more approaches should be explored to further improve the coagulation removal on As（Ⅲ）.This study utilized two methods to achieve this goal:（1）to choose a kind of novel titanium xerogel coagulant（TXC）to eliminate As（Ⅲ）,and（2）to to explore an integrated method of CaO2 oxidation followed with coagulation.The main conclusions were summarized as follows:1、This study compared the removal efficiency of As（Ⅲ）by TXC,Ti（SO4）2,TiCl4 and PFS.The results showed that TXC performed a highest removal efficiency on As（Ⅲ）,where the removal efficiency reached 68-90%with TXC dose of 10 mgTi/L throughout the pH range of 5-10.At pH 7.0,90%of As（Ⅲ）could be removed by 10 mgTi/L TXC.The co-existing ions、organic matter and turbidity showed a negligible effect on As（Ⅲ）coagulation by TXC.TXC can removal As（Ⅲ）and As（Ⅴ）in arsenic system.2、The main mechanism involved in As（Ⅲ）coagulation was the adsorption effect by the in situ formed coagulated flocs.Compared with Ti（SO4）2 and TiCl4,the hydrolysate formed by TXC were in smaller size and exposed more active sites,thus facilitating removing more As（Ⅲ）by adsorption effect;in addition,the remained AcAc in floc skeleton could further improve the binding affinity via forming AcAc-As（Ⅲ）complexes.3、The integrated process of CaO2 oxidation followed with coagulation can efficiently removal As（Ⅲ）,.especially under acidic conditions.For Ti（SO4）2 coagulation in pH range 4-9,the As（Ⅲ）removal efficiency increased from 10-67%to 65-98%by adding 20 mg/L CaO2.4、The enhanced mechanism in CaO2 oxidation-coagulation system was mainly ascribed to two reasons:（1）partial As（Ⅲ）was oxidized into As（Ⅴ）,which was easier to be removed by coagulation,and（2）the solution pH increased to alkaline environment,which was benefical for As（Ⅲ）coagulation.The main active specie for As（Ⅲ）oxidation was ·O2-.Due to the high speed of As（Ⅲ）removal by coagulation,CaO2 can continuously oxidize the remaining As（Ⅲ）in the system,the As（Ⅲ）oxidation and As coagulation were simultaneously occurred in integrated process of CaO2 oxidation followed with coagulation,which is an important reason why the integrated process can effectively remove As（Ⅲ）at low oxidant dose.5、Through research,we found a titanium xerogel coagulant with high efficiency to remove As（Ⅲ）,and the integrated process of CaO2 oxidation followed with coagulation was not only able to remove As（Ⅲ）effectively,but also had strong practical application. |
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