| Arsenic is a highly toxic metalloid element.Because of the additives used in daily life and the development of arsenic in minerals,it has caused a large amount of arsenic pollution in environmental waters,which seriously threatens people's drinking water safety.Therefore,the development of suitable materials for the removal of arsenic in water is the key to the current application of arsenic-containing wastewater and the safety of drinking water.Based on the current arsenic removal technology and membrane technology,polydopamine(PDA)modified iron-manganese composite oxide(FM)was used as adsorbent and loaded into polysulfone membrane(PSF)in this paper,combined with macroscopic adsorption isotherms,adsorption kinetics,filtration experiments and microscopic examination of membrane materials before and after reaction.Characterization,the removal process and mechanism of As(III)and As(V)in water by composite membrane were studied.The main conclusions of this study were as follows:(1)PSF membrane,PDA-doped PSF membrane(PDAP),FM-doped PSF membrane(FMP),PFM-doped PSF membrane(PFMP)were prepared by phase inversion method.The water contact angles of the four membrane materials were PSF,FMP,PFMP,and PDAP from large to small.The change of pure water flux shown a tendency to reverse the contact angle with water,and the lower the water contact angle,the greater the pure water flux.(2)PFMP membrane has the strongest adsorption capacity for As(III)and As(V),and the maximum adsorption capacity was 11.57 mg/g and 12.39 mg/g,respectively.Langmuir model could better fitted the adsorption of As(III)and As(V)on the membrane.The change of pH had no obvious effected on the adsorption of As(III),while the adsorption of As(V)was greatly affected by pH.The PFMP membrane could removed more than 90%of As(V)in the pH range of 3 to 8.However,as the pH continues to increased,the removal efficiency droped dramatically.The reaction rate between the two types of arsenic and PFMP membranes was particularly fast at the beginning,but as the contact time increased,the number of available adsorption sites decreased,the adsorption rate decreased,and the adsorption equilibrium could be reached within 12 hours.The kinetics were in good agreement with the second-order kinetic model.(3)PFMP membrane(effective area 12.56 cm~2)was used to remove As(III)and As(V)with 50,100 and 150?g/L concentration as feed solution in continuous filtration experiments.The permeate concentration above 10?g/L was the volume of arsenic that could be treated by the membrane.As the concentration increased,the amount of treated water decreased significantly.For As(III)solution,the amount that can be treated in sequence were 2030 L/m~2,915 L/m~2,478 L/m~2,respectively,and for As(V)solution,the amount that can be processed in sequence were 2389 L/m~2,1075 L/m~2,677 L/m~2,respectively.The concentration of As(III)and As(V)was adjusted to 100 ug/L in the desorption experiment.PFMP membrane were able to treat 915 L/m~2 of As(III)and 1075 L/m~2 of As(V),respectively.The regenerated membrane could still to treat 637 L/m~2 of As(V)and 677 L/m~2 of As(V).Under the same experimental conditions,the effect of PFMP membrane on As(V)was higher than that of As(III),and the regenerated membrane can still maintain high arsenic removal efficiency,which proved that the membrane material can be recycled many times.(4)XPS mechanism analysis showed that the removal of As(III)was mainly due to the oxidation of As(III)to As(V),Mn(IV)and Mn(III)were converted to Mn(III)and Mn(II),respectively.During the oxidation process,new active adsorption sites were continuously generated,which adsorb As(III)and As(V),and chemical reactions occur simultaneously.As(V)removal was mainly due to adsorption and chemical reaction.(5)The composite membrane prepared by this method has high removal efficiency for As(III)and As(V)in water,and can be used by desorption cycle,indicating that the composite membrane has a good application prospect in the treatment of arsenic pollution in water. |
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