Study On The Removal Of Nitrate And Phosphate From Water By Modified Corn Straw:Characteristics And Mechanism

Anions pollutants such as nitrate(NO3-)and phosphate(PO43-)are common composition in water.They can cause the eutrophication of lakes as well as affect human health.Based on the electronegative of nitrate and phosphate,researchers focus on using adsorption technique to remove them from aqueous solution.In this study,corn straw that is a common agricultural waste in China was modified into modified corn straw(MCS)to remove PO43-and NO3-from water.The effect of NaOH concentration and the temperature of quaternization on the yield and adsorption efficiency of MCS were discussed.The surface morphology and chemical structure of raw corn straw(RCS)and MCS were characterized and analyzed.Then,the removal characteristics and mechanism of nitrate and phosphate by MCS were investigated.To prepare MCS,raw corn straw was firstly treated by NaOH alkaline treatment,and then reacted with epichlorohydrin and finally quaternized with trimethylamine solution.Results showed that the suitable concentration of NaOH solution is 10%(W/V).At the same time the suitable temperature of quaternization is 80?.Characterization methods,such as element analyzer,nitrogen adsorption–desorption experiments,scanning electron microscope(SEM),fourier transform infrared spectrum(FT-IR)and solid state 13 C nuclear magnetic resonance(13C-NMR)were employed to determine the element content,surface morphology and functional groups of raw corn straw and the prepared MCS.The results showed that many cellulosic fibers were exposed on the surface of straw after modification,and the pore area of MCS was increased from 4.820 m2/g to 7.266 m2/g.The content of nitrogen increased to 1.92%,from which the total exchange capacity of MCS was calculated as 1.37 mEq·g-1.The changes of FT-IR and 13C-NMR clearly indicated that a large number of quaternary amino groups were introduced into the corn straw after modifications.Batch adsorption experiments showed that adsorption of nitrate and phosphate on MCS was rapid,and the equilibrium time was less than 20 min.The best removal efficiency of nitrate and phosphate were observed in pH range of 4~8.The adsorption followed Langmuir adsorption model,and the maximum NO3-and PO43-adsorption capacities at neutral p H were 19.9 and 0.164 mg/g at 30°C,respectively.The adsorption process accorded with the pseudo second order reaction kinetic rate equation.It suggested that the adsorption rate is proportional to the square of the adsorption process driving force.MCS exhibited a selectivity for common anions in the order of SO42-> NO3-> PO43-> Cl-and anions were mainly removed through the way of ion exchange with chlorine ions on MCS.Regeneration experiments suggested that MCS has the potential for repeatedly use in removal of nitrate and phosphate.This modification corn straw(MCS)is cheap and environmentally safe.More importantly,the adsorption capacity of corn straw to nitrate significantly increases after the modification.