Simultaneous removal of ammonium and phosphate using lanthanum ion-modified montmorillonite
Nitrogen(N)and phosphorus(P)of high concentrations are the leading causes of water eutrophication,and Phoslock®,a lanthanum ion(La3+)-modified bentonite,has been widely used in the treatment of eutrophication water.Early studies mainly focused on the mechanism and stability of Phoslock® for P removal,and there are few reports on the simultaneous adsorption of coexisting ammonium(NH4+).In this study,La3+-modified high-purity montmorillonite(Mt)was prepared to simulate the Phoslock® key component responsible for P removal and the influences of pH value,adsorption time,and initial concentration on simultaneous removal of NH4+and phosphate(PO43-)by the modified Mt were investigated.The results show that the modified Mt had good P removal stability in the range of pH 4-12,and uptake of NH4+reached the maximum(ca.9.7 mg/g)at pH=10.Compared with the single system,the adsorption of N and P in the coexisting system promoted each other and shortened the individual adsorption equilibrium time.In addition,the coexisting NH4+increased the maximum uptake of P,while the coexisting PO43-decreased the adsorption capacity of NH4+.Adsorption of PO43-was almost unaffected by coexisting ions.Ca2+and Mg2+reduced the amount of adsorbed NH4+,while HCO3‒ and SiO32‒ promoted the adsorption of NH4+.Phosphate was removed through surface precipitation(in LaPO4 form)on Mt,and the steric hindrance stem from the formed LaPO4 at the edge of Mt interlayers reduced the utilization rate of La3+and hindered the ion exchange of NH4+.
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