Adsorption performance of magnetic lanthanum-loaded hydrogel towards low-concentration phosphorus
The magnetic hydrogel adsorbent loaded with lanthanum(M-La-CS/PVA)was prepared using the co-precipitation method with chitosan and polyvinyl alcohol as carriers.The adsorption characteristics and mechanisms of M-La-CS/PVA to phosphate in water were investigated.The saturation magnetization of M-La-CS/PVA was 6.14 emu·g-1,and the saturated adsorption capacity to phosphate was 45.27 mg·g-1 at 25 ℃.When the initial phosphate mass concentration was 0.5 mg·L-1,the phosphate removal efficiency remained 61.40％～92.37％within the wide range of pH=3～10,and the highest removal efficiency occurred at pH=4.The optimum dosage of M-La-CS/PVA was 2.0 g·L-1.The coexisting anions,i.e.NO3-、Cl-and SO42-had slight effects on phosphate adsorption.CO32-anions at 10 mmol·L-1 could inhibit phosphate adsorption,and the phosphate removal rate decreased by 11.34％.The process of phosphate adsorption by M-La-CS/PVA conformed to the pseudo-second-order kinetics and Freundlich isotherm model,which was a type of heterogeneous and multi-molecular layer chemical adsorption.The chemical bonds between P-O and La-O-P and electrostatic adsorption played leading roles in phosphate adsorption.The desorption solution was selected as 3 mol·L-1 NaOH and 1.5 mol·L-1 NaCl,and after five adsorption-desorption cycles,73.03％P adsorption capacity of M-La-CS/PVA still remained.M-La-CS/PVA was a type of highly efficient phosphate adsorbent with magnetic recovery and stable performance.
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