Mechanism of highly selective adsorption of phosphate in water by biochar/Ca/La-LDH
A novel composite adsorbent(CLYK)of coconut shell biochar/Ca/La layered double hydroxide(Ca/La-LDH)was synthesized via a simple co-precipitation method.The materials were characterized by SEM-EDS,BET,XRD,FTIR and XPS,and the effects of metal loading,adsorbent dosage,initial pH value,co-existing ions and organic matter on phosphate adsorption,as well as the characteristics of adsorption kinetics,isotherms,thermodynamics and site energy distribution were investigated.The results showed that CLYK had good adsorption performance for phosphate,with a maximum adsorption capacity of 214.742mg/g at metal loading of 70％,dosage of 1g/L and pH value of 5.Moreover,CLYK displayed a wide range of pH adaptability with significant adsorption capacity observed between pH 3～10.It also demonstrated high selectivity for phosphate in the presence of coexisting ions and organic matter,and the adsorption-desorption cycle test proved that CLYK has a good reusability.The adsorption process of phosphate by CLYK conformed to the Freundlich and quasi-second-order kinetic model,which was multilayer chemisorption,The thermodynamic analysis indicated that the adsorption was a spontaneous endothermic reaction.Chemical precipitation,formation of inner-sphere complexes via ligand exchange,and electrostatic attraction were mechanisms of phosphorus adsorption.
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