Experiment of Phosphate Adsorption Characteristics by Natural Oyster Shells

A batch method was used to investigate the phosphate adsorption characteristics by natural oyster shells.The results showed that the efficiency of adsorption increased with the increasing initial PO43-concentration.The adsorption kinetics can be described by the pseudo-second order model.The isothermal adsorption process of phosphate on oyster shells can be fitted by Langmuir and Freundlich equations with a high correlation coefficients(P 0.01).However,the correlation coefficients of the Langmuir are better,so it can describe the adsorption process more accurately.The efficiency of adsorption increased with the increasing of temperature,and the maximal adsorption capacity which calculated through Langmuir equations increases as the temperature increases in following order:83.53 mg/kg(15℃) 84.75 mg/kg(25℃) 112.36 mg/kg(35℃).The enthalpy change of adsorption was 36.62 kJ/mol and its entropy change was 0.14 kJ/mol · k.An examination of the thermodynamic parameters showed that the adsorption of phosphate by oyster shells was a process occurring spontaneously.The process was also found to be endothermic.The efficiency of adsorption was influenced by usage of substrate,initial PO43-concentration,temperature and pH in orderly.For the adsorption activity,the optimal combination of the influence elements was oyster shells substrate 1g,initial PO43-concentration 30 mg/L,temperature 35℃,and pH 9,respectively,and the maximal adsorption was 875.61 mg/kg.