Study Of The Preparation And Performance Of Modified Oyster Shell As Phosphorus Removal Adsorbents

Laboratory experiments were carried out to study the feasibility of oyster shell as phosphorus removal adsorbents. Kaolin and chemicals like Al2(SO4)3, Al(NO)3, Fe2(SO4)3, Fe(NO)3and FeCl3, were prepared with oyster shell for phosphorus removal. The evaluation of phosphorus adsorption characteristics as well as studying of adsorption mechanisms of modified oyster shell were focused on in this study. Meanwhile, the phosphorus removal performance of adsorbents was investigated with simulated waste water.The adsorption isotherms and kinetics were examined in batch experiments. Two isotherm models of Langmuir and Freundlich were used for data fitting which showed that both models are applicable with R2>0.9. However, the Langmuir isotherm model fitted better than the Freundlich isotherm model. The pseudo-second kinetic equation can be used to describe the adsorption process.KCl-NaOH-HCl sequential extraction was used to identify the forms of phosphorus in saturated adsorbents. Results showed that the adsorbed phosphorus existed with different forms in different adsorbents. Phosphorus adsorbed on oyster shell was mainly Ca-P. Phosphorus adsorbed on OS/K was mainly Ca-P and soluble phosphorus. Phosphorus adsorbed on OS/A1was mainly Ca-P and Al-P. Phosphorus adsorbed on OS/Fe was mainly Ca-P and Fe-P.Modified adsorbents showed better phosphorus adsorbing capacity than original oyster shell in treating simulated wastewater. Using OS/A1and OS/Fe as adsorbents, the phosphorus removal efficiency was higher than90%.Desorbed phosphorus can be recycled by MgNH4PO4crystallization reaction, in which process pH and ratio of Mg to phosphorus have significant influence. By ananlying the precipitates, it was found that the purity of MgNH4PO4decreased with increasing of pH. The optimum reactive conditions were pH from8.5to9.5and the ratio of Mg to phosphorus1.4.