Study Of Adsorbing Phosphate From Wastewater On Palygorskite Iron/Aluminium Hydroxide Nano-compound Materials

The adsorption capabilities and mechanisms of three kinds of palygorskite nanometer compound materials——aluminum hydrate,iron hydrate,aluminum and iron hydrate respectively coated on palygorskite (PNCMⅠ,PNCMⅡand PNCMⅢ),were investigated in this paper. Results demonstrate that the materials were able to effectively remove phosphate from the solutions.Temperature did not appear to affect the removal efficiency of PNCMⅠand PNCMⅢ,which held the L-type adsorption isotherm equation while PNCMⅡshowed an S-type. Adsorption isotherms of three kinds palygorskite nanometer compound material fitted to Langmuir isotherms equation.Because of the△H＞0,△G＜0,△S＞0,and the△G values of PNCMⅠ,PNCMⅡand PNCMⅢwere between -22.0～-29.12kJ/mol,-8.75～-13.13kJ/mol and -25.91～-34.61kJ/mol respectively,the phosphate adsorption on PNCMⅠand PNCMⅢwere spontaneous,endothermic and the coexistence of physical adsorption and chemical adsorption.They were entropy-increasing processes of palygorskite nanometer compound materials.PNCM adsorption phosphrous were fit to the pseudo-second order kinetics model.The apparent adsorption activation energy of adsorption on PNCMⅢis 18.58kJ/mol.A relatively low apparent adsorption activation energy suggest that the adsorption dyestuffs may involve not only chemisorption but also physical adsorption process,which is likely due to its combined control of chemisorption and film diffusion.The adsorption test of phosphate in the aqueous solution from Baohe river by PNCMⅢshows that phosphate removal rate is 95.48%,with ratio of solid to liquidon being 1(g/L),the residual concentration is 0.044 mg/L; phosphate removal rate is 97.69%,with ratio of solid to liquidon being2(g/L), the residual concentration is 0.0225 mg/L.The quality of two effluents is below the second standard of ground water.