Study On The Adsorption Of Nitrate And Phosphate In Aqueous Solution By Zirconium(?)/chitosan/bentonite Composite

The excessive discharge of nitrate and phosphate leads to eutrophication.These nutrients were usually from agricultural,industrial and domestic waste-water.Therefore,it is crucial to find effective method to decrease nitrate and phosphate concentration before its discharge into natural water.Various methods have been applied for the removal of nitrate and phosphate from wastewater including chemical precipitation,ion exchange,biological treatment and adsorption.Among these methods,adsorption is being widely concerned around the world due to these advantages such as high efficiency,simple operation and no second-pollution,etc.Chitosan,as the second largest renewable resource in nature,is widely used in treatment of anion pollutants.However,the instability of CTS limited its broad application.In this study,two adsorbents were prepared for nitrate and phosphate adsorption,respectively.HACC was modified by Zr(IV),and then BT was added to form crosslinked HACC/Zr(IV)/BT composite for the removal of phosphate.CTS was introduced onto Zr(IV)modified BT to prepare crosslinked CTS/Zr(IV)/BT composite for the removal of nitrate.The structures of the two adsorbents were investigated by FTIR,XRD and SEM techniques.The preparation process,adsorption properties and adsorption mechanism of the two adsorbents were discussed.The factors such as concentration of nitrate and phosphate,pH,coexisting anions,temperature,time,adsorption isotherm and adsorption kinetic were investigated as well.The conclusions were obtained as follows:The crosslinked HACC/Zr(IV)/BT composite was prepared successfully and employed for the removal of phosphate from aqueous solution.The effects of various conditions for the phosphate adsorption were investigated systematically.Increasing pH values and the presence of coexisting anions like chloride,bicarbonate and sulfate reduced the adsorption of phosphate.The adsorption of phosphate attained the equilibrium rapidly.The kinetic experimental data were well fitted to the pseudo-second-order model.Langmuir and Freundlich models were used to fit the isotherm data,and the maximum adsorption capacity was 65.35 mg/g at 293 K and natural pH.Thermodynamic data showed the adsorption process was exothermic.The adsorption mechanisms mainly included electrostatic interaction,ligand exchange and hydrogen bond formation between phosphate and HACC/Zr(IV)/BT composite.The crosslinked CTS/Zr(IV)/BT composite was prepared for the removal of nitrate.The presence of coexisting anions like chloride,carbonate,bicarbonate and sulfate reduced the adsorption of nitrate.Increasing or reducing pH values was bad for the nitrate adsorption.The adsorption of nitrate attained the equilibrium rapidly.The adsorption isotherm data were well described by the Langmuir model,and the maximum adsorption capacity was 14.18 mg/g at 293 K and natural pH.Adsorption process mainly included chemical adsorption,the adsorption mechanisms included ligand exchange and hydrogen bond formation between nitrateand CTS/Zr(IV)/BT composite.