Studies On Adsorption Characteristics And Mechanism Of Nitrate And Phosphate From Aqueous Solution On Modified Tea Waste

A large number of nitrogen-phosphorus-containing industrial or agricultural waste water and domestic water are discharged into natural water bodies with improperly treatment or even without any efforts,causing the ecological balance of the water bodies to be destroyed and deterioration of water quality.At present,the adsorption method is widely used to solve these pollution,however,the traditional adsorbent is quite difficult to accelerate extensive application with poor adsorption effect,high cost and strict pH range.Therefore,it is urgent to develop an effective and promising adsorbent to remove excessive nitrate?NO₃^-?and phosphate(PO₄^3-)from water,which is high efficiency,low-cost,and widely-used range of pH.To solve the adsorbent problem,tea waste was used as raw material in this study,and the environmentally friendly biomass adsorbent was modified by amine cross-linking to adsorb the eutrophic pollutants NO₃^-and PO₄^3-in the water body.Besides,the adsorption mechanism was also studied.The main contents of the study are included as follow:?1?The modified tea waste adsorbent was prepared through the cross-linking of amine.The effects of solid to liquid ratio,initial concentration of NO₃^-,adsorption time and solution initial pH of on the adsorption of NO₃^-were investigated.The results showed that with the dosage of amine cross-linking tea waste?ACTW?increasing from 1 g/L to 8 g/L,the removal rate of nitrate could be increased from 57.4%to about 90%;with the increase of ACTW adsorption time,the adsorption amount increases rapidly.Adsorption equilibrium was reached at 30 min.Adsorption capacity of ACTW increased rapidly with the initial concentration of the solution.When the pH of the solution system was in the range of 3 to 11,ACTW still had good absorptive effect.?2?The kinetic study of NO₃^-adsorption by ACTW showed that the process of NO₃^-removal was consistent with the pseudo-second-order kinetic model?R²>0.99?,indicating that the ACTW adsorption process for NO₃^-is a chemical adsorption.In addition,the adsorption isotherm of ACTW adsorbed NO₃^-showed that the adsorption type is in line with the Langmuir adsorption isotherm,and the theoretical maximum adsorption capacity was 136.43 mg/g.?3?The results of static adsorption experiments of PO₄^3-adsorbed by ACTW showed that the adsorption efficiency of PO₄^3-increased gradually with the ACTW dosage.The adsorption capacity increased rapidly in the first 20 min of adsorption and then reached equilibrium at 60 min.Besides,as the initial concentration of the solution system increased,the adsorption capacity of ACTW for PO₄^3-also raised.ACTW has a good adsorption effect on PO₄^3-in the solution system with pH values ranged from 3 to 10.?4?The investigation of adsorption kinetics of PO₄^3-by ACTW showed that the pseudo-second-order kinetics model?R²>0.99?could be described the adsorption process of PO₄^3-by ACTW,suggesting that ACTW adsorption process is also a chemical adsorption.In addition,the adsorption isotherm study of PO₄^3-by ACTW showed that the adsorption type was in line with the Langmuir adsorption isotherm,and the theoretical maximum adsorption capacity was 98.72 mg/g.?5?The SEM,XRD,EDS,FTIR and XPS analysis of the tea waste before and after the modification,and before and after adsorption showed that the surface morphology had undergone significant changes after the modification and adsorption.At the same time,changes in surface functional groups,elements,atomic ratios,and binding energy have to be proved the successful introduction of effective functional groups[—N⁺?CH₂CH₃?₃Cl^-]after modification,which greatly improved the adsorption capacity of ACTW for NO₃^-and PO₄^3-.In this paper,tea waste was used as raw material,and the adsorbent of modified tea waste was prepared by the modification of amines successfully,which has characteristics of good adsorption effect,with no metal residue,low cost,simple operation and environment friendly.The new technology have good application prospect in nitrogen and phosphorus pollution treatments for water body.