Study On The Preparation Of Novel Fe/biochar Binary Adsorbent And The Adsorption Of Phosphate In Water

Rapid expansion of industrial and agricultural activities led to an excessive nutrient input,resulting in eutrophication acceleration.Aquatic eutrophication was a serious environmental threat which caused ecosystem degradation and water quality reduction.To develop a novel adsorbent towards phosphate in water that would be environmentally and economically feasible,straw-derived biochar had been used in the experiment.The experiment would provide an effective guidance on the large-scaled application in phosphate removal from wastewater and the recycling of phosphate.Both extrusion-spheronization approach and rolling-pressing method were conducted to granulate biochar to overcome the bottle-neck for adsorption application in the aqueous phase.Granular biochar(Bg-3)would be convenient to recall from water after exhausted while extra pores and channels generated during granulation would increase the adsorption capacity.Ferric oxides were loaded onto inner and outer surfaces of granular biochar by precipitation process to increase phosphate removal rate.Characterization experiments including SEM,TEM(EELS),BET,XRD and XPS were carried out to investigate the adsorbent properties.The results indicated that the Fe loaded on were mainly FeOOH and Fe2O3,and the precipitation process extremely enlarged surface area and pore volume of the adsorbent.The ferric oxides loaded granular biochar(Bg-FO-1)had a phosphate removal rate of 96.3 %(initial phosphate concentration 20 mg/L)since the extra adsorption sites brought in during loading procedure.The phosphate adsorption on Bg-FO-1 followed pseudo first order kinetic model.The internal structure and surface physical and chemical properties were modified by acid,alkaline and surfactant solution respectively.The characterization and adsorption results indicated that biochar after alkaline modification loaded with ferric oxides(Bg-OH-FO)was the one with the highest phosphate removal rate of 99.2%.Static adsorption and dynamic adsorption behaviors were both studied for phosphate adsorption mechanism on Bg-OH-FO.The pH of the system would directly affect the adsorption capacity,according to the result,pH of 4 was suitable for phosphate adsorption.Co-existing anions experiment indicated that competition effect of anions on phosphate removal could be described as sulfate>nitrate>chloride.And the higher temperature and larger initial phosphate concentration resulted in higher adsorption capacity,which revealed endothermic nature of the phosphate adsorption process.Besides,the optimum isotherm model for Bg-OH-FO was Freundlich model.In the fixed-bed column experiment,the removal rate had a download trend with theincrease of flow rate or bed height.The breakthrough curves were turned out to be fitted to Thomas model and Yoon-Nelson model.