Study On Adsorption Characteristics Of Phosphorus And Chromium By Synthetic Ferrihydrite And Its Application In Foliar Fertilizer

Phosphorus is one of the essential nutrient elements for all life in ecosystems and a leading factor for eutrophication of lakes,while Chromium is one of the most serious heavy metal pollutants.How to effectively control phosphorus and chromiumin the environment is a tough problem.Adsorption is considered as a simple and effective method for the treatment of phosphorus and chromium because the method has advantages such as simple equipment,easy operation and low cost.Ferrohydrite has large specific surface area and strong surface activity,but little research has been done on ferrihydrite used as an adsorbent for the removal of pollutants in the environment or as a carrier of nutrients in agricultural production.In this study,the adsorption of phosphorus and chromium in simulated environment was studied by using synthetic ferrihydrite,and the possible application of ferrihydrite in foliar fertilizer was also studied.The main results were as follows:1.In laboratory,an iron oxide was synthesized by using Fe(NO3)3 and KOH.The results of XRD,SEM,TEM and specific surface area determination showed the iron oxide was a nano-sized amorphous 2 line of ferrihydrite with 540.2 m2/g of specific surface area.2.The ferrihydrite had a good adsorption to phosphorus and chromium(?).The adsorption of phosphorus was reached to equilibrium at 24 h wtih 8.3 mg/g of the maximum adsorption capacity,while the adsorption of Cr(?)was reached to equilibrium at 2 h with 9,72 mg/g of the maximum adsorption capacity.It was observed that the adsorption of phosphorus and chromium on the synthetic ferrihydrite stopped when reached to equilibrium.This maight caused by limitation of surface active sites of ferrihydrite.3.The adsorption of phosphorus and chromium(?)by ferrihydrite was significantly affected by pH.The adsorption capacity decreased gradually by the increasing pH.Greater adsorption capacity was found in acidic than in neutral or alkaline conditions.Besides,it was observed that the adsorption of phosphorus and chromium(?)by ferrihydrite slightly decreased with the increase of ionic strength with the best range of 0.01 to 0.02 mol/L.4.The dynamic changes of adsorption of phosphorus in solution by the ferrihydrite were well discribed by pseudo-second order kinetics equation(R2>0.99),while the thermodynamic changes of the adsorption were well discribed by Freundlich model(R2=0.9926).These indicated that the adsorption process was not limited to a single iron phosphorus molecule layer.In addition,the analysis of the samples after adsorption showed that the adsorption should be dominated by surfacial adsorption.5.The dynamic changes of adsorption of Cr(?)in solution by the ferrihydrite were well discribed by pseudo-second order kinetics equation(R2>0.9997),while the therModynamic changes of the adsorption of Cr(?)were well discribed by Freundlich model(R2=0.9941).These indicated that the adsorption of Cr(?)process was dominated by excangeing or sharing electrons between the ferrihydrite and Cr(?).6.Results from field experiment showed that the application of 3 foliar fertilizers containing ferrihydrite,organic ligand(lipopeptide,polyol or sorbitol)and ZnSO4 was significantly increased the yields of wheat grain and above-ground biomass at the base of reduction of fertilizer use by 20%when the foliar fertilizers were sprayed at tillering,regreening,jointing,booting and grain-filling stages.In conclusion,ferrihydrite can be used as an adsorbent for the removal of pollutants such as phosphorus and chrome in the environment or as a carrier of nutrients in agricultural production.