Preparation Of Fe-based Nanoscale Material-Sugarcane Bagasse Composite And Its Adsorption Behavior And Mechanism Toward PO₄^3-

It is extremely urgent to control the pollution of eutrophication water caused by the discharge of phosphorus,especially waste water containing soluble phosphate.Among the methods of phosphate waste water treatment,biosorption method using waste straw as adsorbent has attracted much attention due to its abundant raw materials and low cost.China is a big agricultural country with an annual output of 262 million tons of waste sugarcane bagasse（SCB）,and comprehensive utilization of waste sugarcane bagasse needs to be developed urgently.For this reason,in the present work three Fe-based nano material loaded sugarcane bagasse composites:ferrihydrite load sugarcane bagasse（FH/SCB）,zero-valent iron load sugarcane bagasse（ZVI/SCB）and metal organic framework material load sugarcane bagasse（MIL-101（Fe）/SCB）were prepared.The adsorption behavior and mechanism of three composites for phosphate ions were studied.The main contents are as follows:（1）FH/SCB composite adsorbent was prepared by in situ precipitation method,the influence of precipitation p H of Fe³⁺and the adsorption performances of the composite were discussed,also,the adsorption behavior and mechanism of the composite prepared at the optimal conditions on phosphate were studied.The results showed that composite（FH/SCB4.5）prepared at Fe³⁺concentration of 50 mmol L^-1 and p H 4.5 showed highest capacity toward phosphate.The results of SEM-EDS,XRD,TEM and FTIR showed that nano ferrihydrite particles were uniformly loaded on bagasse.The results of isothermal adsorption experiments show that the maximum adsorption amount of phosphate at p H 2.0,5.3,9.0,12.5 by FH/SCB4.5 was 180.7,79.3,43.5 and 7.4 mg g^-1,respectively.The experimental data all predicted well by Langmuir model,indicating that the adsorption of phosphate by FH/SCB4.5 was dominated by monolayer adsorption.The kinetic experiments showed that the adsorption of phosphate at p H 2.0,5.3,and9.0 by FH/SCB4.5 conformed to the pseudo-second-order model while to intra-particle-diffusion model at p H 12.5.The experiments of co-existing ions showed that co-existing anion and anion could promote phosphate adsorption.Adsorption mechanism analysis showed that electrostatic attraction and inner-sphere complexation involved in the phosphate adsorption at p H<10.6,while at p H>10.6,inner-sphere complexation and ion exchange involved.At last,the wastewater treatment results showed that,at the adsorbent dosage of 0.5 g L^-1,the removal efficiency of the actual phosphate containing wastewater of 20 mg L^-1 was 99.72%.（2）A dry adsorbent,zero valent iron loaded sugarcane bagasse（ZVI/SCB）composite was prepared by liquid phase reduction,SEM and XRD showed that zero valent iron was successfully loaded on bagasse,and through the stability test,the adsorption amount of ZVI/SCB remained stable for at least half a year under the seal condition.p H and co-existing interference ions experimental results show that ZVI/SCB was a p H dependent adsorbent,and co-existing of both anion and anion could promote the adsorption of phosphate on ZVI/SCB,especially for Ca²⁺and Mg²⁺.The adsorption isotherm of phosphate（p H=5.3）on ZVI/SCB predicted well by Freundlich model,the maximum adsorption capacity of phosphate was 205.2 mg g^-1 and the adsorption kinetics fitted well with the pseudo-second-order model.XPS,XRD,Zeta potential analysis showed that the adsorption mechanism of phosphate was dominated by the formation inner-sphere complex of Fe3（PO4）2 and Fe PO4 and electrostatic adsorption.（3）Metal organic framework loaded sugarcane bagasse composite（MIL-101（Fe）/SCB3）was prepared by hydrothermal method,using bagasse,terephthalic acid and Fe Cl3 as the main raw materials.Composite prepared with bagasse with 200-300 mesh diameter of 0.05g showed the highest adsorption capacity toward phosphate.XRD,EDS-mapping and TEM results showed that MIL-101（Fe）particles were loaded successfully on bagasse.MIL-101（Fe）/SCB3 could be used in a wide p H range from 3.0to 10.0,and Fe release in this range were less than 0.03%.Adsorption isotherm and kinetic experiments showed that the common anionic(Cl^-,NO3^-,SO4^2-)and cationic(Na⁺,K⁺,Ca²⁺,Mg²⁺)ions showed negligible effect on phosphate adsorption capacity and rate on MIL-101（Fe）/SCB3.Maximum amount of phosphate adsorbed on MIL-101（Fe）/SCB3 was 211.0 mg g^-1,which was much higher than that of the blank SCB(0.04 mg g^-1)and MIL-101（Fe）(158.1 mg g^-1).The results of p H experiment,co-existing interference ions experimental,XPS,Zeta potential analysis showed that phosphate adsorption on MIL-101（Fe）/SCB3 were mainly through electrostatic force,ion-exchange and inner-sphere surface complex.