Removal Of Perchlorate From Aqueous Solution By Cross-linked Fe(Ⅲ)-chitosan Complex

Perchlorate is a kind of low molecular and high solubility anion. It has thecharacteristics of high water solubility, high diffusivity, low adsorption and highstability. After entering the human body, it would endanger human body health byinhibiting the absorption of iodine in the thyroid and affecting thyroid hormonesynthesis and secretion. Now the methods of removing perchlorate have limitations,so we need look for a affordable, non-toxic and harmless method. In this work,chitosan impregnated with Fe(III) was prepared and used as an adsorbent foradsorbing perchlorate from water. The characteristics of the composite and theoptimum conditions for perchlorate removal were investigated. The experimental datawere fitted with different isotherms and kinetic models to understand the adsorptionprocess. Moreover, the possible mechanism for perchlorate removal by the adsorbentwas also investigated. The main experimental results and conclusions in our study arelisted as follows:(1) FeCl3·6H2O and glutaraldehyde were the important parts in the process ofsynthesis. The small particles were well-distributed and good adsorption capacity with10%FeCl3·6H2O and12.5%glutaraldehyde.(2) Analysis the characterization of adsorbents by FTIR, SEM and X-EDS. TheSchiff base could be contributed to the–C=O of glutaraldehyde and nitrogen groupsof chitosan, which made the adsorbent insoluble in aqueous solution. The structure ofchitosan had changed after chelating and crosslinking. It owed the net structure, largervolume and porosity, which was contributed to good adsorption capacity. It indicatedthat Fe(III) combined with chitosan by detection of chlorine and ferric iron.(3) When the pH value of solution was less than the pHzpc, the surface of theadsorption was positively charged, which result in removal perchlorate by cross-linkedFe(III)-chitosan. With the increase of initial concentration of ClO4-, the initialadsorption rate and equilibrium adsorption quantity increased. Co-existing anionscould compete with perchlorate in the adsorption process, which affected its adsorption capacity. Chlorine had the less affect.(4) Analysis the adsorption process through adsorption kinetics, adsorptionthermodynamics and adsorption isotherm. It indicated that the process was a chemicaladsorption. The adsorption stage was completed within10min. Intra-particlediffusion was not the rate limiting step for the adsorption process. The adsorption wasphase and heterogeneous. The influence of temperature on the reaction process was notsignificant. The adsorption was endothermic in nature and the adsorption process couldhappen spontaneously. Lower temperature was relatively favorable for the adsorptionreaction.(5) Using NaCl as regenerative agent, when the amount of NaCl was more than2.5%, almost could completely replace the adsorption on the adsorbent ClO4-, andadsorbent had good reuse performance.(6) Mechanism analysis showed that cross-linked Fe(III)-chitosan adsorption ofClO4-was mainly by electrostatic force, part of the adsorption was on the exchangingof Cl-and ClO4-in the solution. Little part of the adsorbent adsorption force comefrom Fe (III) in the center of the adsorbent.