Study On The Preparation, Characterization And Fluoride Adsorption Properties By Rare Earth-modified Chitosan Resin

The treatment methods for fluoride adsorption have been given more attentionrecently. In this study, a series of available fluoride adsorbents were prepared by rareearth-modified chitosan. The preparation, physicochemical characteristics, adsorptionproperties and mechanism of fluoride adsorbents were investigated and the drawingconclusions as follows:1A novel costeffective fluoride adsorbent, CR, was prepared for the first timeby rare earth-modified flake chitosan. The loading dosage of La³⁺and rare earth ontochitosan was discussed according to fluoride adsorption capacity. The results showthat the adsorption capacity was better when the ratio between La³⁺and chitosan was0.3:1.0. In addition, the adsorption capacity was increasing with contact timeincreased, but decreased evidently with pH improved. The adsorption rate wasincreased from19.28%,19.63%to93.51%and94.7%, respectively, when the dosageof adsorbents increased, the adsorption capacity was improved greatly with thefluoride initial concentration increased for adsorbents. The fluoride adsorptioncapacity was decreased with co-ions were existed in the same system, and the effectability obeyed the order of CO₃^2- HCO₃-SO₄^2- Cl-NO₃^-. The analysis of FTIR andXRD on CL, CR interpreted that rare earth metal ions were chelateed on chitosanmolecular chain with the functional groups. Thus, the crystalline was decreasedobviously compared to CS. The experiment results could be fitted well by adsorptionisotherm Langmuir, Freundlich, and pseudo second kinetic equation.2Since flake chitosan is not stable under acidic condition, novel fluorideadsorbents CLB and CLRB were prepared by La³⁺and high content of La³⁺rareearth-modified chitosan by inverse suspension method. The parameters of preparationprocess were studied including the dosage of rare earth, pH, and the dosage ofglutaraldehyde on the basis of fluoride adsorption capacity. The adsorbents werecharacterized by FTIR and DSC, there were two kinds of coordinate bonds as N-La³⁺and N-La³⁺rare earth which had high content of La³⁺existed in the structure ofadsorbents, respectively. Furthermore, schiff base reaction was carried out between the functional groups of-NH2,-OH and glutaraldehyde, so the thermostability of CLBand CLRB were higher than CB. The experiment data were fitted well by Langmuirand Freundlich isothermal model, the maximum adsorbent capacity was3.70mg/g,5.88mg/g, respectively. The whole adsorption process was controlled by chemicaladsorption according to the pseudo second kinetic equation. Finally, CLRB could bereused for10times with little loss.3In order to improve fluoride adsorption capacity, fluoride adsorbents of CCBand CCRB were prepared by cerium and high content of cerium rare earth modifiedchitosan resin. The adsorption properties for fluoride adsorption were discussed bytwo kinds of adsorbents. It was clearly to see that the adsorption capacity wasinfluenced greatly by the parameters of pH, dosage, co-ions and initial concentration,etc.. The experiment data were fitted well by istherm equation of Langmuir andFreundlich, and the maximum adsorption capacity was6.01mg/g,3.34mg/g,respectively. The fluoride adsorption capacity was decreased obviously when thereactive temperature was improved. Sorption kinetics was mainly controlled by twosteps of particle internal diffusion and liquid film diffusion.4Novel magnetic adsorbents were prepared using rare earth-modified chitosanwith Fe3O4nanoparticle, named MCLB and MCLRB, and the specific saturationmagnetization was5.17emu/g,9.90emu/g, respectively. Sorption experiments wereperformed by varying contact time, pH, presence of co-anions, etc.. The fluorideuptake onto two fluoride adsorption adsorbents obeyed both Freundlich and Langmuirisotherms, and the maximum adsorption capacity was20.53mg/g and22.35mg/g.Sorption kinetics was mainly controlled by pseudo-second-order. Fluoride could bemoved easily to the surface of adsorbents by the coordinate bond of Fe-O, and anionexchange is carried out between adsorbents and fluoride, and the fluoride adsorptioncapacity was improved eventually.5Various of fluoride adsorbents were applied in simulated drinking water withhigh content of fluoridel concentration, and achieved better effectiveness. However,the influence of adsorbents dosage on fluoride adsorption capacity was obvious Thefluoride in drinking water can be absorbed effectively and its concentration controlledwell after treatment by conducting adsorbents dosage. Comparison of the traditionalfluoride adsorbents, all of rare earth-modified chitosan adsorbents synthesized in thispaper, have higher fluoride adsorption capacity, faster adsorption rate, more costeffective, better reusable and much more stable, we hope these adsorbents can be used widely in future application.6The concentration of fluoride is higher in the enzymolysis liquid of Antarctickrill. Consequently, it is necessary to remove fluoride from enzymolysis liquid. In thisstudy, MCLRB was choosed as a fluoride adsorbent for its high adsorption capacity,costeffective, and better adsorption rate for removal fluoride. The defluoridationprocess was researched preliminarily, and the better results were obtained, eventually.The results show that the adsorption rate was getting to67.27%when the dosag ofMCLRB was0.3g/25mL, and getting to74.59%under the pH2.0of enzymolysisliquid. After MCLRB treatment, the variation of nutritional ingredients inenzymolysis liquid were investigated to some extent. There was a negative effect onthe content of protein after treatment compare to other nutritional ingredients. In oneword, MCLRB could be used as an effective fluoride adsorbent for removal excessfluoride from enzymolysis liquid to develop some meaningful food products byAntarctic krill with low level of fluoride concentration.All present methods for fluoride removal from drinking water have many owndisadvantages. Fluoride can be removed from drinking water by rare earth-modifiedchitosan, the fluoride is decreased obviously, and utilized the chitosan obtained fromseafood processing wastes. Consequently, those fluoride adsorbents synthesized inthis paper to remove fluoride, could be beneficial to economic, society, and foodsafety.