The Study Of Pb(Ⅱ) Purification From Polysaccharide System By Thiol-functionalized Cellulosic Biomass

With the rapid development of economic, food industry also get the all-round development, and the emergence of "problem foods" is inevitable, so food safety issues received more and more attentions by people, such as the content of heavy metal in fruit juices is out of limit. Due to the thiol group has a good capacity for heavy metal binding, the thiol-functionalized absorbent cotton (TAC) used in this experiment was prepared by esterification reaction under the presence of concentrated sulfuric acid between thioglycollic acid and absorbent cotton, which is a typical and pure cellulose. We used glucose solution containing Pb ion as a substitute for beverages, and mainly investigated the structure characteristics of TAC, lead adsorption on TAC and adsorption mechanism. The structure characteristics of TAC were analyzed by means of scanning electron microscope energy spectrum analysis, zero charge points and Infrared spectral analysis. The purification of lead in simulation beverage were studied as a function of initial pH, sorbent dose, initial lead concentration, initial glucose concentration, ionic strength, coexisting ions, functional group in adsorbents, contact time and temperature, while the concentration of glucose was analysed in the adsorption process. The intraparticle diffusion kinetie, pseudo first order and pseudo second order models were used to fit the experimental data of kineties. Langmuir and Freudlich isotherms were applied to fit the adsorption isotherm models. Additionally, the adsorption mechanism was discussed by comparing the FTIR spectra of adsorbent before and after adsorption.It can be seen from the structure characteristics that the surface of absorbents became rougher, and the ester group and thiol group which could bind heavy metal have been introduced successfully after modification. The research results of lead purification showed that the adsorption capacity of Pb(II) increased and the glucose losses decreased as pH increased from2.0to6.0. TAC was able to adsorb28.7mg/g without loss of glucose at the optimum pH6.0. And Pb(II) adsorption capacity increased with lead concentration, glucose concentration and efficient functional group. The adsorption process was finished within120min and followed the pseudo second order models. The isotherms indicated that the adsorption was described better by Langmuir model, and the adsorption of lead on TAC was spontaneous, entropy increase and endothermic processes in nature. The infrared spectra indicated that lead adsorption mechanism mainly was the complexation between the sulfur atoms and lead ions.