Study On The Adsorption Behavior Of Chinese Fir Bark For Heavy Metal Ions

Using the Chinese fir bark as the raw material,this article applied the method of microwave auxiliary to extract the cellulose,extracted the lignin and polyphenol with other organic solvent method.It was used to modify the bark by means of epichlorohydrin,methanal and nitric acid.And a new HPLC method was studied for simultaneous determination of mixed metal ions,then kept applying this method to analyze the adsorption capacity to heavy metal ions of bark and its cellulose,lignin, polyphenol and its modified products.The microstructure of bark and its modified products had also been studied by SEM and IR.Then the mechanism of adsorption was discussed preliminarily.Finally it was reviewed that the regeneration of Chinese fir bark and its modified products.The results showed that,a new method was feasible for simultaneous determination of Cd²⁺,Pb²⁺,Ni²⁺,Cu²⁺,Cr³⁺,Cr(â…¥)from waste water by reversed phase high-performance liquid chromatography(HPLC),where the heavy metal ions were derived by sodium diethyldithiocarbamate(NaDDTC)before they were analyzed. The method was simple and accurate with a high analytic sensitiveness.It opened up a new way to determinate the content of the heave metal ions from waste water.The extraction of Chinese fir bark and its assaying indicated that,the content of cellulose,lignin and polyphenol was high in Chinese fir bark.The effective components from Chinese fir bark were good at removing metal ions.The sequence of their adsorption capacity was:polyphenol＞lignin＞cellulose,and the capacity to ions was:Cr³⁺＞Cu²⁺＞Pb²⁺＞Cd²⁺＞Ni²⁺.Also the phenolic hydroxyl and carboxyl groups in the cellulose,lignin and tannin were the effective groups to absorption as well as the active ones to modification.The conditions of modification by means of epichlorohydrin were investigated. The optimum conditions were as follow:the amount of epichlorohydrin was 10mL,the concentration of NaOH was 1.0mol/L,the reaction temperature of 60℃,the yield of modified bark by epichlorohydrin was 90.2%.The optimum conditions of modification by methanal were as follow:the reaction temperature of 60℃,the concentration of HCl was 1.0mol/L,the amount of methanal was 0.2g,the yield of modified bark by methanal was 85.2%.The optimum conditions of modification by nitric acid had been chosen as follow:the reaction temperature of 60℃,the concentration of nitric acid was 8%,the reaction time for 3.0h,the yield of modified bark by nitric acid was 86.6%.The microstructure of Chinese fir bark and its modifications had also been studied by SEM and IR.The results showed that non-modified bark kept good fibril structure while the fibril structure after modification was broken at different degree.The Chinese fir bark modified by epichlorohydrin had loosen and hydrophilic network structure,and compared to non-modified bark the adsorption capacity to Cd²⁺,Pb²⁺, Ni²⁺,Cr³⁺,Cu²⁺was improved respectively 41.3%,95.0%,316.7%,12.8%,0.9%.The tannin molecule of Chinese fir bark modified by methanal formed more cage-shaped structure,and the adsorption capacity to Cd²⁺,Pb²⁺,Ni²⁺,Cr³⁺,Cu²⁺was improved respectively 41.5%,170.9%,375%,4.5%,6.1%.And it was found that the hydrophilicity of Chinese fir bark modified by nitric acid increased,the adsorption capacity was improve respectively 5.2%,250.2%,1008.3%,1.7%,3.6%.It is obvious that,the modification of Chinese fir bark has potential application value in water treatment materials.It was reviewed that temperature,amount of the adsorbent,the pH value of solution and adsorption time had influence on the adsorption capacity.According to the results of the adsorption kinetics of Chinese fir bark to heavy metal ions,it showed that the adsorption rate of Cd²⁺,Pb²⁺conforms to first order kinetic model and the adsorption rate of Ni²⁺,Cr³⁺,Cu²⁺conforms to second order kinetic model.In addition,the regeneration of Chinese fir bark and the modified-bark was reviewed.They still possessed good absorption ability for heavy metal ions after regeneration as well as the effect of regeneration was well.