| Combined with the actual conditions of Guangxi, the research on the control of heavy metal pollution with low-cost, effective, and no second pollution has important practical and strategic significance. Cane-sugar industry is one of the distinctive pillar industries in Guangxi, the bagasse with28%～35%of hemicellulose is the main by-product. High density carboxyl would be derived from the side-chain of hemicellulose via chemical modification, and the derivative is capable of metal chelating. This study researched on the extraction of hemicellulose by Microwave-Alkali Method, the component of hemicellulose was analyzed; the hemicellulose was modified by carboxylation and amphoteric modification, and the structure and thermophysical property were characterized before and after chemical modification; the modified production was used to test the adsorption effective of Cu2+、Pb2+、Cd2+as adsorbent, the kinetic and thermodynamic characteristics of adsorption was also studied.1. Extracion of hemicelluloses from sugarcane bagasse under microwave irradiation was studied in this paper. The effect of liquid to solid ratio (V (water):m (stover)), alkali consumption (m(NaOH):m (stover)), time, microwave power, and temperature on the extraction yield of hemicelluloses was investigated. The optimal processing parameters were:liquid to solid ratio of25ml/g, alkali consumption of2.0g/g, time of20min, and microwave power of1200W. The obtained hemicelluloses was qualitatively analyzed by gas chromatography, and results show that, sugarcane bagasse hemicelluloses is a kind of xylan hemicelluloses, mainly consisting of simple sugars like D-xylose, D-arabinose, L-arabinose, D-galacturonic acid, D-galactose and D-mannose.2. Carboxyl is adopted to modify the properties of the sugarcane bagasse hemicelluloses, and effects of the succinic anhydride, N-bromination succinic imide, reaction time and reaction temperature on the modification were studied. The result shows that under the conditions of succinic anhydride for3g, N-bromination succinic imide for0.1g, reaction time for6h and reaction temperature at70℃, modified hemicelluloses can be obtained more satisfied from the1g dried sugarcane bagasse hemicelluloses. Characterization of the hemicelluloses was respectively done through the FT-IR, nuclear magnetic resonance (NMR), thermal analyzer and scanning electron microscopy (SEM) before and after the experiment, and results show that the structure and form of sugarcane bagasse hemicelluloses were changed after the carboxyl modification, and thermal stability was also found declined.3. Modifiers were applied to make amphoteric modification on sugarcane bagasse hemicelluloses, and examined the amount of modifiers, the amount of Sodium hydroxide, reaction temperature, reaction time, the order of modification and other factors on the impact of gender modification, the result shows that, when making cationic modification on the one gram of dried sugarcane bagasse hemicelluloses, we can obtain more satisfactory cationic modified product under the conditions that the amount of3-chloro-2-hydroxypropyl trimethyl ammonium chloride is0.3g, the amount of Sodium hydroxide is0.1g, the reaction time is two hours and the reaction temperature is60℃; when making modification of anion on the one gram of dried sugarcane bagasse hemicelluloses, we can obtain more satisfactory anionic modified product under the conditions that the amount of Chloro-acetic acid is0.4g, the amount of Sodium hydroxide is0.3g, the reaction time is two hours and the reaction temperature is80℃;we can get better Gender modified products as the order of modification that first the Anion and then the cation. IR, NMR, scanning electronic microscopy and thermal analysis are used to do characterization on Gender modified bagasse hemicelluloses. The result shows that the amphoteric method was adopted in this study can draw the Carboxyl and Quaternary ammonium into sugarcane bagasse hemicelluloses, and found that the molecular structure and morphology of sugarcane bagasse hemicelluloses which were made amphoteric modification, its thermal stability decreased.4. Ions i.e. Cu2+, Pb2+and Cd2+were absorbed by the carboxylated bagasse hemicelluloses, and the effect of pH value to the adsorption capacity of metal ion has been studied. Results show that the optimal adsorption pH values for Cu, Pb and Cd were5.5,5.5and7.5, respectively. The adsorption capacity to ions Cu2+, Pb2+and Cd2+increased with increasing initial concentration of the metal ions, and the variations of adsorption capacity decreased in higher initial concentration of the metal ions. Thermodynamics analysis show that the adsorption of Cu2+, Pb2+and Cd2+fits the Freundlich isothermal adsorption model very well. It can be seen from the model that△H<0and△G<0, whichmeans that the absorption reaction was an exothermic reaction and the reaction was spontaneous. Kinetic study shows that absorption of the carboxylated bagasse hemicelluloses to ions Cu2+, Pb2+and Cd2+can be well described by the Pseudo second-order kinetics model. The theoretical values of the maximum absorption capacity qe,cal for ions Cu2+, Pb2+and Cd2+were20.28mg/g,82.64mg/g and30.58mg/g, respectively. In addition, at temperature of293K, the Pseudo second-order kinetics model for ions Cu2+, Pb2+and Cd2+were dqt/dt=0.0623(19.34-qt)2,dqt/dt=0.0237(59.52-qt)2and dqt/dt=0.0433(29.41-qt)2.5. Ions i.e. Cu2+, Pb2+and Cd2+were absorbed by the amphoteric bagasse hemicelluloses, and the effect of pH value to the adsorption capacity of metal ion has been studied as well.The results show that the optimal adsorption pH values for Cu2+, Pb2+and Cd2+are6.5,6.0and7.5, respectively. Net adsorption to ions Cu2+, Pb2+and Cd2+increased with increasing the initial concentration of the metal ions. Thermodynamics analysis show that the adsorption of Cu2+, Pb2+and Cd2+fits the Freundlich isothermal adsorption model quite well. It can be seen from the model that△H<0and△G<0, which means that the absorption reaction was an exothermic reaction and the reaction was spontaneous. Kinetic study shows that absorption of the amphoteric bagasse hemicelluloses to ions Cu2+, Pb2+and Cd2+can be well described by the Pseudo second-order kinetics model. The theoretical values of the maximum absorption capacity qe,cal for ions Cu2+, Pb2+and Cd2+were26.45mg/g,65.79mg/g and36.23mg/g, respectively. In addition, at temperature of293K, the Pseudo second-order kinetics model for ions Cu2+, Pb2+and Cd2+were dqt/dt=0.00936(26.45-qt)2,dqt/dt=0.0231(65.79-qt)2and dqt/dt=0.0428(36.23-qt)2. |
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