| With the rapid decrease of the reserves of oil and coal and constant rising in oil price, biomass resource utilization has attracted increasing attention. Meanwhile, with the high-speed development of modern industry, large amount of wastewater containing heavy metals has caused serious harm to environment and human health, so the reseach and development of adsorbent materials with low cost and good performance to remove heavy metal ions has great significance. Due to its reproducibility, large quantity as well as non-toxic, biodegradable, environmentally friendly features, cellulose have been paid much attention worldwide, and the research on cellulose or biomass based materials has become one of the hot topics.In the present paper, the adsorption properties of cellulose xanthogenates prepared from6kinds of plant materials including E. crassipes were investigated, meanwhile, the optimization of preparation process of cellulose xanthogenate was discussed. The results can provide the theory basis for developing efficient biomass based adsorbent, and enrich the theory and method about biomass modification, and promote the high value utilization of Eichhornia crassipes (E. crassipes) straw resources obtained from eutrophic water bodies. The main conclusions are as follows:(1) In the6kinds of plant material, the cellulose contents of4kinds of terrestrial plants including Sugarcane bagasse, Rape straw, Rice straw and Spruce chip were higher than those of2kinds of aquatic plants including E. crassipes and Alternanthera philoxeroides (the cellulose content of Spruce chip was2.3times as high as that of Alternanthera philoxeroides), but the Cd adsorption capacities of cellulose xanthogenate derived from terrestrial plants were lower than those from aquatic plants. It reflected the superiority of the aquatic plants, especially E. crassipes, as biomass adsorbent materials. The S contents of cellulose xanthogenates of calcium derived from these plants materials presented linear positive correlation with Cd adsorption capacity (r=0.787, n=6), indicating that S in the adsorbent was the key element in adsorption of heavy metals.(2) Compared to Freundlich adsorption isotherm equation, Langmuir adsorption isotherm equations was more suitable for the description of the adsorption of Cd by E. crassipes derived cellulose xanthogenate (ECX). Pseudo-second-order kinetics was more suitable for the description of the adsorption process than pseudo-one-order kinetics, and the adsorption got a good effect. The adsorption could occur spontaneously, and high temperature was beneficial to the adsorption. (3) Alkaline condition was prerequisite for the taking place of etiolation reaction (esterification reaction) of microcrystalline cellulose. Under alkaline condition, CS2was involved in the derivatization reactions, in which the main reactions included that the alkali (sodium hydroxide) dissolved CS2directly reacted with alkalized cellulose to form cellulose xanthogenate of sodium. The substances presented in liquid phase were all produced by side reactions. The higher the alkaline intensity is, the severer the side reactions are. It suggested that pH of the solution had important influence on the composition of adsorbent in the preparation of cellulose xanthogenate from microcrystalline cellulose.(4) In the displacement reaction (step) of xanthogenate preparation, when calcium salt (CaCl2) was employed instead of magnesium salt (MgSO4) which was commonly used to generate cellulose xanthogenate of calcium, and pH value was adjusted to be11before displacement reaction, the production of inorganic salt precipitation impurities, such as Mg(OH)2/MgCO3or Ca(OH)2/CaCO3could be prevented effectively. Adding washing steps after obtaining alkalized cellulose could remove lignin more completely for improving the purity of the alkalized cellulose, and help the pH adjustment before the subsequent displacement reaction. Furthermore, in the washing step of the obtained cellulose xanthogenate of calcium after the substitution reaction, the mixture of alkaline water and alcohol, instead of the mixture of inorganic salt and alcohol commonly used, could improve the product content of effective components (cellulose xanthogenate of calcium) effectively and thus enhance the adsorption effect of heavy metals. |
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