| Eichhornia crassipes (E. crassipes, i.e. water hyacinth) has been listed as one of the world's top ten harmful weeds, due to its strong reproductive capacity. In our lab, there are some researches on the transformation of E. crassipes straw into cellulose xanthogenate as an adsorbent to heavy metals in water bodies. The stem & leaf of E. crassipes could be treated by alkali, and alkali degummed straw be sulfonated by CS2, and substituted by magnesium salts to obtain cellulose xanthogenate. In addition, a bacteria strain named A1 strain which had good degumming effects of pectin, lignin and hemicelluolose, was screened out from the sediment of Lake Nanhu of Wuhan city, China. To deal with the disadvantage of alkali-degumming method which brought large amount of alkaline waste water, different degumming technics in preparation of cellulose xanthogenate from stem & leaf of E. crassipes were investigated and compared. Three degumming methods, including strong alkali (NaOH), microorganism (bacteria A1) and enzyme (pectase), were used to treat stem & leaf straw of E. crassipes, respectively, and the same subsequent CS2 sulfonation and magnesium substitution steps were applied to prepare cellulose xanthogenate. Meanwhile, as a control, microcrystalline cellulose (MCC) as pure cellulose, was also transformed into its cellulose xanthogenate (CCX) according to alkali-degumming method and the same subsequent steps. Efficiency and effects of different degumming treatments were assessed by analyzing the constitute of functional groups, surface morphology and element composition of the plant materials, characterized by FTIR and SEM-EDXA, and the adsorption properties of the adsorbents to different kinds of aqueous heavy metals. Besides, taking alkali-degumming method obtained cellulose xanthogenate (NaOH-ECX) as model adsorbents, the chemical stability of the adsorbents in different practical utilization environment were investigated, and the relative stability of different salts of cellulose xanthogenate (CCX) made from MCC were also investigated. The main results are as follows:(1) FT-IR and SEM-EDXA show, bio-degumming technics, including bacteria A1 strain treatment and pectase treatment, all have similar good effect in degumming of the non-cellulose materials including lignin, hemicellulose and pectin, etc., from the the stem & leaf of E. crassipes as alkali treatment. The surface structure of pectase degummed cellulose xanthogenate (Pect-ECX) was irregular and honeycombed which was beneficial to adsorption, on the contrary, the surface of alkali degummed cellulose xanthogenate (NaOH-ECX) and A1 strain degummed cellulose xanthogenate (A1-ECX) were smooth with big blockshaped substance. Moreover, among the 4 cellulose xanthogenates, the content order of sulfur and magnesium which were the key elements for heavy metal adsorption, was Pect-ECX> NaOH-ECX> A1-ECX> CCX. Surface properties and element constitute have great influence on heavy metals'adsorption performance.(2) Four cellulose xanthogenates, NaOH-ECX, A,-ECX, Pect-ECX, CCX, all have good adsorption capability to Cu2+, Zn2+, Pb2+ and Cd2+.The order of adsorption capability was Pect-ECX> A,-ECX≈NaOH-ECX> CCX. The order of adsorption capability for 4 heavy metals of these 4 adsorbents was Pb2+> Cu2+> Cd2+> Zn2+.(3) The adsorption of Cu2+, Zn2+, Pb2+ and Cd2+ on NaOH-ECX, A,-ECX, Pect-ECX and CCX is very fast. The adsorption equilibrium would be achieved in 60-80 minutes in the adsorption kinetics experiment. The pseudo first-order equation generates the best fit effect to the experimental data of the four investigated adsorption systems. With the increase of concentration of heavy metals, the adsorption rate decreased. There is no rule about the adsorption rate on four adsorbents.(4) In dark condition, NaOH-ECX is unstable in the first 15 days, the content of surfur and magnesium decreased 9% and 10%, respectively. Compared with this, the loss of S and Mg in the material are 2% and 1% which have no significant change in the last 15 days. When NaOH-ECX is exposed in ultraviolet ray, the change rates of sulfur and magnesium content decrease 10% and 12% in the first 15 days, respectively, and decrease 1% and 4% in the last 20 days. This means that the effect of ultraviolet irradiation still exists. After deducting the changes of S and Mg in dark condition, the changes of sulfur are 5%(0-15 day) and 2%(15-30 day), the change of magnesium is 1.5% in the whole experiment period. Ultraviolet irradiation can affect the stability of NaOH-ECX to a certain extent, thus NaOH-ECX should be stored in sealed and dark condition.(5) pH value had great influence on the stability of NaOH-ECX, NaOH-ECX was the most unstable in acid solution, which reflected by its far higher decrease of sulfur and magnesium content in acid solution than in neutral and alkaline solution. When NaOH-ECX is used to deal with water polluted by heavy metals, for minimizing the possible secondary pollution caused by the adsorbent, the adsorption time should not be too long and the acidity of water can not be too high.(6) The order of relative stability of different heavy metals'cellulose xanthogenate was:CCX-Cu>CCX-Pb>CCX-Zn>CCX-Mn>CCX-Ca>CCX-Mg>CCX-Na>CCX-K (pH = 5), CCX-Fe> CCX-A1 (pH= 3). |
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