| So far, chitosan is found as the only alkaline polysaccharide in nature, there are lots of lively amino and hydroxyl groups which can chelate with metal ions to form precipitates connected in molecules chain. The ability of chelating metal ions as well as stability of chitosan can be greatly improved by chemical modification, so that to be widely used in treatment of wastewater containing heavy metal ions.We made use of the structure and characteristics of chitosan and dithiocarbamate (DTC) groups, proceeded chemical modification on chitosan, and introduced dithiocarbamate (DTC) groups into molecular chain of chitosan through xanthation to form a class of DTC-modified chitosan. A series of single factor experiments and orthogonal test were conducted to found out the optimal preparation of DTC-modified chitosan were:methanol volume of 150mL, swelling time of 1.5 h, dropping time of CS2 and ethanol mixed solution of 1.5 h, NaOH concentration at 50%, ratio of CTS (g) /CS2 (mL) at 1:6, water bath temperature at 45℃, bath time of 14h. The influence order of four main experimental factors was:CTS (g)/CS2 (mL)> NaOH concentrations> bath time> bath temperature.Meanwhile, with the scaled and intensive development at the breeding business, large quantity of feed be used, but there are many heavy metal ions in the feed, the ion which unabsorbed by animals may into water through excrement, which may bring about intimidate to water environment.The adsorption of modified chitosan for Cu2+ and Zn2+ was discussed form the medium acidity, modified chitosan dose, reaction temperature, adsorption isotherm, shaking time and ions coexistence. The results showed that:the modification of chitosan widened the range of pH value, the removal rate of trapping agent for Cu2+. Zn2+ significantly increased with the pH value increase, the pH value should controlled in the range of 3.0～5.0 for better results. The dose of modified chitosan had a greater impact on adsorption properties, the optimal dose was 0.15g when the initial concentration of Cu2+ and Zn2+ at 100mg/L. The capture ability of DTC-modified chitosan was not affected too much by temperature, so the experiments were carried out at room temperature. Through analyzing the adsorption type of heavy metal ions, we found the adsorption of modified chitosan for Cu2+ and Zn2+ was monolayer, and this was identical with Langmuir equation. Modified chitosan had a faster absorption rate on Cu2+ and Zn2+, the equilibrium was reached basically in 20minutes. The Cu2+ and Zn2+ equilibrium adsorption capacity were separately 33.801 mg/g and 31.182 mg/g in co-exist solution with initial Cu2+ and Zn2+ concentrations both at 100mg/L, this indicated that DTC-modified chitosan had a better selectivity on Cu2+Through the treatment of livestock wastewater containing heavy metal ions with modified chitosan, we could found that the modified chitosan have a good treatment effect on actual wastewater under complex systems. The adsorption efficient for Cu2+ was higher than Zn2+, and the residual concentrations of Cu2+ and Zn2+ in effluent both reached the national emission standards.
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