Study On The Application Of Water-soluble Carboxymethyl Chitosan In Remediation Of Heavy Metals Contaminated Soils

The remediation of the heavy metals contaminated soil is a hot research field of thecurrent environmental science. Phytoremediation and electroremediation of heavy metalscontaminated soil were studied in this paper. The studies based on the researches of athome and abroad and combined actual conditions. The combination of water-solublecarboxymethyl chitosan and electrokinetic remediation, phytoremediation may enhance thetreatment effectiveness of single electrokinetic remediation and phytoremediation forheavy metals contaminated soil. In this paper, the main contents and results aresummarized as follows:1.Water-soluble carboxymethyl chitosan (WSCC) with high water solubility andcoordination ability for heavy metal was synthesized by the reaction of chitosan withchloroactic acid under alkaline condition. The infrared spectra showed that the carboxymethyl groups were added with the help of O-carboxy methyl reaction, which results inenhancement of solubility. The ultraviolet and infrared spectra showed that WSCCcoordinated with heavy metal through the amino and carboxyl groups.2.The solubilization experiments about lead and cadmium carbonate showed thatWSCC had obvious solubilization for lead and cadmium carbonate，when the concentrationof WSCC reached2g/L, the aqueous lead and cadmium concentration was about600mg/Land275mg/L, respectively. A high organic matter content in soil resulted in a lowerdesorption efficiency of WSCC for lead and cadmium in soil，and the desorption efficiencyof lead and cadmium increased with increasing pH，ionic strength and initial concentrationof WSCC. The data of lead and cadmium desorption in soil were well fitted by thepseudo-second-order rate equation. The exchangeable fraction of lead in soil increasedobviously in the presence of WSCC. 3.The electrokinetic remediation of heavy metals from contaminated soil showedthat the electric current first increased then decreased with increasing time and reachedsmooth finally. The cumulative EOF increased with increasing time and concentration ofWSCC. pH of soil increased gradually from anode to cathode, the moisture content anddecreased gradually from anode to cathode. The total removal efficiency of the lead andcadmium is not very high, but most of the lead and cadmium migration to the cathodedirection under the electric field finally. So the electrokinetic remediation was applied tothe heavy metal contaminated soil.4.The Phytoremediation of heavy metals from contaminated soil showed that lowconcentration of lead was in favour of the growth of plants, but high concentration of leadinhibited the growth of plants. The concentration of lead in the plants was related to theconcentration of lead in soil. The content of lead in the plants increased with increasingconcentration of the soil. After added WSCC, the content of lead in the plants and themigration abilities from the root to stem increased.5. The toxicology analysis of Scenedesmas obliquus showed that lead and cadmiumcan significantly inhibit the growth of algae. The96h-EC50of lead and cadmium were744μg/L and122.77μg/L, cadmium was more poisonous than lead. The WSCC was non-toxicand can reduce the toxicity of lead and cadmium.