Studies On Modification Of Natural Macromolecular Chitosan And Its Adsorption Performance For Trace Heavy Metals

Chitosan has advantages of high adsorption capability and biodegradationaccording to much domestic and foreign literature. Chitosan was modified to preparethe sorbents. We systematically studied the adsorption performance of trace cadmium,lead and copper on modified chitosan with flame atomic absorption spectrometry sothat a new simple, rapid and accurate with high efficiency and sensitivity method fordetermination of trace harmful element was developed. The major contents werelisted as follows:1. We described the severity and harm of the pollution of heavy metals. It brieflysummarized the methods of separation and enrichment for trace heavy metals. Thestructure, property, modification and application on solid-phase extraction as sorbentof chitosan were described in detail.2. CRN （crosslinked chitosan modified with triethylenetetramine） was prepared bymodifying chitosan with triethylenetetramine. The synthesized CRN wascharacterized with elemental analysis and FT-IR. Using CRN as sorbent we studiedthe adsorption behavior of trace cadmium on CRN. The adsorption mechanism wasalso discussed. It was found that the static saturated adsorption capacity was31.0mgg^-1. The detection limit of this method was24.6ng mL^-1and the relative standarddeviation （RSD） was2.1%for cadmium of1.0μg mL^-1at7levels. The proposedmethod was applied to determination of trace cadmium in slag samples withsatisfactory results.3. A new method was developed for separation and enrichment of trace lead usingCRN as sorbent prior to determination with FAAS. The linear range was0.2～20gmL^-1with the linear regression equation of A=0.164c-0.0006. The detection limit was38.2ng L^-1and the RSD was1.15%. The proposed method was applied todetermination for trace lead in environmental waters with recoveries between97.4%and102.2%.4. Si-CCTS （chitiosan modified with silica-gel） was prepared by modifyingchitosan with silica-gel. The synthesized Si-CCTS was characterized with SEM andFT-IR. Using Si-CCTS as sorbent, the conditions of simultaneous adsorbing anddesorbing of cadmium and copper on Si-CCTS was studied systematically. Thedetection limit for cadmium and copper was0.45g L^-1and0.58g L^-1, respectively. The RSD was2.62%and2.85%, respectively. The proposed method was applied tothe simultaneous adsorption and determination for trace cadmium and copper withsatisfactory results.5. The adsorption performance was studied in detail using a micro-column packedwith Si-CCTS. Trace copper could be quantitatively adsorbed by Si-CCTS at pH5.0,sampling flow rate of5.5mL min^-1and time of100s. The copper sorbed ontoSi-CCTS could be completely eluted with0.1mol L^-1HNO₃at a flow rate of2.0mLmin^-1. The proposed method was applied to the determination of trace copper inpolygonum multiflorum and isatis root with satisfactory results.