Preparation And Application Of Novel Chelating Resins In Removal And Analysis Of Heavy Metals

In recent years, the contamination of seawater by heavy metal is becoming more and more serious resulting from the discharge of industrial and urban household wastewater. These heavy metals accumulated by the sea products like seaweed and marine fish have already presented a threat to man's health and life safety. Therefore, heavy metal detection and removal for contaminated water of this kind seems to be particularly important. Since the concentrations of heavy metals in water environment are usually found at trace or ultratrace levels, a preconcentration step is often needed before detection. Chelating resin is generally preferred for the extraction and preconcentration of trace metal ions from aqueous solutions due to its high adsorption capacity and selectivity, easy handling, good reusability and excellent acid and alkali-resistance. In this thesis, four kinds of novel chelating resins were prepared and the structures were characterized by element analysis and FTIR. The adsorption properties of the resins for several metal ions, especially that for Hg(â…¡) were investigated. Two of them were selected for the detection and removal of heavy metals in seawater.It is mainly manifested as follows:1. Four kinds of novel chelating resins were prepared by inducing four N, N-S, N-O or N-S-O type heterocyclic ligands onto chloromethylated polystyrene (PS-Cl), respectively; The influence of experimental conditions such as reaction solvent, reaction temperature and molar ratio of reagents of synthesis were discussed. The resin structures were confirmed by FTIR.2. The adsorption properties of four resins for Hg(â…¡) in aqueous solutions were investigated in the form of batch and column processes. Batch studies showed that all the four resins had powerful adsorption capabilities for Hg(â…¡) in HAc-NaAc medium at 298K. The statically saturated adsorption capacities of BITR, ATDR, ABMR and AMIR were 160.1,581.2,312.5 and 301.3 mg/g, respectively; Maximum recovery of Hg(â…¡) absorbed by BITR, ABMR and AMIR, at 100%, were achieved with 2.0,1.0 and 2.0 mol/L HNO3 eluent solutions, respectively. For this three resins, the adsorption capacities for Hg(â…¡) did not noticeably change (only a maximum 4% change was observed) during the five-time repeated adsorption-desorption operations. No satisfying eluent had been found for ATDR during the experiments, the maximum recovery was only 73.4% under the experimental conditions; Isotherms studies revealed that the adsorption followed the Langmuir model. Kinetics studies showed that the adsorption process obeyed pseudo-second-order kinetics, which suggested that chemisorption was the rate-controlling step. Thermodynamics studies suggested that the adsorption process of ATDR for Hg(â…¡) was mainly chemisoption, while those for BITR, ABMR and AMIR for Hg(â…¡) were the reusluts of both physisorption and chemisorption; Column studies showed that the dynamic saturated adsorption capacities of BITR, ABMR and AMIR were 170.1,354.1 and 318.9 mg/g, respectively. The Thomas model was successfully applied to experimental data to predict the breakthrough curves and to determine the characteristics parameters of the column useful for process design. SEM results showed that much granular substance was observed on the surface of BITR and AMIR after adsorption, which was proved to be mercury by further analysis with EDS; TGA results showed that the adsorption process led to the deterioration of the thermal stability of BITR and AMIR, and the adsorption and desorption operations were apt to be carried out under 100 C.3. The application of BITR and AMIR for removal and detection of heavy metals in seawater system was investigated. The experimental results showed that:(1) In the mixed metal ion system, BITR showed high removal rate and good recovery for Hg(â…¡), Pb(â…¡) and Cu(â…¡); AMIR showed high removal and recovery rate for Hg(â…¡). In addition, the removal dynamics indicated that the adsorption was relatively fast.(2) A new methord for determination of ultratrace mercury in seawater samples was developed by employing AMIR as a new packing material for microcolumn preconcentration coupled with ICP-MS. The proposed method was applied to the analysis of seawater samples.