Preparation Of Novel Solid-phase Chelate Extractants For Heavy Metal Removal From Aqueous Solution

Heavy metal as one of the important pollutants in water becomes a severe public health concern because of its persistent nature and negative effect on the environment. They are difficult to remove from aqueous waste streams with trace quantities using conventional methods such as chemical precipitation. The process of sorption/ion exchange appears to be one of the few alternatives available for such situations. To explore the availability of different kinds of adsorbents associated with convenient procedures for obtaining high efficiency has been a hot topic recently.This paper discussed the hazardous effect of heavy metal ions in aqueous solution and the development of treatment technologies for heavy metal removal. Based on the viewpoints of speciation of heavy metals in waters, the distribution of different species of heavy metals and the binding mechanism with adsorbents were investigated. To develop new efficient solid adsorbents by chemical modification or combining it with liquid extractants, four different kinds of solid extractants were prepared including PS-EDTA resin, MR-PVA beads, PVA/EDTA resin beads and PVA/TL beads. Then these new adsorbents were characterized with FTIR, SEM and TGA. Furthermore, adsorption experiments in a batch or/and column method were carried out to examine the adsorption performance for some heavy metal ions. Many models such as kinetic, thermodynamic, equilibrium models were used to fit the experiment data to understand the adsorption mechanisms.1. A bipolar chelating PS-EDTA resin was prepared as an adsorbent to remove zinc ions from aqueous solutions. The maximum adsorption capacity of PS-EDTA resins was 57.8 mg/g at pH 6.0. From kinetic studies, it is found that the adsorption of Zn2+ is fast for the initial 15min and it reaches equilibrium around approximately 20 min. The kinetics of adsorption of zinc was found to follow pseudo-second-order model indicating the applicability of this kinetic equation for this system and the process controlling the rate may be a chemical sorption. The equilibrium adsorption data are tested with various isotherm models among which Tempkin and Freundlich models fit the experimental data well. In the column study, adsorption of zinc by PS-EDTA resins followed the Yan model better than the Thomas model.2. Novel MR-PVA beads were prepared and MR-PVA is found to be a better adsorbent for selective removal of Pb (II) from micro-polluted water. The maximum adsorption capacity of Pb(II) (213.89 mg/g) onto MR-PVA beads is obtained at pH 6.0. From kinetic studies, it is found that the adsorption of Pb (II) is fast for the initial 30min and it reaches equilibrium around approximately 2.5h. Tempkin and Langmuir models fit the experimental data well. The kinetics of adsorption using MR-PVA beads is explained by the second-order kinetic model. Although the presence of other ions such as Zn2+, Cu2+, Na+ and Cl- are found to have effect on Pb (II) adsorption, MR-PVA beads show a good selective removal of Pb(II)from multi-metal ions solution.3. The work evaluated the PVA/EDTA resin containing hydroxyl, carboxyl and amine functional groups for removing target pollutant Zn (II) from aqueous solutions. Based on the adsorption isotherm studies the uptake capacity of Zn (II) on PVA/EDTA resin is larger than those of other bio-sorbents. For all the system studied, chemical reaction seems significant in the rate-controlling step and the pseudo-second-order chemical reaction kinetic provides the best correlation of the experimental data. Furthermore, The PVA/EDTA resin could be effectively regenerated (>95%).4. Removal of mercury from its aqeous solutions using ionic liquid [A336][MTBA]-immobililized PVAbeads (PVA/IL) were studied. The results revealed that pH 5.8 and the adsorbent dosage 1 g L-1 are the optimum conditions for its operation in batch mode. More than 99% of mercury ions can be removed after 18h with the maximum adsorption capacity of 49.89 mg/g and the pseudo-second-order chemical reaction kinetics provide the best correlation of the experimental data. Moreover, the competitive experiments showed that even in the solutions including high concentration of Cu (II) and Pb (II), PVA/IL beads kept the same adsorption removal efficiency of Hg(II).