Studies On Adsorption For Heavy Metal Ions And Surface Imprinting For Rare Earth Ions Based On Chelating Material PAO/SiO₂ With Composite-Type

Because of amidoxime chain section containing amine and oxime-based bidentate ligand groups, amidoxime type chelating adsorption material have a strong sequestration on a variety of rare earth and heavy metal ions. In the paper, acrylonitrile (AN) was graft-polymerized on micron-sized silicon particles. Subsequently, the grafted PAN was converted to poly (amidoxime) via amidoximation reaction, and composite-type chelating adsorption particles PAO/SiO₂ were obtained. The chelating adsorption behaviours of PAO/SiO₂ towards heavy metal ions were examined and the preparation of surface imprinting materials on the separation of the application of rare earth elements. The results of this study have obvious scientific significance and value in the field of environmental science and the field of rare earth ion separation technology.Micron-sized silicon particles were chemically surface-modified with coupling agent KH570, and grafted particles PAN/SiO₂ were obtained. The graft polymerization of acrylonitrile (AN) on the surfaces of particles PAN/SiO₂ was performed in a solution polymerization system. The transform reaction of nitrile groups of the grafted PAN to amidoxime groups (AO) was conducted with hydroxylamine hydrochloride as reagent in the presence of Na2CO3, resulting in functional composite-type particles PAO/SiO₂, on which poly (amidoxime) macromolecules were chemically anchored. The two kinds of particles were characterized with FTIR, TGA and SEM methods. The effects of the main factors on the graft polymerization of AN and on the amidoxime transform reaction of the grafted PAN were examined. The experimental results show that in the graft polymerization process, the grafting degree of PAN can get up to 14g/100g by controlling the consistence of acrylonitrile, the used amount of initiator, the amount of the double bond, temperature and time. The amidoxime transform reaction of the grafted PAN is liable to be carried out. The conversion ratio of the nitrile groups is affected greatly by the pH value of the medium, temperature, consistence of hydroxylamine hydrochloride and time. The suitable reaction conditions are as follows: pH=6-7, T=70℃, c(hydroxylamine hydrochloride)=1.0mol/L and t=4h. Under the appropriate conditions, the functional particles PAO/SiO₂ with a nitrile group conversion ratio of 78% can be obtained.In this work, the chelating adsorption behaviours of PAO/SiO₂ towards several heavy metal ions were examined, the adsorption mechanism and adsorption thermodynamics were mainly studied. The experimental results show that the composite-type chelating adsorption material PAO/SiO₂ has strong chelating adsorption ability for heavy metal ions by right of the synergy of electronic interaction and coordination chelation between amidoxime groups of PAO/SiO₂ and heavy metal ions. Especially, PAO/SiO₂ possesses very strong chelating adsorption ability for Pb²⁺ ion, and the adsorption capacity can get up to 12g/100g at room temperature. The adsorption process is chemical adsorption process driven by entropy, and raising temperature will facilitate the adsorption process and increase the adsorption capacity. In a pH range in which the hydrolysis of heavy metal ions can be inhibited, to increase pH value of the medium will strengthen the chelation adsorption ability of the composite-type chelating adsorption material PAO/SiO₂ towards heavy ions. For the different metal ions, PAO/SiO₂ exhibits different adsorption abilities, and the order of the adsorption capacity is Pb²⁺>Cu²⁺>>Cd²⁺>Ni²⁺.The ionic imprinting towards the grafted PAO was performed with Gd³⁺ ion as template ion and glutaral as crosslinking agent by using the novel surface-molecular imprinting technique established by our research group, and the Gd³⁺ ion–imprinted material IIP-PAO/SiO₂ was prepared. Rare earth element Eu and Sm are adjacent to Gd in lanthanum elements, and the ionic radius difference between Eu³⁺ and Sm³⁺ ions and Gd³⁺ ion is only 1-3pm. In this work, with Eu³⁺ and Sm³⁺ ions as contrast substances, both static and dynamic methods were adopted to study the binding properties and ion recognition character of IIP-PAO/SiO₂ for Gd³⁺ ion. The experiment results show that IIP-PAO/SiO₂ have specific recognition selectivity and excellent binding affinity for Gd³⁺ ion, and the selectivity coefficients of IIP-PAO/SiO₂ for Gd³⁺ ion with respect of Eu³⁺ ion and Sm³⁺ ion are 7.49 and 7.93, respectively. Besides, IIP-PAO/SiO₂ has excellent elution property, with diluted HCl solution as eluent, the desorption ratios of Gd³⁺ ion reach 99.54% in 29 BV. The selectivity coefficients affected greatly by the pH value of the medium and temperature the used amount of glutaral. The suitable reaction conditions are as follows: pH=5.5 and v(glutaral)=1ml.