Syntheses And Adsorption Properties Of Silica-gel Supported Amido-amine Chelating Resin

Under conditions of various temperature, several multifunctionalized N donor compounds (Ethanolamine, Diethanolamine, Ethylenediamine, Diethylenetriamine, Triethylene tetraamine) were incorporated onto silicas to obtain chelating resins denoted as I, II, III, IV, V, VI, VII, respectively. Fourier transform-infrared spectra (FTIR), X-ray diffraction (XRD), thermogravimetry (TG) and elemental analysis were employed to character their structures. Metal ions Au³⁺, Ag⁺, Pb²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Hg²⁺ and Ni²⁺ were chosen as representatives to investigate the adsorption capacities of the above-mentioned functionalized silicas. The results of adsorption for metal ions showed that the resins had good adsorption capacities for Au³⁺, Ag⁺, Cu²⁺ and Hg²⁺, especially for Au³⁺ and Ag⁺. The experiments showed that amino-terminated silica exhibited better adsorption capabilities than hydroxyl-terminated ones. The adsorption kinetics and adsorption isotherms of the seven resins for Au³⁺, Ag⁺, Cu²⁺ and Hg²⁺ were studied. The results showed that the adsorption kinetics of the seven resins can be modeled by G. E. Boyd equation wonderfully, and Langmuir and Freundlich equations could well interpret the adsorption of I^VII for Ag⁺, Cu²⁺, Hg²⁺ and Langmuir equation for Au³⁺. The following results were obtained through a series of experiments:1. Fourier transform infrared spectroscopy test indicate that ethanolamine, diethanolamine, ethylenediamine, diethylenetriamine and triethylenetetramine were successfully grafted to silica gel surface;element analysis indicates that the functional content of II, III, IV, VI and VII were 0.585, 1.414, 4.073, 4.875 and 5.253 mmol/g respectively with the actual value smaller than the theoretic theoretical value; the results of X-ray diffraction analysis indicate that the resin had excellent mechanical stability; the pore structure analysis indicate that,the BET surface area, BJH average adsorption pore diameter and pore volume of amino-ending resin IV, VI and VII decreased gradually with the increase of N content in the silica gel surface.2. The experimental results of static adsorption indicate that the adsorption capacities of amino-ending products were greater than those of hydroxy-ending products; their adsorbability to Au³⁺ and Ag⁺ was better than that to Cu²⁺, Hg²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cd²⁺.3. The adsorption kinetics experiments indicated that the adsorption kinetics and dynamic adsorption conformed to G. E. Boyd equation within the experimental concentration range, showing that the adsorption process was following liquid membrane diffusion mechanism.4. The adsorption thermodynamics experiments indicated that the adsorption process to Au³⁺ conformed to Langmuir model within the experimental concentration range; the adsorption process to Ag⁺ and Hg²⁺, Au³⁺ conformed to Langmuir and Freundlich model and the adsorption process to Cu²⁺ conformed to Freundlich model.5. The dynamic adsorption experiments indicated that the adsorption of all other products to Au³⁺, Ag⁺, Cu²⁺ and Hg²⁺ conformed to G. E. Boyd equation, showing that the adsorption process was following liquid membrane diffusion mechanism. There may exist various adsorption mechanisms for the adsorption of hydroxyl-ending resin to Cu²⁺ and Hg²⁺.6. The influence of pH value on adsorption capacity indicated that the optimum pH value for Au³⁺, Cu²⁺, Hg²⁺ and Zn²⁺ adsorption was 2⁵, 6, 3 and 6, respectively.