Selective removal of aluminum ions from rare earth solutions by using ion-imprinted polymers

Abstract

Remove of trace Al3+ from rare earth solutions is a challenging task. In the present study, an aluminum ion imprinted polymer (Al (III)-IIP) has been fabricated by surface-imprinting method. Al (III)-IIP was obtained by grafting silica gel with aminopropyl triethoxysilane and acrylic acid (AA). The structure and morphology of the polymer were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and thermogravimetric analysis (TG). The densification degree and the number of grafted functional groups were regulated by changing the synthesis conditions, and the optimal synthesis conditions are obtained as template ion: functional monomer: crosslinker = 1:8:8, and the optimal synthesis temperature is 333.15 K. The adsorption performance and selectivity properties of Al (III)-IIP were also investigated. The results show that at 298.15 K, the optimal pH for Al3+ adsorption is 4. The maximum adsorption capacity is 106.0 mg·g−1 at an Al3+ ion concentration of 1000 mg·L−1, which is 50% higher than that of reported recently. In addition, the adsorption process reaches equilibrium within 180 min. Furthermore, among many adsorption models and isothermal models, pseudo-second-order (PSO) adsorption model and Langmuir isothermal model are more suitable for the adsorption process. The selectivity coefficient of the Al3+ ion in binary mixtures of Nd3+, Ca2+ or Mg2+ are 17.76, 16.72 and 11.09, respectively. In addition, the adsorption mechanism of Al3+ is most probably caused by the formation of ionic bond between the Al3+ ions and the carboxyl functional groups on Al (III)-IIP and template effect. Results show that Al (III)-IIP has a great potential for a selective separation of aluminum ions from rare earth solutions.