Synthesis of mesoporous silica containing group 2-metal cations and their performance behavior in rare earth cation adsorption

Herein, mesoporous silica was prepared using the co-precipitation process by adding Mg, Ca, or Sr. The specific surface areas of silica were maintained with the incorporation of Mg or Ca substitutes with several tens mol%; however, they were observed to decrease significantly due to the Sr substitution. Further, the applicability of Mg, Ca, and Sr as modifiers was estimated using XPS spectra. The simultaneous ion-exchange in the mesoporous silica hybrids was confirmed by testing an aqueous solutions containing 12 coexisting rare earth metal cations. A higher degree of adsorption was obtained as the ionic radius of the cations decreased. In addition, the concave tetrad effect demonstrated that adsorption occurred through the ion-exchange reaction at specific active sites. To investigate the kinetics of the ion-exchange reaction, rate constants were estimated from time-dependency measurements. The measured rate constants for the hybrids were approximately 5.4×10-3, 5.2×10-3, and 1.5×10-3 min−1, for Mg, Ca, and Sr, respectively. Silica hybrids containing Mg and Ca exhibited mesoporous structures that proved to be advantageous on accelerating the reaction rates obtained for lanthanoid adsorption.