Selective isolation of rubidium with mesoporous silica loaded with ammonium phosphomolybdate via an in-pore crystallization reaction

Abstract

The scarcity of rubidium (Rb) in ore form makes it a valuable metal, prompting the need to develop reusable adsorbent materials for effective separation of rubidium (Rb+) from salt lake brine, which holds significant importance. Herein, a novel Rb+ selective composite adsorbent was prepared by in-pore crystallization. Macromesoporous silica was prepared using polyoxyethylene (10) octadecyl ether (Brij S10) as a templating agent and the effect of different templating agents on the pore size was investigated. An AMP-SiO2 composite adsorbent for Rb+ was obtained by “growing” ammonium phosphomolybdate on the macro-mesoporous silica by in-pore crystallization reaction. The results indicated that the adsorption of Rb+ by the AMP-SO2 adsorbent adhered to monolayer chemisorption, which was verified by fitting the adsorption data using the pseudo-second-order kinetics and the Langmuir isotherm model, respectively. The loading of AMP was 29.4 %, which increased the adsorption capacity by 115 %. Furthermore, the adsorption rate of Rb+ on AMP-SO2 when interfering ions were present still reached 73.2 % (KCl), 76.4 % (CaCl2), and 86.6 % (MgCl2). Density functional theory simulation indicated that AMP-SiO2 exhibited a higher adsorption energy for Rb+ (−9.79 eV) than K+, Li+, Ca2+, and Mg2+. The Rb 3d and Mo 3d X-ray photoelectron spectra of AMP-SiO2 before and after adsorption of Rb+, indicated that the ion-exchange process between rubidium and lattice cations is the controlling mechanism. In addition, AMP-SiO2 also showed good regeneration performance and maintained a high adsorption rate after five adsorption-resolution experiments. In summary, the AMP-SiO2 composite adsorbent can effectively expose adsorption sites and improve mass transfer efficiency, and has significant potential for future application in rubidium separation and extraction.