Synthesis of mesoporous and microporous amine and non-amine functionalized silica gels for the application of rare earth elements (REE) recovery from the waste water-understanding the role of pH, temperature, calcination and mechanism in Light REE and Heavy REE separation

The aim of this research project was to investigate the impact of surface modified silica for the purpose of rare earth elements (REE) recovery from both artificial and real waste water. The four silanes used for the functionalization of silica gels during the course of study were 3-Aminopropyl triethoxysilane (APTES), 3-Aminopropyl trimethoxysilane (APTMS), Trimethoxymethylsilane (MTM) and Chlorotrimethylsilane (TMCS). The analysis of silica gel surfaces was conducted using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Brunauer Emmett Teller (BET) and Zeta potential measurements to better understand about the surface modification of the gels. The important yardstick for experimental analysis is the comparative REE removal efficiency of the silica gels in real and artificial waste water and how the trend of Light REE (LREE) and Heavy REE (HREE) removal changes with the effect of temperature and the presence of other competing ions. In addition, the influence of particle size, the effect of pH, the significance of calcination post silanization in the process of the selective REE removal as well as the silica leaching in both real and test waste water conditions has also been studied and addressed. The most effective results were observed for mesoporous silica gel A, with a particle size of 15–20 μm, in most of the cases for both calcined and non-calcined adsorbents. Amino-functionalized APTES/APTMS silica gels demonstrated the most impressive behavior among the four adsorbents in all the cases. However, the calcination seems to have affected the performance of such gels in the removal of the target elements.