A non-destructive technique to analyze Si content in evaluation of pore blockage of ferrihydrite-modified diatomite using XANES and BET

A non-destructive technique was developed in this study to analyze Si content. Pore blockage of ferrihydrite-modified diatomite (FHMD) by Si-containing ferric oxides was investigated using X-ray absorption near-edge structure (XANES) spectroscopy and Brunauer–Emmett–Teller (BET) analysis. The Si content of Si-containing ferric oxides of FHMD was represented by relative heights of pre-edge peak in Si L3,2-edge TEY XANES spectra. The relative heights of the pre-edge peak in the spectra of reference Si-containing ferric oxides were best fit by a sigmoidal function. The Si content of ferric oxides of FHMDs made with FeCl2 concentrations of 0.5, 1, 1.5, 2, and 2.5 M determined using this function were 0.23, 0.19, 0.12, 0.03, and 0.01, respectively. These results indicate the Si-containing ferric oxides present on the surface of 0.5- and 1-FHMD are ferrihydrite; on the surface of 1.5-FHMD are ferrihydrite and lepidocrocite; and on the surface of 2- and 2.5-FHMD are hematite. BET analyses indicated a sharp shift toward lower pore diameters in the pore size distributions of 0.5- to 1.5-FHMD and the presence of a type H2 hysteresis loop in the nitrogen adsorption–desorption isotherms; these were attributed to the deposition of ferrihydrite. In 2- and 2.5-FHMD, the significant increase in the pore volume of larger mesopores (between 10 and 50 nm) and the presence of a type H3 hysteresis loop were attributed to the deposition of hematite.