Effect of dry grinding on the physicochemical properties of silica materials prepared from kaolin residue

The present study evaluates the effect of dry grinding on the physicochemical properties of silica materials prepared from kaolin residue. The kaolin residue was ground at varying times and then treated with sulfuric acid (20 mass%) at 100 °C for 2 h. X-ray diffraction, scanning electron microscopy, Fourier transformation infrared spectroscopy, and N2 adsorption techniques were used to examine the effect of grinding on the raw materials and products. The SiO2 content was also analyzed to compare with the raw materials. The degree of amorphization calculated from X-ray diffraction (XRD) data of silica increased with grinding time. The band intensities of SiOAl and AlOH were decreased by the grinding process, which was beneficial to the subsequent leaching. Morphologic and structural studies revealed that the crystalline structure of kaolin residue was destroyed during grinding. The SiO2 content of ground leached samples varied with grinding time, and the maximum value was above 92%. Grinding caused the surface area of the silica to increase to 167.84 m2/g, but decrease with longer grinding time. The formation of micropores contributed to the increase of the surface area. Structural breakdown by grinding is considered as the main reason for the enhancement of leaching behavior and improvement of the SiO2 content and porous properties.

Graphical abstractThe kaolin residue was ground and then treated with sulfuric acid. The band intensities of Si–O–Al and Al–OH were decreased by the grinding process, which was beneficial to the subsequent leaching. Structural breakdown by grinding is considered as the main reason for the enhancement of leaching behavior and improvement of the SiO2 content and porous properties.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Grinding causes the fibrous kaolin residue to fragment and form spheroidal particles. ► The degree of amorphization of silica increased with grinding time. ► The band intensities of SiOAl and AlOH were decreased by the grinding process.