X-RAY-DIFFRACTION AND SCANNING ELECTRON-MICROSCOPE STUDIES OF PROCESSED RICE HULL SILICA

The structure and composition of processed rice hull ash were studied to better understand its adsorption of the soy oil components, lutein and free fatty acids. The silica-rich ash was composed largely of low order cristobalite and tridymite in the form of opal CT, with variable particle size. On heating of the ash there was conversion to a more ordered form of opal C, fusing of particles, and loss of potassium. Acid washing, following heating, also removed potassium and slightly reduced particle size further. Crystal form, particle size, particle fusion and potassium content may be important factors influencing ash adsorption of soy oil components. © 1990 AOCS Press.