Characterization and boron adsorption capacity of vermiculite modified by thermal shock or H2O2 reaction and/or sonication

Abstract

Micron grade vermiculite from Palabora (South Africa) was modified by thermal shock (700 °C), chemical exfoliation (80 °C in the presence of H₂O₂) and ultrasonic treatments (20 kHz, H₂O or H₂O₂) to improve the adsorption of boron. The modified vermiculites showed a changed particle morphology and reduced sizes (observed by scanning electron microscopy and laser granulometry), a density decrease and a modification of the surface (pH of the vermiculites and number of OH surface groups by titrations). Structural changes were not observed as shown by X-ray diffraction and infrared spectroscopy. The boron adsorption was highly dependent on the modification process. A pronounced exfoliation and size reduction under ultrasound in the presence of H₂O₂ increased the adsorption uptake compared to raw vermiculite (from 0.015 mmol g^− 1 for raw vermiculite to 0.151 mmol g^− 1 for modified one). The adsorption isotherms were fitted with the Freundlich model.