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

Micron grade vermiculite from Palabora (South Africa) was modified by thermal shock (700 degrees C), chemical exfoliation (80 degrees 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. (C) 2010 Elsevier B.V. All rights reserved.