The Effect of Thermal and Mechanical Treatments on Kaolinite: Characterization by XPS and IEP Measurements

• Published in: Journal of colloid and interface science 1999-07, Vol.215 (2), p.339-344
• Main Authors: Torres Sánchez, R.M, Basaldella, E.I, Marco, J.F
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; General, apparatus; isoelectric point; kaolin transformations; photoelectron spectroscopy; Surface physical chemistry
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1006/jcis.1999.6241

The surface transformations induced on kaolinite by different thermal and mechanical treatments have been investigated by means of X-ray photoelectron spectroscopy (XPS), Bremsstrahlung induced Auger spectroscopy, and isoelectric point (IEP) measurements. Heating the kaolinite at temperatures between 500 and 750°C results in the change of a substantial fraction of surface Al from octahedral to tetrahedral coordination, which we associate with the dehydroxylation of kaolinite. Heating at 900 and 980°C brings about the development of an octahedral Al fraction which is associated with the formation of γ-Al2O3. The development of an Al tetrahedral component in the Al KLL spectra of the mechanically treated (ground) samples has been also observed. The Si/Al atomic ratio obtained by XPS in the thermally treated samples is the same as that shown by the original kaolinite. However, the XPS data show a clear reduction of the Si/Al atomic ratio in the mechanically treated samples, which suggests that the mechanical treatment has induced an Al enrichment of the kaolinite surface. The IEP values indicated a thermal transformation to metakaolinite and mullite with the increase of temperature (750 to 980°C). The IEP change for the milled samples can be only explained by assuming a 30% kaolinite coating by the Al oxide neoformed by grinding.