Modification of surface charge properties during kaolinite to halloysite-7 angstrom transformation

• Type: Article in International Scientific Journal
• Date: 1999

Authors

Tari, G (Author) Other; Bobos, I (Author) Other; Gomes, CSF (Author) Other; Ferreira, JMF (Author) Other

Journal

Title: Journal of Colloid and Interface Science

Vol. 210

Pages: 360-366

ISSN: 0021-9797

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 114 Citations

Scopus - 122 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-001-53V

DOI: 10.1006/jcis.1998.5917

Abstract (EN): The surface charge properties of well and poorly ordered kaolinite and halloysite-7 Angstrom, representing three different stages of kaolinite to halloysite-7 Angstrom transformation identified in the kaolin deposit of Sao Vicente de Pereira (Portugal), were studied. Mineralogical (X-ray diffraction, Fourier transformation-infrared) and chemical data (analytic electron microscopy) showed that the gradual transformation from kaolinite to halloysite-7 Angstrom minerals was accompanied by an increase in hydration and a decrease in Si/Al ratio. In particular, the replacement of Si(IV) by Al(III) in the tetrahedral layer caused an electrical charge unbalance and a modification of surface charge properties during the kaolinite to halloysite transformation. Accordingly, the cation exchange capacity (CEC) gradually increases when passing from well-ordered kaolinite to halloysite-7 Angstrom, attesting the direct correspondence existing among the structural order of the samples, number of tetrahedral substitutions, and CEC. Electrophoretic experiments provided further evidences of the origin of surface charge properties and the variation encountered during kaolinite to halloysite-7 Angstrom transformation. The curves of zeta-potential versus pH show the same pH dependency for the three minerals, but a gradual increase of zeta-potential when passing from well ordered kaolinite to halloysite-7 Angstrom through the poorly ordered kaolinite. The results can unambiguously be attributed to the increase of permanent charge due to the higher degree of isomorphic substitution, more than to the increase of structural and ionizable water. (C) 1999 Academic Press.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 7