Influence of Ionic Environment and pH on the Electrokinetic Properties of Ball Clays

Carmen Galassi1, Anna Luisa Costa1 and Paolo Pozzi2
1 IRTEC-CNR, Via Granarolo 64, I-48018 Faenza (RA), Italy
2 Dip. di Chimica, Università di Modena e Reggio Emilia, Via Campi 183, I-41100 Modena, Italy
E-mail of corresponding author: acosta@racine.ra.it

Abstract: Three ball clays (SP from England, TSMA from France and UK from the Ukraine) were characterized for their dry and wet colloidal properties. On the basis of X-ray diffraction and chemical analyses the clays were classified as kaolinite-rich clay, smectitic kaolinite-rich clay and illitic kaolinite-rich clay. The ζ (zeta) potential at the clay-water interface as a function of pH, in three different electrolytes, was investigated using an electroacoustic technique. Starting from measurements of dynamic mobility, the calculated ζ potential was found to be almost constant as a function of pH for the TSMA and UK clays, while it increased from −20 to −60 for the SP clay, when potassium nitrate was used as an electrolyte. The behavior of the three clays in calcium and magnesium nitrate was slightly different: SP showed a smaller increase in ζ potential, while a small deviation from the constant behavior of the UK clay was found. The results are explained in terms of the surrounding-ion atmosphere in light of the chemical-physical properties measured. Our results may well be of use to those involved in ceramic processing.

Key Words: Cation Exchange Capacity • Clay Minerals • Electroacoustic • Electrolytes • Structural Properties • Surface Charge • ζ Potential

Clays and Clay Minerals; June 2001 v. 49; no. 3; p. 263-269; DOI: 10.1346/CCMN.2001.0490309
© 2001, The Clay Minerals Society
Clay Minerals Society (www.clays.org)