Electrokinetic properties of clinoptilolite with mono- and multivalent electrolytes Bahri Ersoy a,1 , Mehmet S. C ß elik b, * a Afyon Kocatepe University, Iscehisar Technical School, 03300 Afyon, Turkey b Istanbul Technical University, Mining Faculty, Minerals and Coal Processing Section, Ayazaga 80626, Istanbul, Turkey Received 25 February 2002; received in revised form 22 May 2002; accepted 27 May 2002 Abstract In this study, electrokinetic properties of clinoptilolite have been determined. A series of systematic zeta potential measurementshavebeenperformedtodeterminetheisoelectricpoint(iep)andpotentialdeterminingions(pdi),andthe effect of mono- and multivalent salts such as NH 4 Cl, CaCl 2 , Al(NO 3 ) 3 on the zeta potential of clinoptilolite. Clinop- tiloliteinwaterexhibitsanegativesurfacechargeandmaintainsthischaractereveninveryacidicconditionsofpH2–3. This reveals that clinoptilolite has no iep in the pH range of 2–12. H þ and OH  ions are the pdi for clinoptilolite. Excluding the trivalent Al 3þ cations, monovalent and divalent cations are not able to reverse the surface sign of clinoptilolite.ThisisattributedtotheionexchangeabilityofclinoptiloliteandthestrongspecificadsorptionoftheAl 3þ counterions. A schematic adsorption model which accounts for the adsorption of mono- and multivalent ions in the electrical double layer of clinoptilolite is proposed. Ó 2002 Elsevier Science Inc. All rights reserved. Keywords: Zeta potential; Clinoptilolite; Zeolite; Isoelectric point; Adsorption 1. Introduction Electrokinetic properties of fine particles in an aqueous solution such as the isoelectric point (iep) and potential determining ions (pdi) play a signif- icant role in understanding the adsorption mecha- nism of inorganic and organic species at the solid/ solution interface. They also govern the flotation, coagulation and dispersion properties in suspen- sionsystems.Inflotation,thesepropertiesareused tounderstandthemodeofcollectoradsorptionon minerals, selection of appropriate flotation re- agents and examination of activation mechanisms [1,2]. In coagulation, an important step in many solid–liquid separation processes including waste- watertreatmentsystems,itisnecessarytoknowthe zeta potential and the iep of particles [3,4]. In the ceramics industry and in the design of nanocom- posite materials, especially in clay-water colloidal systems, the electrokinetic properties of the colloi- dal particles identify the optimal conditions of a well dispersed system [5–7]. Microporous and Mesoporous Materials 55 (2002) 305–312 www.elsevier.com/locate/micromeso * Corresponding author. Fax: +90-212-285-6128. E-mail addresses: bersoy@aku.edu.tr (B. Ersoy), mcelik@ itu.edu.tr (M.S. C ß elik). 1 Fax: +90-272- 341-4882. 1387-1811/02/$ - see front matter Ó 2002 Elsevier Science Inc. All rights reserved. PII:S1387-1811(02)00433-X