JOURNAL OF COLLOID AND INTERFACE SCIENCE 198, 157–163 (1998) ARTICLE NO. CS975272 H / / Li / and H / /K / Exchange on Delaminated Muscovite Mica Maged A. Osman,* ,1 Walter R. Caseri,² and Ulrich W. Suter² * Swiss Federal Laboratories for Materials Testing and Research, CH-8600 Du ¨bendorf, Switzerland; and ² Department of Materials, Institute of Polymers, ETH, CH-8092 Zu ¨rich, Switzerland Received July 22, 1997; accepted October 24, 1997 ered silicates have been published (6, 7), little is known Muscovite mica was delaminated by heating with concen- about this reaction in muscovite mica and there are many trated lithium nitrate solution. The delamination occurred open questions ( 5, 8, 9 ) . This is probably due to the analyti- through partial replacement of the alkali counterions originally cal difficulties arising from its small surface area, i.e., the present by lithium. The H / / Li / exchange was studied in dilute relatively low ion exchange capacity of this mineral which nitric acid. With delaminated mica it was possible to follow the is typically around one hundred times lower than that of ion exchange by measuring the change in conductivity of the vermiculite or montmorillonite. However, this problem can reaction mixture. The exchange was also followed by measuring be overcome by delaminating muscovite through heating the amount of released lithium and was found to be fast. When with lithium nitrate (10), thus increasing its surface area. In the adsorbed lithium ions were replaced by potassium, the mica platelets collapsed to stacks with lower accessible surface area, this way, a mica with one hundred times higher ion exchange and the ion exchange capacity was reduced to one-fifth of the capacity was obtained (11). Another advantage of delami- original value. This was attributed to the smaller short-range nated mica is its chemically uniform surface, i.e., the pres- repulsive (hydration) forces of the potassium ions. The H / /K / ence of one single type of ion on the surface, which simpli- exchange on delaminated mica was slower than the correspond- fies the study of the exchange reaction. ing H / / Li / exchange and its equilibrium constant was much Ion exchange studies are usually performed in aqueous smaller than that of the H / / Li / . The affinity of oxonium ions media and knowledge of the exchange of surface ions to the muscovite surface is much higher than that of lithium against H / or H 3 O / is therefore of fundamental impor- but is comparable to that of potassium.  1998 Academic Press tance. In montmorillonite for example, the exchangeable Key Words: muscovite; mica; ion exchange; oxonium ion; lith- ions can be almost completely replaced by oxonium ions ium; potassium; equilibrium constant; exchange capacity; conduc- (13). However, in acidic solutions whose concentrations tivity. are as low as 0.01 N, ion exchange is accompanied by decomposition of the clay as reflected in the release of Al 3/ into the solution ( 13 – 15 ) . The presence of any Al 3/ INTRODUCTION in a dilute H / solution results in a preferential adsorption of Al 3/ to H / . In contrast, muscovite seems to be more The ion exchange properties of natural aluminosilicates stable against acids than montmorillonite ( 14, 15 ) . Gaines have been recognized for over a century. Because of their and Rutkowski (16) reported that on treating muscovite importance in plant nutrition, considerable effort has been mica with 0.1 N HCl for 24 h, aluminum was extracted devoted to the study of such materials as ion exchangers. from the edges of the particles but less than 1% of the Layered silicates, especially muscovite, have received in- mica sample was dissolved. Pashley ( 17 ) concluded from creasing attention not only in basic research but also in in- surface force measurements that no damage was done to dustry, e.g., in electrical insulation, in anticorrosion paints, a mica surface in acid solution at pH 3.0. and as fillers in polymer composites. Most of these applica- In the present work, we studied the protonation of delami- tions depend on the surface properties of mica, which in turn nated muscovite mica whose surface was saturated with ei- depend on the type of ions present on the surface. In contrast ther lithium or potassium. to other expandable layered silicates, the exchangeable ions in muscovite are only those on the surface. The counterions in the interlayers of muscovite are not released under ambi- EXPERIMENTAL ent conditions (1–5). Chemical Reagents Although many reports on ion exchange in different lay- Suprapure nitric acid and pro analysis grade chemicals 1 To whom correspondence should be addressed. (Merck, Darmstadt, Germany) were used without further 157 0021-9797/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.