1408
GEORGEL. GAINES,JR.
Vol. 61
THE ION-EXCHANGE PROPERTIES OF MUSCOVITE MICA BY GEORGEL. GAINES,JR. General Electric Research Laboratory, Schenectady, N . Y . Received May 9, 1067
The ion-exchange capacity of a high quality muscovite mica has been studied by a variety of methods. Exchange proceeds readily with naturally occurring potassium ions on exposed cleavage surfaces, but little or no penetration or attack on the crystal lattice occurs in dilute neutral aqueous solutions at room temperature. The exchange capacity is directly proportional to the exposed surface area and is in reasonable agreement with the value calculated from the crystal !atthe parameters. The possibility of utilizing ion exchanged mica as an interesting substrate for surface studies is emphasmed.
Introduction had also stated that no tendency to swell was obThe ion-exchange properties of naturally occur- served with his ground mica samples. Qualitaring alumiiiosilicates such as the clays and zeolites tively, of course, no swelling is detectable when large have been recognized for over a century. Because pieces of mica are immersed in water for moderate of their importance in plant nutrition and the effect lengths of time. These observations suggest that of ionic substitutions on the mechanical properties solutions do not penetrate into the mica crystal a t of the materials, considerable effort has been de- any practically observable rate, which suggests voted in recent years to the study of such ma- that intracrystalline exchange does not occur. terials as ion exchangers. Since the structure of Apparently, no attempt has been made to prepare the micas is similar to that of some of the clays,’ samples of micas in carefully fractionated particle ion exchange might be expected with these minerals, size ranges and correlate exchange capacity with too. Gardiner and Shorey2 found that muscovite surface area. As will be pointed out below, this liberated potassium on soaking in (NH4)zS04 is not easily accomplished because of the strong solutions a t room temperature. After the crystal adhesion between mica surfaces. As a widely-distributed soil component, mica has structure of mica had been elucidated by Pauling, Kelley and Jennya found that the amount of ion practical interest as an ion exchanger. Moreover, exchange depended on the fineness t o which the further importance is attached t o external surface sample had been ground, and suggested that the ion exchange if the suggestions made in regard to K + ions on cleavage planes were exchanged for the adhesion of mica to mica’o are valid. The cations in solution. Jackson and Truog4 were possibility of altering the surface in this controlled able to liberate all of the K + in a muscovite sample manner should provide an interesting substrate for by soaking it in ammonium acetate solution after other investigations of surface properties as well. wet grinding for three days. Schacht~chabel,~The starting point in all of this work consists in using ground muscovite, found that equilibrium determining the extent of ion exchange by mica. was reached slowly, and suggested that ions from The present report describes results of this study. solution could slowly penetrate the K+-ion Experimental planes within the mica particles and induce exAll of the experiments described have utilized a highchange inside as well as on the external surfaces of grade Bengal Ruby muscovite mica. Clear block (at least the particles. Other workers6+ have shown that 0.05 inch thick and several inches s uare), showing no inparticle size decreases and base exchange capacity clusions, was obtained directly from &e importer (the Otto increases with continued grinding of mica. Gerdau Co., New York). The material is transparent and Whether exchange is liinited to external surfaces light reddish brown in color. X-Ray diffraction patterns a sample which had been ground, water-washed and or can take place with “internal” IC+ ions as sug- of sieved to 80-100 mesh agreed well with those for muscovite.11 gested by Schachtschabel has not yet been clearly Chemical analyses, carried out by Ledoux and Co., Teaneck, decided. Barshad9 measured the c-axis spacing IT. J., using standard methods12 are given in Table I. in muscovite particles of 5-50 I.L and less than 0.5 p sizes, and found no change whether the sample TABLE I was dry, saturated with water or saturated with CHEMICAL ANALYSIS OF BENGAL RUBYMUSCOVITE, % glycerol. Paragonite, a micaceous mineral conSi02 45.9 KzO 10.2 taining Na+ instead of I
