Apparent Charge Heterogeneity in Kaolins in Relation to Their 2:1 Phyllosilicate Content

Oscar Talibudeen and Keith W. T. Goulding
Rothamsted Experimental Station, Harpenden, Herts., AL5 2JQ, United Kingdom

Abstract: Measurements of the differential heats of K-Ca exchange are used to show that 6 groups of sites (ranging from −13.8 to −5.1 kJ/eq and with as many as 4 in any one sample) exist in kaolins that range from 0 to 15% in their 2:1 phyllosillicate content. These heat values, coupled with entropies of exchange, suggest that 0.1–10% vermiculitic, micaceous, and smectitic layers are present, presumably interstratified with kaolinitic layers which are assumed to have no permanent charge. Changes in the activity coefficients of adsorbed K with K saturation confirm these conclusions qualitatively. Thus, fK values at x → 0 correlate inversely (r2 = 0.655) with the content of vermiculite + partially expanding micas, and x values at maximum fK indicate the content of vermiculite + nonexpanding mica + partially expanding micas (r2 = 0.732).

Key Words: Cation exchange • Enthalpy • Heat • Kaolin • Smectite • Surface charge

Clays and Clay Minerals; April 1983 v. 31; no. 2; p. 137-142; DOI: 10.1346/CCMN.1983.0310208
© 1983, The Clay Minerals Society
Clay Minerals Society (www.clays.org)