Abstract--The cation exchange process between tris(ethylenediamine)cobalt(llI) and Na + on montmoriUonite was studied by atomic absorption spectrophotometry, X-ray diffraction, differential thermal analysis, and nitrogen sorption at 78~ The exchange of Co(en)33+ for Na § was found to be extremely favorable, with a tendency toward segregation of the two kinds of cations in the mixed clays studied. Small amounts of Co(en)a § were found to lower the nitrogen sorption capacity of Na § montmorillonite while clays with high Co(en)3 +a content had greatly enhanced sorption. An explanation is offered in terms of a dual role of the Co(en)3 +~ in determining the kind and amount of nitrogen sorption in the exchanged montmorillonite. INTRODUCTION THE~E have been many studies of nitrogen sorption by homoionic montmorillonite clay minerals. Some recent examples are Aylmore (1970); Barter (1967);Slabaugh (1971) and Thomas (1968). However, relatively little has been reported on nitrogen sorption by clays containing varying ratios of two different kinds of exchangeable cations. Barrer et al. (1963) showed that a study of the change in nitrogen sorption as a function of degree of exchange between two kinds of cations on a montmorillonite can give some information on the exchange process. This technique is most useful when the two cations involved give homoionic clays of. greatly different sorption characteristics. Barrer's study did not cover a wide range of cation ratios and his data implied a linear change in nitrogen sorption with change in mixed cation ratios.In the present study it was found that by preparing a Co(en)3 +3 montmorillonite from a Na + montmorillonite, the nitrogen sorption capacity of the clay was increased by over 500 percent. Also, the sorption isotherm in the partial pressure range studied (P/Po = 0.05-0.25) changed from B.E.T. for the Na § clay to Langmuir for the Co(en)z +3 clay. Since the sorption capacities and isotherm characteristics of these two clays were so different, nitrogen sorption was used to study various mixed

Abstrac~Nitrogen sorption by various homoionic montmorillonites was studied at 78~ The adsorption isotherms in the relative pressure range P/Po = 0.05-0.25 were found to be either Type I or Type II in the BET classification. The nitrogen sorption process was considered to be predominantly interlamellar when described by a Type I isotherm. With a Type II isotherm, the adsorption was assumed to be predominantly on those surfaces not in the interlamellar regions.It was concluded that only cations within a certain size range promote significant interlamellar nitrogen penetration in montmorillonites. The role of the smaller cations in nitrogen sorption by montmorillonites seems to be their influence on the external aggregate structures, Very large cations tend to clog up the interlamellar pores as well as some of the external voids.

No abstract