Department of Chemistry, University of North Bengal, Dist. Darjeeling-784 480 Manuscript received 16 September 1982, revised 15 September 1983, accepted 11 February 1984 The nature of the exchange isotherms of tris-trimethylene diamine Co(lll) onto Na-montmorillonite and Na-Laponite together with the desorption data of Co\((tn)^{2+}_3\) from the clay matrices by different organic ions reveals that Co\((tn)^{2+}_3\) is more strongly bound in Na-montmorillonite than in Na-Laponite, a synthetic hectorite, which may be attributed to the higher charge density of the former mineral. The release of Co\((tn)^{2+}_3\) The nature of the exchange isotherms of tris-trimethylene diamine Co(lll) onto Na-montmorillonite and Na-Laponite together with the desorption data of Co\((tn)^{2+}_3\) from the clay matrices by different organic ions reveals that Co\((tn)^{2+}_3\) is more strongly bound in Na-montmorillonite than in Na-Laponite, a synthetic hectorite, which may be attributed to the higher charge density of the former mineral. The release of Co\((tn)^{2+}_3\) from both the clay surfaces follows the order (C4H9 )4N+ >(C2 H7 )4 N+>(C2H5)4 N+ > (CH2)4 N+ opto certain exchange levels beyond which a reversal of the sequence is observed. The desorption efficiency of the long-chain surfactants and alkane diammonium ions increases with chain length in both the minerals. The smaller tetraalkyJ. ammonium and alkanediammonium ions release more Co\((tn)^{2+}_3\) than the larger surfac. tants from the montmorillonite complex while in Laponlte the situation Is just the opposite. The selectivity coefficients of the long chain monovalent Ions are higher than the bivalent short chained ions or tefraalkylammonium ions for both the minerals, suggesting that for ion exchange reactions involving organic ions, size is more important than charge.