Hamyrolysis of Illite and Montmorillonite: An Experimental Investigation

Abstract

<p> The short term (5000 hours) stability of illite and montmorillonite in sea water was studied by suspending 5.00 gm. aliquots of A.P.I. reference clays Montmorillonite # 25b and Illite # 35 in 500 ml. of artificial sea water (tradename "Instant Ocean") . After 5000 hours, in the montmorillonite samples, Ca and Si concentrations had increased (0.490 mmoles/l and 0.289 mmoles/l respectively), the cation exchange capacity had decreased (104.36 meq/100 gms. to 81.42 meq/100 gms.), the pH had decreased (8.40 to 7.94) but no major mineralogical change was observed. After 5000 hours, in the illite samples, Si concentration had increased (0.045 mmoles/l), the cation exchange capacity remained the same, the pH increased (7.22 to 7.60) and no major mineralogical change was observed. The release of Ca in the illite samples was complicated by the dissolution of calcite and significant changes in concentration of other cations (Na, K, Mg) were not observed.</p> <p> The data for Si, cation exchange and exchangeable cations are compared to that of Lewis (1950), Whitehouse and McCarter (1956), Carrol and Starkey (1958), MacKenzie et al (1965) (1967) and Russell (1970), a model developed by Houston (1972) is used to explain the Ca and Si data for the montmorillonite samples, and the implications of the apparent stability of these minerals to the case for authigenic clay formation from detrital material are discussed.</p>