Evaluation of Standard Free Energies of Formation of Clay Minerals by an Improved Regression Method

Chandrika Varadachari, Mahammad Kudrat and Kunal Ghosh
Department of Agricultural Chemistry and Soil Science, University of Calcutta, 35 B.C. Road, Calcutta 700 019, India

Abstract: An improved regression method for the evaluation of standard free energies of formation (ΔG°f) of clay minerals is here proposed in an attempt to remove some of the limitations of the earlier method (Chen, 1975). Particularly, this method suggests a procedure for the assignment of rankings for Σ ΔG°f, i values. Moreover, an iterative least-squares fitting technique is applied to solve the exponential equation to obtain the estimated ΔG°f. The estimated ΔG°f data for the various standard clay minerals are derived and compared with data available in the literature; in general, there is good agreement between the values. It is also shown how the regression method can be extended to clay minerals of variable composition. The ΔG°f's for several such minerals have been evaluated; a large number of combination equations required for such computations have been listed, so that for other similar minerals the process of evaluation of ΔG°f is greatly simplified.

Key Words: Clay minerals • Free energies of formation • Regression method

Clays and Clay Minerals; June 1994 v. 42; no. 3; p. 298-307; DOI: 10.1346/CCMN.1994.0420308
© 1994, The Clay Minerals Society
Clay Minerals Society (www.clays.org)