Solubility of Two High-Mg and Two High-Fe Chlorites Using Multiple Equilibria1

J. A. Kittrick
Department of Agronomy and Soils, Washington State University Pullman, Washington 99164
1 Scientific Paper No. SP5881. College of Agriculture Research Center, Washington State University, Pullman, Washington. Project 1885.

Abstract: High-Mg chlorites from Vermont and Quebec and high-Fe chlorites from Michigan and New Mexico were equilibrated at room temperature in the near-neutral pH range. Gibbsite, kaolinite, and hematite of known stability were added to the samples to control unmeasurable variables at calculable levels. Equilibrium solution compositions were obtained from undersaturation and from supersaturation. Other indicators of equilibrium were good agreement between successive analyses over a long period of time, between duplicate samples, between independent systems, and between independent measures of equilibrium. All four chlorites were stable relative to brucite and, with a few exceptions, relative to talc under the conditions of study. When in equilibrium with gibbsite, the pH − ½Mg2+ value of the chlorites ranged from 6.3 to 6.5, at a pH4SiO4 value of 4.0. These values are in good agreement with prior estimates of chlorite stability. The calculated standard free energy of formation of the chlorites is dependent upon solution Fe2+ calculated from the sample Eh and assumed equilibrium with hematite, with the assumption that the Fe2+-Fe3+ couple is at the same Eh as the sample.

Key Words: Chlorite • Free energy of formation • Iron • Magnesium • Solubility • Stability

Clays and Clay Minerals; June 1982 v. 30; no. 3; p. 167-179; DOI: 10.1346/CCMN.1982.0300302
© 1982, The Clay Minerals Society
Clay Minerals Society (www.clays.org)