Thermochemical Study of Natural Montmorillonite

L. P. Ogorodova ^a, I. A. Kiseleva ^a, L. V. Melchakova ^a, M. F. Vigasina, and V. V. Krupskaya ^b

^a Geological Faculty, Moscow State University, Leninskie gory, Moscow, 119991 Russia

^b Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Russian Academy of
Sciences, Staromonetnyi per. 35, Moscow, 109017 Russia

e-mail: logor@geol.msu.ru

Received November 18, 2011; in final form, December 15, 2011

Abstract—The paper reports results of an experimental thermochemical study (in a heat-flux Tian–Cal-
vet microcalorimeter) of montmorillonite from (I) the Taganskoe and (II) Askanskoe deposits and (III)
from the caldera of Uzon volcano, Kamchatka. The enthalpy of formation (298.15 K) of dehy-
drated hydroxyl-bearing montmorillonite was determined by melt solution calorimetry: –5677.6
7.6 kJ/mol for Na_0.3Ca_0.1(Mg_0.4Al_1.6)[Si_3.9Al_0.1O₁₀](OH)₂ (I), –5614.3 7.0kJ/mol for
Na_0.4K_0.1[Si_3.9Al_0.1O₁₀](OH)₂ (II), –5719 11 kJ/mol for
K_0.1Ca_0.2Mg_0.2[Si_3.7Al_0.3O₁₀](OH)₂ (III), and –6454 11 kJ/mol for water-bearing mont-
morillonite (I) Na_0.3Ca_0.1(Mg_0.4Al_1.6)[Si_3.9Al_0.1O₁₀](OH)₂ 2.6H₂O. The paper reports estimated enthalpy of
formation for the smectite end members of the theoretical composition of K-, Na-, Mg-, and Ca-mont-
morillonite and experimental data on the enthalpy of dehydration (14±2 kJ per mole of H₂O) and dehy-
droxylation (166 10 kJ per mole of H₂O) for Na-montmorillonite.

Keywords: montmorillonite, dehydration, dehydroxylation, enthalpy of formation, Calvet microcalorim-
etry

DOI: 10.1134/S0016702913040058

Pleiades Publishing home page | journal home page | top

If you have any problems with this server, contact webmaster.