The reaction kinetics of laumontite under hydrothermal conditions
Savage, David; Cave, Mark R.; Haigh, Dale; Milodowski, Antoni E.; Young, Maureen E.
European Journal of Mineralogy Volume 5 Number 3 (1993), p. 523 - 536
published: Jun 14, 1993
manuscript accepted: Dec 16, 1992
manuscript received: May 7, 1992
ArtNo. ESP147050503007, Price: 29.00 €
Abstract Quantification of the rate of mass transfer in diagenetic and hydrothermal systems requires a knowledge of the kinetics of mineral-fluid reactions at elevated temperature and pressure and at chemical conditions close to equilibrium. This communication describes an experimental study of the reaction kinetics of laumontite, a Ca-zeolite, at 80, 120 and 150°C, 50 MPa using batch (close to equilibrium) and flow (far from equilibrium) experimental techniques in the pH range 7-10. Fluid and mineral buffers were employed to constrain chemical conditions during the experiments. The dissolution of laumontite is non-stoichiometric, with Ca being preferentially removed from the laumontite structure. SEM observations of reacted laumontite grains are consistent with a surface controlled reaction mechanism. Dissolution rates obtained by the batch and flow techniques showed good agreement. The dissolution rate of laumontite is independent of hydrogen ion activity in the fluid phase at 80°C, but increases slightly with increasing hydrogen ion activity at 120 and 150°C. Measured dissolution rates range from 3x10-11 (80°C) to lx10-9 (150°C) molm-2s-1 and are 10-50 times greater than that of heulandite at 25°C. The activation energy of dissolution is ≈ 58 kJmol-1.