The reaction kinetics of laumontite under hydrothermal conditions

The reaction kinetics of laumontite were studied at 80, 120 and 150 degrees C and 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 used 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. The dissolution rate of laumontite is independent of hydrogen ion activity in the fluid phase at 80 degrees C, but increases slightly with increasing hydrogen ion activity at 120 and 150 degrees C. Measured dissolution rates range from 3 x 10 (super -11) (80 degrees C) to 1 x 10 (super -9) (150 degrees C) mol/m (super 2) /s and are 10-15 times greater than that of heulandite at 25 degrees C. The activation energy of dissolution is approx 58 kJ/mol.