RAMAN-SPECTRA OF POTASSIUM CARBONATE AND BICARBONATE AQUEOUS FLUIDS AT ELEVATED-TEMPERATURES AND PRESSURES - COMPARISON WITH THEORETICAL SIMULATIONS

One-molal solutions of potassium carbonate and potassium bicarbonate w ere investigated by Raman spectroscopy from 22 degrees to 550 degrees C and from 1000 to 2000 bar. Experiments were performed in a special h ydrothermal pressure vessel fitted with conical diamond windows. Frequ encies and half-widths of the vibrational modes were measured for both carbonate and bicarbonate as a function of temperature and pressure. In the case of potassium carbonate solutions, dissolved bicarbonate ap peared with its concentration dramatically increasing with increasing temperature and decreasing density. The opposite behavior occurred in the case of potassium bicarbonate: the relative concentration of disso lved carbonate increased relative to total bicarbonate. In addition, a t temperatures above 300 degrees C, dissolved aqueous carbon dioxide a ppeared with its concentration continuing to increase with increasing temperature and decreasing density. Simulations using theoretically-pr edicted mass action constants were used to compute changes in solution speciation for these solutions as they were subjected to increased te mperature and pressure. Results resulting from these predictions match ed those discovered in the spectral measurements. (C) 1998 Elsevier Sc ience B.V. All rights reserved.