THE EFFECT OF CACL2-H2O BRINES ON THE DEHYDRATION OF CA-EXCHANGED MONTMORILLONITE (SWY-1) AT ELEVATED TEMPERATURES AND PRESSURES

摘要

The dehydration temperature of a Ca-exchanged montmorillonite (Clay Minerals Society Clay SWy-1) in montmorillonite-CaCl2 mixtures containing 0.0, 0.9, 1.8; 5, 10, 20, and 30 wt% CaCl2 was determined at pressures to 700 bars, using high-pressure-differential thermal analysis (HP-DTA). The calculated concentrations of the resulting solutions range from 0.0 to 72.8 wt% (0.0-30.3 mol%) CaCl2. A substantial decrease of the dehydration temperature was observed, which is caused by the reduction of f(H2O) in these solutions. The relationship between the CaCl2 concentration of the fluid, temperature, and the fugacity coefficient (T-H2O) was determined to 600 degrees C. T-H2O ranges from 0.125 at 300 degrees C to 0.34 at 600 degrees C in a 30.3 mol% CaCl2 fluid and from 0.53 at 300 degrees C to 0.70 at 600 degrees C in a 0.91 mol% CaCl2 fluid. In the presence of moderately concentrated brines and at slightly elevated temperatures, Ca-rich smectite in sedimentary basins may he capable of buffering the fluid pressure. [References: 33]