Waste Isolation Pilot Plant Brine Field pH Measurements: Technique and Interpretation.

摘要

pH measurements made in conjunction with the Waste Isolation Pilot Plant Materials Interface Interactions Test (MIIT) are interpreted. The pH drop noted over time is correlated with other changes associated with MIIT brine evaporation. Magnesium buildup appears important, because a combination of high concentrations and elevated temperatures (about 90/degree/C) can produce hydrochloric acid through hydrolysis of the magnesium ion, possibly explaining why the brines appeared to become more acid over time. For pH measurement techniques in concentrated brines, pH papers were useless in concentrated saline solutions. When traditional glass pH electrodes were substituted, other complications arose. For mildly acidic brines of known hydrogen ion concentration, the measured pH generally fell below the expected value. Also, the electrode responded differently to different salts. Magnesium chloride had a greater effect than sodium chloride, which in turn had a greater effect than potassium chloride. For nearly neutral brines, electrode drift became a serious problem, and when the meter finally stabilized, readings were significantly above those of the solutions from which the brines were prepared. The size of this positive deviation depended on the electrode being used and its previous conditioning. Both drift and the unusual high values were mitigated or eliminated in brines where a buffer was present in concentrations greater than about 0.001 molar. 22 refs., 11 figs., 9 tabs.