Hydraulic and physicochemical properties of dense thin bentonite layers permeated with variably mixed alkaline solutions of KOH and CaCl2 at various temperatures (25-75 degrees C) for 3 years

Abstract

Hydraulic conductivity tests were performed using mixed alkaline solutions of KOH and CaCl2 (pH ~12) on thin Na-bentonite layers under various temperature conditions (25-75 & DEG;C) for 3 years. For dense thin Na-bentonite (dry density of 1.12 Mg/m(3)) in a mixed alkaline solution of 0.03 M KOH and 0.03 M CaCl2, the hydraulic conductivities at 50 & DEG;C and 75 & DEG;C were approximately 10 times higher than that at 25 & DEG;C. The bentonite samples permeated with the mixed solution at 50 & DEG;C and 75 & DEG;C achieved almost complete cation exchange of Na ions by Ca and K ions. However, only slight cation exchange occurred in the bentonite specimens permeated at 25 & DEG;C, regardless of the type of permeant. The free swell index of the reacted bentonite permeated with a mixed solution of 0.03 M KOH and 0.03 M CaCl2 significantly decreased at 50 & DEG;C and 75 & DEG;C compared with that at 25 & DEG;C. X-ray diffraction analysis revealed that the decreases in the relative intensities of the peaks of accessory minerals, such as opal-cristobalite/tridymite, quartz, and feldspar, were enhanced at 50 & DEG;C and 75 & DEG;C.