Mineralogy and some Physical Properties of the San Jose Bentonite - A Natural Analogue to Buffer Material Exposed to Saline Groundwater

摘要

Bentonite clay has an important buffer function in several of the proposed systems for nuclear waste repositories. Some proposed repository locations have significant concentration of sodium and calcium chloride in the ground-water, and others may be under sea-level for part of their life-time. A crucial question is consequently if there will be any long term effects on the stability of clay minerals due to exposure to saline conditions and thereby also on the desired physical properties. In the present study we used material from a small bentonite habitat at San JosS, southeastern Spain, as a natural analogue to a bentonite buffer exposed to high saline ground-water. The composition of the bentonite material was determined by use of XRD, ICP/AES, and cation exchange capacity (CEC) analyses both of bulk material and of fine fraction. The important physical properties swelling pressure and hydraulic conductivity were measured for a range of densities and NaCl concentrations. The observed smectite structure and the measured properties of the San lose bentonite were similar to those found in Wyoming bentonite and no obvious effects of the harsh saline environment were observed.