MECHANICAL AND THERMAL TESTS OF A BENTONITE CLAY FOR USE AS A LINER FOR SOLAR PONDS

The use of clays has been discussed as an alternative for liners in solar ponds. The bentonite used in this experiment was a Ca-montmorillonite. It has a thermal conductivity of 1.14 W/m°C at 50°C before being under the influence of NaCl brine, and a value of 0.42 W/m°C at the same temperature after four months under the influence of the NaCl hot brine. When fresh hot water was used at a temperature of 50°C, the vertical permeability was 1.3 × 10-7 cm/s. After the four months under the hot brine, salinity saturation in the effluent became 70% after filtering it through the clay, and 1.09 × 10-7 cm/s was the lower permeability reached. Under drastic changes in temperature (10°C or more) the clay starts to form small fissures that increase permeability. However, if these severe changes are not carried out in a solar pond, the clay can be used as a liner. Therefore, it is possible to state that the thermal conductivity and the permeability of this clay are better than those of a kaolinite clay. These properties are reduced by the influence of a hot brine during long exposure periods due to the ion exchange which permits it to be used as a liner. © 1990.