What type of clays can be used as liners for NaCl solar ponds?

Abstract

A calcic almost nonswelling clay was studied as a liner for solar ponds. Its chemical analysis showed the following cations: Ca ++ 31.9 meq 100 g of soil , Mg ++ 15.96 meq 100 g of soil , Na + 1.96 meq 100 g of soil and K + 0.66 meq 100 g of soil . The soil has a texture of 68% of clay, 14% of sand and 18% of silt. Under hot water, the permeability was of the order of 10 −8 cm/s and the thermal conductivity was about 1.5 W/m °C. Nonetheless, when this clay was under hot NaCl brine (50°C), the permeability started to increase until 10 −6 cm/s or more. However, under cold brine, the permeability was also of the order of 10 −8 cm/s. In order to try to understand the behavior of this clay, additional studies were done. An X-ray diffraction analysis, a differential thermal analysis, and an electron microscopy study showed that this clay was an illite with a combination of others. This clay under the influence of a hot electrolyte as the NaCl brine, flocculates and makes the voids higher and therefore more permeable. As a conclusion, it is possible to affirm that not every Ca-clay can be used as a liner for NaCl solar ponds. To know which one is convenient for liners, the simple equipment we used (presented in this article) directly measured the permeability and with this parameter it was possible to decide if the clay soil was or was not convenient as a liner.