Abstract:

To analyze the effect of various factors such as temperature, strength of alkali solution and dry density on the thermal conductivity of bentonite, thermal conductivity of MX80 bentonite in alkali-thermal environment was measured by a thermal probe method. Meanwhile, the X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were carried out on selected samples to reveal the micro-mechanism of thermal conductivity evolution of MX80 bentonite under alkaline and thermal environment. The results show that the thermal conductivity of MX80 bentonite increases with the increase of alkali solution content and dry density. The thermal conductivity of bentonite increases with the increase of temperature under different content conditions, and the higher alkali solution content is, the more significant the temperature effect of thermal conductivity is. When the dry density is small, the influence of thermal conductivity λ of bentonite increases with the increase of temperature. The main reason is that temperature facilitates the latent heat transfer of water vapor inside the sample. At the same dry density and temperature, the thermal conductivity decreases with the increase of pH value, the higher the pH value is, the greater the decrease range of λ is. The main reason is that the strong alkali solution erodes the montmorillonite and quartz of bentonite, increases the porosity of bentonite, thereby reduces the thermal conductivity of bentonite, which is consistent with the XRD and SEM image results of the tested samples.

Key words: bentonite, alkali-thermal environment, thermal conductivity, pore characteristics, scanning electron microscope(SEM)