Effects of chemical solution components on the contact angle of typical minerals in soil: quartz, orthoclase and plagioclase.

Different chemical solutions can significantly change the contact angle (CA) of soil, but few studies have studied the change rule and action mechanism of the CA from the mineral composition of soil essence. In unsaturated soil mechanics, the CA is an important parameter to calculate the wet suction between soil particles in unsaturated soil. When the chemical composition of the soil pore liquid changes, the CA will also change, which will affect the wet suction and other parameters, thus changing the macroscopic mechanical properties of the soil. In this study, the CA of air-solution-mineral phases with different solution components (pH, type and concentration of salt solution) of different minerals (quartz, orthoclase and plagioclase) were measured. The results show that the CAs of quartz, orthoclase and plagioclase all rise first and then drop with the rise of pH. The peak CAs are pH = 5, pH = 4 and pH = 3, respectively. Quartz, orthoclase and plagioclase all have valley values in different concentrations of NaCl and KCl solutions. In CaCl solution, only quartz has valley value, while orthoclase and plagioclase increase monotonously. Quartz in soil plays a main role in the influence of soil CA, followed by orthoclase and plagioclase. The CA of different minerals in different chemical solutions is mainly controlled by electric double layer interaction and functional groups interaction. In different salt solution environment, in addition to the above two effects, the mineral CA is also affected by the surface tension.