Wettability of crushed air-dried minerals

The importance of soil particle wettability has been recognised in mining engineering, soil science and geomorphology but to a lesser extent in geotechnical engineering, perhaps due to the assumption that soils, or in general most common minerals, are always wettable. From the soil science and geomorphology literature, changes in soil wettability are known to influence soil processes such as infiltration, erosion and post-wildfire debris flows. Organic matter has been identified as one of the most important factors controlling the wettability of natural soils. However, its occurrence is very shallow and often shallower than the depth of interest for geotechnical processes. Therefore, it becomes essential to determine the wettability of minerals, in particular because it can be linked to processes that involve crushing or abrasion of soil particles. This paper examines the wettability of 21 common, freshly crushed minerals (sulfides, oxides and silicates) by measuring wettability via contact angles with the sessile drop method and the Wilhelmy plate method, including particle attributes such as aspect ratio and sphericity. The results revealed a wide range of contact angles for the uncoated minerals, with the sulfides showing strong water-repellent behaviour and the silicates remaining very wettable. Higher contact angles are associated with mineral particles that converge to the shape of a sphere and for those that have a larger aspect ratio.