CAPILLARY DROPLETS EMBEDDED IN A LUBRICATING FILM: ENHANCING ROCK-LIQUID SOLUTE TRANSFER
As film passage dilutes solutes along the matrix interface, solute transfer will be driven by diffusion between film and matrix. Waves on the gas-liquid interface can in turn increase exchange by small advective components. However, capillary droplets provide a much greater exchange potential than either flat or wavy films. The increased pressure gradient provided by capillarity in the droplet creates a scenario where they become collectors of liquid and solute. Because of the increased rate of chemical leaching, a potential application of embedded capillary droplets is in either contaminant remediation or in mineral extraction. This is especially valuable when increasing the solute exchange is more important than increasing the volume of fluid transported. For example, in heap-leach methods for gold extraction, an aqueous cyanide solution is sprinkled or dripped onto a heap of ore rock. The solution leaches the gold from the ore as it percolates through the heap. Because the process of dissolution of ore occurs by diffusion of the cyanide solution into the permeable rock, the formation of embedded capillary droplets could play an important role in suctioning dissolved components from the rock matrix.