Rapid Elemental Extraction from Ordered and Disordered Solutes by Acoustically-Stimulated Dissolution

Abstract

Alkaline industrial wastes (e.g., slags: ordered crystalline solids, and fly ashes: disordered solids) represent abundant reservoirs of elements such as silicon and calcium. Rapid elemental extractions from these wastes, however, have often relied on the use of “stoichiometric additives” (i.e., acids or bases). Herein, we demonstrate that acoustic stimulation enhances the release of network-forming Si species from crystalline blast furnace slags and amorphous fly ashes at reaction temperatures less than 65 °C. These additive-free enhancements are induced by cavitation processes which reduce the apparent activation energy of solute dissolution (Ea, kJ/mol) by up to 40% as compared to unstimulated conditions. Because of the reduction in the apparent activation energy, acoustic stimulation features an energy intensity that is up to 80% lower in promoting dissolution, as compared to other additive-free methods such as enhancing the solute’s surface area, introducing heat, or convectively mixing the solvent. Based on atomic topology analysis, we show that the reduction in apparent dissolution activation energy upon acoustic stimulation scales with the number of weak topological constraints per atom in the atomic network of the dissolving solute, independent of their ordered or disordered nature. This suggests that sonication breaks the weakest constraints in the solute’s atomic network, which, in turn, facilitates dissolution. The results suggest the ability of acoustic stimulation to enhance waste utilization and circularity, by enabling efficient resource extraction from industrial wastes.