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 (E a, 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.

Dissolution Amplification by Resonance and Cavitational Stimulation at Ultrasonic and Megasonic Frequencies

“…The parabolic model is an empirical fit. Although there is no physical meaning to the square root of time, parabolic kinetics have been observed to hold for up to 1 week of dissolution …”

“…Although there is no physical meaning to the square root of time, parabolic kinetics have been observed to hold for up to 1 week of dissolution. 11 Obsidian, calcite, and class F FA particles of the smallest particle size fraction were collected after dissolution, filtered through 11 μm filter paper (Whatman Filter 1, Cytiva, Marlborough, MA) under vacuum, and then dried overnight at 50 °C. Undissolved particles and dried particles after dissolution experiments were characterized using scanning electron microscopy (SEM, Phenom ProX G2, Nanoscience Instruments, Phoenix, AZ) to assess surface changes, visually, following dissolution.…”

“…Sonication has been proposed as an efficient pathway to facilitate dissolution of sparingly soluble minerals and industrial wastes, thereby liberating desirable species such as Ca, − Mg, − K, − Na, Al, , Si, ,, and Ni for the sustainable manufacture of mineral products. The cavitation induced by acoustic stimulation promotes extraction of elements from the solute by concentrating energy at the particle surface, resulting in localized temperature increases by up to 5000 K and pressure increases up to 1000 bar .…”