Isothermal Stimulation of Mineral Dissolution Processes by Acoustic Perturbation

Abstract

On the basis of systematic experimental interrogation of the aqueous dissolution behavior of a large selection of minerals, whose dissolution rates vary by several orders of magnitude, this study demonstrates that acoustic perturbation yields an unprecedented enhancement in dissolution kinetics, which scales with the mineral's hardness and average bond energy. The dissolution enhancement produced is described by an Arrhenius-like formulation that reveals the energy imparted to the solute's surficial atoms by sonication. From an energy landscape perspective, it is highlighted that sonication perturbs surficial solute atoms from their equilibrium positions. As a result, upon contact with a solvent, sonicated atoms need a smaller amount of energy for dissolution to occur by bond rupture. Therefore, the activation energy of dissolution under sonication is consistently smaller than that under sonication-free conditions. Altogether, this study suggests that the enhancement in mineral dissolution over the course of acoustic perturbation under macroscopically isothermal conditions results from the excitation of the surficial atoms and is negligibly associated with temperature rise or surface area amplification as has been previously suggested.

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

“…The observation that the reduction in apparent activation energy is solely proportional to the number of weak constraints (i.e., the curve passes through the origin) originates from the fact that a solid with no ("zero") weak constraints (e.g., quartz 69 ) would not exhibit any decrease in apparent activation energy since no constraint would be broken upon sonicationwhich agrees with earlier studies that found no dissolution enhancement of quartz when exposed to ultrasonic stimulation. 16,18 Crucially, a plot of ΔE a vs the number of strong constraints per atom (not shown) gives a y-intercept of −19 kJ/mol, demonstrating that if no strong constraints were present, the activation energy reduction by sonication would be significantly different from zero. These results suggest that Si extraction from minerals is essentially a bond-breakage process.…”

“…Acoustic stimulation produces chemical and physical effects through cavitation and can greatly expedite dissolution 56 by reducing activation barriers associated with (net) reactions. 16 Herein, isothermal slag dissolution was carried out at temperatures from 25 to 60 °C (i.e., to match Figure 2c) for a fixed vibration amplitude, i.e., 60 μm, of the horn tip. The rate enhancement of Si-dissolution by sonication as a function of temperature is shown in Figure 2d.…”

“…The dramatic decrease in the apparent activation energy indicates a lower-energy-barrier pathway for Si release when exposed to acoustic stimulation. 16 Some of the decrease in apparent activation energy is due to decreasing cavitation at high temperature, but the magnitude of the decrease is too great to be solely due to reduced cavitation. In a previous study of the acoustically accelerated Grignard reaction, the reduction of the apparent activation energy was attributed to mechanical activation, i.e., creation of activated dislocations, by the action of the liquid microjets.…”

“…This has been attributed to the ability of acoustic energy to (1) induce solute fracture, 18 (2) activate dislocations on the solute's surface, 18 and (3) reduce the activation energy of the dissolution reaction. 16 Large particles have been directly observed to be broken into flakes by ultrasound, further facilitating dissolution. 17 These results have explained the mechanisms of dissolution enhancement by sonication; however, the energy intensity of acoustic stimulationas an approach for enhancing dissolutionhas not been robustly ascertained.…”

Calcination-free production of calcium hydroxide at sub-boiling temperatures

“…[26][27][28][29] Therefore, with a specic goal of enhancing waste utilization, resource recovery and reutilization, and circular economy, we demonstrate an approach to extract Ca-from alkaline industrial wastes, 30,31 and produce Ca(OH) 2 via a calcination-free process. While herein we focus on alkaline industrial wastes, of course, the broad contours of this process are also applicable to alkaline rock species, which although harder to solubilize unless externally stimulated, 32,33 offer the potential to offer a near-limitless source for alkaline element extraction.…”