Electrochemically Enhanced Dissolution of Silica and Alumina in Alkaline Environments

Abstract

Dissolution of mineral surfaces at asymmetric solid–liquid–solid interfaces in aqueous solutions occurs in technologically relevant processes, such as chemical/mechanical polishing (CMP) for semiconductor fabrication, formation and corrosion of structural materials, and crystallization of materials relevant to heterogeneous catalysis or drug delivery. In some such processes, materials at confined interfaces exhibit dissolution rates that are orders of magnitude larger than dissolution rates of isolated surfaces. Here, the dissolution of silica and alumina in close proximity to a charged gold surface or mica in alkaline solutions of pH 10–11 is shown to depend on the difference in electrostatic potentials of the surfaces, as determined from measurements conducted using a custom-built electrochemical pressure cell and a surface forces apparatus (SFA). The enhanced dissolution is proposed to result from overlap of the electrostatic double layers between the dissimilar charged surfaces at small intersurface separation distances (<1 Debye length). A semiquantitative model shows that overlap of the electric double layers can change the magnitude and direction of the electric field at the surface with the less negative potential, which results in an increase in the rate of dissolution of that surface. When the surface electrochemical properties were changed, the dissolution rates of silica and alumina were increased by up to 2 orders of magnitude over the dissolution rates of isolated compositionally similar surfaces under otherwise identical conditions. The results provide new insights on dissolution processes that occur at solid–liquid–solid interfaces and yield design criteria for controlling dissolution through electrochemical modification, with relevance to diverse technologies.

Thermodynamic equilibrium and kinetic fundamentals of oxide dissolution in aqueous solution

“…6(a)]. Such an enhanced dissolution was reported in a recent experiment, which showed that the dissolution rates of silica and alumina were increased by up to 2 orders of magnitude over the dissolution rates of isolated compositionally similar surfaces under otherwise identical conditions when the surface electrochemical properties were changed either by an applied potential or close to a dissimilar surface [180]. In addition, similar experimental results were also reported at interfaces between oxides and a metal [181].…”

Mineral Dissolution under Electric Stimulation

“…A previous study has shown that the ion adsorption rate on solute surfaces is affected by electric potential, especially for conductive materials . On the other hand, counterion sorption to mineral surfaces has been observed to induce changes in mineral dissolution rates by up to 1 order of magnitude. , Besides ion adsorption, applying an electric potential within an electrolytic solution could also increase the rate of ion transport, especially at interfaces, which could affect mineral dissolution rates. , Herein, significant enhancements in dissolution rates when a potential is applied, e.g., for calcite, are observedunder isothermal conditionsonly under conditions of mass transport (pH 4) and mixed kinetic control (pH 6.5) ,, but not when dissolution is interface-controlled (pH 10). , Significantly, the recent work of Dobbs et al shows that electric potential has limited, if any, effect on bulk dissolution rates (i.e., at large surface-to-surface separations when the EDLs of neighboring solute surfaces do not interact) under surface-controlled conditions. This may suggest that an applied potential has a greater influence on ion transport than on ion adsorption, thus affecting mineral dissolution rates only under conditions of mass-transport control …”

“…The rates and mechanisms of calcite’s dissolution are strongly affected by the solvent’s pH, solution saturation state, the abundance and type of co-ions present in solution, and its ionic strength and temperature. − While the vast majority of studies have examined passive approaches for affecting mineral dissolution rates, less is known, for example, of how active stimulation as induced by an electric field may affect dissolution behavior. Some studies have shown how electric potential-induced acidification of the solvent in the proximity of the anode can enhance calcite’s (and other mineral’s) dissolution rates. , Other than the pioneering studies of Kristiansen et al and Dobbs et al, comparatively less is known, however, of how potential-induced ion transport and changes in the structure of the electric double layer (EDL) that is present at the mineral–water interface may affect mineral dissolution, particularly at subcritical potentials (i.e., at ambient temperatures, water dissociates for Δ V ≥ 1.23 V), wherein water’s acidification can be excluded.…”

“…The ions beyond the IHP are bound more loosely to the surface and therefore can be influenced by an applied electric field. , This can produce alterations in the structure (i.e., in the region between the IHP and the shear plane) and properties of the EDL, including its compactness and the magnitude of its potential. In this work, we reveal the consequent effects on the dissolution of mineral particulates (i.e., bulk dissolution rather than dissolution in a narrow gap , ) by (i) varying the solution’s ionic strength ( I , M), which affects the Debye length (κ –1 , nm), and/or (ii) application of direct current (DC) subcritical electric potential. Special focus is paid to elaborate on how electric potential may affect dissolution under conditions of surface and/or transport control.…”

The Effect of Silica Dissolution on Reservoir Properties during Alkaline-Surfactant-Polymer (ASP) Flooding

“…(Steinwinder & Beckingham, 2019) reported that the mineral dissolution can significantly change the porosity and permeability of the wellbore. Moreover, several studies have found that silica dissolution is closely related to the pH of the solution, as the alkaline solutions are the main cause of dissolving high portions of silica ions due to the high pH (above 9) promoted around the wellbore, resulting in the dissolution of quartz Arensdorf et al, 2010;Dobbs et al, 2019;A. K. Elraies et al, 2016).…”