Compositional controls on melting and dissolving a salt into a ternary melt

We explore theoretically the controls on dissolution of salt A, in an undersaturated brine of salts A and B. We show that, as the concentration of B increases, the dissolution rate of A decreases, for brine of given temperature. We also show that there is a sharper decrease in dissolution rate with increasing concentration, for concentrations of B above a critical value, where B limits the equilibrium concentration. We explore the implications of the predictions for dissolution of KCl or NaCl, by a mixed brine of NaCl and KCl, a common reaction that may arise in dissolution of evaporites. We predict that, with mixed-composition brine, KCl crystals dissolve more rapidly than NaCl crystals, unless the (far-field) brine is nearly saturated in KCl. We also predict that the dissolution rate of these salts is largely independent of fluid temperature and is controlled by compositional diffusion

Dissolution of Cavities and Porous Media: a Multi-Scale View

Dissolution of underground cavities or porous media involves many different scales that must be taken into account in modeling attempts. This paper presents a review of some of these problems. The paper starts with an introduction to non-equilibrium models, which play an important role in understanding dissolution physics for such media. In particular, their fundamental importance in catching dissolution instability diagrams is emphasized. A second multi-scale aspect is the introduction of the concept of effective surface for dealing with heterogeneous and/or rough surfaces. All these concepts may be used to develop efficient large-scale simulations. Examples are given for simple situations which emphasize the strong coupling between dissolution and buoyancy plumes generated within the dissolution boundary laye

Holistic approach to dissolution kinetics : linking direction-specific microscopic fluxes, local mass transport effects and global macroscopic rates from gypsum etch pit analysis

Dissolution processes at single crystal surfaces often involve the initial formation and expansion of localized, characteristic (faceted) etch-pits at defects, in an otherwise comparatively unreactive surface. Using natural gypsum single crystal as an example, a simple but powerful morphological analysis of these characteristic etch pit features is proposed that allows important questions concerning dissolution kinetics to be addressed. Significantly, quantitative mass transport associated with reactive microscale interfaces in quiescent solution (well known in the field of electrochemistry at ultramicroelectrodes) allows the relative importance of diffusion compared to surface kinetics to be assessed. Furthermore, because such mass transport rates are high, much faster surface kinetics can be determined than with existing dissolution methods. For the case of gypsum, surface processes are found to dominate the kinetics at early stages of the dissolution process (small etch pits) on the cleaved (010) surface. However, the contribution from mass transport becomes more important with time due to the increased area of the reactive zones and associated decrease in mass transport rate. Significantly, spatial heterogeneities in both surface kinetics and mass transport effects are identified, and the morphology of the characteristic etch features reveal direction-dependent dissolution kinetics that can be quantified. Effective dissolution velocities normal to the main basal (010) face are determined, along with velocities for the movement of [001] and [100] oriented steps. Inert electrolyte enhances dissolution velocities in all directions (salting in), but a striking new observation is that the effect is direction-dependent. Studies of common ion effects reveal that Ca2+ has a much greater impact in reducing dissolution rates compared to SO42−. With this approach, the new microscopic observations can be further analysed to obtain macroscopic dissolution rates, which are found to be wholly consistent with previous bulk measurements. The studies are thus important in bridging the gap between microscopic phenomena and macroscopic measurements

Rupture Test and Bioavailability of Oil-Soluble Vitamins

In lieu of an abstract, here is the article\u27s first paragraph: Bioavailability of multi-vitamins as dietary supplements has always been a concern. Dissolution studies have been successfully used to predict drug release of bioactive molecules, but with vitamins there are some exceptions. United State Pharmacopoeia (USP) defines the dissolution requirements of multi-vitamin supplements based on the composition and type of dosage form. As oil-soluble vitamins do not meet the criterion of “dissolution”, the performance of dosage forms containing such vitamins is evaluated by disintegration studies primarily. Dissolution studies are not applicable for such dosage forms [1]

Simulation of rock salt dissolution and its impact on land subsidence

Extensive land subsidence can occur due to subsurface dissolution of evaporites such as halite and gypsum. This paper explores techniques to simulate the salt dissolution forming an intrastratal karst, which is embedded in a sequence of carbonates, marls, anhydrite and gypsum. A numerical model is developed to simulate laminar flow in a subhorizontal void, which corresponds to an opening intrastratal karst. The numerical model is based on the laminar steady-state Stokes flow equation, and the advection dispersion transport equation coupled with the dissolution equation. The flow equation is solved using the nonconforming Crouzeix-Raviart (CR) finite element approximation for the Stokes equation. For the transport equation, a combination between discontinuous Galerkin method and multipoint flux approximation method is proposed. The numerical effect of the dissolution is considered by using a dynamic mesh variation that increases the size of the mesh based on the amount of dissolved salt. The numerical method is applied to a 2D geological cross section representing a Horst and Graben structure in the Tabular Jura of northwestern Switzerland. The model simulates salt dissolution within the geological section and predicts the amount of vertical dissolution as an indicator of potential subsidence that could occur. Simulation results showed that the highest dissolution amount is observed near the normal fault zones, and, therefore, the highest subsidence rates are expected above normal fault zones

Diffusion-controlled dissolution of a binary solid into a ternary liquid with partially-molten zone formation

We build a theoretical model of equilibrium dissolution of a homogeneous, solid mixture of two salts A and B, KCl and NaCl being used as the type example, into an aqueous solution of the two salts, with diffusive transport. We find that there are two sharp dissolution fronts, separating fluid, a partially molten zone containing a single solid and mixed solid. The phase change happens almost entirely at the two sharp fronts. In equilibrium, the leading front exhibits a small amount of precipitation of NaCl, simultaneous with complete dissolution of KCl. There is a unique surface in the space of far-field fluid KCl concentration, far-field fluid NaCl concentration and solid composition, dividing conditions where NaCl is the solid in the partially molten zone, from conditions where KCl is the solid in the partially molten zone. The movement rates of the dissolution fronts decrease as the concentration of either salt in the far-field fluid is increased. The movement rates of the dissolution fronts increase as either far-field temperature is increased, but this effect is smaller than that of concentration. In most circumstances, the dissolution front for a given salt moves more slowly, the more of that salt is present in the original solid, although the mass dissolution rate is not greatly affected by the solid composition

Influence of presence of ammonium in the hydrothermal illitization of smectite

During diagenesis, several reactions induce changes both in phyllosilicates and organic matter, which in basins associated to the production of hydrocarbons leads to ammonium fixation in illite and micas [1] and to dissolution induced by organic acids [2] [3]. Dissolution processes may contribute to the smectite-to-illite transformation, stabilized by fixation of K (and NH4 +). Ammonium is a weak acid in solution. Under neutral conditions where the concentration of hydronium is very low (<10-7 M), ammonium contributes to smectite dissolution. The effect of organic acid on silicates dissolution is partially known, but the potential role of ammonium is completely novel.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

MOCCA Survey Database I: Dissolution of tidally filling star clusters harbouring BH subsystems

We investigate the dissolution process for dynamically evolving star clusters embedded in an external tidal field by exploring the MOCCA Survey Database I, with focus on the presence and evolution of a stellar-mass black hole subsystem. We argue that the presence of a black hole subsystem can lead to the dissolution of tidally filling star clusters and this can be regarded as a third type of cluster dissolution mechanism (in addition to well-known mechanisms connected with strong mass loss due to stellar evolution and mass loss connected with the relaxation process). This third process is characterized by abrupt cluster dissolution connected with the loss of dynamical equilibrium. The abrupt dissolution is powered by strong energy generation from a stellar-mass black hole subsystem accompanied by tidal stripping. Additionally, we argue that such a mechanism should also work for even tidally under-filling clusters with top-heavy initial mass function. Observationally, star clusters which undergo dissolution powered by the third mechanism would look as a 'dark cluster' i.e. composed of stellar mass black holes surrounded by an expanding halo of luminous stars (Banerjee & Kroupa 2011), and they should be different from 'dark clusters' harbouring intermediate mass black holes as discussed by Askar et al. (2017a). An additional observational consequence of an operation of the third dissolution mechanism should be a larger than expected abundance of free floating black holes in the Galactic halo.Comment: 14 pages, 14 figures, accepted to MNRA