Intrinsic Kinetics of Gypsum and Calcium Sulfate Anhydrite Dissolution: Surface Selective Studies under Hydrodynamic Control and the Effect of Additives

Abstract

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Importance of Mass Transport and Spatially Heterogeneous Flux Processes for in Situ Atomic Force Microscopy Measurements of Crystal Growth and Dissolution Kinetics

“…49 The solubility (C sat ) of gypsum, as the total amount of calcium/sulfate dissolved at equilibrium, was calculated to be 16.2 mM in pure H2O using the numerical code MINEQL+ (Environmental Research Software, version 4.5), 50 in agreement with experimental measurements. The boundary condition applied to the numerical models, as defined in Figure 1, are as follows: the vertical external walls of the diffusion cell, the 'inactive' parts of the basal crystal surface and the AFM fluid cell walls, i.e.…”

“…41 Although forced convection provides access to higher transport rates, a number of studies using the rotating disk (RD) 56,57 and high flow rate channel flow cell (CFC) 49 41 This is at least two orders of magnitude higher than the rates extracted from step velocity measurements via in-situ AFM (Table 2). This is a significant difference given that the surfaces in the macroscopic studies and AFM measurements are the same and the rates deduced from AFM and macroscale measurements can supposedly be compared free from mass transport effects.…”

Dissolution of uranium dioxide in nitric acid media: what do we know?

“…The primary importance of the knowledge of this mechanism has been widely documented in the literature concerning the kinetics of solid/liquid reactions [39,40,55], and its absence in most of the studies results in the impossibility to know if the measured dissolution rates correspond to the chemical reaction or diffusion kinetics.…”

Dual-Barrel Conductance Micropipet as a New Approach to the Study of Ionic Crystal Dissolution Kinetics

“…Other ionic crystals have a wide range of dissolution rates, including KF which has a reported rate constant of ~3x10 -8 cm s -1 37 and CaSO3 which, in its common form of gypsum, has a dissolution rate of ~6x10 -4 cm s -1 . 14 We assumed a meniscus height of 300 nm, as deduced from a control measurement on SiO 2…”

“…12 The composition of the effluent from flow cells can also be analyzed with a range of quantitative analytical techniques. 14,15 The primary limitation of these hydrodynamic systems is that, typically, they require crystalline material in the form of large flat surfaces, or samples embedded in a support material, and the measured dissolution rate is averaged over large areas of the surface, which potentially hides local intrinsic rate differences. 8 A different approach to dissolution and growth measurements involves the use of scanning probe microscopy techniques, for example, in-situ atomic force microscopy (AFM), [16][17][18][19][20] and scanning electrochemical microscopy (SECM).…”