IUPAC-NIST Solubility Data Series. 95. Alkaline Earth Carbonates in Aqueous Systems. Part 1. Introduction, Be and Mg

Abstract

The alkaline earth carbonates are an important class of minerals. This volume compiles and critically evaluates solubility data of the alkaline earth carbonates in water and in simple aqueous electrolyte solutions. Part 1, the present paper, outlines the procedure adopted in this volume in detail, and presents the beryllium and magnesium carbonates. For the minerals magnesite (MgCO 3 ), nesquehonite (MgCO 3 Á3H 2 O), and lansfordite (MgCO 3 Á5H 2 O), a critical evaluation is presented based on curve fits to empirical and=or thermodynamic models. Useful side products of the compilation and evaluation of the data outlined in the introduction are new relationships for the Henry constant of CO 2 with Sechenov parameters, and for various equilibria in the aqueous phase including the dissociation constants of CO 2 (aq) and the stability constant of the ion pair MCO 0 3 ðaqÞ (M ¼ alkaline earth metal). Thermodynamic data of the alkaline earth carbonates consistent with two thermodynamic model variants are proposed. The model variant that describes the Mg 2þ ÀHCO À 3 ion interaction with Pitzer parameters was more consistent with the solubility data and with other thermodynamic data than the model variant that described the interaction with a stability constant.

Numerical Modeling of CO2, Water, Sodium Chloride, and Magnesium Carbonates Equilibrium to High Temperature and Pressure

“…The average absolute deviations are all under 10%. Figure 2a posts all of the experimental data (which are judged as reliable by Visscher et al [52]) and the calculated results with dots, most of which are quite close to the equal line (y = x). Figure 2b shows the nesquehonite solubility varying with CO 2 partial pressure at various temperature.…”

“…To test the model behavior, we compared the model results with the existing experimental data of MgCO 3 mineral solubility. Visscher et al [52] carefully compared the experimental data and checked the reliability of the data. We defined average absolute deviation (AAD) to measure the difference between model results and experimental work:…”

Thermodynamically Consistent Force Field for Molecular Dynamics Simulations of Alkaline-Earth Carbonates and Their Aqueous Speciation

“…This is particularly critical for the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 techniques, such as dielectric relaxation spectroscopy, 67 to determine the ion-pairing equilibrium constants and thereby the free energy, which instead has to be inferred by measuring the residual free ion concentrations in solution either by titration methods or ion selective electrode measurements. 68 These experimental techniques rely on the choice of a model that accounts for the possible equilibria in solution, which, particularly in the case of CaCO 3 , may be more complex than for other species. 1,3 Moreover, for ion-selective electrode measurements it is not clear whether species…”

Scale Prediction and Control at Ultra HTHP

“…Calcium carbonate is one of the most widely studied mineral in literature. For calcite solubility prediction, the primary source of data is selected from a recent IUPAC-NIST review [20,21] of 120 references. In the IUPAC-NIST compilation of data, six crystallographic varieties of calcium carbonates (calcite, aragonite, vaterite, monohydrocalcite (CaCO 3 ·H 2 O), ikaite (CaCO 3 ·6H 2 O), "amorphous" calcium carbonate) were distinguished in addition to a group of "unknown" or not clearly specified amorphous calcium carbonate solid.…”

“…However, the prediction of equilibrium constants at high temperatures and pressures are highly uncertain [24,33]. The numerical values may vary considerably by different solution models [21,26]. Pitzer theory is one of the most popular approaches to predict the activity coefficients of mixed electrolytes [31,83].…”