Erich Koenigsberger

The solubility of solid calcium oxalate monohydrate (CaC2O4·H2O, COM) has been measured in aqueous solutions of four 1:1 electrolytes (NaCl, KCl, CsCl, and Me4NCl) at temperatures T = 298.15, 323.15, and 343.15 K. Solubilities at industrially relevant electrolyte concentrations of up to 5.0 mol·kg–1 were determined by atomic absorption spectrophotometry of the dissolved calcium ions. The solubility of COM in 1.0 mol·kg–1 electrolyte solutions was 2–4 times higher than in pure water but varied little at higher ionic strengths for all of the systems studied. Most of the observed solubilities were well correlated at all temperatures and electrolyte concentrations using a simple Specific Ion-interaction Theory (SIT) model with only one adjustable, temperature-independent, interaction parameter. For Me4NCl solutions, an additional empirical ionic strength dependence of the SIT parameter significantly improved the fit.

No thermodynamic data for the solution of Cl in ferrous alloys were found in the literature. This is in accord with recent Accelerator Mass Spectroscopy (AMS) analyses which showed that Cl contents in stainless steel (SS) are in the order of a few ppb. However, based on older chemical analyses of Cl in the order of 100 ppm, SS that has been irradiated with thermal neutrons in nuclear reactors is considered a major source of the long-lived 36Cl isotope in nuclear waste. In this study, the potential Cl contamination of SS originating from production and refinement processes is investigated. Unlike ferrous alloys, blast-furnace and steelmaking slags can dissolve significant amounts of Cl. The equilibrium distribution of Cl species between slags and gas phase was calculated for various steelmaking processes using the FactSage 7.2 software and databases. The results showed that despite the high volatility of metal chlorides at high temperatures, significant fractions of Cl can be retained in the slag phase even at 1600 °C. Chloride may also be incorporated in non-metallic inclusions originating from secondary refining. Based on these results and on several further assumptions, various scenarios for explaining, and also avoiding, Cl contamination of steel are discussed.

Solubility data have frequently been reported without sufficient attention to experimental detail, including a proper description of apparatus and measurements, the evaluation of uncertainties, and the validation of the experimental protocol. This editorial focuses on solubility measurements of solids in liquids at atmospheric pressure. It provides guidelines that are intended to help researchers to select and validate appropriate experimental techniques, and consequently improve the accuracy of their measured data. It should also assist reviewers in assessing the reliability of solubility data considered for publication in this Journal.

Although most kidney stones are found in the calyx, they are usually initiated upstream in the nephron by precipitation there of certain incipient mineral phases. The risk of kidney stone formation can thus be indicated by changes in the degree of saturation of these minerals in the nephron fluid. To this end, relevant concentration profiles in the fluid along the nephron have been calculated by starting with specified urine compositions and imposing constraints from the corresponding, much less variable, blood compositions. A model for supersaturation within ten sections of both long and short nephrons has accordingly been developed based on this ‘reverse engineering’ of the necessary substance concentrations coupled with chemical speciation distributions calculated by our Joint Expert Speciation System (JESS). This allows the likelihood of precipitation to be assessed based on Ostwald’s ‘Rule of Stages’. Differences between normal and stone-former profiles have been used to identify sections in the nephron where conditions seem most likely to induce heterogeneous nucleation.

The composition and structures of the two protonated species formed from uncharged molybdic acid, MoO2(OH)2(OH2)20, in strongly acidic solutions have been investigated using a combination of density functional theory calculations, first-principles molecular dynamics simulations, and Raman spectroscopy. The calculations show that both protonated species maintain the original octahedral structure of molybdic acid. Computed pKa values indicated that the ═O moieties are the proton acceptor sites and, therefore, that MoO(OH)3(OH2)2+ and Mo(OH)4(OH2)22+ are the probable protonated forms of Mo(VI) in strong acid solutions, rather than the previously accepted MoO2(OH)2–x(OH2)2+xx+ (x = 1, 2) species. This finding is shown to be broadly consistent with the observed Raman spectra. Structural details of MoO(OH)3(OH2)2+ and Mo(OH)4(OH2)22+ are reported.

The solubility of solid sodium oxalate (Na2Ox) has been measured in a variety of concentrated aqueous electrolyte solutions at T = 298.15, 323.15, and 343.15 K by titration of dissolved oxalate with permanganate. The electrolyte solutions studied (not necessarily at all temperatures) were NaCl, NaClO4, NaOH, LiCl, KCl, Me4NCl, and KOH at concentrations ranging from approximately 0.5 mol·kg–1 to at least 5 mol·kg–1. Where comparisons were possible, the present results were in excellent agreement with literature data. The solubility of Na2Ox(s) decreased markedly with increasing concentrations of Na+(aq), due to the common ion effect. This decrease was almost independent of the electrolyte anion. A number of ternary mixtures of these electrolytes were also investigated at constant ionic strength. Consistent with the binary mixtures, the solubility of Na2Ox(s) showed almost no dependence on solution composition at constant Na+(aq) concentrations. Solubilities in non-Na+ media, with the exception of Me4NCl, showed small but regular increases with increasing concentration of added electrolyte, probably reflecting activity coefficient variations. The solubility data in certain Na+-containing media could be correlated accurately at all temperatures and concentrations using a relatively simple Pitzer model with interaction parameters for Na2Ox(aq) assumed to be identical to those available in the literature for Na2SO4(aq).

The standard equilibrium constant, K⊖(T), for a chemical reaction is a dimensionless quantity defined by K⊖(T)=exp{−ΔrG⊖(T)/RT}, where ΔrG⊖(T) is the change in the standard molar Gibbs energy due to the reaction. The value of K⊖(T) depends on the choice of the standard state, which must be specified. The standard equilibrium constant is, like all standard thermodynamic quantities, independent of pressure and composition (Ewing et al. 1994; Cohen et al. 2008).