Volume 83, Issue 5

<div>The 14th International Symposium on Solubility Phenomena and Related Equilibrium Processes (ISSP-14) was held at the Montanuniversität, Leoben, Austria, on 25-30 July 2010, co-chaired by Profs. Helmut Antrekowitsch and Heinz Gamsjäger. As part of the scientific program, a workshop on chemical modeling including kinetic effects was held over several days. The Symposium attracted scientists from all continents, save South America. Speakers at the Symposium covered an astonishing range of topics concerned with solubility phenomena in their widest sense. Oral presentations spanned the fields of analytical chemistry, physical chemistry, and modeling of aqueous and nonaqueous solutions, supersaturation, environmental chemistry, ecotoxicology, ionic liquids, solid solutions and phase relationships, and metallurgy. Aside from oral presentations, two lively poster sessions attracted some 43 presentations, also ranging across the above-mentioned topics.<br /><br />This volume of <I>Pure and Applied Chemistry</i> presents papers based on eight of the key lectures and one of the invited oral presentations at the Symposium. Subjects include the applications, experimental data and theory of the chemistry of salts in aqueous solutions, computational thermochemistry, impurities and calcium sulfate hydrates in hydrometallurgical processes, kinetics of diffusive phase transformations, environmental remediation, free energy minimization methods, supersaturation and phase transformations, and melt corrosion of refractories. These papers offer a glimpse of current research activity in diverse practical and applied aspects of solution chemistry and provide an up-to-date commentary on them.<br /><br />The Organizing Committee is delighted that these papers have been gathered together in one volume and thanks the International Union of Pure and Applied Chemistry for its continuing support in bringing the above-mentioned topics to the attention of the wider scientific community.<br /><br /><b>Peter A. Williams</b><br />Conference Editor<br /><br /></div>

Salts comprise a very large and important group of chemical compounds. Natural occurrence of salts and industrial processes of their recovery, conversion, purification, and use depend on solubility phenomena and their chemistry in aqueous solutions, mostly in multi-ion systems. Modeling of these processes as well as developing new ones requires knowledge of the properties of the aqueous salt solutions in extended T-p-x ranges including a growing number of components in solutions (CO 2 , SO 2 , lithium salts, salts of rare earth metals, actinides, etc.). At least for the thermodynamic properties, the general accepted methodology is to use thermodynamic databases of aqueous species and solids in combination with an appropriate ion-interaction model to perform equilibrium calculations for species distributions in solution and phase equilibria. The situation in respect to available thermodynamic models and data for their parameterization is discussed at selected examples. Thereby, the importance of accurate experimental determinations of phase equilibrium data for derivation of model parameters is emphasized. Furthermore, it is concluded that experimental investigations should follow a chemical systematic. Simple physical models or quantum chemical calculations cannot predict unknown quantities in the databases with sufficient accuracy. Finally, solubility changes in salt-water systems at enhanced temperatures are considered. Systems, which can be considered as molten hydrates, display interesting phase behavior and chemical reactivity as protic ionic liquids. The latter can be exploited in chemical syntheses to substitute mixtures of concentrated acids like HNO 3 /H 2 SO 4 by simple salts like ferric nitrate. For an understanding of the chemical and phase behavior of water-salt systems in terms of structure–property relations, a renaissance of chemical guided basic investigations of such systems would be worthwhile.

The paper gives an overview of the general theoretical background of computational thermochemistry as well as recent developments in the field, showing special application cases for real world problems. The established way of applying computational thermodynamics is the use of so-called integrated thermodynamic databank systems (ITDS). A short overview of the capabilities of such an ITDS is given using FactSage as an example. However, there are many more applications that go beyond the closed approach of an ITDS. With advanced algorithms it is possible to include explicit reaction kinetics as an additional constraint into the method of complex equilibrium calculations. Furthermore, a method of interlinking a small number of local equilibria with a system of materials and energy streams has been developed which permits a thermodynamically based approach to process modeling which has proven superior to detailed high-resolution computational fluid dynamic models in several cases. Examples for such highly developed applications of computational thermodynamics will be given. The production of metallurgical grade silicon from silica and carbon will be used to demonstrate the application of several calculation methods up to a full process model.

Deposit of CaSO 4 in hydrometallurgical processes involving heavy metals usually decreases production quality and harms the production process. To avoid its formation at false time and sites, a sound understanding of the solubility behavior of CaSO 4 in the quaternary systems CaSO 4 + H 2 SO 4 + (heavy metal)SO 4 + H 2 O over large ranges of temperature and concentration is a prerequisite. Up to now, although a large amount of solubility data has been reported in these systems, little information is available on the solubility of anhydrite, especially at salt concentrations near saturation points. In this paper, we introduce the effect of CaSO 4 in hydrometallurgical processes involving heavy metals, review published solubility data of calcium sulfate and its hydrate in relevant systems, and report our newly determined solubility results involving anhydrite in the quaternary systems CaSO 4 + H 2 SO 4 + MSO 4 + H 2 O (M = Cu,Zn,Mn) at 348.1 and 363.1 K. Based on the newly obtained data some application examples were given. On account of the complexity of the solubility phase diagram of these quaternary systems, where the calcium sulfate solubility is a function of its crystal type, temperature, compositions of sulfuric acid, and heavy metal sulfate, a complete solubility phase diagram is not available until some basic data measurement, for instance, water activity at temperatures higher than 298 K, and final modeling has been finished.

The constrained Gibbs energy method has been developed for the use of immaterial entities in the formula conservation matrix of the Gibbs energy minimization problem. The new method enables the association of the conservation matrix with structural, physical, chemical, and energetic properties, and thus the scope of free energy calculations can be extended beyond the conventional studies of global chemical equilibria and phase diagrams. The use of immaterial constraints enables thermochemical calculations in partial equilibrium systems as well as in systems controlled by work factors. In addition, they allow the introduction of mechanistic reaction kinetics to the Gibbsian multiphase analysis. The constrained advancements of reactions are incorporated into the Gibbs energy calculation by using additional virtual phases in the conservation matrix. The virtual components are then utilized to meet the incremental consumption of reactants or the formation of products in the kinetically slow reactions. The respective thermodynamic properties for the intermediate states can be used in reaction rate formulations, e.g., by applying the reaction quotients.

Impurities in hydrometallurgical process liquors frequently impact on product quality and yield, change physicochemical properties of the liquor, and form hard scale on heat exchangers and condensers. Organic compounds are of particular concern especially in the Bayer process, where impurities build up in the recycled liquor if not controlled. Depending on the redox state of the liquor, such compounds can undergo a variety of complex chemical reactions, including the formation of volatiles that can potentially cause environmental, health, and safety concerns. To aid in the development of appropriate control strategies, robust thermodynamic models for multicomponent aqueous systems containing large numbers of electrolytes and nonelectrolytes are required. Applications of thermodynamic models are discussed that range from the partitioning of volatile compounds in flash trains to the prediction of mixing properties of organic impurities with major Bayer liquor components.

Supersaturations and depletion or enrichment of solute/solvent are known to be the driving forces for phase transformations. In the present work, a series of different experiments is presented where in a single phase or a two-phase mixture supersaturation or enrichment/depletion of solute occur in at least one of the phases. In all cases the result is a phase transformation, particularly either the precipitation of a secondary phase out of a primary phase, or the migration of the interface in a two-phase mixture. It is demonstrated that solute transport in the phase exhibiting faster kinetics controls the phase transformation process.

A thermochemical approach was implemented to study the dissolution mechanisms of a wide range of refractory oxides and silicates in slags of the nonferrous metals industry and electric arc furnaces. First of all, the slags have been characterized regarding their working range, phase assemblage, and melting behavior. Subsequently, the interactions of different combinations of refractory and slag have been examined, and emphasis has been placed on the determination of possible reaction products formed during dissolution and the solubilities of the refractory oxides and silicates in various slags. Direct dissolution, decisive in the case of high corrosion rates, as well as indirect dissolution have been described. Varying operation conditions (e.g., temperature, atmosphere) have been incorporated into the investigations. In addition to the thermochemical calculations, the solubility of magnesia in fayalite slags has been determined experimentally with the quenching method and the calculated results have been compared to published corrosion studies of other authors. These studies revealed that thermochemical calculations are a suitable tool to examine melt corrosion. The thermochemical approach provides information that can be incorporated into product development and in the operation mode, giving a proper choice of process conditions.

It is a prerequisite for the occurrence of diffusive phase transformations that the system is in an off-equilibrium condition. The time-dependent development of the variables until equilibrium or steady-state conditions are reached can be calculated by solving the evolution equations that can be derived from the principle of maximum entropy production. These equations provide the theoretical framework for the kinetics of diffusive phase transformations. In this work, the development from sharp interface-local equilibrium (SI-LE) models to thick interface-finite mobility (TI-FM) models is reviewed and presented in the light of the above-mentioned principle. Experimental results indicate that the kinetics of diffusive solid-state phase transformations can, at least in certain ranges of composition and temperature, be modeled in a satisfactory manner by the TI-FM approach only.

This paper reviews progress made over the last decade with the shrinking object approach to the kinetics of batch dissolution. It demonstrates how the O’Connor–Greenberg equation leads to three dissolutions: those that remain well undersaturated, those that saturate with a great excess of solid left-over, and those in the middle ground where saturation is approached or attained, but where much of the solid originally added dissolves. The equations that describe these conditions are discussed, alongside sample results that validate their use with test substances, for example, salts, sucrose, silica gel, and gypsum. The equations are then shown to be consistent with the hydrodynamic approach to dissolution. Finally, further work with middle-ground dissolutions of gypsum lead to a mechanism for the back-reaction, which involves the CaSO 4 0 ion-pair. After comparison with existing studies of calcium carbonate dissolution, it is argued that this is a universal mechanism for salt dissolutions. The work improves batch dissolution as a technique to the point where it can be used synergistically with chemo-stat and rotating disc approaches. Suggestions are made for greater standardization in dissolution conditions, especially in environmental work where the data collected has to have global consistency.

Biomolecular screening is now a crucial component of the drug discovery process, and this glossary will be of use to practitioners in the field of screening and to those who interact with the screening community. The glossary contains definitions related to various aspects of the screening process such as assay types, data handling, and relevant technologies. Many of the terms used in this discipline are not covered by existing glossaries, and where they are, the definitions are often not appropriate for this field. Where appropriate, this document provides new or modified definitions to better reflect the new context. The field of biomolecular screening is multidisciplinary in nature, and this glossary, containing authoritative definitions, will be useful not only for regular practitioners, but also for those who make use of data generated during the screening process.

The units of time (both absolute time and duration) most practical to use when dealing with very long times, for example, in nuclear chemistry and earth and planetary sciences, are multiples of the year, or annus (a). Its proposed definition in terms of the SI base unit for time, the second (s), for the epoch 2000.0 is 1 a = 3.1556925445 × 10 7 s. Adoption of this definition, and abandonment of the use of distinct units for time differences, will bring the earth and planetary sciences into compliance with quantity calculus for SI and non-SI units of time.

The numerical modeling of Cd II speciation amongst the environmental inorganic ligands Cl – , OH – , CO 3 2– , SO 4 2– , and PO 4 3– requires reliable values for the relevant stability (formation) constants. This paper compiles and provides a critical review of these constants and related thermodynamic data. It recommends values of log 10 β p,q,r ° valid at I m = 0 mol kg –1 and 25 °C (298.15 K), along with the equations and empirical reaction ion interaction coefficients, ∆ ε , required to calculate log 10 β p,q,r values at higher ionic strengths using the Brønsted–Guggenheim–Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, ∆ r H , are reported where available. Unfortunately, with the exception of the Cd II -chlorido system and (at low ionic strengths) the Cd II -sulfato system, the equilibrium reactions for the title systems are relatively poorly characterized. In weakly acidic fresh water systems (–log 10 {[H + ]/ c °} < 6), in the absence of organic ligands (e.g., humic substances), Cd II speciation is dominated by Cd 2+ (aq), with CdSO 4 (aq) as a minor species. In this respect, Cd II is similar to Cu II [2007PBa] and Pb II [2009PBa]. However, in weakly alkaline fresh water solutions, 7.5 < –log 10 {[H + ]/ c °} < 8.6, the speciation of Cd II is still dominated by Cd 2+ (aq), whereas for Cu II [2007PBa] and Pb II [2009PBa] the carbonato- species MCO 3 (aq) dominates. In weakly acidic saline systems (–log 10 {[H + ]/ c ϒ} < 6; –log 10 {[Cl – ]/ c °} < 2.0) the speciation is dominated by CdCl n (2– n )+ complexes, ( n = 1–3), with Cd 2+ (aq) as a minor species. This is qualitatively similar to the situation for Cu II and Pb II . However, in weakly alkaline saline solutions, including seawater, the chlorido- complexes still dominate the speciation of Cd II because of the relatively low stability of CdCO 3 (aq). In contrast, the speciation of Cu II [2007PBa] and Pb II [2009PBa] in seawater is dominated by the respective species MCO 3 (aq). There is scope for additional high-quality measurements in the Cd 2+ + H + + CO 3 2– system as the large uncertainties in the stability constants for the Cd 2+ -carbonato complexes significantly affect the speciation calculations.

Errata: Glossary of terms used in photocatalysis and radiation catalysis (IUPAC Recommendations 2011). (S. E. Braslavsky, A. M. Braun, A. E. Cassano, A. V. Emeline, M. I. Litter, L. Palmisano, V. N. Parmon, N. Serpone). Pure Appl. Chem. 83, 931–1014 (2011); doi:10.1351/PAC-REC-09-09-36.