Volume 79, Issue 5

The series of International Symposia on Solubility Phenomena and Related Equilibrium Processes (ISSP) brings together chemists from a wide range of fields where solubility plays an important role. This variety was well reflected at the 12th ISSP where the plenary and invited lectures included: gas solubilities (Maurer) and gas hydrates (Sloan); solubility limitations to lithium-air batteries (Salomon); studies of solubilities at high pressures (Sawamura); solubility considerations in radioactive waste management (Wanner); kinetics of precipitation and dissolution in hydrothermal systems (Wesolowski); crystal growth and dissolution processes (Koutsoukos); and preferential crystallization (König). Those presented here illustrate this breadth of subject matter and highlight the combination of fundamental and applied research that characterizes this field. A tradition has developed in the ISSP series of holding a workshop on one topic of particular interest, in parallel with the scientific program. This yearís workshop related to the current state of thermodynamic databases that could be used in understanding and predicting the properties of complex systems, for example, those encountered in constructing waste management facilities. A paper summarizing the workshop discussions is included in this compilation. The series of Solubility Phenomena grew out of the work of the IUPAC Solubility Data Commission and has been continued through the auspices of IUPAC's Subcommittee on Solubility and Equilibrium Data. The first in this biennial series of meetings was held in 1984 at the University of Western Ontario, and, while subsequent meetings have commonly been held in North America (Newark and Troy) or Europe (Guildford, Moscow, Leoben, Varna, and Aveiro), meetings in Buenos Aires, Hammamet, and Niigata have ensured that all continents have hosted these enjoyable meetings. The ISSPs are consistently friendly and interesting meetings that bring together scientists and friends from many fields and all parts of the world. The 12th ISSP, held from 23 to 28 July, was entirely in keeping with this tradition with over 100 participants from 30 countries converging on the charming town of Frieberg in Saxony where traditional German hospitality combined with the weather to make a memorable meeting. Earle Waghorne Conference Editor

The formation of sparingly soluble salts from aqueous solutions and their dissolution has attracted broad research interest. Of particular importance is the formation and transformation of minerals exhibiting polymorphism or encountered in more than one crystalline phase as, for example, in the case of calcium phosphates, formed in biological mineralization and in industrial-scale deposits. Understanding of these processes depends primarily on the equilibrium between the mineral phases considered and the aqueous medium in contact. Precipitation takes place in supersaturated solutions with rates depending on the solution supersaturation. The experimental investigation may reveal mechanistic details if done at sustained supersaturation. The kinetics of crystal growth depends either on surface diffusion or on bulk diffusion, which in turn is controlled by the medium fluid dynamics. In the case of magnesium ammonium phosphate (struvite), the presence of water-soluble organic compounds is responsible for the retardation both of the time needed for the onset of precipitation and for the kinetics of growth of the supercritical nuclei. Dissolution processes are controlled by the same mechanisms. In the case of calcitic marble, the dissolution in alkaline solutions is controlled by surface diffusion. Compounds active at the marble/water interface may in this case be used as protective agents.

A review is presented of the present state-of-the-art of Li-air cells and batteries. We examine the properties of this unique system in terms of the effects of solubilities of reactants and products in both nonaqueous (aprotic) and aqueous electrolyte solutions. Definite trends are observed, such as increasing cell-specific energy and capacity as both the oxygen solubility increases and viscosity decreases in organic solvents, but quantitative analyses are limited owing to the complex relations between solubility, solution viscosity, oxygen diffusion, and electrolytic conductivity. Adding to this complex relation is the dependence of the nature of the carbon-based air cathode (surface area and pore volume) upon practical specific capacities, which can be realized with Li-air cells that far exceed the specific energies and capacities of all present commercial metal-air and Li-ion cells and batteries.

We have measured the solubilities of several inorganic and organic compounds at high pressures up to 400 MPa. For this purpose, care should be exercised in instrumentation. The results include solubility values for aqueous solutions of NaCl, NaCl.2H 2 O, toluene, anthracene, phenanthrene, and amino acids (Gly, Ala, Val, Leu, and Ile). In addition, we determined the solubility of C 60 in n -hexane and toluene. The data for individual systems served to elucidate the mechanisms of dissolution. For example, the data for toluene, anthracene, and phenanthrene in water provided insight into hydrophobic hydration.

Radioactive waste arises mainly from the generation of nuclear power but also from the use of radioactive materials in medicine, industry, and research. It occurs in a variety of forms and may range from slightly to highly radioactive. It is a worldwide consensus that radioactive waste should be disposed of in a permanent way which ensures protection of humans and the environment. This objective may be achieved by isolating radioactive waste in a disposal system which is located, designed, constructed, operated, and closed such that any potential hazard to human health is kept acceptably low, now and in the future. For highly radioactive waste and spent nuclear fuel, which are the waste types representing the highest potential danger to human health, an effective isolation from the biosphere is considered to be achievable by deep geological disposal. Disposal concepts rely on the passive safety functions of a series of engineered and natural barriers. Since total isolation over extended timescales is not possible, radionuclides will eventually be released from the waste matrix and migrate through the engineered and natural barriers. The assessment of their mobility in these environments is essential for the safety demonstration of such a repository. The solubility of many radionuclides is limited and may contribute significantly to retention. Reliable predictions of solubility limitations are therefore important. Predictions of maximum solubilities are always subject to uncertainties. Complete sets of thermodynamic and equilibrium data are required for a reliable assessment of the chemical behavior of the radionuclides. Gaps in the thermodynamic databases may lead to erroneous predictions. Missing data and insufficient knowledge of the solubility-limiting processes increase the uncertainties and require pessimistic assumptions in the safety analysis; however, these are usually not detrimental to safety owing to the robustness of the multi-barrier approach.

Performance assessment studies in underground disposal of radioactive or toxic waste need to consider all reactive interactions between waste and its surroundings. Thermodynamic equilibrium and reaction path calculations represent an important tool for this purpose. The reliability of the results depends first of all on the quality of the thermodynamic database used for the calculations. Several quality criteria of thermodynamic databases are discussed in connection with the characteristics of current database projects [Nuclear Energy Agency Thermochemical Database (NEA-TDB), Yucca Mountain database, Dortmund Databank (DDB), Common Thermodynamic Database (CTD), FreeGS, and Thermodynamic Reference Database (THEREDA)] including the situation for molten salts. The future role of the IUPAC standard for thermophysical and thermochemical data storage is emphasized.

Complex formation between Cu II and the common environmental ligands Cl - , OH - , CO 3 2- , SO 4 2- , and PO 4 3- can have a significant effect on Cu II speciation in natural waters with low concentrations of organic matter. Copper(II) complexes are labile, so the Cu II distribution amongst these inorganic ligands can be estimated by numerical modeling if reliable values for the relevant stability (formation) constants are available. This paper provides a critical review of such 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 specific ion interaction coefficients required to calculate log 10 β p,q,r values at higher ionic strengths. Some values for reaction enthalpies, Δr H m, are also reported where available. In weakly acidic fresh water systems, in the absence of organic ligands, Cu II speciation is dominated by the species Cu 2+ (aq), with CuSO 4 (aq) as a minor species. In seawater, it is dominated by CuCO 3 (aq), with Cu(OH) + , Cu 2+ (aq), CuCl + , Cu(CO 3 )OH - , Cu(OH) 2 (aq), and Cu(CO 3 ) 2 2- as minor species. In weakly acidic saline systems, it is dominated by Cu 2+ (aq) and CuCl + , with CuSO 4 (aq) and CuCl 2 (aq) as minor species.