Vol. 24, No. 6
Solubility Data Projects
the major functions of the IUPAC Subcommittee on Solubility and Equilibrium
Data (formerly IUPAC Commission V.8) is to publish authoritative texts
on all aspects of solubilities. The main output of this subcommittee
is the ongoing series of volumes in the IUPACNIST Solubility Data
Series, or simply the SDS. The priority subjects to be pursued
over the next three years within the framework of this Solubility Data
Project were approved by the Analytical Chemistry Division on 2 July
2002. In this context, compilations and evaluations of experimental
solubility data in the following three fields are in progress:
Solubility Data of Compounds Relevant to Mobility of Metals in the Environment
in aqueous media of sparingly soluble metal salts such as carbonates
play an important role in chemical processes. Solubility phenomena (i.e.,
dissolution and precipitation reactions) frequently control procedures
for preparing, separating, and purifying chemicals. Moreover, interactions
of the hydrologic cycle with the cycle of rocks, as well as the naturally
occurring dissolution of minerals in water and their precipitation on
the ocean floor and in sediments of rivers and lakes, can often be simply
described in terms of solubility equilibria.
solubility measurements have been shown to be a powerful tool for the
determination of thermodynamic properties of sparingly soluble metal
salts. The total concentration of alkaline earth and transition metals
in carbonate-bearing natural waters is predominantly determined by the
solubilities of the respective hydroxides, oxides, hydroxide carbonates,
and neutral carbonates. A careful determination of thermodynamic data
of sparingly-soluble metal salts is an essential prerequisite for the
geochemical modeling of the release of trace elements from waste repositories.
Clearly, a comprehensive compilation and evaluation of the existing
solubility data is an invaluable basis for all sorts of predictive models
in this field. Presently three volumes are in preparation: 1) alkaline
earth metal carbonates; 2) metal
carbonates (Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, Hg, Pb); and 3) inorganic
Solubility Data Related to Oceanic Salt Systems
oceanic salt system comprises the ions Na+, K+,
Mg2+, Ca2+, Cl-, and SO42-.
Extended evaporitic deposits in Europe (Germany, Netherlands, Spain,
France, Poland, Russia); North America (Canada); South America (Brasilia);
Africa (Congo); and Asia had been formed from these ions during the
evaporation-crystallization processes of seawaters in geological times.
Geological surveying of these deposits, potash mining, rock salt mining,
fertilizer production, and usage of rock salt mines as repository for
nuclear or chemical wastes require the exact knowledge of solubility
equilibria in the multicomponent oceanic salt system within a broad
range of temperatures. At present, solution mining of magnesium chloride
for magnesium metal production is performed or is in the planning stage
in a number of places (Netherlands, Congo, Thailand, and Uzbekistan).
In addition, evaporation and aerosol formation from oceans are important
controlling factors for the worlds climate. In order to formulate
material and energy exchange models, it is crucial to understand the
coupling of evaporation and crystallization processes within the droplets
transported into the upper atmosphere. Climate changes from past time
periods are manifested in the complex evaporitic deposition patterns,
which are interpreted on the basis of the solid-liquid equilibria of
the multicomponent oceanic salt system.
two volumes are under way: 1) binary systems containing sodium,
potassium, and ammonium sulfate; and 2) magnesium
chloride-water and calcium chloride-water and their mixtures.
Solubility Data Related to Industrial Processes
solubility is one of the fundamental properties of various gas absorption
processes in the chemical industry. The removal of carbon dioxide from
gas mixtures is a necessary and expensive step in many processes. It
is of particular importance, for example, in the purification of ammonia
synthesis gas, in the synthesis of liquid fuels from coal, and in the
upgrading of fuel gases. Absorption with suitable solvents provides
a convenient method for the removal of CO2. In enhanced oil
recovery, carbon dioxide is used to displace the hydrocarbons from the
reservoir and the solubility of CO2 in the hydrocarbons is
important to ensure that miscibility occurs, with a concomitant increase
in the oil recovered. In addition, processing using supercritical fluids
is an increasingly important area worldwide. Systems that employ carbon
dioxide as the solvent are particularly attractive as CO2
is environmentally friendly.
of accurate and reliable information on the equilibrium solubility of
CO2 in absorbing solvents as a function of temperature and
pressure is of utmost importance in the rational design of gas-treating
units. Such data will allow more economical construction and more nearly
optimum operation of gas-treating plants. Thus, compiled and evaluated
data on the solubility of CO2 in various industrially important
aqueous solvents and solvent mixtures are very much sought after.
three volumes are in preparation: 1) CO2
in aqueous non-electrolyte solutions; 2) CO2
and the lower alkanes at pressures above 2 bar: part 1, methane
to butane; and 3) solids
and liquids in supercritical CO2.
of the diversity of industrial processes sometimes pending problems
have to be tackled when there is sufficient individual expertise and
interest from contributors. Thus, volume four concerning the solubility
of lead sulfate is in preparation. Lead sulfate in aqueous and non-aqueous
solvents continues to present problems in the design and manufacture
of the still very important lead-acid batteries.
is one of the best extractive distillation solvents for separation of
close boiling paraffinic and olefinic hydrocarbons. As the chemical
process industry seeks more efficient and less energy-intensive separation
techniques, liquid-liquid extraction based on selective solubilities
is becoming more common. Volume five, which is being produced, covers
by Heinz Gamsjäger,
chairman of Subcommittee on Solubility and Equilibrium Data.