The importance of complexing in controlling the solubility, transport and precipitation of ore metals in aqueous solutions is a recurrent theme of this book. In this chapter experimental results obtained at the Institute of the Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences, Moscow during the past ten years are reviewed. The results presented here, on the solubility and complexing of a disparate range of metals in aqueous solutions, are linked together by a common methodological approach: the investigation, where possible, of simple systems to determine equilibrium constants for specific complex formation. The scope of this paper is unashamedly idiosyncratic. Some elements have received detailed and extensive study, others only limited investigation. However, the authors attempt to describe the results of many years work to characterize some Fluids in the Crust: Equilibrium and transport properties.

At present Na-Al-P-glass is used in Russia as matrix for high level nuclear waste which include a sufficient portion of 90Sr and 137Cs isotopes. It has been known that this type of glass is characterized by relatively poor hydrothermal stability above 120°C (Krilova et al., 1990 [1], Balukova et al., 1987 [2]). Although careful studies were devoted to the glass, some questions of geochemical behavior of Sr and Cs in the limits of the nearest repository environment have remained undecided. For example, these have been left uncertain: the mechanism of the glass leaching, phenomena limiting the glass dissolution, the detailed composition of newly formed phases, temperature dependence of the glass solubility. The main purpose of the present experimental investigation was to detect factors controlling Sr and Cs concentrations of aquous solutions and to study the possibility of new solid phase formation as a factor slowing down migration of Cs and Sr in water satureted circumstance.

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