Abstract. Structural parameters and thermodynamic properties of strontianite -witherite solid solutions have been studied by X-ray powder diffraction, heat flux Calvet calorimetry and cation-exchange equilibria technique. X-ray study of the synthetic samples have Cation-exchange reactions between carbonates and aqueous SrC12-BaC12 supercritical solutions (fluids) were carried out at 973 and 1073 K and 2 kbar. Calculated Margules model parameters of the excess free energy are: for orthorhombic carbonate solid solutions Wsr=WBa=ll.51+0.40kJ*mo1-1 (973 K) and Wsr= W~,= 12.09_+0.95 kJ,mo1-1 (1073 K); for trigonal carbonate solid solutions WSr = WBa = 13.55___ 0.40 kJ* mol-1 (1073 K).

Slow cooling of phosphate melt at liquid nuclear waste solidification yields glass-crystalline material. Partial crystallization during melt solidification results in elemental partitioning among crystalline phase and glass: Al, Cr, Fe are concentrated in the crystalline phosphate phase while Ca, Ni, La, U enter predominantly in the residual glass. Glass dissolution rate and leach rate of La and U as rare earth and actinide surrogates depends strongly on the glass composition, for example reduction of Al2O3 content in the glass to ∼10-12 wt.% increases leachability by three orders of magnitude as compared to the glass with specified composition (∼18-22 wt.% Al2O3).

The article discusses the types of mineral raw materials that can be used to manufacture clay barrier materials. The paper evaluates the characteristics of materials governing the performance of clay barriers: grain size, mineral and chemical composition, physical, mechanical (in dry state) and colloidal properties, stability in the environment. It considers the methods used to identify these characteristics and provides relevant examples.

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