Behavior of nickel and cobalt in water as it evolves towards water-rock equilibrium (granitic zones)

The study of processes governing the chemical composition of granitic areas waters is essential before the modification of such a site by radioactive waste storage. This work needs the sampling and the chemical determination of various advance degree to water rock equilibrium waters, from leaching waters to equilibrated ones. Nickel and cobalt are contained in this waste. As they are traces in natural environment, a little is known about their behaviour. A recent analytical method allows their measurements. One shows that their amounts are principally linked to their mineralogic origin and that the redox state of water together with the amounts of sulfur control their precipitation. In close to water-rock equilibrium waters, where the mineralization state can be characterized by chloride amounts, alkali elements solubility is constrained by the water charge before the alkali-earth ones. Before this, Ca and Mg amounts are regulated by an adsorption process. Fe and Mn amounts are regulated by a one proton exchange adsorption process, and the redox state of the solution is the determinant factor permitting their insoluble forms appearance. (author)