COMPLEX-REACTIONS BETWEEN TOXIC-CHEMICAL WASTES AND HIGH SALINE SOLUTIONS TAKING INTO ACCOUNT UNDERGROUND REPOSITORY CONDITIONS

The complex reactions between high saline solutions and toxic chemical wastes were investigated by means of laboratory experiments and geoch emical modelling. The specific boundary conditions of an underground r epository in salt formations were taken into account. In order to dete rmine the chemical equilibrium compositions of the resulting solutions a new leaching procedure was developed and successfully employed with several toxic wastes. The results for a fly ash waste stemming from a glass smelting furnace are given in detail. Zinc and cadmium are the two most prominent heavy metals, that accumulate significantly in the leachates. In order to gain an insight into the complex dissolution an d precipitation processes in such multi-component systems, geochemical modelling was performed using the program code EQ3/6 and the Fitter f ormalism for calculating the activity coefficients. The thermodynamic database used was extended and Fitter coefficients for Zn and Cd in hi gh saline solutions were derived from literature data and added to the database. The results of the geochemical modelling of the investigate d reactions were in good agreement with the experimental data. On this basis the maximum concentrations that can be leached from the investi gated fly ash into a Mg-rich saline solution, that is typical for a sa lt repository in Northern Germany, are predicted to be 0,181 mol/kg H2 O zinc and 0,00317 mol/kg H2O cadmium, respectively.