ABSTRACT
Alteration experiments involving intermediate level nuclear waste (ILW) glass in contact with hardened cement paste (HCP) were performed to assess its behavior under simulated repository conditions. Batch experiments were conducted at 20 °C and 50 °C in several artificial cement pore water (ACW) samples (pH from 10 to 13), in the presence of HCP (CEM-I, CEM-V and low pH), with a ratio of glass surface to volume of solution of 8000 m-1 and a ratio of mass of HCP to volume of solution of 10 g L-1. Glass alteration rates increase up to â¼4 × 10-2 g m-2 d-1 with pH in contact with HCP, notably with CEM-I. This value decreases by 2 orders of magnitude in low pH cement solution and also for residual alteration rates. The effect of calcium on glass alteration was observed, mainly in Ca(OH)2 saturated solution, with an incubation effect on the release of Si in solution. Experimental data were successfully modeled with the PhreeqC geochemical code. Glass and HCP samples were characterized via SEM/EDX and micro-Raman studies. This work showed that vitrified glass exhibits good performance in terms of low alteration rates (â¼10-4 g m-2 d-1), the absence of secondary phases, and the formation of a gel layer at the surface, when in contact with low pH conditions (in the presence or absence of low pH HCP).
ABSTRACT
We propose here a procedure which combines experiments and simple analytical formulas that allows us to determine good estimations of the size and charge of ionic micelles above the critical micellar concentration (cmc). First, the conductivity of n-tetradecyltrimethylammonium bromide and chloride (TTABr and TTACl, respectively) aqueous solutions was measured at 25 degrees C, before and above their cmc. Then, an analytical expression for the concentration dependence of the conductance of an ionic mixture with three species (monomers, micelles, and counterions) was developed and applied to the analysis of the experiments. The theoretical calculations use the mean spherical approximation (MSA) to describe equilibrium properties. Here, we propose new expressions for the electrical conductivity, adapted to the case of electrolytes that are dissymmetric in size, and applicable up to a total surfactant concentration of 0.1 mol L(-1). Moreover, we show that they are good approximations of the corresponding numerical results obtained from Brownian dynamics simulations. Since the analytical formulas given in the present paper involve a small number of unknown parameters, they allow one to derive the size and charge of macroions in solution from conductivity measurements.
