Dissolution Rates of Amorphous Silica in Highly Alkaline Solution

Abstract

Cement is an essential materials to construct the subsurface radioactive waste disposal system. However, cementitious materials alter the groundwater pH to highly alkaline condition about 13. To comprehend the effect of such a hyperalkaline condition on the repository surroundings, this study focused on the dissolution rates of amorphous silica at [NaOH]=l0-1 mol·dm-3 . The used samples were three kinds of pure commercial silica and a natural silica scale which was obtained from inside wall of the hot-water pipe of a geothermal power plant. The observed dissolution rates were interpreted with using the model, which assumed that the particle sizes decrease with the progress of dissolution. Moreover, due to the particle size distribution anticipated in the natural silica scale, this analysis assumed it contained particles with various initial diameters. In the results, (1) all pure silica samples and at least 60 wt% of the silica scale showed good agreement of the activation energy of the dissolution in the range of 77 through 88 kJ-mol-1 in the highly alkaline solution, (2) these rate constants were of the order of 10-s_ 10-7 mol·m-2 -s-1 at around 310 K and were definitely larger than those already reported for quartz, (3) the specific surface area based on BET method was revealed to be an important factor to give the main difference in the dissolution rates between the synthetic silica and the natural silica.

Experimental Evaluation of Efficient Si Dissolution from Perlite at Low Level Activator’s Concentration

“…According to Figure 3a-c, it is observed that for each temperature, the SiO 2 /Na 2 O mass ratio increases inversely proportional to the concentration of NaOH solution in the aqueous phase. In addition, it is clearly seen that this ratio also increases as a function of the temperature, for the same alkalinity of solution and the same activation time, in accordance with similar studies of the literature [28][29][30][31][32]. Therefore, the higher curing temperatures of the geopolymer pastes as well as the lower NaOH concentrations of the solutions result in higher SiO 2 /Na 2 O mass ratios in the slurries.…”

Key Factors Affecting Strength Development of Steel Slag-Dredged Soil Mixtures

“…This database contains detailed thermodynamic properties of minerals forming at low temperatures, including hydrates like C-S-H that form in cements. The dissolution rate constants and the surface area of silica-bearing phases obtained from previous studies [27][28][29][30][31] were loaded in the model to understand and identify the phases responsible for the supply of Si ions to form C-S-H. The silica-bearing phases listed in Table 2 and portlandite were input in the model as reactants.…”

The Effect of Aluminum in Solution on the Dissolution of Amorphous Silica and its Relation to Cementitious Systems

“…The dissolution mechanism of amorphous silica is still under discussion. [12][13][14] Considering the disordered structure of amorphous silica, Dove et al 12 proposed a model based on etch pit-driven dissolution, similar to that found for crystalline silica. This involves the creation of vacancy islands on a rumpled Q 3 surface, followed by the retreat of newly created Q 2 step edges.…”