The aim of the current study was to investigate and model particle size dependence of the dissolution process of Ca(OH)2, CaCO3, and oil shale ash. In the samples of the self-regulating equilibrium system H2O–dissolved CO2–solid CaCO3 filtered through a 0.45 μm filter no nanoparticles were detected. The nanoparticles appeared when the pH had been increased to 12.3 and the value of the product of the molar concentrations of the Ca2+ and OH– ions reached the value of the solubility product constant Ksp. When different amounts of Ca(OH)2 were added to degassed water, the pH increased and nanoparticles started to appear in the solution containing 0.5 g/L of solid Ca(OH)2 (pH = 12.3). Up to this value of the pH all particles had dissolved. Due to the better solubility of small particles connected to the rise of the value of the solubility product constant Ksp for nanoscale particles, the solubility of Ca(OH)2, the concentration of Ca2+ ions, and the pH increased. The pH of oil shale ash leachate increased with the increasing of the amount of ash, as the quantity of nanoparticles increased in a similar manner as described for the solubility of Ca(OH)2.
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