MEASUREMENT AND PREDICTION OF PORTLANDITE SOLUBILITY IN ALKALI SOLUTIONS

The solubility of Ca(OH)(2) has been determined in sodium and potassium hydroxide solutions to 4 molal concentration at 25 degrees C. These data and other solubility and EMF measurements in the Ca-K-Cl-OH-H2O system have been used to refine Pitzer ion interaction parameter data for the Ca(OH)(2) . H2O system. Applications of these parameters to the results of 15 independent studies of portlandite solubility in pure water yield an average solubility product of -logK(sp) 5.19+/-0.04. The resultant model yields an excellent representation of all available portlandite solubility data in CaCl2, CaSO4, NaCl, NaOH, KCl, Na2SO4 and K2SO4 solutions and their mixtures. The refined parameters will provide an improved representation of portlandite solubility in cement/water systems whose ionic strengths are typically beyond the limits for the application of Debye-Huckel based ion pairing equilibria models.