The solubility of calcium zineate (CaZn2(OH)(6)center dot 2H(2)O)

Ca zincate (CaZn2(OH)(6). 2H(2)O) plays an important role in the geochemica l behaviour of Zn in cementitious systems. This paper describes the determi nation of a solubility product for Ca zincate and its range of application. Calcium zincate was synthesized and characterised by X-ray diffraction (XR D). Samples were then equilibrated at 25 degreesC and an ionic strength of 0.1 M in a pH range between 11.4 and 12.7. A solubility product, logK(s)0 = 43.9, was determined for infinite dilution using the Davies equation for t he following reaction. CaZn2(OH)(6). 2H(2)O((s)) + 6H((aq))(+)<----> Ca-(aq)(2+) + 2Zn((aq))(2+) 8H(2)O The solubility product can be used to successfully interpret the results of experiments in which Zn is equilibrated with C-S-H(I) at pH values between 11.7 and 12.78 at 25 degreesC and an ionic strength of 0.1 M. However, the solubility product is not able to model both the Zn and Ca concentration a t a given pH value because dissolution is incongruent. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.