Determination of Ca2+ complexation constants by monomeric silicate species at 25°C with a Ca2+ ion selective electrode

The description of water soluble calcium silicate species is still subject of controversy because of little experimental literature on this topic. In this study, the complexation of Ca2+ by deprotonated silicate species has been investigated by a calcium ion selective electrode performed under carefully controlled conditions, in which the precipitation of calcium silicate has been avoided as far as possible. The resulting complexation constants are found to be significantly lower than those published in the literature. Our experimental results are supported by DFT modeling highlighting the stability of the different calcium silicate species.