NMR Evidence of Silicate and Carbonate Competition for Cations in Solution at Low Temperature:  Case of Ca2+, Zn2+, Pb2+, and Al3

The characterization of solids obtained by mixing soluble silicates and carbonates with metal salts containing cations such as Zn2+, Pb2+, Ca2+, or Al3+ has been performed. X-ray diffraction, scanning electron microscopy, and high-resolution 29Si and 27Al NMR of these solids have been carried out. Pb and Ca form crystallized carbonate precipitates and amorphous silicates. Al and Zn form only amorphous silicates. The speciation of the different complexes formed is achieved by decomposition of the 29Si NMR spectra. It is then possible to explain the reaction mechanisms occurring between the soluble silicates and the cations. In no case is there any silica formed in the precipitate (no Q4 entity). The most reactive silicate species present in the samples are formed by Q3 units.