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 an d carbonates with metal salts containing cations such as Zn2+, Pb2+, C a2+, or Al3+ has been performed. X-ray diffraction, scanning electron microscopy, and high-resolution Si-29 and Al-27 NMR of these solids ha ve been carried out. Pb and Ca form crystallized carbonate precipitate s and amorphous silicates. Al and Zn form only amorphous silicates. Th e speciation of the different complexes formed is achieved by decompos ition of the Si-29 NMR spectra. It is then possible to explain the rea ction mechanisms occurring between the soluble silicates and the catio ns. In no case is there any silica formed in the precipitate (no Q(4) entity). The most reactive silicate species present in the samples are formed by Q(3) units.