Reaction of layered sodium disilicate SKS-6 with calcium chloride solution as revealed by solid state NMR spectroscopy: Exploring the calcium ion extracting mechanism of SKS-6

Solid-state 1H, 29Si NMR and 23Na MQMAS NMR spectroscopy combined with X-ray powder diffraction (XRD) technique was used to study the reaction between layered sodium disilicate SKS-6 and calcium chloride solution with different concentrations. Based on the experimental results the calcium ion extracting mechanism of SKS-6 was demonstrated to be via ion replacement, during which calcium ions replace sodium ions and combine with the non-bridging oxygen in SKS-6 for charge compensation, and simultaneously sodium ions leave the interlayer. This ion-replacement process was greatly influenced by the substitution of sodium ions by protons as well as the calcium ions concentration. Increasing calcium ions concentration favors the replacement of sodium ions by calcium ions, but prevents sodium ions from being substituted by protons.