Solubility and water-softening properties of a crystalline layered sodium silicate, SKS-6
Abstract
The solubility and water-softening capabilities of a crystalline layered silicate, SKS-6 (Na2Si2O5), have been evaluated and compared with those of an amorphous silicate of similar composition. Both silicates readily broke down to yield amorphous silica on contact with aqueous solutions and were found to be appreciably soluble, even at 25 °C. The bulk of calcium and magnesium was precipitated from hard-water solutions as silicates and/or hydroxides within a few minutes of reaction. Magnesium was removed more effectively than calcium, owing to the lower solubility of the Mg-silicates. The amorphous silicate exhibits greater solubility, better magnesium removal and inferior calcium removal when compared to SKS-6. Solution-state NMR, solid-state NMR, X-ray powder diffraction and chemical analysis have been used to characterise the silicates in the solution and solid phases. The interactions between metal ions and silicates are discussed with reference to the observed results.