SOLUBILITY AND WATER-SOFTENING PROPERTIES OF A CRYSTALLINE LAYERED SODIUM-SILICATE, SKS-6

The solubility and water-softening capabilities of a crystalline layer ed silicate, SKS-6 (Na2Si2O5), have been evaluated and compared with t hose of an amorphous silicate of similar composition. Both silicates r eadily broke down to yield amorphous silica on contact with aqueous so lutions and were found to be appreciably soluble, even at 25-degrees-C . The bulk of calcium and magnesium was precipitated from hard-water s olutions as silicates and/or hydroxides within a few minutes of reacti on. 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 remo val when compared to SKS-6. Solution-state NMR, solid-state NMR, X-ray powder diffraction and chemical analysis have been used to characteri se the silicates in the solution and solid phases. The interactions be tween metal ions and silicates are discussed with reference to the obs erved results.