Synthesis, structure and ion exchange properties of 11 Å tobermorites from newsprint recycling residue

Al-substituted 11 Å tobermorites were obtained from stoichiometrically adjusted mixtures of newsprint recycling waste, sodium silicate and calcium oxide via hydrothermal synthesis at 100 °C. Hydrothermal processing in water yielded a highly crystalline 11 Å tobermorite product with a Cs⁺ cation exchange capacity of 85 meq 100 g⁻¹ and selective Cs⁺ distribution coefficient of ∼5500 cm³ g⁻¹. Conversely, a product of inferior crystallinity was obtained from hydrothermal synthesis in alkaline liquor whose Cs⁺ ion exchange capacity and selective Cs⁺ distribution coefficient were found to be 66.3 meq 100 g⁻¹ and ∼700 cm³ g⁻¹, respectively. Silicate chain configuration was found to have a modest impact on the number of cation exchange sites per unit cell, whereas the influence of structural defects on selectivity was more pronounced. The structures and ion exchange credentials of both 11 Å tobermorite products corresponded well with those of their essentially phase-pure counterparts.