Abstract:

: Synthetic 11 Å tobermorite (Ca 5Si 6O 16(OH) 2.4H 2O) and its Al-substituted analogue are layer-lattice ion-exchangers with potential applications in nuclear and hazardous wastewater treatment. The present study reports the facile one-pot hydrothermal synthesis of an Al-tobermorite-rich cation-exchanger from a combination of paper recycling ash, post-consumer container glass, and lime, with compositional ratios of [Ca]/[Si + Al] = 0.81 and [Al]/[Si + Al] = 0.18. The reaction products were characterized by powder X-ray diffraction analysis, 29Si magic angle spinning nuclear magnetic resonance spectroscopy, and scanning electron microscopy. Hydrothermal processing in 4 M NaOH (aq) at 100 °C for 7 days yielded an Al-tobermorite-rich product that also contained katoite (Ca 3Al 2SiO 12H 8), portlandite (Ca(OH) 2), calcite (CaCO 3), and amorphous silicate gel. The hydrothermal product was found to have a Cs + cation exchange capacity of 59 ± 4 meq 100 g −1 and selective Cs + distribution coefficients ( Kd) of 574 ± 13 and 658 ± 34 cm 3 g −1 from solutions with molar ratios [Cs +]:[Na +] and [Cs +]:[Ca 2+] of 1:100. In a batch sorption study at 20 °C, the uptakes of Pb 2+, Cd 2+, and Cs + were determined to be 1.78 ± 0.04, 0.65 ± 0.06, and 0.36 ± 0.03 mmol g −1, respectively. The kinetics of Pb 2+, Cd 2+, and Cs + removal were described by the pseudo-second-order rate model, which gave respective rate constants ( k 2) of 0.010, 0.027, and 1.635 g mmol −1 min −1, and corresponding correlation coefficients ( R 2) of 0.997, 0.996, and 0.999. The metal ion sorption properties of the tobermorite-rich product compared favorably with those of other waste-derived tobermorites reported in the literature. Potential strategies to improve the yield, crystallinity, and sorption characteristics of the product are discussed.

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