Sorption of Co 2+ and Sr 2+ by waste-derived 11 Å tobermorite

• Published in: Waste management (Elmsford) Vol. 26; no. 3; pp. 260 - 267
• Main Authors: Coleman, Nichola J., Brassington, David S., Raza, Atiya, Mendham, Andrew P.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2006
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2005.01.019

Newsprint recycling gives rise to significant volumes of waste sludge which can be de-watered and combusted for energy-recovery. The residual combustion ash, whose primary crystalline constituents are; gehlenite (Ca 2Al 2SiO 7), åkermanite (Ca 2MgSi 2O 7), β-dicalcium silicate (Ca 2SiO 4) and anorthite (CaAl 2Si 2O 8), is currently consigned to landfill disposal. It is demonstrated herein that a mixed product of Al-substituted 11 Å tobermorite (Ca 5Si 6O 18H 2 · 4H 2O) and katoite (Ca 3Al 2SiO 12H 8) can be synthesised from newsprint recycling combustion ash via a hydrothermal route. Batch sorption studies confirm that this mixed product is an effective sorbent for the exclusion of Co 2+ and Sr 2+ from acidic aqueous media. Kinetic sorption data are analysed in accordance with the pseudo-first- and pseudo-second-order models, and steady-state data is fitted to the Langmuir and Freundlich isotherms. The Langmuir and pseudo-second-order models are found to provide the most appropriate descriptions of the sorption processes. The maximum uptake capacities for Co 2+ and Sr 2+ at 20 °C are 10.47 and 1.52 mg g −1, respectively, and the respective apparent pseudo-second-order rate constants are estimated to be 5.08 × 10 −3 and 6.96 × 10 −3 g mg −1 min −1.