Sorption of Co and Sr by waste-derived 11 A 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: 01.01.2006
• ISSN: 0956-053X
• 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 (Ca2Al2SiO7), akermanite (Ca2MgSi2O7), beta -dicalcium silicate (Ca2SiO4) and anorthite (CaAl2Si2O8), is currently consigned to landfill disposal. It is demonstrated herein that a mixed product of Al-substituted 11 A tobermorite (Ca5Si6O18H2·4H2O) and katoite (Ca3Al2SiO12H8) 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 Co2+ and Sr2+ 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 Co2+ and Sr2+ at 20 °C are 10.47 and 1.52 mgg-1, respectively, and the respective apparent pseudo-second-order rate constants are estimated to be 5.08X10-3 and 6.96X10-3 gmg-1min-1.