Sorption of Co^2^+ and Sr^2^+ by waste-derived 11 A tobermorite [An article from: Waste Management]

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Description:
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), akermanite (Ca"2MgSi"2O"7), @b-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 A tobermorite (Ca"5Si"6O"1"8H"2.4H"2O) and katoite (Ca"3Al"2SiO"1"2H"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 ^oC 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.