Adsorption kinetic, isotherm and thermodynamic studies of Sr2+ onto hexagonal tungsten oxide

Hexagonal tungsten oxide (hex-WO3) with exchangeable sodium and ammonium cations located in hexagonal channel was synthesized by a facile hydrothermal treatment of sodium tungstate dihydrate in concentrated HCl solution in the presence of ammonium sulfate. An attempt was made to assess the potential of hex-WO3 for the adsorption of Sr2+ ions from acidic radioactive waste solutions. Adsorption of Sr2+ reached equilibrium very quickly in 2 h in acidic aqueous solution. Maximum removal of Sr2+ ions occurred at pH 4. Equilibrium studies showed that the extent of Sr2+ ions uptake by hex-WO3 was better described by the Freundlich isotherm in comparison with the Langmuir model. The thermodynamic parameters showed that the adsorption of Sr2+ ions onto hex-WO3 was spontaneous and exothermic under the studied conditions. (author)