Uranium removal from aqueous solutions by raw and modified thermal power plant ash

The U(VI) removal from aqueous solutions (concentration range 125-2,000 mg/L, pH 3) by raw and NaOH-modified power plant ash was investigated by means of a batch method under the following experimental conditions: NaOH concentration 5 M, contact time 1 h, respectively 4 h, temperature 70, 90 A degrees C. The amount of sorbed uranium was determined spectrophotometricaly using the Arsenazo III method. The sorbents were examined prior and after the sorption experiments by scanning electron microscopy/energy dispersive spectroscopy. Typical sorption isotherms were calculated and modeled by the Langmuir and Freundlich equations. The experimental data showed that all materials can remove considerable amounts of uranium from acidic aqueous solutions. The maximum removal efficiency (q (max)) values obtained, are 126 mg U/g for raw ash and 206 mg U/g for NaOH-modified. Sorption kinetics measurements were performed at 298, 308 and 323 K and thermodynamic parameters were calculated. The kinetic data obey a pseudo-second order equation.