Adsorption of thorium from aqueous solution by HDTMA+-pillared bentonite

The ability of hexadecyltrimethylammonium cation pillared bentonite (HDTMA(+)-bentonite) has been explored for the removal and recovery of thorium from aqueous solutions. The adsorbent was characterized using small-angle X-ray diffraction, high resolution transmission electron microscopy and Fourier transform infrared spectroscopy. The influences of different experimental parameters such as solution pH, initial thorium concentration, contact time and temperature on adsorption were investigated. The HDTMA(+)-bentonite showed the highest thorium sorption capacity at initial pH of 3.5 and contact time of 60 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, a dagger GA degrees (298 K), a dagger HA degrees and a dagger SA degrees were determined to be -31.78, -23.71 kJ/mol and 27.10 J/mol K, respectively, which demonstrated the sorption process of HDTMA(+)-bentonite towards Th(VI) was feasible, spontaneous and exothermic in nature. The adsorption on HDTMA(+)-bentonite was more favor than Na-bentonite, in addition the saturated monolayer sorption capacity increased from 17.88 to 31.20 mg/g at 298 K after HDTMA(+) pillaring. The adsorbed HDTMA(+)-bentonite could be effectively regenerated by 0.1 mol/L HCl solution for the removal and recovery of Th(VI). Complete removal (99.9 %) of Th(VI) from 1.0 L industry wastewater containing 16.8 mg Th(VI) ions was possible with 7.0 g HDTMA(+)-bentonite.