Adsorption of U(VI) on bentonite in simulation environmental conditions

The bentonite derived from Huangshan County was used as adsorbent for the adsorption of uranium (U(VI)). The effect of environmental factors, such as contact time, pH, ionic strength, HA and reaction temperature, on U(VI) adsorption on bentonite surface was investigated in detail. The adsorption capability of bentonite for U(VI) is obviously rest with pH value and ionic strength. The presence of HA in solution strongly enhance and reduce the adsorption of U(VI) on bentonite at low and high pH, respectively. The Langmuir and Freundlich models were applied to simulate the adsorption isotherms of U(VI) at three different temperatures of 298 +/- 1, 318 +/- 1 and 338 +/- 1 K, respectively. The thermodynamic parameters (Delta H-0, Delta G(0) and Delta S-0) calculated from the temperature-dependence adsorption isotherms indicates that U(VI) adsorption on bentonite is an endothermic and spontaneous process. At pH < 7, the adsorption of U(VI) was dominated by the outer-sphere surface complexation and ion exchange with H+/Na+ on bentonite surfaces; At pH > 7, the inner-sphere surface complexation was the main adsorption mechanism. Based on the experimental analysis results, bentonite is an appropriate material for the enrichment and solidification of U(VI) ions. The results are important for the radioactive waste management. (C) 2017 Published by Elsevier B.V.