Influence of initial concentrations and pH conditions on uranium adsorption in clays

Batch adsorption experiments were performed to investigate influences of experimental conditions such as initial uranium concentrations (0, 1 x 10^-3, 1 x 10^-2, 0.1, 0.5, 1 mg/L) and pHs of solution (4, 7 and 9.5) on uranium adsorption in three types of clay (kaolinite, montmorillonite, and bentonite). For all experiments, the adsorption of uranium could be described by the linear isotherm model at solution concentrations less than 1 mg/L, showing high values of correlation coefficient (R2 > 0.98). The adsorption efficiencies of montmorillonite and kaolinite for all pHs are more than 91% and 87%, respectively. The effect of pH on the adsorption of uranium was not found in kaolinite and montmorillonite for all initial concentrations. However, the adsorption efficiency of bentonite was lower than other clay types (< 75%). Solutions with low initial concentrations (< 1 x 10^-2 mg/L) achieved high efficiencies for adsorption of uranium (> 99%) at all pHs, while low efficiencies were observed in solutions with high initial concentrations (> 0.1 mg/L) at pH 4 (47%), pH 7 (59%) and pH 9.5 (43%). It is concluded that montmorillonite and kaolinite can be used as an effective adsorbent for removing uranium from aqueous solutions.