Sorption of Uranium on Some Natural Modified Clay Mineral Deposits.

Abstract

Bentonite and Kaolinite clay sediments - as low cost adsorbents- were prepared, characterized, and tested for uranium removal from uranium rich-soil of Wadi Um Hamad region S.W. Sinai which have total uranium 260 mg/ kg . Some factors that influence the uranium removal efficiency onto clay samples: initial uranium concentrations, contact time and pH were also studied in detail. Modification of clay samples were carried out by acid activation. Results showed that the U adsorption was pH dependent. The maximum U adsorption value was at pH 5 and 6 for bentonite and kaolinite, respectively. In addition, results indicated that temperature had not any influence on the adsorption efficiency. The adsorption capacities of the two minerals after 90 min are almost similar. Our obtained results revealed that by increasing U ions concentrations from 50 mg/L to 200 mg/L adsorption was stable for kaolinite while for bentonite there was slight decrease, after that with increasing in the U (VI) ions concentration the efficiency decreased for both adsorbents. Calcination is more effective in increasing the removal efficiency of bentonite than acid activation. Calcination of the kaolinite (heating the clay at 400oC followed by agitating with 1.5 N HCl) increased that removal efficiency from 42% to 90%. XRD pattern show the destruction of the characteristic diffraction peaks of the kaolinite (7.15 A° and 3.15 A°) at (70oC or 400oC). This is similar to behavior of bentonite, as the acid treatment with HCl has broken its lattice structure more than heating to 400oC. U removal efficiency by bentonite and kaolinite were 95.4% and 90.8%, respectively. Four adsorption isotherm models were tested and revealed that achieved experimental data fitted well with langmuir- model. The uranium adsorption efficiency follow Langmuir isotherm with a capacity 18.68 mg/g for modified kaolinite and 27.4 mg/g for modified bentonite. Comparing the adsorption capacity of both minerals after modification, it could be noticed that, it is almost similar 93% and 90% for bentonite and kaolinite, respectively.