Sorption and desorption of uranyl ions by silica gel: pH,particle size and porosity effects |
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| Institution: | 1. Parks College of Engineering, Aviation and Technology, Saint Louis University, St. Louis, MO 63103, USA;2. Faculty of Mechanical Engineering, University of Engineering and Technology, Lahore, Pakistan;3. School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, E1 4NS, UK;4. New Green Way Pte. Ltd., 51 Goldhill Plaza, #7-10/11, Singapore 308900, Singapore;1. School of Chemistry, Madurai Kamaraj University, Madurai, India;2. Department of Chemistry, Fatima College, Madurai, India;3. Research Department of Chemistry, Aditanar College of Arts and Science, Tiruchendur, India;4. Department of Industrial Chemistry, Alagappa University, Karaikudi, India;5. Department of Inorganic Physical Chemistry, Indian Institute of Science, Bangalore, India;1. Key Laboratory of the Three Gorges Reservoir Region’s Eco-Environment, Ministry of Education, Chongqing University, Chongqing 400045, PR China;2. State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, PR China;3. College of River and Ocean Engineering, Chongqing Jiaotong University, Chongqing 400074, PR China;4. Department of Chemistry, School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, PR China;1. Department of Agricultural Biotechnology, Seoul National University, Seoul 151-921, Republic of Korea;2. Department of Microbiology, Changwon National University, Changwon-si 641-773, Republic of Korea |
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| Abstract: | Uranium sorption by silica gel was shown to be very sensitive to pH; the optimum pH range is ca. 5–5.5, which coincides with the appearance of hydrolysed forms of uranyl. A two-phase surface mechanism is proposed: first the adsorption of hydrolysed forms, which precipitate later on the surface of the oxide, then the removal of residue at the new sorbing surface by adsorption or precipitation. Particle size and pore characteristics have a limited effect on equilibrium concentration, but greatly influence sorption kinetics. A two-phase kinetic mechanism is proposed which gives external and intraparticle mass transfer coefficients of the order of 10?7?10?5 and 10?8?10?7 m min?1, respectively. Both a mesoporous and a microporous silica gel were examined in order to determine the influence of pore size on sorption kinetics: the ratio between solute size and pore diameter appears to be the major factor in governing the uptake rate. The desorption of silica gel was also studied, particularly concerning the nature and concentration of the elution agent. Acid solutions are most effective at removing uranium. Using a batch system the number of moles of acid needs to be eight times greater than those of uranium in order to obtain a desorption efficiency higher than 90%. In dynamic desorption, on the other hand, 0.5 M hydrochloric acid gives both total desorption and optimal metal recovery. Eluate concentrations as high as 100–200 g l?1 can be obtained. Furthermore, when seven sorption-desorption cycles were carried out using the column system, removal performances were maintained and the sorbent could be re-used. |
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