Kinetic, Thermodynamic and Adsorption Mechanism of Uranium (VI) Ions from Aqueous Solutions Using Mg/Al Layered Double Hydroxide

Layered double hydroxide (Mg/Al; 3:1) was synthesized by co-precipitation method and used to adsorb uranium from aqueous solutions. Various environmental parameters such as contact time, pH, initial uranium concentration and temperature were investigated. The maximum adsorption capacity occurred at pH=3 (99 mg/g). The adsorption of U(VI) onto LDH decreased with increasing pH at pH>6.5, because of the formation uranyl carbonate complexes (69 mg/g). The thermodynamic parameters (i.e., ΔH0, ΔS0 and ΔG0) indicated that the adsorption process of U(VI) on LDH was an endothermic and spontaneous process. At pH<6.5, the probable mechanism of adsorption of U(VI) was governed by inner-sphere surface complexation with OH groups on LDH surfaces, while the dominant mechanism at pH>6.5 was inner-sphere surface complexation and ion exchange with NO3¯. Based on the experimental results, LDH is a very suitable material for the removal of U(VI) ions from aqueous solutions in a wide range of pH.