Adsorption Behavior Of Neptunium In Nitric Acid Solution On Silica Gel

In this paper,the adsorption behavior of quadrivalent,pentravalent and hexavalent neptunium on silica gel in nitric acid solutions was investigated by batch experiment. The effects of equilibrium time,acidity of the solution,temperature,concentration of redox reagents on the adsorption of neptunium by silica gel were carried out. Desorption and isotherm adsorption experiments were also performed.The results are shown as follows:The equilibrium for adsorption of neptunium on silica gel reached rapidly. In high acidities,neptunium is hardly adsorbed on silica gel. But in high pH solutions,neptunium is adsorbed strongly on silica gel. Adsorption distribution coefficients increase with the increasing of temperature. The concentrations of redox reagents have light effects on adsorption within the studied concentration range. High concentration of nitric acid can be used as desorption reagent of neptunium adsorbed on silica gel. The desorption experiments in the same pH of solutions as adsorption experiments show that the desorption coefficient is bigger than the adsorption coefficient,so the adsorption of neptunium on silica gel in nitric acid belongs to irreversible process. Comparing the experimental results of 239Np with that of 237rvftyif is.concluded that the adsorption behaviour of 239Np is the same as that of 237Np.The adsorption isotherm of neptunium on silica gel correspond to the form of Langmuir isotherm. According to Clausius-Claperon equation,from the slope in InKd vs 1/T plot,adsorption heat could be estimated. From the data of adsorption heat it is concluded that the adsorption of neptunium on silica gel in nitric acid solutions belongs to chemical adsorption and the adsorption process is an endothermic reaction.