Comparative study on Np(V) sorption on oxides of aluminum and silicon: effects of humic substance and carbonate in solution

Abstract

The sorption of Np(V) (total concentration 10 −5 mol/L) onto alumina and silica was studied by a batch technique under ambient aerobic conditions at 25 °C. The effects of pH, ionic strength, humic substance (HS), and added carbonate in aqueous solutions on the sorption of Np(V) onto alumina and silica were investigated. The sorption isotherms of Np(V) on alumina and the relationships between the equilibrium concentrations after sorption onto silica and the initial concentration before sorption in the absence and presence of HS and added carbonate in solutions were determined. It was found that as compared with the sorption of Np(V) onto alumina, the sorption by silica on the basis of mass is tremendously less, negative sorption of Np(V) onto silica occurs, the relative rate of sorption onto silica is quicker the sensitivity of sorption onto silica to ionic strength is higher, the pH dependence of sorption onto silica is less, and consequently the characteristics of Np(V) sorption onto alumina and silica are distinctly different. The effect of addition of HS or carbonate in solution was studied. Little effect of addition of HS (20 mg/L) on sorption onto alumina and silica were found. The addition of carbonate (0.001 mol/L) increased Np(V) sorption onto silica at pH values below 10 and decreased it at pH values above 10.