Sorption and desorption of neptunium(V) on loess: batch and column experiments

SummaryThe sorption and desorption isotherms and the corresponding distribution coefficients (Kd, mL/g) of Np(V) for untreated loess and three kinds of treated loesses were determined by using the batch technique at moderate concentrations (∼10-5mol/L) under ambient aerobic conditions in the presence of 0.01mol/L CaCl2. For the treated loesses, selective extraction methods were used to remove CaCO3and organic matter (OM) from the loess. The isotherms were analyzed with the Freundlich equation. The relative contributions of OM and CaCO3to the Np(V) sorption on the loess were investigated from the parameters of the Freundlich equation. The effects of adding fulvic acid (FA) from the loess and the carbonate in solution on the sorption of neptunium(V) on the loess were studied. The breakthrough curves (BTCs) and displacement curves (DPCs) of Np(V) on the untreated loess column and on the treated loess columns were determined under ambient aerobic conditions at moderate concentration (1.1×10-4mol/L) in the presence of 0.01mol/L CaCl2. The results of column experiments are in accord with the results of batch experiments. It was found that (1) Np(V) in the loess under the present experimental conditions was relatively mobile and the distribution coefficients were relatively low at moderate concentrations, (2) the sorption/desorption hysteresis of Np(V) on the loess occurs, (3) the sorption of Np(V) on the loess was mainly determined by the clay minerals, (4) the addition of FA or carbonate in the aqueous solutions had an obvious positive effect on the Np(V) sorption on the loess, (5) the retardation of Np(V) migration in the loess at moderate concentrations was inconsiderable.