Solute transport analysis of bromide, uranin and LiCl using breakthrough curves from aquifer sediment

The transport behavior of lithium, uranin, bromide and chloride was studied in column experiments using sediment from an unconfined aquifer at the Kra uthausen test site. Sorption isotherms of uranin, bromide and chloride were determined in batch experiments. In addition, a sorption/desorption isothe rm of uranin was determined. Inverse parameter estimation and asymptotic an alysis of solute transport processes were used to interpret measured BTCs. The log transformed BTCs of bromide and chloride showed a linear decrease o f the tailing part with time. Depending on the shape of the tail in the BTC s, a CDE with retardation or a mobile/immobile model was adjusted successfu lly. Measured uranin BTCs were described using either the CDE with hysteret ic Freundlich sorption or the CDE with linear kinetic sorption. In addition , one of the measured uranin BTCs provided evidence for the presence of non linear nonequilibrium sorption. The discrimination and identification of th e different types of sorption processes was based to a large extent on asym ptotic analysis. However, in a few experiments asymptotic analysis did not provide information on the sorption process because the tailing concentrati ons fell below the detection limit before convergence to one of the asympto tic solutions could be observed. For none of these cases, the models analyz ed in this work were able to describe the complete BTCs (including the tail ). For two BTCs showing sorption hysteresis, the observed concentrations co uld be predicted using data from independent measurements almost without pa rameter fitting. Only a slight modification of the distribution coefficient was needed in one case. Lithium transport could be described either by Fre undlich sorption or linear kinetic sorption. Field BTCs of uranin showed a qualitatively similar behavior as the BTCs observed in column experiments. Evaluation of the slope of log-log transformed field BTCs suggested that ur anin sorption may be described by a nonlinear nonequilibrium sorption or hy steretic Freundlich sorption model. (C) 1999 Elsevier Science B.V. All righ ts reserved.