Adsorption of organic pollutants onto a Romanian soil: Column dynamics and transport

Abstract The main objectives of this study were to obtain data and assess the processes of transport and migration of organic pollutants in natural soils, in particular adsorption–desorption, in dynamic mode. The experiments were conducted to study the effects of some significant parameters such as soil column height, influent flow rate and initial concentration of the dye in influent solution on Congo red (CR) behavior in a Romanian soil. Some models such as: Thomas, Adams–Bohart, Wolborska, Yoon–Nelson and BDST were applied to predict the behavior of CR in a protosoil collected from NE of Romania. Column experiments were performed in order to reproduce field conditions, with the goal to obtain information not available from batch studies. Breakthrough curves were used to evaluate the mobility of CR in soil columns. It was observed that, at low CR concentration there is a relative slower transport determined by a declining in diffusion coefficient and mass transfer coefficient values. The saturation time was achieved earlier and the breakthrough time appears quicker when the initial CR concentration increases. This phenomenon can be explained by the larger number of active adsorption centers covered at higher concentrations of CR. The transport parameters of CR depend on the initial dye concentration in solution and influent flow rate, as well as soil column height. This behavior confirms the high mobility potential of CR in the investigated soil. Desorption studies using different eluents showed that the rate of desorption was higher in the first minutes of the process, when more than 80% of the uptaken CR molecules were desorbed, showing a high potential mobility and transport in investigated soil.