Transport, Sorption and Desorption of Organic Dye Through Quartz Sand Particles

In this work, the effects of various factors such as the aqueous phase pH, the temperature, the ionic strength, the flow velocity and the electrolyte cation nature on the retention, the mobility and the release of Methylene Blue (MB) through quartz sand (QS), used as porous medium, were investigated. Thus, step-input column experiments were carried out to study the transport, sorption and the desorption mechanisms of the MB molecules through a porous medium made of quartz grains. Hence, the five main parameters related to the adsorption experimental conditions, were varied in order to elucidate the adsorption-desorption mechanisms of MB through the QS medium. The MB adsorbed amount, Qads, was found to decrease by decreasing either the pH, in the range 9.5-4, or the temperature, in the range 333-293°K. Similar decrease of Qads was also obtained by increasing the flow rate, Q, in the range 45-90 ml. h-1, or by increasing the affinity of the divalent cation (Ca2+, Cu2+, Zn2+ and Ba2+) toward the QS surface. However, slight decrease in the MB adsorbed amount, was observed by increasing the ionic strength, in the range 10-3-10-1M. The overall data indicate that, electrostatic interaction forces, which occur between the cationic organic pollutant and the negative surface of the quartz substrate, mainly control the adsorption process. In addition, the increase of the adsorbed amount with the temperature, suggests that the adsorption is endothermic in nature.