Sorption of Synthetic Dyes Onto River Sediments: A Laboratory Study

Abstract

This work deals with sorption of cationic synthetic dye thioflavine T (ThT) onto the river sediment obtained from the Váh River under conditions of batch and column system using spectrophotometric methods. We found that sorption of ThT onto river sediment was a rapid process with reaching of concentration equilibrium within 2 h of interaction. The values of distribution coefficient (DC) defined as concentration ratio [ThT]_sediment : [ThT]_solution were linearly increased with increasing concentration of river sediment in solution within the range C_sediment 1.25 - 10.0 g/dm³ and minimally changed in the range of initial pH values 2 - 6. The increasing concentration of ThT in model solution caused exponentially decrease in the value of DC. The sorption processes characterized by dependence between equilibrium specific sorption Q_eq and ThT concentration C_eq in solution were better described by adsorption isotherm according to Freundlich (R² = 0.979) than according to Langmuir adsorption isotherm (R² = 0.914). From evaluation of ThT sorption onto river sediment in column system containing of 5 cm sediment layer with 30 cm of water column on the basis of ThT concentration changes in infiltrated water we found that these processes were significantly dependent on the rate of infiltrated water flow through the sediment layer R_iw as well as on qualitative and quantitative composition of water. The highest ThT desorption from the sediment layer was found in seepage of 50 % (v/v) ethanol (EtOH) solution through the sediment and efficiency of ThT desorption decreased in the order: 50 % (v/v) EtOH > 0.1 mol/dm³ HCl > deionized water. Obtained data from the point of view of physico-chemical characteristics of the river sediment, such as pH, pH_zpc (potentiometric titration), cation-exchange capacity (CEC) and elemental composition (X-ray fluorescence spectrometry), was also discussed.