Adsorptive removal of 2,4-dichlorophenol from aqueous solution using micronized oil shale

Abstract This study investigated the utilization of a unique oil shale as a sorbent for the removal of 2,4-dichlorophenol (2,4-DCP) from aqueous solutions. The influence of various process parameters, including the contact time, sorbent/liquid ratio, pH, and temperature, on the sorption process was evaluated. The results indicated the near-complete sorption of 2,4-DCP within 24 h. Favorable sorption was observed either at a sorbent/liquid ratio of 1:10, at elevated temperatures (40 °C), or at lower pH values (pH = 5) within the examined range. The maximum adsorption capacity at 40 °C has the potential to reach up to 20.0 µmol/g. Langmuir, Freundlich, and Sips isotherms were applied to the experimental data, but the Sips isotherm provided a superior fit, suggesting a heterogeneous sorption. Kinetic studies revealed a two-stage process: intraparticle diffusion dominated the initial stage, whereas other rate-limiting mechanisms may have contributed to the second stage. The first- and second-order kinetic models suggested a combined mechanism. According to the thermodynaic study, the adsorption process was spontaneous and exothermic, as indicated by the negative Gibbs free energy change and enthalpy change, which suggest that physisorption predominated. These findings demonstrate the potential of the investigated oil shale as an unconventional and cost-effective sorbent, potentially serving as a substitute for activated carbon in 2,4-DCP removal. Graphical abstract