The influence of temperature on the adsorption of CTAB on coals

The influence of temperature on the adsorption behavior of the cationic surfactant cetyltrimethyl amonium bromide (CTAB) has been studied. Batch mode was used for the adsorption of CTAB on three different types of coal, namely oxidative altered coal (BO), subbituminous coal (SB) and bituminous coal (BC). Adsorption from aqueous solutions was carried out at 25, 40, 60 and 80 °C. The linear as well as nonlinear regression of experimental data confirmed that the adsorption process can be described using the Langmuir adsorption theory of monolayer coverage. Thus, the equilibrium constant of adsorption could be calculated from the Langmuir binding constant b. Further, thermodynamic parameters such as enthalpy ΔHads, entropy ΔSads and Gibbs energy ΔGads were determined from the dependence of the b constant on temperature. The calculated thermodynamic parameters indicate that the adsorption of CTAB on coals is an exothermic (ΔHads < 0) and spontaneous (ΔGads < 0) process. It was proved that the adsorption capacity of CTAB on coal increased with a rise in temperature for all the studied samples; the highest adsorption capacity was observed for the oxidative altered coal. Moreover, a close relationship between the adsorption capacity and the critical micelle concentration (CMC) of CTAB has been discovered. In addition, measuring the zeta potential proved that the adsorbed amount of CTAB on the coal surface corresponded to the zeta potential value. Addition of the cationic surfactant (CTAB) affects the value of ξ-potential, making the zeta potential values more positive.