Sorption of non-ionic organic pollutants onto a humic acids-zeolitic tuff adduct: thermodynamic aspects.

Sorption isotherms from water solutions for toluene, cyclohexane, o-xylene, benzyl alcohol, phenol and cyclohexanol onto a humic acid-zeolite adduct were determined at 4, 14, 24 and 34 °C and utilized to calculate the isosteric enthalpy (ΔadsHi) and isosteric entropy (ΔadsSi) of the process. For hydrocarbon compounds, toluene, cyclohexane and o-xylene, both ΔadsHi and ΔadsSi were negative, the process was exothermic. In contrast, for hydroxyl compounds, benzyl alcohol, phenol and cyclohexanol, ΔadsHi and ΔadsSi were positive, the increase in entropy possibly reflecting the release of water molecules during sorption. The results suggest that sorption/desorption of either class of compounds could be controlled by operating on the temperature.