Abstract:

The adsorption and desorption behaviors of Zn(II) on water-goethite interfaces under various particle concentrations (Cp) and temperatures were studied using traditional batch experiments. The Zn(II)/α-FeOOH adsorption system exhibited a significant particle concentration effect, in other words adsorption isotherms decreased as Cp increased. The adsorption also became less reversible because as the Cp increased which was demonstrated by the hysteresis angle (θ) and thermodynamic index of irreversibility (TII) as derived fromadsorption and desorption isotherms. This agrees with the explanation of the particle concentration effect as postulated in metastable-equilibrium adsorption (MEA) theory. Furthermore, the particle concentration effect became more obvious at lower temperatures. Adsorption of Zn(II) on goethite surfaces was found to increase greatly with the increase of temperature and the adsorption became more reversible. These results further confirmed that the Cp effect is the result of changes in adsorption reversibility. The study also showed that the adsorption was a simultaneous (positive △S value of 195.71 J·mol-1·K-1) and endothermic (positive △H value of 34.07 kJ·mol-1) chemisorption process.

Key words: Temperature, Particle concentration effect, Adsorption reversibility, Adsorption-desorption, Zn(II), Goethite