Adsorption and thermodynamic properties of the alumina–polyacrylic acid solution system

Free energies of polyacrylic acid (PAA) adsorption (ΔG∘) on an alumina (Al2O3) surface in the temperature range 15–35 °C were estimated on the basis of adsorption–desorption measurements of the inorganic radioactive ions 36Cl, 45Ca, and 55Fe. Adsorbing polymer macromolecules caused the desorption process of previously adsorbed radioactive ions. The free energy of Ca-PAA surface complex formation (ΔG∘) was estimated to be close to the free energy of Ca2+ ions adsorption (polymer causes about 50% desorption of these ions). Moreover, a free energy of polymer molecule adsorption increase with the increasing temperature was observed. The obtained values of ΔG∘ were compared with those calculated from the adsorption data. Additionally, the amount of polymer adsorbed and the thicknesses of polymer adsorption layers were determined in the temperature range 15–35 °C. The changes of polymer chain conformation with the temperature increase are responsible for the increase of PAA adsorption as well as thickness of polymer adsorption layers in the studied temperature range.

Free energies of PAA adsorption on the Al2O3 surface as a function of temperature.Figure optionsDownload as PowerPoint slide