Impact of environmental conditions on the sorption behavior of Pb(II) onto attapulgite

This paper examined the application of attapulgite as an adsorbent for the removal of Pb(II) from heavy metal-contaminated water under various conditions. The sorption results indicated that the sorption of Pb(II) on attapulgite was strongly dependent on ionic strength at pH < 7.0. Outer-sphere surface complexation or ion exchange may be the main sorption mechanism of Pb(II) on attapulgite at low pH values. No drastic difference of Pb(II) sorption was observed at pH 7.0–10.0, and the sorption at pH > 10.0 was mainly dominated by inner-sphere surface complexation. The sorption of Pb(II) on attapulgite was affected by foreign ions in solution at pH < 7.0, and was not affected by foreign ions at pH > 7.0. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) were evaluated from the temperature-dependent sorption isotherms, and the results indicated that the sorption process of Pb(II) on attapulgite was spontaneous and endothermic in nature.