Adsorption of Pb(II) on diatomite as affected via aqueous solution chemistry and temperature

To better understand the application of diatomite as an adsorbent for the removal of Pb(II) from heavy metal-contaminated water, in this paper, diatomite was used to adsorb Pb(II) from aqueous solution under various conditions. The results demonstrated that the adsorption of Pb(II) was strongly dependent on ionic strength at pH < 7.0, outer-sphere surface complexation or ion exchange may be the main adsorption mechanism of Pb(II) on diatomite at low pH values. No drastic difference of Pb(II) adsorption was observed at pH > 7.0, and the adsorption at high pH values was mainly dominated via inner-sphere surface complexation. The presence of HA/FA showed great influence on Pb(II) adsorption on diatomite. The adsorption of Pb(II) on diatomite was dependent on foreign ions (herein K+, Na+, ClO4−, NO3− and Cl−) in solution at pH < 8.0, and was independent of foreign ions at pH > 8.0. The thermodynamic parameters (i.e., ΔH°, ΔS°, ΔG°) were evaluated from the temperature dependent adsorption isotherms. The results indicated that the adsorption process of Pb(II) on diatomite was spontaneous and endothermic in nature.