Sorption of Pb(II) on Na-rectorite: Effects of pH, ionic strength, temperature, soil humic acid and fulvic acid

Sorption of Pb(II) from aqueous solution to Na-rectorite was studied under ambient conditions using batch technique. The effect of pH, ionic strength, humic acid and fulvic acid on the sorption of Pb(II) to Na-rectorite was also investigated. The results indicated that sorption of Pb(II) was strongly dependent on pH values. The sorption was dependent on ionic strength at low pH values, but independent of ionic strength at high pH values. Outer-sphere complexes were formed on the surface of rectorite at low pH values, whereas inner-sphere complexes were formed at high pH values. The presence of humic acid and/or fulvic acid enhanced the sorption of Pb(II) at low pH values, but decreased the sorption at high pH values. The thermodynamic values of enthalpy (ΔH°), entropy (ΔS°) and Gibbs free energy (ΔG°) were calculated from the temperature dependent sorption isotherms. The results indicated that the sorption was endothermic and spontaneous process and the sorption increased with increasing temperature.