Validation of TOF-SIMS and FE-SEM/EDS Techniques Combined with Sorption and Desorption Experiments to Check Competitive and Individual Pb(2+) and Cd(2+) Association with Components of B Soil Horizons

Sorption and desorption experiments were performed by the batch method on the B horizons of five natural soils: Umbric Cambisol, Endoleptic Luvisol, Mollic Umbrisol, Dystric Umbrisol, and Dystric Fluvisol. Individual and competitive sorption and desorption capacity and hysteresis were determined. The results showed that Pb(2+) was sorbed and retained in a greater quantity than Cd(2+) and that the hysteresis of the first was greater than that of the second. The most influential characteristics of the sorption and retention of Pb(2+) were pH, ECEC, Fe and Mn oxides and clay contents. For Cd(2+) they were mainly pH and, to a lesser extent, Mn oxides and clay content. The combined use of TOF-SIMS, FE-SEM/EDS and sorption and desorption analyses was suitable for achieving a better understanding of the interaction between soil components and the two heavy metals. They show the preferential association of Pb(2+) with vermiculite, chlorite, Fe and Mn oxides, and of Cd(2+) with the same components, although to a much lesser extent and intensity. This was due to the latter’s higher mobility as it competed unfavourably with the Pb(2+) sorption sites. TOF-SIMS and FE-SEM/EDS techniques confirmed the results of the sorption experiments, and also provided valuable information on whether the soil components (individually or in association) retain Cd(2+) and / or Pb(2+); this could help to propose effective measures for the remediation of contaminated soils.