Sorption of Pb in chemical and particle-size fractions of soils with different physico-chemical properties

Purpose: Lead (Pb) sorption capacity (Pb _Smax ) and distribution in chemical and particle-size fractions of six soils with different physico-chemical properties were investigated to explore the principal properties of soils that affect Pb sorption. Materials and methods: A series of experiments of Pb sorption and soil chemical and particle-size fractionation of sorbed Pb were conducted with six soils of different texture, mineralogy, organic matter concentration, cation exchange capacity (CEC), and Fe-Mn concentrations. Results and discussion: Soils either developed from volcanic ash or containing smectite showed relatively higher Pb _Smax than the other soils. Across the soils, clay content, organic matter concentration, and total Fe concentrations were significantly (p < 0.05) correlated with Pb _Smax . Concentrations of Pb bound with Fe-Mn and exchangeable Pb sorbed on to negatively charged sites were greater than the other chemical fractions. In the particle-size fractions, clay-sized particles had the greatest Pb concentration, suggesting that this fraction was most responsible for Pb sorption. The Pb concentration in coarse particle fractions (silt and sand) showed a positive relationship with organic matter concentration, indicating that organic matter in coarse particles was a factor determining Pb sorption. However, such relationship was not found for clay-sized particles, suggesting that complexation with organic matter was not a key mechanism for Pb sorption onto clay-sized particles. Conclusions: Our study which combined sorption and chemical and particle-size fractionation experiments suggests that complexation of Pb with Fe and Mn oxides and interaction with negatively charged sites of clay-sized particles are the key processes of Pb sorption in the studied soils. For coarse particles, it was suggested that association with organic matter is a Pb sorption mechanism.