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

Abstract

Lead (Pb) sorption capacity (PbSmax) 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. 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. Soils either developed from volcanic ash or containing smectite showed relatively higher PbSmax than the other soils. Across the soils, clay content, organic matter concentration, and total Fe concentrations were significantly (p < 0.05) correlated with PbSmax. 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. 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.