Reducing lead solubility in kaolinitic and oxidic soils by application of limed sewage sludge

Abstract

Little attention has been paid to the effects of soil mineralogy on remediation efficiency of sewage sludge. To fill this gap, we applied limed sewage sludge to Pb‐contaminated soil samples of an Oxisol rich in hematite (309 g kg−1) and gibbsite (322 g kg−1) and to an Inceptisol rich in kaolinite (683 g kg−1). Soil samples were collected from B horizon, being both of them acid, clayey, and poor in organic matter. Soil samples were incubated for 40 days and evaluated for Pb after fractioning. Limed sewage sludge neutralized the soluble and exchangeable‐Pb forms in the kaolinitic and oxidic soils primarily as a result of pH increase. It was measured increased concentrations of unavailable forms of Pb such as precipitated‐Pb, Fe and Mn oxide‐Pb, gibbsite and kaolinite‐Pb, and residual‐Pb in the kaolinitic Inceptisol. Likewise, it measured increased concentrations of precipitated‐Pb, organic matter‐Pb, Fe and Mn oxide‐Pb, and residual‐Pb in the Oxisol. Results have demonstrated that limed sewage sludge decreases concentrations of Pb fractions more susceptible to leaching or more bioavailable, while increasing Pb fractions that pose lower risks to the environment. Such results indicate that limed sewage sludge can be used for the remediation of Pb‐contaminated soils regardless of soil mineralogy.