Effects of Soil on Trace Metal Leachability from Papermill Ashes and Sludge

Understanding trace metal leachability is important for successful land application of papermill residues. Trace metal leachability from papermill ashes (Ash 1 and Ash 2) and papermill sludge (Sludge), and the effects of a soil on their leachability were determined by leaching the three papermill residues packed on top of a soil in a column. The leachates were analyzed for pH, electrical conductivity (EC), dissolved organic carbon (DOC), and concentrations of six metals (Cd, Cr, Cu, Pb, Se, and Zn). Ash 1 behaved significantly differently from Ash 2 during the leaching experiment, primarily due to its high pH and Na contents. Application of papermill residues significantly increased the pH, EC, and DOC concentrations in leachates, with Ash 1 having significantly greater impacts than Ash 2 and sludge. Soil columns under alkaline leaching of Ash 1 appeared bleached due to the dissolution of solid‐phase organic matter. Significant amounts of Zn were leached from all papermill residues, whereas significant amounts of Cr, Se, and Cu were leached only in the Ash 1 treatments. The presence of a soil (especially a Bh horizon) generally enhanced metal leachability in the Ash 1 treatments due to the extremely high pH of Ash 1, whereas it decreased metal leachability in the Ash 2 and sludge treatments. Thus, organic matter enhances metal sorption when present as a solid phase, but it increases metal leachability when present in dissolved form under alkaline conditions.