Fixation of lead in contaminated soils by co‐agglomeration with metal binding agents*

Abstract

Abstract Adsorption of lead from an aqueous solution by both agricultural peat moss and soil has been measured. The results may be described by a Langmuir isotherm model. Adsorption isotherms fitted the “H”; type described in the Giles classification. Saturation adsorption was reached at equilibrium lead concentrations > 3000 mg/L for peat, compared with ∼ 250 mg/L for soil. Calculation of the isotherm parameters showed the maximum lead adsorption to be 150 mg lead/g of peat. This compared with only 12.64 mg/g of lead for soil alone. Several tests were carried out to evaluate the lead binding capacity of peat in a spiked soil sample. Results from leaching tests (Environmental Protection Agency, EPA, Toxicity Characteristic Leaching Procedure, TCLP, at pH 2.9) on soil‐peat mixtures confirmed the excellent metal binding capacity of peat in the samples tested. The amount of lead leached from a soil sample, spiked with 1840 mg/kg of water‐soluble lead, decreased with increasing amounts of peat loading. Total fixation was achieved at a peat loading of 20%. In addition to peat, several other agents were tested for their suitability as fixing agents in heavy‐metal contaminated soils. These included: gypsum, lime, autoshredder residue, fly ash, and a sample of oil sands fines. Liquid phase agglomeration was used to coagglomerate these materials with soil as a means to fix lead in artificially contaminated samples. The agglomeration process is advantageous in that it allows concurrent fixation of heavy metals and solvent extraction of organic contaminants. In terms of material handling and equipment, a combined process will be more economical than conventional methods requiring separate extraction and leaching steps.