Lead extraction from soils as affected by lead chemical and mineral forms

Soil washing is one of several technologies for the removal of lead (Pb) from soil. Recent studies have focused on washing efficiency using artificially contaminated soils; however, data may not reflect the efficiency of Pb removal for aged, field-contaminated soils. A Glynwood silty clay loam, a river sediment and a sand were artificially contaminated with PbSO4. These, and soil material from a battery recycling/smelting Superfund site, were washed in batch tests with ethylenediaminetetraacetic acid (EDTA), pyridine-2,6-dicarboxylic acid (PDA) (0.0225 M, 0.0375 M, and 0.075 M) or hydrochloric acid (HCl) (0.1 and 1.0 N). Using a sequential extraction procedure, 96% or more of the Pb in the artificially contaminated soils and 65% of the Pb in the Superfund soil were determined to be extractable. X-ray diffraction techniques revealed the presence of both anglesite (PbSO4) and hydrocerrusite (Pb-3[CO3](2)[OH](2)Pb) in the Glynwood and sand, and in the river sediment, massicot (PbO) was also detected. Metallic Pb and anglesite occurred in the Superfund soil. EDTA was the most effective extractant for all soils, removing 100% of the Pb in the Glynwood and sand at all three EDTA concentrations, and 50-58% from the Superfund soil. Lead removal efficiency using PDA in the Superfund soil ranged from 31-56%, and from 12-100% for the artificially contaminated soils. Lead removal in the Superfund soil using HCl was maximal at 30%, and removal in the artificially contaminated soils ranged from 30-51% using 1.0 N HCl. The presence of insoluble Pb minerals (e.g., metallic Pb) in the Superfund and similar, aged soils should be expected to limit the success of soil washing in a field situation.