Cleanup of Lead Contaminated Soil from Battery Reprocessing Sites

Abstract

The hazards of lead in the environment have been a matter of increasing concern over the past several years. The most common sources of lead contaminated soils are those related to abandoned lead battery reclamation sites. There are over 200 such sites in the United States and several real and potential sites in Minnesota. Under present regulations such contaminated soil must be removed and placed in an approved and licensed landfill. The purpose of this study was to demonstrate that by applying conventional mineral dressing techniques it is possible to detoxify a significant percentage of the soil and thereby reduce the cost of landfill disposition. Prior test work at the Natural Resources Research lnstitute's Coleraine Minerals Research Laboratory (CRL) on a sample from a battery reprocessing site in Wisconsin demonstrated that partial detoxification of the soil was practical. The object of this study was to apply similar techniques to material from a Minnesota site. The Shafer Metal site on north Plymouth avenue in Minneapolis was selected for this study after consultation with personnel from the Minnesota Pollution Control Agency and the Minnesota Department of Transportation who own the property. The lead contamination at the Shafer Metal battery reprocessing site occurs in three principal modes: lead metal fragments, surficial coatings of precipitated lead sulphate and lead dioxide, and lead incorporated into fused plastic material. The lead metal consists primarily of fragments of battery plates and connectors. The precipitated lead compounds occur as coatings on the rock and sand particles in the soil. The fused plastic material could have resulted from melting and casting of the lead, or operation of an incinerator. After preliminary sampling to confirm the distribution of lead contaminated soil at the site, three bulk samples of about 800 pounds each were collected for testing. These three samples were subjected to a series conventional mineral processing techniques involving attrition scrubbing, screening, and gravity separation. The tests demonstrated that over 60% of the material can be separated as a clean rock and sand product that can be disposed of on site. About 5% to 10% of the material can be recovered as a lead-rich product that would be acceptable feedstock to a lead smelter. About 25% of the weight would contain so much lead that it would have to be treated as hazardous material. Some 5% to 10% of the material would be rejected as a coarse trash product eligible for disposal in conventional landfills. The EPA Synthetic Precipitation Leach Test for Soils (Method 1312) was run on the rock and clean sand portion which represents over 60% of the material. The tests demonstrated that this material had been effectively detoxified and could be disposed of on site. Based on these test data a treatment flow sheet to detoxify the material represented by the bulk samples taken at the Shafer Metal site was developed. The flow sheet includes the following process steps: I) Coarse screening to remove tramp trash; 2) attrition scrubbing to remove the lead compounds from the coarser rock and sand particles; and 3) gravity concentration to separate a high lead product, a clean rock and sand reject, and a lead-bearing fused plastic product. A minus 165 mesh fines fraction is also produced containing the natural fines from the soil and the lead released by the attrition scrubbing. The recommended treatment flow sheet is based on using conventional mineral processing equipment. The equipment could be sized small enough to be truck mounted, or set up as semi-portable units for on-site treatment. Engineering such a portable treatment plant was included in the extended project, but is beyond the scope of this abbreviated study. Whether treatment of the Shafer Metal site is practical depends upon the cost of building and operating such a treatment plant on site as opposed to direct disposal. It is recommended that this study be extended to include the design and engineering of a portable or semi-mobile treatment plant and that further continuous pilot plant operations be supported to confirm some of the coarse gravity separation steps. There are other similar sites in Minnesota that are contaminated by lead that would be amenable to similar treatment. Costing out the plant required and demonstration of the viability of the treatment flow sheet would make it possible to offer alternatives to the expensive disposal of such hazardous material in a licensed disposal site.