Technology:
Physical separation and acid leaching
- Demonstration included two vendors - one used physical separation and acetic acid (weak acid) leaching; the other used physical separation and hydrochloric acid (strong acid) leaching
- Physical separation for both vendors included screening to remove oversize debris, including bullets and bullet fragments; hydrodynamic separation; density separation; froth flotation; and magnetic separation
- Following separation, the soil was mixed with the acid in a tank; for the acetic acid leaching, three tanks were used in series; for the hydrochloric acid leaching, one mix tank was used
- The treated soil slurry was separated from the leachate and dewatered (filter press); leachate was regenerated (preciptiation)
- Average processing rate - 2.8 tons/hr (acetic acid) and 6.3 tons/hr (hydrochloric acid)
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Cleanup Authority:
RCRA
Army Contact:
Richard O'Donell
Lisa Miller
Army Environmental Center |
Contaminants:
Heavy Metals - Lead
- Stockpiled untreated soil had a lead assay of 0.5% |
Waste Source:
Small arms testing |
Type/Quantity of Media Treated:
Soil
- Acetic acid leaching process - 263 tons
- Hydrochloric acid leaching process - 835 tons |
Purpose/Significance of Application:
Demonstration of physical separation and acid leaching to treat metals in soil |
Regulatory Requirements/Cleanup Goals:
- TCLP for lead of 5 ug/L
- Total metals concentration for lead, copper, zinc, and antimony - 1,000 mg/kg each for acetic acid leaching and 500 mg/kg each for hydrochloric acid leaching |
Results:
Soil from physical separation alone was tested for TCLP lead; did not meet cleanup criteria
Acetic Acid Leaching:
- Initially, approximately 93% total lead, 93% total copper, 77% total zinc, and 70% total antimony removed
- During the demonstration, both total and leachable lead levels in treated soil rose due to buildup of lead in regenerated leachate as a result of inadequate precipitation
- Total lead was reduced from 2,828 mg/kg in untreated soil to 122-1,443 mg/kg in processed soil; data on TCLP lead levels was not provided
Hydrochloric Acid Leaching:
- Met both total and TCLP lead targets throughout demonstration
- Removed 96% total lead, 97% total copper, 89% total zinc, and 60% total antimony
- Total lead was reduced fro 4,117 mg/kg in untreated soil to 165 mg/kg in treated soil
- Average TCLP lead level in treated soil was 2 mg/L |
Cost Factors:
- Costs from the acid leaching demonstration were not analyzed because of the operational difficulties experienced with leachate regeneration
- Costs for physical separation and hydrochloric acid leaching demonstration were $1,400/ton for the 835 tons of soil processed
- Projected full-scale costs for physical separation and hydrochloric acid leaching are $170/ton based on 10,000 tons of soil |
Description:
A demonstration of physical separation and acid leaching of soil from a small arms testing range at Fort Polk was conducted from August to December, 1996. Two types of acid leaching were demonstrated - one using acetic acid to demonstrate a weak acid and one using hydrochloric acid to demonstrate a strong acid. Soil containing heavy metals was excavated from the small arms range and stockpiled for the demonstration. The soil was sent through physical separation followed by acid leaching. The treated soil was separated from the leachate, and dewatered; the leachate was regenerated and reused in the process.
Results showed that treating soil using physical separation alone did not meet the cleanup goals. While the acetic acid leaching initially removed metals, operational problems with the regeneration of the leachate resulted in increasing levels of lead in the treated soil. The hydrochloric acid leaching process met the cleanup goals for all metals throughout the demonstration. Projected full-scale costs for physical separation and hydrochloric acid leaching are $170/ton based on 10,000 tons of soil treated. |
