Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2001
Publication Date: N/A
Interpretive Summary: Research experiments were conducted to investigate treatments for protecting surface and groundwater resources from heavy metal contamination. The objective was to determine the efficiency of diammonium phosphate treatments for immobilizing cadmium, lead, and zinc release and transport from a smelter-contaminated soil. Addition of diammonium phosphate to the contaminated soil reduced the total amount of heavy metals leached from the soil. This indicated that diammonium phosphate could prevent the spread of metal contamination from soils to water resources. Treatment of the contaminated soil with diammonium phosphate also led to the formation of extremely stable minerals which suggests the protective effects may last for an extended time. Results from this research are important to the EPA, environmental consulting companies, and scientific researchers because it identifies a potential heavy metal remediation technology for protecting water resources near mining and smelting areas.
Technical Abstract: Phosphate treatments can reduce metal dissolution and transport from contaminated soils. However, diammonium phosphate (DAP) has not been extensively tested as a chemical immobilization treatment. This study was conducted to evaluate DAP as a chemical immobilization treatment and to investigate potential solids controlling metal solubility in DAP-amended soils. Soils contaminated with Cd, Pb, Zn, and As was collected from a former smelter site. DAP treatments of 460, 920, 2300 mg P/kg and an untreated check were evaluated using solute transport experiments. Increasing DAP decreased total metal transported. Application of 2300 mg P/kg was the most effective for immobilizing Cd, Pb, and Zn eluted from the contaminated soil. Metal elution curves fitted with a transport model showed that DAP treatment increased retardation (R) 2-fold for Cd, 6-fold for Zn and 3.5-for Pb. Distribution coefficients (Kd) also increased with P application from 4.0 to 9.0 L/kg for Cd, from 2.9 to 10.8 L/kg for Pb, and from 2.5 to 17.1 L/kg for Zn. Increased Kd values with additional DAP treatment indicated reduced partitioning of sorbed/precipitated metal released to mobile phases and a concomitant decrease in the concentration of mobile heavy metal species. Activity-ratio diagrams indicated that DAP decreased solution Cd, Pb, and Zn by forming metal-phosphate precipitates with low solubility products. These results suggest that DAP may have potential for protecting water resources from heavy metal contamination near smelting and mining sites.