Use of diammonium phosphate to reduce heavy metal solubility and transport in smelter-contaminated soil.
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. Soil contaminated with Cd, Pb, Zn, and As was collected from a former smelter site. The DAP treatments of 460, 920, and 2300 mg P kg-1 and an untreated check were evaluated using solute transport experiments. Increasing DAP decreased total metal transported. Application of 2300 mg P kg-1 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-fold for Pb. Distribution coefficients (Kd) increased with P application from 4.0 to 9.0 L kg-1 for Cd, from 2.9 to 10.8 L kg-1 for Pb, and from 2.5 to 17.1 L kg-1 for Zn. Increased Kd values with additional DAP treatment indicated reduced partitioning of sorbed and/or precipitated metal released to mobile metal 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.
McGowen
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Dep. of Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK 74078, USA.
Basta
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Brown
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D007221:Industry; D019216:Metals, Heavy / Q000737:chemistry*; D008906:Mining; D010084:Oxidation-Reduction; D010710:Phosphates / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D012995:Solubility; D014876:Water Pollution / Q000517:prevention & control
D019216:Metals, Heavy; D010710:Phosphates; D012989:Soil Pollutants; C024788:ammonium phosphate