Chemical and Mineralogical Characterization of Arsenic, Lead, Cadmium and Zinc in a Smelter Contaminated Soil.

Soil samples collected from a former smelting site in Stockton, Utah contained elevated concentrations of potentially toxic elements, an environmental hazard associated with mining, milling and smelting activities. Total metal contents after acid digestion were 7,525 mg/kg arsenic, 66,440 mg/kg lead, 156 mg/kg cadmium, and 10,640 mg/kg zinc. These concentrations raise human and ecological health concerns. For detailed mineralogical characterization, x-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed. Metal oxide, sulfides, and sulfates were identified, including massicot (PbO), anatase (TiO₂), galena (PbS), and arseno-pyrite (FeAsS). Non-crystalline pyrite and goethite were observed by scanning electron microscope and energy dispersive X-ray spectroscopy and suggested that these minerals are associated with arsenic and lead. The metal phases of interest were found predominantly in the silt fraction (2-53 μm) and appeared to be secondary minerals. This complex mineralogy and metal distribution will be employed further in risk assessment and design of an in-situ remediation strategy.

Key words: heavy metals, chemical immobilization, trace elements, arsenic, soils