TRACE-ELEMENT SOLID-PHASE ASSOCIATIONS IN SEWAGE-SLUDGE AND SLUDGE-AMENDED SOIL

A scheme involving the use of particle size, density, and magnetic susceptibility was applied to sewage sludge and sewage-sludge-amended soil to isolate trace-element-bearing solids for identification by x-ray diffraction (XRD) and scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDXRA). The heavy-density (> 2.96 Mg m-3) fractions of the sludge and amended soil contained barite, celestite, lead silicate, lead phosphate, chromium oxide or oxyhydroxide, sphalerite, and chalcopyrite. Vanadium was associated with Ti, Ca, Si, and Fe in amended soil particles, suggesting its occurrence in titanite. The heavy-density fractions also contained trace-element-bearing particles of industrial origin, including Sb, Cr-Fe, Cr-Ni-Fe, Zn-Sn, Cr-Zn-Fe, Sn-Fe-Cu-Zn, Pb-Cr, Pb-Sn, W-Se, and Co-Cr elemental associations. Trace-element-bearing particles contained in the light-density (< 2.10 Mg m-3) fractions of the sludge and sludge-amended soil were similar to those identified in the heavy-density separates. Their presence was apparently due to particle agglomeration with organic matter. The physicochemical particle fractionation scheme was effective in concentrating trace-mineral phases for detection by SEM/EDXRA. However, crystalline trace-element-bearing minerals were not sufficiently concentrated for XRD identification.