Morphology and Chemistry of Lead Particulate Matter in Air-Filters from a Lead-acid Battery Smelter: Mapping the Transfer to Residential Soils, East Los Angeles, California, U.S.A.

Primary smelting associated with processing of ore can generate substantial quantities of dust containing metallic particles. Secondary smelting of lead batteries at recycling facilities employs many of the same processing steps as primary smelters, and also generates significant metallic dust. The objectives of this study were to document the morphology, mineralogy, and chemistry of smelter emissions as represented by dust particles emitted from a former lead battery recycling facility in East Los Angeles, CA, during operation, closure, and dismantling of the site. Together with Pb isotopic compositions of the particulate matter (Ayuso et al., this abstract volume), we seek to evaluate contributions of smelter-derived particulate matter to soils in residential neighborhoods surrounding the facility.

Air filter (HEPA) media were collected from monitors installed around the periphery of the recycling facility. Filter paper samples (~1x2cm) were mounted on stubs and studied by back-scatter-electron-field emission-scanning electron microscopy (20 kV, WD=10mm) and qualitative energy dispersive spectroscopy at µm to nm scales. Particulate matter trapped in-situ in the air filter media show a wide range in size, shape, and composition. The particles include (A) distinctive, metallic (Cu, Fe, Pb, Si) micro-to-nanospheres (<10 µm to 100 nm), (B) subspherical to irregular shapes (rods) of Pb and Pb admixed with silica and other metals, (C) irregular flakes and angular clumps of Fe and other base metals, aluminosilicate mineral dust (~5 to >50 µm-wide), and (D) pollen grains (~10-50 µm).

Four main categories of metallic spheres were identified based on dominant composition and size range: Si (<12 µm), Fe (<5 µm), Cu (<3 µm to 100 nm), and Pb (<500 nm). Small subspherical to irregular grains and rods of Pb and Sn were also identified in the filter media. Aluminosilicate mineral debris and fine scrap (Fe-based) occur both as irregular flakes and fragments (>50 to ~20 µm wide) and as finely comminuted dust. Metallic spheres as described here are rarely found as natural products of surficial processes. However, the spheres and observed particle size ranges are well-documented features of the fine fractions of metallic dust emitted from primary smelter operations. Coarser fractions of smelter dust (>10 µm) can have other shapes (cubes, rods, needles, subrounded) depending on the interplay of metals and anions in dynamic flow paths of baghouses and smelter stacks. Thus, the spherical shapes, size distributions, and chemistry of the particles trapped in the air filters are consistent with particle emissions originating from a smelter.

Lead isotopic compositions of leachates of the filter media generally are isotopically similar to that of Pb-contaminated soils near the smelter (as analyzed by TIMS and HR-ICPMS). The Pb isotopic compositions trace the path of Pb-bearing dust emanating from the smelter plant to the air filters, which we interpret were likely also distributed by atmospheric deposition to surrounding residential neighborhoods. Mineralogical, elemental, and isotopic data for air filter media can be used in combination with air quality data to identify possible pathways of Pb contamination from primary and secondary smelter operations.