Quantitative Speciation of Lead in Selected Mine Tailings from Leadville, CO JOHN D. OSTERGREN,* ,† GORDON E. BROWN, JR., †,‡ GEORGE A. PARKS, † AND TRACY N. TINGLE § Departm ent of Geological & Environm ental Sciences, Stanford University, Stanford, California 94305-2115, Stanford Synchrotron Radiation Laboratory, SLAC, Stanford, California 94309, and Center for Materials Research, Stanford University, Stanford, California 94305 We have characterized Pb speciation in selected tailings from the Leadville, CO, area using a variety of analytical techniques, including X-ray absorption fine structure (XAFS) spectroscopy. Samples from three locations were analyzed, including two chemically distinct tailings piles located within the city limits [Apache (pyrite-rich, low pH) and Hamms (carbonate-rich, near-neutral pH)] and tailings material deposited as overbank sediments along the Arkansas River approximately 13 km downstream from Leadville (Arkansas River tailings). Extended XAFS (EXAFS) spectra of these multicomponent samples were fit using linear combinations of model compound spectra. In accordance with pH differences among the samples, adsorbed Pb accounts for ∼50% of total Pb (Pb T ) in fine fractions of the near-neutral pH Hamms tailings, whereas Pb- bearing jarosites account for the majority of Pb T in the fine fractions of the low pH Apache and Arkansas River tailings. EXAFS analyses following sequential extraction by M gCl 2 and EDTA show evidence of significant redistribution (readsorption) of Pb during the MgCl 2 extraction and for removal of adsorbed Pb and dissolution of Pb-carbonates during the EDTA extraction. Changes in Pb speciation with water extraction (dissolution of anglesite and precipitation of plumbojarosite) are observed in one sample of Arkansas River tailings. These molecular-scale results show that Pb speciation varies dramatically among environments in the Leadville area and that Pb occurs in a number of phases not amenable to definitive characterization by conventional microanalytical and/or chemical extraction techniques. Introduction More than 130 years of mining and smelting in Leadville generated large quantitiesofwaste materials,includingwaste rock, tailings, and slags. The potential health risks and environmentalhazards posed bythese wastes prompted the U.S. Environmental Protection Agency (EPA) to place the area on its National Priority (i.e., Superfund) List 1983. Since that time, a number of investigations have assessed the relationships among metal speciation, mobility, and bio- availablility in the Leadville area (e.g., refs 1-4) (the term speciation as used here includes oxidation state, molecular structure, and phase association, including the mode of surface attachment for adsorbates and both the structure and composition ofprecipitate phases).For example,in vivo swine studies have shown that Pb bioavailabilityranges from less than 5%for tailings materials where the majorityoftotal Pb (Pb T) occurs as galena (PbS) to 45%for surface soils where the majority of Pb T occurs as “Fe -Mn -Pb oxide” phase(s) (4). Distinguishing between and characterizing such species therefore provides the foundation for identifying and un- derstanding the geochemical processes that control metal transport and bioavailability in environmental media. While great progress has been made in recent years applying modern microanalytical techniques, such as scan- ning electron microscopy (SEM) and electron probe mi- croanalysis (EPMA), to determine Pb speciation in environ- mental samples (e.g., refs 5 and 6), these techniques are not well suited to characterizing a number of species that may pose significant threats to human health and the environ- ment. For example, their insensitivity to submicron scale chemicaland/orphysicalheterogeneitiesprecludesdefinitive characterization of materials such as fine-grained and/or poorly crystalline (hydr)oxides of Fe and Mn which play important roles in metal bioavailability and transport in the Leadville area (e.g., refs 1 and 3) and elsewhere (e.g., refs 7-9). Distinguishing between, for instance, adsorption to and (co)precipitation with such materials is basic information needed to understand and predict metal fate in natural systems.Surface-specific spectroscopies (e.g.,XPS,SALI,and SIMS) have been used to identify sorbed metals in envi- ronmental materials (e.g., refs 10 and 11), but the chemical speciation information derived from these techniques on environmental samples has thus far been limited. In this study, we characterize Pb speciation in selected tailings materials from the Leadville area using a variety of analyticalmethods,includingX-rayabsorption fine structure (XAFS) spectroscopy. On the basis of previous work in the Leadville area (e.g., refs 12-15), three different tailings deposits were selected for analysis in the present study, includingtwo chemicallydistinct tailings piles located within the city limits (Apache and Hamms) and tailings material deposited as overbank sediments along the Arkansas River approximately 13 km downstream from Leadville (Arkansas River tailings) (see Supporting Information for site map). The Apache and Hamms tailings represent endmembers in tailings composition in the Leadville area,the Hamms being carbonate-rich with a near-neutralpH (6-8),andtheApache being sulfide-rich with a correspondingly low pH (2-6) (13). This difference in pH is expected to have a dramatic affect on the type(s) of sorbed species found in these materials. Our primary goal in analyzing Pb speciation in the Arkansas River tailings materials was to provide a more detailed understanding of why the lability of Pb changes so dramati- callybetween samplescollected alonga verticalcross-section as reported earlier for these samples (15). As a probe of local structure, XAFS spectroscopy is well suited to characterize and distinguish among the many fine grained and/or poorlycrystalline Pb species found in tailings materials. In lieu of direct analytical techniques, these materialsare commonlycharacterized indirectlybychemical extraction techniques (e.g., refs 1, 3, and 7-9). Although problemssuch asnonselectivityand redistribution ofphases during extraction are well documented (e.g., refs 16-18), *To whom correspondence should be addressed at Stanford University, Building 320, Room 118. Phone: (650) 723-7513. Fax: (650) 725-2199. E-mail: johno@pangea.stanford.edu. † Department of Geological & Environmental Sciences. ‡ Stanford Synchrotron Radiation Laboratory. § Center for Materials Research; deceased. Environ. Sci. Technol. 1999, 33, 1627-1636 10.1021/es980660s CCC: $18.00  1999 American Chemical Society VOL. 33, NO. 10, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 1627 Published on Web 04/03/1999