Quantitative Speciation of Lead in Selected Mine Tailings from Leadville, CO

Abstract

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 MgCl 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.