Petrographic and spectroscopic characterization of phosphate-stabilized mine tailings from Leadville, Colorado


The use of soluble PO43- and lime as a heavy metal chemical stabilization agent was evaluated for mine tailings from Leadville, Colorado. The tailings are from piles associated with the Wolftone and Maid of Erin mines; ore material that was originally mined around 1900, reprocessed in the 1940s, and now requires stabilization. The dominant minerals in the tailings are galena (PbS), cerrusite (PbCO3), pyromorphite (Pb-5(PO4)(3)Cl), plumbojarosite (Pb0.5Fe3(SO4)(2)(OH)(6)), and chalcophanites ((Pb,Fe,Zn,Mn)Mn2O5.2H(2)O). The tailings were treated with soluble PO43- and lime to convert soluble heavy metals (principally Pb, Zn, Cu, Cd) into insoluble metal phosphate precipitates. The treatment process caused bulk mineralogical transformations as well as the formation of a reaction rind around the particles dominated by Ca and P. Within the mineral grains, Fe-Pb phosphosulfates, Fe-Pb sulfates (plumbojarosite), and galena convert to Fe-Ca-Pb hydroxides. The Mn-Pb hydroxides and Mn-(+/-Fe)-Pb hydroxides (chalcophanites) undergo chemical alteration throughout the grains during treatment. Bulk and surface spectroscopies showed that the insoluble reaction products in the rind are tertiary metal phosphate (e.g. (Cu,Ca-2)(PO4)(2)) and apatite (e.g. Pb-5(PO4)(3)Cl) family minerals, pH-dependent leaching (pH 4,6,8) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 150 for many metals; particularly Pb2+, Zn2+, Cd2+, and Cu2+. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca2+, PO43-, Pb2+, Zn2+, Cd2+ and Cu2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids. (C) 2002 Elsevier Science Ltd. All rights reserved.


Mechanical Engineering

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Waste Management



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Copyright © 2002, Elsevier