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

Heavy metal stabilization in municipal solid waste combustion dry scrubber residues using soluble phosphate.

Abstract Heavy metal chemical stabilization with soluble PO 4 3À was assessed for bottom ash from combustion of municipal solid waste. Bottom ash can contain heavy metals (e.g. Pb) that can leach. An experimental dose of 0.38 mols of soluble PO 4 3À per kg of residue was used without optimizing the formulation for any one heavy metal. The reduction in the fraction available for leaching according to the total availability leaching test was 52% for Ca, 14% for Cd, 98% for Cu, 99% for Pb, and 36% for Zn. pHdependent leaching (pH 4, 6, 8) showed that the treatment was able to reduce equilibrium concentrations by 0.5 to 3 log units for these heavy metals. Bulk and surface spectroscopies showed that both crystalline and amorphous precipitates were present as insoluble metal phosphate reaction products. Dominant reaction products were calcium phosphates, tertiary metal phosphates, and apatite family minerals. Observed phases included, b-Ca 3 (PO 4 ) 2 (tertiary calcium phosphate); Ca 5 (PO 4 ) 3 OH (calcium hydroxyapatite); Pb 5 (PO 4 ) 3 Cl (lead chloropyromorphite); and Pb 5 (PO 4 ) 3 OH (lead hydroxypyromorphite). These are considered to be very geochemically stable mineral phases. The geochemical thermodynamic equilibrium model MINTEQA2 was modi®ed to include both extensive phosphate minerals and simple ideal solid solutions in order to better model pH-dependent leaching. .

Heavy metal stabilization in municipal solid waste combustion bottom ash using soluble phosphate

Heavy metal chemical stabilization with soluble PO43- was assessed for bottom ash from combustion of municipal solid waste. Bottom ash can contain heavy metals (e.g. Pb) that can leach. An experimental dose of 0.38 mols of soluble PO43- per kg of residue was used without optimizing the formulation for any one heavy metal. The reduction in the fraction available for leaching according to the total availability leaching test was 52% for Ca, 14% for Cd, 98% for Cu, 99% for Pb, and 36% for Zn. pH-dependent leaching (pH 4, 6, 8) showed that the treatment was able to reduce equilibrium concentrations by 0.5 to 3 log units for these heavy metals. Bulk and surface spectroscopies showed that both crystalline and amorphous precipitates were present as insoluble metal phosphate reaction products. Dominant reaction products were calcium phosphates, tertiary metal phosphates, and apatite family minerals. Observed phases included, beta-Ca-3(PO4)(2) (tertiary calcium phosphate); Ca-5(PO4)(3)OH (calcium hydroxyapatite); Pb-5(PO4)(3)Cl (lead chloropyromorphite); and Pb-5(PO4)(3)OH (lead hydroxypyromorphite). These are considered to be very geochemically stable mineral phases. The geochemical thermodynamic equilibrium model MINTEQA2 was modified to include both extensive phosphate minerals and simple ideal solid solutions in order to better model pH-dependent leaching. Both end members [e.g, Pb-5(PO4)(3)Cl, beta-Ca-3(PO4)(2)] and ideal solid solutions [e.g. (Pb-2,Ca)(PO4)(2)] were observed as controlling solids for Ca2+, Zn2+, Pb2+, and Cu2+. Controlling solids were not identified for Cd2+ because pH dependent concentrations were generally below detection limits. The divalent metal cations in bottom ash were effectively stabilized by treatment with soluble PO43-. (C) 2000 Elsevier Science Ltd. All rights reserved

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 (Pb5(PO4)3Cl), plumbojarosite (Pb0.5Fe3(SO4)2(OH)6), and chalcophanites ((Pb,Fe,Zn,Mn)Mn2O5 ·2H2O). 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,Ca2)(PO4)2) and apatite (e.g. Pb5(PO4)3Cl) 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. Copyright © 2002 Elsevier Science Ltd