Details

Autor(en) / Beteiligte

• Crannell, Bradley S.
• Eighmy, T.Taylor
• Krzanowski, James E.
• Eusden, J.Dykstra
• Shaw, Elisabeth L.
• Francis, Carl A.

Titel

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

Ist Teil von

• Waste management (Elmsford), 2000-01, Vol.20 (2), p.135-148

Ort / Verlag

Oxford: Elsevier Ltd

Erscheinungsjahr

2000

Link zum Volltext

Quelle

Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)

Beschreibungen/Notizen

• Heavy metal chemical stabilization with soluble PO 4 3− 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 3− 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, β-Ca 3(PO 4) 2 (tertiary calcium phosphate); Ca 5(PO 4) 3OH (calcium hydroxyapatite); Pb 5(PO 4) 3Cl (lead chloropyromorphite); and Pb 5(PO 4) 3OH (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(PO 4) 3Cl, β-Ca 3(PO 4) 2] and ideal solid solutions [e.g. (Pb 2,Ca)(PO 4) 2] were observed as controlling solids for Ca 2+, Zn 2+, Pb 2+, and Cu 2+. Controlling solids were not identified for Cd 2+ because pH dependent concentrations were generally below detection limits. The divalent metal cations in bottom ash were effectively stabilized by treatment with soluble PO 4 3−.