Mechanisms for the aging-induced reduction of lead solubility in scrubber residues from municipal solid waste combustion

Abstract

This manuscript elucidates the mechanisms responsible for aging-induced reduction in lead leaching from scrubber residues. Leaching tests (JLT13) were conducted on 48 types of scrubber residues and lead solubility was found to be significantly reduced independent of incinerator type or type of gas treatment method. Reaction kinetics that result in lead solubility reduction were shown to be proportional to carbon dioxide partial pressure and in many cases were limited by mass transfer to the residue. With forced gas convection through the residue and a CO₂ partial pressure of 0.3%, the concentration of lead in leachate was reduced from 84 mg L^-1 to < 0.5 mg L^-1 in two days. Ettringite analogs (Ca₆Al₂(SO₄)₃(OH)₂•26H₂O) were identified by X-Ray Diffraction in the wetted scrubber residues early in the aging process; these appear to have been converted into gypsum (CaSO₄•2H₂O) and vaterite (CaCO₃) in the aged material. All of these solid phases are believed to substitute lead into their crystal structure and evidence for this attenuation mechanism is presented.

Keywords

Lead heavy metals municipal solid waste wetted scrubber residues solubility aging leaching XRD EPMA wmr 440-4

Get full access to this article

View all access options for this article.

References

Fallman, A. N. , Eighmy, T. T. , and Salaneck, W. R. (1999) Aging reaction in residues (final report), Swedish Environmental Protection Agency, AFR-report 252

Johnson, C. A. , Kersten, M. , Ziegler, F , and Moor, H. C. (1996) Leaching Behaviour and Solubility - Controlling Solid Phases of Heavy Metals in Municipal Solid Waste Incinerator Ash, Waste Management, 16 (1-3), 129-134.

McConnell, D. (1973) Apatite: Its Crystal Chemistry, Mineralogy, Utilization, and Geologic and Biologic Occurrences, Applied Mineralogy, Springer - Verlag, N.Y.

Meima, J. A. and Comans, R. N. J. (1997) Geochemical Modeling of Weathering Reactions in Municipal Solid Waste Incinerator Bottom Ash, Environmental Science & Technology, 31 (5), 1269-1276.

Meima, J. A. and Comans, R. N. J. (1998) Application of Surface Complexation/Precipitation Modeling to Contaminant Leaching from Weathered Municipal Solid Waste Incinerator Bottom Ash, Environmental Science & Technology, 32 (5), 688-693.

Shimaoka, T. , Miyawaki, K. , and Hanashima, M. , et al. (1998) Insolubility of Hazardous Heavy Metals in Wet Fly Ashes of Municipal Solid Waste, Proceedings of WASTECON/ISWA World Congress '98, 419-431.

Steketee, J.J. , Duzijn, R.F. , and Born, J.G.P. (1997) Quality Improvement of Bottom Ash by Enhanced Aging, Washing and Combination Processes, The International Conference for the Environmental and Technical Implications of Construction with Alternative Materials, Proceedings of WASCON '97, Session BW1.

Whiting, K.J. (1998) An Overview of Current Practices and Future Alternative for the Management of Ash Residues from Waste-to-Energy Processes in Europe, Proceedings of IT3 Conference, International Conference on Incineration and Thermal Treatment Technologies, 459-464.

Zevenbergen, C. , Van Reeuwijk, L. P. , Bradley, J. P. , Bloemen, P. , and Comans, R. N. J. (1996) Mechanism and Conditions of Clay Formation during Natural Weathering of MSWI Bottom Ash, Clays and Clay Minerals, 44 (4), 546-552.