63    CHARACTERIZATION AND EXTRACTION OF METALS
FROM WASTE RESIDUES
Audrey D. Levine, Assistant Professor
Michael E. Bain, Graduate Research Assistant
Kent D. Bienlien, Graduate Research Assistant
Department of Civil and Construction Engineering
Iowa State University
Ames, Iowa 50011
INTRODUCTION
The American public generates over 150 million tons of municipal solid waste (MSW) each year.
Changes in environmental legislation and landfill management policies are precipitating a revaluation of MSW disposal practices. Alternatives to landfilling MSW include recycling, energy and
resource recovery, and combustion of processed or non-processed wastes. Refuse derived fuel (RDF)
is produced from MSW1,2,3 and is often used as a supplemental fuel in power plants. Another option
using combustion is mass burning of MSW where minimal processing occurs prior to combustion.
While combustion processes serve to produce energy from wastes and reduce the total volume of
waste materials, residues resulting from combustion pose a different waste management problem.
Ash residues from coal combustion have been shown to contain recoverable metals such as aluminum
and iron.3,4 However, waste residues from co-combustion processes using RDF have not been studied
as extensively as coal waste residues.1,3 Better characterization of these residues is necessary to
determine the content of the residues, potential environmental risks, and to determine if recovery
schemes for metals are feasible.
The objectives of this chapter are to evaluate methods of characterizing waste residues produced
from co-combustion of RDF and coal. Solid phase characteristics are examined and various extraction tests are compared in terms of their potential for solubilizing metals from solid residues.
BACKGROUND
The quantity and composition of waste residues varies depending on the type of facility and specific
operating practices. To provide background information, previous studies on characteristics of waste
residues are reviewed and background information on methods for characterization of waste residues
using scanning electron microscopy (SEM) and extraction tests are discussed.
Characteristics of Waste Residues
Characterization of waste residues is necessary to determine the quantity of metals and other
compounds remaining from combustion processes and the potential for solubilization and release into
the environment. Currently, about 15% of the municipal solid wastes (MSW) generated in the United
States is processed by resource recovery.5 A typical processing scheme consists of reducing the MSW
in size, removing ferrous metal by magnetic separation, and removing grit and glass. The light
fraction remaining is processed into refuse derived fuel (RDF) and is used as a supplemental fuel to
coal, wood, or oil.
The RDF contains organic material and inorganic components that are not removed by separation
processes. Inorganic components that are part of the RDF, such as metals, are combusted and may be
released with the stack gases or concentrated in either fly or bottom ash. The distribution of metals is
dependent on several factors, including the MSW processing scheme, boiler type and operating
parameters, fuel admixture, energy and moisture content of the RDF, halogens present, and concentrations of individual metals.1,3
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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