| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 93 === Abstract
The thermite reaction is defined as the oxidation-reduction reactions
between a metal and other metallic/ non- metallic oxides which are
characterized by large exothermic heat and the self-sustaining of the process.
The large exothermic energy can be used as an extremely efficient energy for
purifying ores for some metals, or for the detoxifying of the MSWI fly ash.
Typical thermite reaction (a type of aluminothermic reaction) is one in which
aluminum metal is oxidized by an oxide of another metal, most commonly iron
oxide.
These thermite reactants can be provided with by industrial waste streams
containing aluminum and related oxides, thus giving an excellent opportunity
to develop effective thermite from wastes for energy. Accordingly, this study
tried to develop thermites from wastes (referred to as wastes-derived-thermite,
WDTs) , and further to evaluate the feasibility of treating the MSWI fly ash by
use of the WDTs. In this study, except for aluminum scrap, five types of
candidate dust and sludge were primarily screened based on the analysis of the
waste compositions and possible thermite reactions estimated, these candidate
wastes including aluminum scrap/dross, converter sludge from steel making
plants (Convert-sludge), printed circuit board sludge (PCB-sludge), hot rolling
wet dust (HR-dust) and electric arc furnace dust (EAF dust) from steel making
plants, and sludge from cotton mill industry wastewater treatment plants
(referred to as fabric dyeing sludge, FD-sludge). The proper formula for the
WDTs were to be generated on the evaluation of the performance criteria
such as the effective energy generated by the unit WDT, the sustainability of
the reaction, and the mobility of heavy metals during the reaction.
Laboratory testing results showed that proper formula (i.e., iron oxide
containing waste : aluminum scrap, wt%) generated for the five tested wastes,
in the increasing order of the dust/sludge percentage were EAF dust (67wt.%),
converter sludge (72wt.%), FD-sludge (72wt.%), HR-sludge (75wt.%), and
PCB-sludge (82wt%), indicating the reactive oxides decreased in as the weight
percentage for dust/sludge increased. WDT from PCB-sludge outperformed the
other WDTs in melting 0-29.1wt% MSWI fly ash (reaching a melting
temperature ranging from 2286 to 1168℃). The larger treating capacity for
MSWI fly ash showed that high thermite energy released by the copper oxide
in the plating sludge contributed to the melting process. WDT from converter
sludge also showed a 0-21.5 wt% treating capacity for MSWI fly ash (reaching
a melting temperature ranging from 2047 to 1263℃). The hot-rolling sludge
showed less treating capacity for MSWI fly ash (0-16.3wt%, with temperature
reaching 1766 to 1198℃). The results of the TCLP test for all the recovered
slags generated form the melting process of WDTs and fly ash showed that the
leaching concentrations of target metals were all in compliance with the
USEPA's regulatory threshoulds, ensuring the safety of the slag. The common
components identified by the XRD techniques included Al2O3, Fe, CaAl4O7,
and SiO2 for all tested WDTs except for WDT from PCB-sludge in which Cu
was identified. This results reported here suggest that it is feasible to generate
aluminothermic thermite from aluminum scrap/dross and wastes containing
iron oxide, copper oxide, and/or other related oxides.
These WDTs can not only recover slag and alloy by thermite reactions, but
also be used as fuel in detoxifying MSWI fly ash by melting process, showing a
promising energy efficient, recycling-beneficial alternative.
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