Abstract
Introduction: The primary treatment of municipal solid waste (MSW) in Japan is by using the thermal treatment that 80.3% of its MSW treated by using an incinerator in 2017. Incinerators can reduce volume and mass of waste (around 90% and 70%), destroy pathogenic agents, and recover energy. Byproducts from the incineration process are bottom ash and fly ash. Municipal solid waste incineration (MSWI) fly ash contains a high concentration of heavy metals and toxic organic compounds that can be harmful to the environment. Heavy metals are entrapped into mineral aggregate or as chlorides or sulfates condensed into fly ash particles. In fly ash particle, heavy metal leachability control by their association. Therefore, our previous study estimated possible metal speciation by using correlation analysis in the individual level of
fly ash from stoker [1]. Correlation analysis, is using an elemental mapping from SEM-EDX observation, can be useful for the comprehensive characterization of heavy metal speciation with other analyses such as XRD analysis. SEM-EDX can detect possible metal speciation at individual fly ash particles even at low concentration and regardless of the
crystalline or amorphous phase. This study aims to propose new possible metal speciation in the fly ash particle from the fluidized bed.
Materials and methods: MSWI Fly Ash
MSWI fly ash produced from fluidized bed incinerator in Japan were analyzed in this study. The chelate reagent
had treated MSWI fly ash samples. Three kinds of leaching methods were used: Japan leaching test 46 (JLT 46),
toxicity characteristic leaching procedure (TCLP), and Japan leaching test 19 (JLT 19) to observe semi-soluble component and insoluble core component of fly ash particles.
Microscopic observation Morphological characteristics and elemental composition of MSWI fly ash particles were observed using a scanning electron microscope coupled with energy-dispersive x-ray spectroscopy (SEM-EDX JSM-6610LA, JEOL Ltd.,
Japan). After measurement by SEM-EDX, each single-particle elemental mapping was divided into five sections equally. Correlation coefficients (r) between major elements and heavy metal were calculated based on the intensity data in a specific horizontal section.
Result and discussion: Chromium (Cr) was mostly detected in the core of fly ash from a fluidized bed. The positive correlation between Cr with other elements was obtained by correlation analysis. Cr shows a positive correlation with Mg were shown in
Figure 1, that offered new possible Cr speciation is magnesium chromium spinel (MgCr2O4). The formation of
MgCr2O4, which Cr(VI) thermal decomposition could result in the formation of MgCr2O4, has been observed in a previous study. So, there is a possibility during the incineration process, Cr formed into magnesium chromium spinel. A positive correlation with Al also observed in this fly ash particle. It might be suggested new possible metal speciation as Al-chromite or Cr2O3 included in the Al-based core of fly ash. Cr in the core of fly ash, mainly as Cr(III), is due to the reduction of Cr(VI) with aluminum. Al present in the fly ash can control Cr leaching by reducing Cr(VI) released from
the solid phase by dissolution into Cr(III) formed. Therefore, the Al-based matrix in the fly ash might inhibit Cr
leaching into the environment.
fly ash from stoker [1]. Correlation analysis, is using an elemental mapping from SEM-EDX observation, can be useful for the comprehensive characterization of heavy metal speciation with other analyses such as XRD analysis. SEM-EDX can detect possible metal speciation at individual fly ash particles even at low concentration and regardless of the
crystalline or amorphous phase. This study aims to propose new possible metal speciation in the fly ash particle from the fluidized bed.
Materials and methods: MSWI Fly Ash
MSWI fly ash produced from fluidized bed incinerator in Japan were analyzed in this study. The chelate reagent
had treated MSWI fly ash samples. Three kinds of leaching methods were used: Japan leaching test 46 (JLT 46),
toxicity characteristic leaching procedure (TCLP), and Japan leaching test 19 (JLT 19) to observe semi-soluble component and insoluble core component of fly ash particles.
Microscopic observation Morphological characteristics and elemental composition of MSWI fly ash particles were observed using a scanning electron microscope coupled with energy-dispersive x-ray spectroscopy (SEM-EDX JSM-6610LA, JEOL Ltd.,
Japan). After measurement by SEM-EDX, each single-particle elemental mapping was divided into five sections equally. Correlation coefficients (r) between major elements and heavy metal were calculated based on the intensity data in a specific horizontal section.
Result and discussion: Chromium (Cr) was mostly detected in the core of fly ash from a fluidized bed. The positive correlation between Cr with other elements was obtained by correlation analysis. Cr shows a positive correlation with Mg were shown in
Figure 1, that offered new possible Cr speciation is magnesium chromium spinel (MgCr2O4). The formation of
MgCr2O4, which Cr(VI) thermal decomposition could result in the formation of MgCr2O4, has been observed in a previous study. So, there is a possibility during the incineration process, Cr formed into magnesium chromium spinel. A positive correlation with Al also observed in this fly ash particle. It might be suggested new possible metal speciation as Al-chromite or Cr2O3 included in the Al-based core of fly ash. Cr in the core of fly ash, mainly as Cr(III), is due to the reduction of Cr(VI) with aluminum. Al present in the fly ash can control Cr leaching by reducing Cr(VI) released from
the solid phase by dissolution into Cr(III) formed. Therefore, the Al-based matrix in the fly ash might inhibit Cr
leaching into the environment.
| Original language | English |
|---|---|
| Journal | Japan Society of Material Cycles and Waste Management |
| DOIs | |
| Publication status | Published - 18 Sept 2020 |
