“…The Fe content in the samples after magnetic separation could be reduced from 3.05 to 1.26%. At 700 °C, the Fe removal could reach the maximum (62.8%), lower than that found in the literature, 23 but the Fe content in the nonmagnetic fraction is similar. This might be due to the fact that some Al in CFBFA is wrapped in the Fe-bearing phase or coexists with the Fe-bearing phase, as shown in Figure 2 .…”
Section: Results
and Discussioncontrasting
confidence: 71%
“…Sun et al 22 removed Fe from PCFA by magnetic separation and acid leaching, which obtained a higher Fe removal than only by magnetic separation. To improve the Fe removal efficiency, Fe-bearing minerals could be deeply reduced and transformed into Fe at 1000 °C, as shown by Wang et al, 23 and the impurity Fe could be completely removed by both magnetic separation and the acid leaching method. In addition, it is demonstrated that 24 some transition metal elements, such as Fe, Mn, Ni, Cu, and so on, could be enriched in magnetic fractions after magnetic separation from PCFA.…”
Alumina (Al
2
O
3
) extraction from circulating
fluidized bed (CFB) fly ash (CFBFA) is one of the most important pathways
for value-added utilization. However, in CFBFA, impurity iron (Fe)
normally coexists, resulting in complicated separation processes,
low Al
2
O
3
extraction efficiency, and substandard
Al
2
O
3
-based products. How to remove Fe impurity
effectively from CFBFA has become an important issue. For an effective
Fe removal from CFBFA, spinel ferrite transformation by carbothermal
reduction at a low temperature was discussed in the paper. The effects
of the reduction temperature and reduction time on the removal efficiency
of Fe and the recovery of aluminum (Al) as well as the removal of
other metals were systematically investigated, and the transformation
mechanisms of Fe-containing phases were investigated by X-ray diffraction,
X-ray photoelectron spectroscopy, and a scanning electron microscope–energy
dispersive spectrometer. The results showed that Fe in CFBFA was present
in the form of weakly magnetic α-Fe
2
O
3
, leading to a Fe removal of about 17.1% after magnetic separation;
however, the recovery efficiency of Al reached 97.4%. Weakly magnetic
hematite (α-Fe
2
O
3
) could be converted
to strongly magnetic spinel-type ferrite (MFe
2
O
4
) after carbothermal reduction at 700 °C for 60 min, and the
Fe removal efficiency could reach 62.8% after magnetic separation;
however, the recovery of Al was 81.2%, which was decreased compared
to the recovery of Al under the condition without carbothermal reduction
treatment. However, the carbothermal reduction–magnetic separation
process did not have a major effect on the existing form and leaching
behavior of Al, Li, and Ga. Simultaneously, it could be observed that
some transition metal elements such as Mn, Cr, and so forth could
be enriched in spinel-type MFe
2
O
4
and removed
after magnetic separation, which also provided a way for transition
metal enrichment and extraction of transition metals from other tailings.
“…The Fe content in the samples after magnetic separation could be reduced from 3.05 to 1.26%. At 700 °C, the Fe removal could reach the maximum (62.8%), lower than that found in the literature, 23 but the Fe content in the nonmagnetic fraction is similar. This might be due to the fact that some Al in CFBFA is wrapped in the Fe-bearing phase or coexists with the Fe-bearing phase, as shown in Figure 2 .…”
Section: Results
and Discussioncontrasting
confidence: 71%
“…Sun et al 22 removed Fe from PCFA by magnetic separation and acid leaching, which obtained a higher Fe removal than only by magnetic separation. To improve the Fe removal efficiency, Fe-bearing minerals could be deeply reduced and transformed into Fe at 1000 °C, as shown by Wang et al, 23 and the impurity Fe could be completely removed by both magnetic separation and the acid leaching method. In addition, it is demonstrated that 24 some transition metal elements, such as Fe, Mn, Ni, Cu, and so on, could be enriched in magnetic fractions after magnetic separation from PCFA.…”
Alumina (Al
2
O
3
) extraction from circulating
fluidized bed (CFB) fly ash (CFBFA) is one of the most important pathways
for value-added utilization. However, in CFBFA, impurity iron (Fe)
normally coexists, resulting in complicated separation processes,
low Al
2
O
3
extraction efficiency, and substandard
Al
2
O
3
-based products. How to remove Fe impurity
effectively from CFBFA has become an important issue. For an effective
Fe removal from CFBFA, spinel ferrite transformation by carbothermal
reduction at a low temperature was discussed in the paper. The effects
of the reduction temperature and reduction time on the removal efficiency
of Fe and the recovery of aluminum (Al) as well as the removal of
other metals were systematically investigated, and the transformation
mechanisms of Fe-containing phases were investigated by X-ray diffraction,
X-ray photoelectron spectroscopy, and a scanning electron microscope–energy
dispersive spectrometer. The results showed that Fe in CFBFA was present
in the form of weakly magnetic α-Fe
2
O
3
, leading to a Fe removal of about 17.1% after magnetic separation;
however, the recovery efficiency of Al reached 97.4%. Weakly magnetic
hematite (α-Fe
2
O
3
) could be converted
to strongly magnetic spinel-type ferrite (MFe
2
O
4
) after carbothermal reduction at 700 °C for 60 min, and the
Fe removal efficiency could reach 62.8% after magnetic separation;
however, the recovery of Al was 81.2%, which was decreased compared
to the recovery of Al under the condition without carbothermal reduction
treatment. However, the carbothermal reduction–magnetic separation
process did not have a major effect on the existing form and leaching
behavior of Al, Li, and Ga. Simultaneously, it could be observed that
some transition metal elements such as Mn, Cr, and so forth could
be enriched in spinel-type MFe
2
O
4
and removed
after magnetic separation, which also provided a way for transition
metal enrichment and extraction of transition metals from other tailings.
“…Crystal phase compositions of FA are mainly gypsum, mullite, and quartz. The presence of gypsum in FA can be attributed to the capture of SO 2 in the carbon combustion tail gas in a power plant 27 . And the main constituent of the PC observed by XRD analysis is C 3 S.Figure 1SEM images of materials (( a ) NC1; ( b ) NC2; and ( c ) FA).Figure 2Particle size distributions of materials.Figure 3XRD analysis of materials.…”
The mechanisms underlying the effects of nano-calcium carbonate (NC) on the strength of high volume fly ash (FA) mortar are discussed. Two NCs are used as 2%, 4%, 6%, and 8% by weight of cementitious materials. Hydrated products of fly ash mortar containing NC was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG) and differential thermal gravity (DTG) analysis. Results indicate that NC could improve strength of FA mortar due to the more rapid growth of hydrated products induced by NC through additional nucleation sites. Corresponding to the highest measured strength of FA mortar, the optimal contents of NC are around 2%. In addition, the presence of 2% NC improved the microstructure of FA mortar after 180 days due to the formation of calcium carbonaluminate hydrate.
“…With the rapid growth of coal consumption, a large amount of fly ash has been discharged into the environment, which has brought tremendous pressure on the environment. It is estimated that the world produces nearly 780 million tons of coal fly ash per year, and China accounts for about 1/6 (about 120 million tons) . Nevertheless, the coal fly ash utilization rate is only 40 % to 50 %.…”
In this study, ZSM‐5 zeolite with hierarchical porosity structure was synthesized by hydrothermal method using Al(OH)3, SiO2 extracted from coal fly ash as aluminum source and silicon source. The optimal synthesis parameters of ZSM‐5 zeolite were determined via an orthogonal analysis table. The optimum synthesis conditions were: SiO2/Al2O3/Na2O/hexadecyltrimethylammonium bromide/tetrapropyl ammonium bromide/H2O = 1/0.08/0.25/0.05/0.17/50, and the optimum crystallization temperature and crystallization time were 160 °C and 48 h, respectively. Scanning electron microscopy showed that the synthesized ZSM‐5 zeolite exhibited a spherical shape. Nitrogen adsorption‐desorption and Brunauer‐Emmett‐Teller measurement analysis displayed that the best sample ZSM‐5 molecular sieve showed a typical type IV isotherm, and the micropores and mesopores coexisted in the sample, indicating the successful preparation of ZSM‐5 zeolite with hierarchical porosity structure. The crystal growth of ZSM‐5 under different hydrothermal conditions follows the “S” adjustment.
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