The effects of bean straw (BS) on ash fusion behaviors of coals (Jiaozuo (JZ) and Zaozhuang (ZZ)) with high ash fusion temperature (AFT) and the regulating mechanism were investigated from the perspectives of ash chemical composition and mineralogical property. The results showed that the AFT of JZ ash mixture decreased as the BS ash mass ratio increased, while the AFT of the ZZ ash mixture decreased rapidly (0−12%) and then increased slowly (>12%). The existence form of Al 2 O 3 and SiO 2 was converted from high-melting-point (high-MP) mullite into low-melting-point (low-MP) aluminosilicates and their eutectics with BS ash addition, leading to a decrease in AFT. With increasing BS ash ratio, the major mineral reducing the AFT was changed from feldspar into leucite. Magnesia spinel had a weaker effect on improving the AFT than that of mullite or quartz, because of their different molecular structures. The experimental ash samples were divided into three categories, based on the total contents of SiO 2 and Al 2 O 3 (A): I, A ≥ 78.6%; II, 72.2% ≤ A< 78.6%; and III, 62.7% ≤ A < 72.2%. As the A content decreased, the existing form of Na 2 O and K 2 O was transformed from feldspar into leucite and nepheline; the CaO, together with some FeO and MgO, was transformed from anorthite or cordierite into the more easily fusible melilite and clinopyroxene.
The acid-leached
waste residue, produced during Al extraction from
coal ash, has been destroying the environment seriously. To use this
high silicon residue (70% or more) and accelerate the industrialization
of Al and Si extraction from coal ash, a high-silicon coal was selected
to prepare catalytic gasification ash (CGA) and combustion ash (CA).
Then, the obtained CGA and CA were leached by H2SO4 to remove aluminum and obtain a silica-rich residue. After
that, the acid-leached catalytic gasification residue (ACGR) and acid-leached
combustion residue (ACR) were leached by NaOH aqueous solution to
extract SiO2. In this process, some possible influential
factors, such as the NaOH concentration, liquid–solid ratio,
reaction temperature, and reaction time, on the extraction yield of
SiO2 (EY-SiO2) and modulus of sodium silicate
(SSM) were investigated. Besides, orthogonal experiments L9(34) were conducted to analyze their interrelationship.
In addition, to acquire the variation of the crystal structure, the
method of X-ray diffraction analysis was conducted. Moreover, with
the help of an ultraviolet–visible spectrophotometer, the content
of SiO2 in residues was accurately determined. The results
showed that the reactivity of CGA in the acid-leaching process was
much higher than that of CA, resulting in the content of SiO2 in the ACGR reaching 89.65% and the dominant mineral being amorphous
SiO2. It is the amorphous structure that the ACGR has better
reactivity compared to the ACR. Simultaneously, the orthogonal experiments
indicate that the NaOH concentration and liquid–solid ratio
are the significant influencing factors for SSM, while the temperature
is the significant influencing factor for EY-SiO2. More
significantly, relatively high SSM can be produced using the ACGR,
and this can help to break through the bottleneck of sodium silicate
production by the wet process.
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