Burnt coal cinder (BCC), the main solid waste in coal and electric power industries was used to prepare the geopolymer ceramics (GC) in this study. The optimum preparation technology of BCC-based GC and the effects of calcination and calcification on the compressive strength of BCC-based GC were studied. Through the calcification of BCC with CaO, NaAlO 2 and sodium silicate solution (SS) were separately used as the co-activator and silica additive to prepare BCC-based GC. The optimal single-factor conditions determined by the experiment were BCC:CaO:NaAlO 2 :SS = 18:3:2:4 (g:g:g:mL) and the liquid-solid ratio was 0.46. The compressive strength of BCC-based GC was 32.78 MPa (28 days). It was obtained that the calcination of calcified BCC below the temperature of 1000 • C can effectively remove the fixed carbon in BCC but will destroy amorphous active aluminosilicate. The microstructure study showed that BCC reacted in the ternary system of Ca-Al-Si to form a variety of amorphous products (C-(A)-S-H and (N, C) -A-S-H). Along with the three-dimensional amorphous gel structure as the dominant phase, the coexistence and interlacing of various amorphous gels made the microstructure more compact and increased the compressive strength of the BCC-based GC. GCs with various amorphous phases have been successfully prepared at low temperature, and it also provided a new idea for the utilization of low-activity silicate solid wastes.
In order to address the low thermal efficiency of low-rank
coal
combustion and the accompanying serious environmental issues, formed
coke was prepared using a carbonization consolidation method with
low-rank coal semi-coke. The test for briquetting and carbonation
consolidation conditions revealed that the optimal parameters were
a briquetting pressure of 93.63 MPa, moisture content of 16%, Ca(OH)2 binder amount of 10%, and a CO2 concentration
of 30% at 20 °C. Under these conditions and a carbonation consolidation
time of 60 min, high-quality formed coke was produced, exhibiting
a compressive strength of 1256.2 N/a, redrying strength of 286.2 N/a,
and a dropping strength of 10.6 number/a. The combustion characteristics
of the prepared formed coke were investigated, revealing that ignition
temperatures (345.39 °C), burnout temperatures (495.57 °C),
and peak of the maximum weight loss rate temperatures (437.93 °C)
are slightly higher than those of bituminous coal. The low calorific
value of the briquette was 20.4 MJ/kg. During the combustion process,
the emission concentrations of SO2, NO
X
, and solid particles from the formed coke were significantly
lower than those of bituminous coal, indicating that it is a cleaner
energy source. Moreover, adding Ca(OH)2 effectively reduced
SO2 emissions and achieved sulfur fixation and emission
reduction.
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