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Abstract: Samples of two high-aluminum coals and an associated fly ash were collected from a coal-fired power plant and a coalfield in Inner Mongolia, China. The mineralogy and physicochemical characteristics of low-temperature ash (LTA), high-temperature ash (HTA), and fly ash from those coals were studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), and field scanning electron microscopy with energy dispersive X-ray spectroscopy (FSEM-EDX). The transformation of typical aluminum-bearing minerals at high temperature was investigated by systematic drop tube furnace (DTF) experiments and thermogravimetric analysis. The results show that the aluminum-bearing minerals in the high-Al coal are mainly boehmite and kaolinite. High temperature treatment transforms the aluminum-rich minerals to gamma alumina (γ-Al2O3), corundum (α-Al2O3), and an amorphous phase. γ-Al2O3 is the main mineral in the HTA (17.4wt.%), while α-Al2O3 and mullite are the main minerals in the fly ash. The high-aluminum fly ash particles are irregular and their shapes are related to their compositions. The degree of irregularity of the high-aluminum fly ash particles is proportional to their aluminum content. The phase transformation of boehmite in the coal during high temperature treatment appears to have involved four stages including: boehmite dehydroxylation, transitional θ-Al2O3 formation, crystal nucleation and α-Al2O3 formation, and growth of α-Al2O3 crystals. The DTF experimental results indicated that the growth of α-Al2O3 crystals has a significant impact on PM emissions. Understanding the mineral transformation mechanism is therefore helpful in reducing PM emissions. [Copyright &y& Elsevier]

[Display omitted] • The organic or inorganic affinities of trace elements are speculated and determined. • The proportions of trace elements going into fly ash are positively correlated with their volatility. • Volatilization of trace elements during laboratory combustion has been divided into three stages. Partitioning behavior of 17 deleterious trace elements in Ge-rich coals during coal combustion was studied in a bench-scale combustion apparatus in a laboratory and in full-scale combustion in a coal-fired power plant. Methods used in this study include spectrophotometry, tube furnace combustion, inductively coupled plasma mass spectrometry (ICP-MS), and statistical evaluation. A comparison of the results obtained at these two scales and of the factors affecting their volatilization behavior during combustion are discussed. These seventeen trace elements tend to be volatilized more completely during combustion in coal-fired power plant than in a laboratory-scale combustion environment due to the differences in operating conditions. The average proportions of elements going into fly ash from feed coals during combustion are positively correlated with the trace element volatilities. Volatilization behavior of trace elements in laboratory-scale combustion involves three stages: initial release (<500 ℃), relative stability (500–1,000 ℃), and secondary release or stability (>1,000 ℃). The seventeen trace elements can be classified into four groups according to their behavior during the above-mentioned stages. Factors affecting behavior of elements in combustion, such as combustion conditions, modes of occurrence, concentrations, and geochemical affinities, are discussed. A new insight into the behavior of potentially deleterious trace elements during combustion is given, which provides further guidance to controlling their emissions. [ABSTRACT FROM AUTHOR]