Abstract
The float-sink test is a commonly used technology for the study of coal washability, which determines optimal separation density for coal washing based on the desired sulfur and ash yield of the cleaned coal. In this study, the float-sink test is adopted for a high-sulfur Late Permian coal from Hongfa coalmine (No.26), southwestern Guizhou, China, to investigate its washability, and to analyze the organic affinities and distribution behaviors of some toxic and valuable trace elements. Results show that the coal is difficult to separate in terms of desulfurization. A cleaned coal could theoretically be obtained with a yield of 75.50%, sulfur 2.50%, and ash yield 11.33% when the separation density is 1.57 g/cm3. Trace elements’ distribution behaviors during the gravity separation were evaluated by correlation analysis and calculation. It was found that Cs, Ga, Ta, Th, Rb, Sb, Nb, Hf, Ba, Pb, In, Cu, and Zr are of significant inorganic affinity; while Sn, Co, Re, U, Mo, V, Cr, Ni, and Be are of relatively strong organic affinity. LREE (Light rare earth elements), however, seem to have weaker organic affinity than HREE (Heavy rare earth elements), which can probably be attributed to lanthanide contraction. When the separation density is 1.60 g/cm3, a large proportion of Sn, Be, Cr, U, V, Mo, Ni, Cd, Pb, and Cu migrate to the cleaned coal, but most of Mn, Sb and Th stay in the gangue. Coal preparation provides alternativity for either toxic elements removal or valuable elements preconcentration in addition to desulfurization and deashing. The enrichment of trace elements in the cleaned coal depends on the predetermined separation density which will influence the yields and ash yields of the cleaned coal.
Highlights
The coal washing operation is a process that depends on gravity and the difference in density between coal and its impurities, which is widely carried out as a primary coal preparation technology due to its versatility, relatively low cost, and environmental friendliness [1,2]
This puts forward new requirements for coal washing, to remove hazardous trace elements from coal while reducing the sulfur contents and ash yields [13,14]
Permian high-sulfur coal, aiming to investigate the distribution behaviors and cleaning potentials of toxic elements based on a washability study
Summary
The coal washing operation is a process that depends on gravity and the difference in density between coal and its impurities, which is widely carried out as a primary coal preparation technology due to its versatility, relatively low cost, and environmental friendliness [1,2]. As, F, Hg, and Se in Chinese coal have drawn much attention in recent years as they have been considered as culprits in coal burning endemic diseases [8,9,10,11,12] This puts forward new requirements for coal washing, to remove hazardous trace elements from coal while reducing the sulfur contents and ash yields [13,14]. The effect of coal washing on trace elements removal can be effectively investigated by examining the elements’ variation in washed and untreated coal that is sampled directly from coal preparation plants [15,16] These studies are imperfect as a coal washing plant may have a blended supply of ROM coals, and the processing technology may vary for coal with distinct properties. Permian high-sulfur coal, aiming to investigate the distribution behaviors and cleaning potentials of toxic elements based on a washability study
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