Arsenic in Coal: Modes of Occurrence, Distribution in Different Fractions, and Partitioning Behavior during Coal Separation—A Case Study
2016
Zhou, Chang-Chun | Zhang, Ning-Ning | Peng, Chang-Bin | Cong, Long-Fei | Ouyang, Chang-Heng | Han, Rui
The content and modes of occurrence of arsenic and its distribution in Yunnan coal of China as well as its partitioning behavior during the coal separation process were investigated. The following laboratory equipment such as proximate analyzer, ultimate analyzer, sulfur analyzer, inductively coupled plasma mass spectrometer and the methods including sequential chemical extraction process, screening analysis, float-and-sink analysis, heavy liquid separation, and progressive release flotation were frequently used during the research process. The coal sample has a high sulfur content of 8.21%, and its arsenic content is 15.1 μg/g, which is within the range of the mild enrichment level. Content relationship among the various modes of occurrence in order is sulfide-associated form (47.38%) > organically bounded form (18.09%) > silicate-associated form (17.51%) > carbonate-associated form (12.04%) > ion-exchangeable form (3.84%) > water-soluble form (1.14%). The sulfide-associated form is the dominant mode of occurrence of arsenic in the raw coal, which means arsenic has an affinity to sulfur. Arsenic in the sulfide-associated form mainly occurs in the inorganic sulfide minerals (especially in pyrite). Besides, the arsenic content increases with the decrease of coal particle size, and arsenic is concentrated in high-density products. There is a good correlation between the removal rate of arsenic and clean coal ash in either gravity separation or flotation, and arsenic removal rate of 57.96% and 70.77% could be obtained through gravity separation and flotation, respectively. In order to ensure arsenic removal rate and clean coal yield, a combined approach of physics and chemistry should be developed.
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