Arsenic in Coal: Modes of Occurrence, Distribution in Different Fractions, and Partitioning Behavior during Coal Separation—A Case Study

Abstract

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.

Removal of Mercury from Fine Coal Based on Combined Coal Processing Approaches

“…Furthermore, they also confirmed that the size of Hg carrier materials is also an important factor that affects the removal degree of Hg because Hg would be more likely to be enriched in the fine size fractions of coal samples. However, removal limitation always exists during single conventional coal cleaning processing, especially for the removal of Hg. , Similar results concerning removal limitation were also found in our previous studies focused on the removal arsenic and fluorine in coal. , …”

“…15,23 removal limitation were also found in our previous studies focused on the removal arsenic and fluorine in coal. 24,25 Froth flotation and gravity separation are conventional methods used in the coal cleaning process, and chemical leaching is an advanced method that also plays an important role in mineral processing and coal cleaning. Studies showed that chemical leaching is often able to achieve the desired coal cleanliness effect when there is difficulty with conventional coal preparation methods.…”

Speciation Characteristics and Mobility of Trace Elements Across Ultralow Emission Air Pollution Control Devices

“…As can be seen in Figure , most of As was associated with an oxidizable fraction (22.1%–67.8%) and a residual fraction (25.3%–77.9%) in coal. Only unit #3 has higher reducible fraction (41.7%), which indicated that a certain amount of As was bonded with oxides in the coal of unit #3, whereas for other units, As was bonded with organic and sulfides in coal . In fly ash, over 70% of As fractionated as residual form and the rest of As distributed in F1, F2, and F3 fractions at equal level.…”

Modes of occurrence and removal of toxic elements from high‐uranium coals of Rongyang Mine by stepped release flotation

“…Stepped release flotation uses differences in surface properties to separate minerals from coal; elements Sc, Co, Ni, Cu, Zn, Cd, Sb, Pb, As, Se, Sb, Bi, and Hg mainly occurred in pyrite, , while elements Be, F, V, Cr, Ba, W, Cs, and Tl dominantly occur within clay minerals, or other minerals, or organic matter . Thus, the distributions of Sc, Co, Ni, Cu, Zn, Sb, Pb, As, Se, Sb, Bi, and Hg in the products of stepped release flotation are different from those elements Be, F, V, Cr, Ba, W, Cs, and Tl.…”

“…At present, the most widely applied method of removing toxic elements from coal is gravity separation . However, there are few studies on the removal of toxic elements from coal by flotation . Rongyang Mine is located in the southwest of China, and the coals from Rongyang are characterized by their high S and U contents.…”