PARTITIONING OF TOXIC TRACE ELEMENTS DURING HIGH-SULFUR COAL PREPARATION FROM SOUTHWEST CHINA

The southwest of China is one of the largest coal-producing regions. However, most coals from the regions have a high sulfur content. Some representative high-sulfur coals from Reshuihe Mine (S_t,d, 5.4%; S_p,d, 5.19%) and Ganhe Mine (S_t,d, 12.09%; S_o,d, 10.09%), Yunnan Province, and from Rongyang Mine (S_t,d, 5.44%; S_p,d, 4.19%), Guizhou Province were selected for float-sink and flotation experiments in order to study the distribution of sulfur and toxic trace elements in different coal separation products. Mineralogical and geochemical compositions of these coals were studied by XRD, SEM-EDX, HTEM, EPMA, XRF, and ICP-MS.

Enriched elements As and Hg in the Reshuihe coals are mainly derived from epigenetic hydrothermal fluids, and mainly occur in pyrite, and they can easily be liberated from coals by gravity separation.The As and Hg contents in low-density fractions are as low as 1.1 and 0.14 μg/g, while in heavy fractions they can be up to 75.8 and 3.8 μg/g, respectively. Enriched elements U, V, Mo, Se, and Cr in Rongyang and Ganhe coals are mainly derived from exfiltrational hydrothermal fluids in the stage of syngenesis or early diagenesis, and mainly associated with fine grained minerals, such as clay minerals, pyrite, anatase, and guadarramite and organic components. These elements are difficult to remove effectively by gravity separation, and they are almost of the same content in feed coals as in cleaned coals from Ganhe Mine. Additionally, elements U, V, Mo, and Cr in Ganhe coals can’t be effectively removed by flotation. Compared to other size fractions, most elements in the fractions with particle sizes of 6-13 mm and <0.5 mm can be more easily removed. Thus, in order to fully remove toxic elements from coal, the feed is advised to be ground to <0.5 mm in diameter before gravity separation.