Arsenic and Fluorine Contents and Distribution Patterns of Early Paleozoic Stonelike Coal in the Daba Fold Zone and Yangtze Plate, China

摘要

Stonelike coal (SLC) is combustible black shale with low caloric value and a high degree of coalification, which is hosted in the early Paleozoic strata. The SLC is widely used for domestic purposes in the Daba fold zone in southern Shaanxi Province, China. Forty three channel samples of stonelike coal (SLC) were collected from the Daba fold zone to determine their elemental content. The results show that the contents of F, As, and Se in the Daba SLC are about 10-50 times more than those in the coals from the Permo-Carboniferous or later stages. The content of As varies from S to 277 mg/kg, and its average in the carbonate-hosted SLC of the Cambrian, mainly distributed in the southern Ankang district, is 112 mg/kg, while the average in the igneous-rock-hosted SLC of the Silurian, mainly distributed in the north Ankang district, is 78 mg/kg. The content of Se ranges from 1 to 62 mg/kg, and its average in the carbonate-hosted SLC is 29.21 mg/kg, while the average in the igneous-rock-hosted SLC is 9.91 mg/kg. The content of F ranges from 42 to 4532 mg/kg, with most samples ranging 600-2000 mg/kg. The average content of Hg is 0.66 mg/kg. Most of the SLC is enriched in As, Se, F, and Hg. The contents of F and As in the Daba SLC are about 10-50-times more than those in the coals of Permo-Carboniferous or later stages. As and Se are mainly enriched in the lower Cambrian carbonate-hosted SLC, and F is mainly enriched in the igneous-rock-hosted SLC of Silurian. The contents of As and F are comparatively lower in the carbonate-hosted SLC of the middle and upper Cambrian. The SLC of the middle and upper Cambrian is recommended for indoor use by local residents. It is suggested that local residents do not use the lower Cambrian SLC and igneous-rock-hosted SLC of Silurian for heating and cooking indoors as far as possible.