Determination of the Mode of Occurrence of As, Cr, and Hg in Three Chinese Coal Samples by Sequential Acid Leaching

Abstract

Sequential acid leaching was used to leach minerals and the trace elements they contain. One-step leaching uses concentrated nitric acid as solvent, while three-step leaching uses 5M hydrochloric acid, concentrated hydrofluoric acid, and concentrated hydrochloric acid as solvents. The sequential acid leaching by three-and one-step leach was also examined. The results showed that one-step leaching could leach over 80% of arsenic from coal samples, and also could leach mercury to a certain degree. During one-step leaching, little chromium is removed, but it is available to leach by three-step leaching; and during the sequential acid leaching by three- and one-step leaching, almost 98% of ash is leached. The result of acid leaching could also give detailed information on mode of occurrence of As, Cr, and Hg, which could be classified into: silicate association, pyrite association, organic association, and carbonates and sulfates association. Over half of chromium in the three coals is associated with organic matters and the rest is associated with silicates. The mode of occurrence of arsenic and mercury is mainly associated with different mineral matters depending on the coal samples studied.

Keywords:

• acid leaching
• coal
• minerals
• mode of occurrence
• trace elements

Acknowledgments

Financial support of this work by Natural Science Foundation of China (No. 90210001) is gratefully acknowledged, and the authors also thank Ms. Dongyan Liu for the ICP-AES analyses.

Notes

^{a a} By difference.