Effectiveness of Hydrothermal Treatment of Coal with Lime for Removal of Trace Elements

Abstract

The possibility of applying chemical cleaning method to remove trace elements from coal was examined. The hydrothermal reaction with CaO followed by HCl washing was carried out for three different coals. Most of the mineral matter was removed by this treatment, except a small amount of clay and pyrite. The removal percentage of trace elements was generally lower in comparison with that of mineral matter. This is because a substantial portion of trace elements is associated with organic matter or mineral matter that could not be removed by this treatment.

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

“…The result in this study shows that through the sequential leaching of three-step and one-step acid leaching, most of the minerals in coal can be removed, As and Hg can also be removed to a large extent and Cr to a lesser extent. Matsuoka et al (2002) concluded that if pyrite is completely removed by some other coal cleaning methods (e.g., HNO 3 leaching), Cr and Hg may be removed to a larger extent. This point was confirmed by this study, which further revealed that the different trace elements in coal have different modes of occurrence.…”

“…The proposed method by Wang et al (2003) can only distinguish the mode of occurrence of trace elements as organic association and pyrite association. Matsuoka et al (2002) used Cao/HCl treatment to classify the occurrence mode of trace elements in coal as (1) iron exchanged metals, carbonates; (2) excluded clays, excluded silicates; and (3) included clay, included silicate, pyrite, organic. Their method could not distinguish the trace elements associated with silicates, pyrite, and organic matters in detail.…”