Effect of occurrence mode of heavy metal elements in a low rank coal on volatility during pyrolysis

Abstract

The harmful trace elements will be released during coal utilization, which can cause environment pollution and further endangering human health, especially for heavy metal elements. Compared to combustion, the release of heavy metal elements during coal pyrolysis process, as a critical initial reaction stage of combustion, has not received sufficient attention. In the present paper, a low rank coal, from Xinjiang province in China, was pyrolyzed in a fixed bed reactor from room temperature, at atmospheric pressure, with the heating rate of 10°C/min, and the final pyrolysis temperature was from 400 to 800°C with the interval of 100°C. The volatility of heavy metal elements (including As, Hg, Cd and Pb) during pyrolysis process was investigated. The results showed the volatility of all heavy metal elements increased obviously with increasing temperature, and followed the sequence as Hg [ Cd [ As [ Pb, which was mainly caused by their thermodynamic property and occurrence modes in coal. The occurrence modes of heavy metals were studied by sink-andfloat test and sequential chemical extraction procedure, and it can be found that the heavy metal elements were mainly in the organic and residual states (clay minerals) in the raw coal. And most of the organic heavy metals escaped during the pyrolysis process, the remaining elements were mainly in the residual state, and the elements in Fe-Mn state also tended to remain in the char.

Distribution of Some Ecotoxic Elements in Fuel and Solid Combustion Residues in Poland

“…Knowledge of the content and distribution of EE in coal may facilitate, among others things, determination of enrichment or depletion of these elements in fly ash, slag/bottom ash, and coal pyrolysis products; it may also facilitate the forecasting of EE leaching efficiency from coal, from mineral overgrowth of coal and from solid coal combustion products. It also has a significant impact on the behavior of elements during coal enrichment, conversion, and weathering [8][9][10][11][12][13][14][15][16]. It is assumed that, during the combustion of coal, the elements bound in coal mainly with the organic and sulfide fraction first evaporate, and then they easily adsorb on fine particles during the cooling of the flue gas.…”

Archives of Mining Sciences

“…Moreover, it has a significant impact on the behaviour of elements during coal conversion and weathering (i.a. Bhangare et al, 2011;Hower et al, 2016;Pan et al, 2018;Xu et al, 2003;Zhao et al, 2018;Zhou et al, 2019).…”