Variation in Endogenous Trace Elements during Methane Generation from Different Coal Ranks

摘要

To investigate the variation in endogenous trace elements in different coal ranks during methane production, a series of biological gas production experiments were carried out using low- and high-rank coals. Changes in the content and status of occurrence of eight representative beneficial trace elements (i.e., Fe, Co, Ni, Mn, Zn, Cu, and Sn) in the gas production process were analyzed in this study. Under the same conditions, endogenous trace elements were 580.22 ppm in high-rank coal, a higher proportion than in low-rank coal (466.72 ppm). This indicates that the effect of the rank of coal is much more significant than the impact of endogenous trace elements. The average post-reaction rates of trace element content change in low-and high rank coals are 43.6 and 28.7%, respectively. This result shows that the proportion of trace elements in low-rank coal is more important than that in high-rank coal because of their contribution to response magnitude. Trace elements in different coal ranks exhibit a similar trend during different stages of biogas production. In other words, free and humic states conform to a "increase-decrease-increase" trend, while both the inorganic and macromolecular states exhibit tendencies to decrease. Results show that variation in the occurrence time of trace elements in high-rank coal is backward. Thus, this study addresses trace element variation during the process of biological gas production in different ranks of coal and augments our understanding of the process of coal-derived biogenic methane production. This study also provides a fundamental research basis for a more detailed understanding of the effect of trace elements as degradation substrates in the biogas production process.