Detection and semi-quantitative analysis of naphthenic acids in coal and gangue from mining areas in China

Naphthenic acids (NAs), herein were referred to as a class of carboxylic acid mixtures, are believed to be emitted as byproducts of petroleum production and processing. Extensive research has indicated their widespread distribution in the environment, along with local ecological impacts. Due to the similar fossil power of coal and petroleum, NAs were detected in coal as well. However, few studies correlated with coal. In this study, we established a comprehensive set of extraction and analytical methods for detecting NAs in coal. By combining solid-phase extraction and ultra-performance liquid chromatography–mass spectrometry, and after conducting preliminary experiments, we selected NaOH as the primary extractant. A total of 71 distinct NAs were identified in coal samples during this experiment. Upon comparison with a petroleum-derived NA standard, significant differences between coal-derived NAs and those from petroleum were observed. Consequently, the concentrations of NAs in the samples ranged from 17.6 to 56.9 μg/g, providing evidence for the presence of a substantial amount of NAs in coal. This suggests that coal and coal gangue may be significant sources of NAs in the environment.