Evidence of Sulfuric-acid Emitted from the Underground Coal-fire at Wuda of the Inner Mongolia of North China

Abstract

The emission of pollutants from the continuous spontaneous combustion of coal seams and coal gangue may leads to serious destruction of the global environment and ecology in the 21st century. The persistent coal fire in the Wuda coalfield in Inner Mongolia, China is a typical coal fire in north China, and it attracts global attention. In this paper, Coal fire sponge (CFS) samples were collected from the Wuda coalfield and tested in the laboratory. The results show extremely low pH value (0.30 ~ 0.96, n = 33) and extremely high sulfate concentration (125 ~ 427mg/g, n = 33). It is confirmed that 90% of the sulfate exists in the form of sulfuric acid according to further analysis. This fact reveals that the emission of sulfur from spontaneous combustion of coal and coal gangue is mainly in the form of sulfuric acid (H2SO4·nH2O), which comes from conversion of sulfur in coal and coal gangue, and the accompanying emission of sulfur dioxide is secondary. Glauber's salt condensate, which is common in exposed rock cracks and voids in the Wuda coalfield, further indicates that at least in this coalfield, the spontaneous combustion of underground coal seams and coal gangue will inevitably emit sulfuric acid into the atmosphere. The strong water absorption of sulfuric acid droplets and the resulting condensation and nucleation in the atmosphere are the key factors leading to regional haze events and global climate radiation suppression. Anyway, this work reveals an important and unknown source of sulfuric acid emissions, and it is likely to be another way for coal fires to affect and endanger the global environment and ecology.