Atmospheric emission of NO_x from mining explosives: A critical review

High-energy materials such as emulsions, slurries and ammonium-nitrate fuel-oil (ANFO) explosives play crucial roles in mining, quarrying, tunnelling and many other infrastructure activities, because of their excellent transport and blasting properties. These explosives engender environmental concerns, due to atmospheric pollution caused by emission of dust and nitrogen oxides (NO_x) from blasts, the latter characterised by the average emission factor of 5 kg (t AN explosive)⁻¹. This first-of-its-kind review provides a concise literature account of the formation of NO_x during blasting of AN-based explosives, employed in surface operations. We estimate the total NO_x emission rate from AN-based explosives as 0.05 Tg (i.e., 5 × 10⁴ t) N per annum, compared to the total global annual anthropogenic NO_x emissions of 41.3 × 10⁶ t N y⁻¹. Although minor in the global sense, the large localised plumes from blasting exhibit high NO_x concentration (500 ppm) exceeding up to 3000 times the international standards. This emission has profound consequences at mining sites and for adjacent atmospheric environment, necessitating expensive management of exclusion zones. The review describes different types of AN energetic materials for civilian applications, and summarises the essential properties and terminologies pertaining to their use. Furthermore, we recapitulate the mechanisms that lead to the formation of the reactive nitrogen species in blasting of AN-based explosives, review their implications to atmospheric air pollution, and compare the mechanisms with those experienced in other thermal and combustion operations. We also examine the mitigation approaches, including guidelines and operational-control measures. The review discusses the abatement technologies such as the formulation of new explosive mixtures, comprising secondary fuels, spin traps and other additives, in light of their effectiveness and efficiency. We conclude the review with a summary of unresolved problems, identifying possible future developments and their impacts on the environment with emphasis on local and workplace loads.