Emission of Trace Elements from HEMMs Used in Opencast Coal Mines: Chemical Composition of Used Engine Oil and Diesel Soot

Abstract

Air pollution and source apportionment studies in mining areas often neglect heavy earth-moving machinery (HEMMs) generated pollutants due to the lack of their chemical fingerprints and sampling complexity. This study investigates the chemical composition of diesel soot and used engine oil (UEO) collected from different HEMMs. The morphology and elemental composition of diesel soot were analyzed through FE-SEM with EDX and CHNS analyzer. The FE-SEM image specifies the fractal structure (≥ 150 nm) of agglomerated soot particles (50–100 nm) generated from nano-sized primary soot particles (≤ 25 nm). The peak values of infrared (IR) spectroscopy of DS are almost similar for all HEMMs. The IR spectroscopy of UEO indicated that major spectral peaks occurred at nearly equal wavenumbers of 1377, 1460–64 and 2850–2971 cm⁻¹ for all HEMMs. The trace elements (TEs) concentration in diesel soot and UEO samples were investigated through ICP-OES and AAS (Pb-only) analyzer. The mean TEs concentration (mg kg⁻¹) in UEO were (Ca > Na > 1000) followed by (100 < Al < Fe < Mg < B < Si < Zn < Rb < P < 1000); (10 < Cr < Cu < Ni < V < 100); (01 < Co < Pb < Ti < Sr < Ba < Mo < 10) and (Cd < 1). The mean TEs concentration (mg kg⁻¹) in diesel soot were (Fe > Ca > Al > 5000) followed by (1000 < Mg < Na < P < 5000); (100 < Ba < Pb < Ni < Mo < Ti < Si < Cr < B < Zn < Rb < 1000); (10 < Co < V < Sr < Cu < 100) and (Cd < 05). The increased elemental concentration and higher wear index values (> 1) in UEO samples indicate Cu, Na, B, Fe, Cr, Mo, Cd, Pb, Al, Rb, Co, Ti and Ni as potential marker elements due to engine wear of HEMMs. The observations of this study add valuable information related to chemical fingerprints of HEMMs-generated pollutants for source apportionment studies in mining areas. Overall, this study gives insight into the chemical characteristics of HEMMs generated pollutants.