Mineralogical, Geochemical Characteristics And Oxidative Potential Of Deposited Dust In Underground Coal Mine

Various lung diseases have been thought to be intimately linked to coal mine dust inhalation.Beyond the total mass concentration,the duration of exposure,individual genetic predisposition,particle size,morphology,and physicochemical characteristics also play an essential role in inducing pneumoconiosis.However,due to the limitations of the mining method in the underground coal mine,studies focused on the mineralogical,geochemical characteristics of dust in the underground coal mines are rare,resulting in unclear understandings of the source of dust in different sites within the underground coal mine,and the mechanism of the dust diffusion and deposition.On the other hand,as the inhomogeneities of coal mine dust,the coupling relationship between its compositional and toxic characteristics is unclear,leading to controversy over the causative factors of pneumoconiosis.This study systematically collected coal samples from the working front and deposited dust samples from different sites within underground coal mines（air uptake gallery,working front,air out gallery close to working front,and air out gallery far away to working front）,and separated the respirable fractions of deposited dust using rotary cylinder.The field emission scanning electron microscopy equipped with an energy-dispersive X-ray spectrometry（SEM-EDS）,Malvern Mastersizer laser diffractometer device coupled to Hydro G 2000,powder X-ray diffraction（XRD）,and inductively coupled plasma atomic emission spectrometry（ICP-AES）,and inductively coupled plasma–mass spectrometry（ICP-MS）were employed to identify the particle size distribution,mineralogical,and geochemical characteristics of deposited dust.The variability between deposited dust and the relevant coal seam and the spatial variation of deposited dust characteristics were analyzed in combination with the coal chemical,mineralogical and geochemical characteristics of the mined coal seams,to investigate the main material sources of deposited dust collected in different sites and the compositional differentiation during the dispersion process.In addition,the toxicity of respirable fractions segregated from deposited dust was tested using three complementary oxidation potential（OP）testing methods,and the main controlling factors driving the oxidation potential were explored based on the integrated mineralogical and geochemical characteristics.Finally,the potential health risks of miners in different coal mines and different sites within underground coal mines are assessed,and the main potential hazardous fractions are identified,furthermore,relevant recommendations are made for system and measures of dust control in the underground coal mine.In the study,the particle size distribution pattern of the deposited dust in the underground coal mines is dominated by a single-peak,with some variabilities in the diameter corresponding to 50%of the cumulative particle size distribution（d50,μm）in different coal mines and in different sites.The d50 in the Jincheng mine is larger than that in the Henan mine,while the working front sample has the largest d50,followed by the near air out and the air uptake（AU）gallery samples,and the far air out gallery samples have the smallest value.The spatial variation in the particle size characteristics of the deposited dust is consistent with the general rule of dust dispersion in underground coal mines,where finer particle sizes are carried further away and then deposited under the effect of the ventilation system,while coarser particle sizes are more likely to undergo near-source deposition.In addition,the characteristics of the mined coal seam influence the content of the fine fractions in the deposited dust,i.e.,the lower the moisture contents and ash yields of coal seams have,the higher volatile matter yields and more fine fractions produce.The ash yield of the deposited dust is higher than that of the coal seam to varying degrees and shows some varieties at different sites.These varieties reflect the mixing of non-coal material in the dust during dispersion and the fractionation of organic and inorganic matter.By comparing the differences in mineral composition and content with the relevant coal seam,we found that the sources of illite may be from non-coal rock（coal roof,floor and gangue）of coal measure strata,instead of mined coal seam;clinochlore and anatase,in addition to originating from the mined coal seam,may have been from the dust of non-coal rocks and tend to deposit near the working front;kaolinite and quartz may come from coal seam,as well as dust of non-coal rocks,and tend to deposit in air out gallery far from working front;besides the non-coal rocks of coal-bearing strata and mined coal seam,calcite may have other origins,such as dust generated by cement spraying in the air uptake and air out gallery.The dust formed during weathering the cement stored on the ground and train in air uptake gallery can increase the calcite content;tobelite and ankerite mostly originate from the coal seam and tend to deposit away from the working front.Compared to the mined coal samples,the deposited dust of Henan coal mine is slightly enriched in K,Cr,Zn,Rb and Pb,and enriched in As.The elemental contents of Jincheng deposit dust are inordinately higher than the average contents of Chinses coal,which is slightly enriched in Si,K,Na,Li,Cr,Zn,Ga,Rb,Cs,Ba,Pb and Th,enriched in As,and highly enriched in Sb.The major and trace elements in the respirable dust are similar to those in the corresponding deposited dust.Combined with the modes of occurrence of enrichment elements,it is suggested that the B,Li and Se in the respiratory fractions from Henan coal mines originated from the coal seam,while the Cs,Rb,W and Ba may be from the mixture of non-coal material.In addition,Sb,As,Pb,and Co,Zn and Mo,may be enriched by the superposition of both of these two factors.In the Jincheng samples,W,Cu,Co,Ni and B are mainly derived from dust generated by mining coal seams,K,Al,Ca,Mg,Sc and Nb are primarily from mixture of non-coal materials,and Li,Ge,Pb,As,Sb and Se come from a combination of above two sources.What’s more,the heavy metal elements Cr and Co in this study have high non-carcinogenic and inhalation carcinogenic risks,and As in some coal mines has inhalation carcinogenic risk.Therefore,controlling the levels of Cr and Co requires restraining the generation and inhibiting the dispersion of dust containing Co and Cr,thus reducing the corresponding health risks.In comparison to other types of particulate matter,such as atmospheric,diesel and firewood particles,the respirable dust in this study has a higher oxidation potential（OP）of dithiothreitol(OP^DTT),similar or lower oxidation potential of ascorbic acid(OP^AA)and dichloro-dihydro-fluorescein(OP^DCFH).In addition,the OP of respirable dust in the Henan coal mine is higher than that of the samples from the Jincheng mine.And the samples of respirable dust in the Henan coal has relatively high OP^DTTvalues near air out gallery and working front,and OP^AAand OP^DCFHvalues far away from the air out gallery.Anatase and siderite,as well as B,As,Nb,Li,B,Co and Sr,play an active role in driving OP^DTT;illite and Ca,Be,Mn and Zn play an important role in driving OP^AA;clinochlore,kaolinite,anatase and calcite,combined with Al,Ca,Cs,Na and Ga,play an important role in driving OP^DCFH.Different oxidation potentials have different sensitivities to different species.Also,there are differences in the driving factors at different sites within underground coal mine.Therefore,relevant dust control measures and systems should be developed in conjunction with the different driving factors.