Estimating the maximum size of explosive iron sulfide particles

Introduction. There are estimates of the maximum size dcr of explosive particles of the two types of sulfide ores. The estimates are based on a qualitative approach to the dispersion analysis of combustible ore specimens (Soundararajan, Amyotte & Pegg, 1996): 49 μm < dcr, PO < 63 μm for pyrrhotite (PO) and 85 μm < dcr, PY < 145 μm for pyrite (PY). The task was to refine these estimates using the quantitative method of the mentioned analysis, taking into account the lower explosive limit (LEL) of flame propagation in terms of ore suspensions. Experimental data processing method. Continuous functions F of particle size distribution d were constructed for the two polydisperse specimens of pyrrhotite (LELPO,1 = 475 g/m3 and LELPO,2 = 1,375 g/m3) and two polydisperse specimens of pyrite (LELPY,1 = 375 g/m3 and LELPY,2 = 500 g/m3). The obtained functions FPO,1(d), FPO,2(d), FPY,1(d) and FPY,2(d) were converted using Rosin – Rammler distributions, filling the gaps between the discrete data of the grain-size analysis of the specimens. dcr rating. The procedure for estimating dcr (Poletaev, 2014) was employed to find the values of dcr, PO and dcr, PY using the following equations: FPO,1(dcr, PO)/FPO,2(dcr, PO) = LELPO,2/LELPO,1 and FPY,1(dcr, PY)/FPY,2(dcr, PY) = LELPY,2/LELPY,1. The solutions were presented in the visual graphic format. Discussion of the results. Due to the low values of explosion parameters of pyrrhotite and pyrite in a 20‑liter chamber (maximum explosion pressure Pmax ≤ 350 kPa, index Kst ≤ 2 MPa ∙ m/s), the validity of classifying ores as explosive dusts was discussed. Low explosion values have proven that sulfur is the main fuel in the air suspension. The explosiveness of ores is proven empirically (Selle & Zehr, 1954) by estimating the combustion temperature, which exceeds 1,000 °С. Conclusions. The values of dcr for sulfide ores have been refined: for pyrrhotite, dcr = 40 μm; for pyrite dcr = 107 μm. In the air suspensions of ores, only sulfur is burnt out, which substantially reduces the explosiveness of ores.