Estimating the maximum size of explosive iron sulfide particles

Introduction. There are estimates of the maximum size d_cr 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 < d_cr, PO < 63 μm for pyrrhotite (PO) and 85 μm < d_cr, 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 (LEL_PO,1 = 475 g/m³ and LEL_PO,2 = 1,375 g/m³) and two polydisperse specimens of pyrite (LEL_PY,1 = 375 g/m³ and LEL_PY,2 = 500 g/m³). The obtained functions F_PO,1(d), F_PO,2(d), F_PY,1(d) and F_PY,2(d) were converted using Rosin – Rammler distributions, filling the gaps between the discrete data of the grain-size analysis of the specimens. d_cr rating. The procedure for estimating d_cr (Poletaev, 2014) was employed to find the values of d_cr, PO and d_cr, PY using the following equations: F_PO,1(d_cr, PO)/F_PO,2(d_cr, PO) = LEL_PO,2/LEL_PO,1 and F_PY,1(d_cr, PY)/F_PY,2(d_cr, PY) = LEL_PY,2/LEL_PY,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 P_max ≤ 350 k_Pa, index K_st ≤ 2 M_Pa ∙ 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 d_cr for sulfide ores have been refined: for pyrrhotite, d_cr = 40 μm; for pyrite d_cr = 107 μm. In the air suspensions of ores, only sulfur is burnt out, which substantially reduces the explosiveness of ores.

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