Migration and particle size distribution of high-bench throwing-blasting dust in open-pit mines

High-bench throwing blasting dust in open-pit mines exhibits essential differences in diffusion dynamics compared with conventional blasting dust. However, existing numerical models are mostly established under conventional blasting conditions and have not been adjusted or accurately characterized to capture the characteristics of throwing blasting dust. In addition, key input parameters for numerical simulations lack sufficient field-measured data support, which restricts the prediction accuracy and engineering applicability of simulation results. To address these problems, field monitoring was conducted using high-speed photographic observation technology. The results showed that the dust migration process could be divided into an impact motion stage, a "mushroom cloud" formation stage, and a diffusion motion stage. After blasting, dust concentration first rose rapidly, then fluctuated continuously, and finally decayed. Dust was dominated by medium-sized particles (20–100 μm), accounting for 56.2% of the cumulative proportion; fine particles (＜20 μm) accounted for 34.4%; and coarse particles (＞100 μm) accounted for only 9.4%. A three-dimensional geometric model of dust migration from high-bench throwing blasting in open-pit mines was established, and transient numerical simulations of dust migration were carried out using Fluent. The results indicated that ① during the initial rapid-release stage, dust exhibited highly aggregated distribution characteristics under the dominant effects of gravity and inertial forces; subsequently, during the sustained transport stage, dust was significantly lifted and expanded laterally under the effects of buoyancy and ambient wind fields; and finally, in the diffusion–settling stage, overall dust concentration decreased markedly due to gravitational settling and dilution by turbulent diffusion. ② Coarse dust particles settled rapidly, medium dust particles migrated with the airflow, and fine dust particles remained suspended for a long period and were transported over long distances.