Characterization of dust emission during ore unloading and analysis of its influencing factors

Dry bulk terminals at ports generate dust in the process of ore loading / unloading and transfer, and these particulate matters disperse to the atmospheric environment causing pollution and endangering human health. This study focuses on the funnel unloading point of a portal crane at a port terminal, and the variation characteristics of dust emission under different mass flow rates, ambient wind speeds, and moisture contents are investigated. The microscopic features of ore powders, i.e., wetting time, contact angle, particle size, specific surface area and pore structure, as well as microscopic morphology, are also determined to explore the intrinsic mechanism between wettability, moisture content, and dust emission. The impact of mass flow rate, ambient wind speed, and moisture content on dust emission is evaluated by employing the orthogonal test range method and response surface method. The experimental data reveals that the dust at the unloading point is dominated by coarse particles of total suspended particulate (TSP), and increasing the moisture content effectively reduced the dust emissions, with a suppression efficiency of TSP > PM10 > PM2.5. The experimental results on the microscopic features of the ore powders indicate that the above difference is attributed to wettability, which weakens with diminishing particle diameter. It is also concluded that the wettability of Australian ore 1 is determined to be superior to bauxite 394. Therefore, Australian ore 1 exhibits an excellent dust suppression effect at a moisture content of 4% ~ 5%, whereas bauxite 394 requires a moisture content of approximately 5% ~ 7% to achieve the same dust suppression. By conducting the orthogonal test range method, the three factors on the dust emission, in descending order, are moisture content > ambient wind speed > mass flow rate. According to the response surface method, the optimal parameter combination is determined and the dust emission is minimized as 4.149 μg/s, which corresponds to 0.386 mg TSP/ton, with the conditions of mass flow rate 10.356 kg/s, ambient wind speed 4.289 m/s, moisture content 6.983%.