A new technique for characterizing the efficacy of fugitive dust suppressants

Morphology and mineralogical composition of sandblasting dust particles from the Taklimakan Desert

The physicochemical characteristics of dust particles from the Taklimakan Desert are the fundamental basis for the assessment of particle variation during their long-distance transport and the subsequent environmental effects. In this study, 43,222 individual sandblasting dust particles, which were mobilised using a chamber with surface soils of sand dunes and Gobi (the two types of surfaces constituting the desert) were analysed to statistically quantify the shape and mineralogical composition of dust particles from the desert. The mode of the number-size distribution of particles from the sand dunes was 0.5-0.7 μm and that of particles from Gobi soils was approximately 1.0 μm. In contrast, the distributions of particle number fractions versus shape factors such as aspect ratio and roundness were similar, despite the irregular shape of the particles. Clay mineral particles were most frequently composed of chlorite and kaolinite, accounting for 66.74 ± 12.08% of the particles from both types of soils. Quartz and feldspar particles accounted for 9.57 ± 4.52% and 2.84 ± 1.28%, respectively. The mineralogical composition of particles smaller than 1.0 μm, in both soil types, was dominated by chlorite (Al-Si-O-Mg), kaolinite (Ai-Si-O), and quartz (SiO). Gypsum (CaS) and halite (NaCl) were the major salt components in particles from both soil types. Gypsum-containing particles existed in a wide size range and occupied 3.42%-8.98% of the particles from Gobi soils and 0.27%-2.18% of the particles from sand dunes. Most gypsum-containing particles were mixed with Si-containing minerals in the form of silicate or aluminosilicate; the remaining gypsum-containing particles were gypsum crystals or mixtures of gypsum and Ca-containing minerals. These results provide a comprehensive statistical profile of dust particles released by the sandblasting process from the Taklimakan Desert to the atmosphere.

Dust emission source characterization for visibility hazard assessment on Lordsburg Playa in Southwestern New Mexico, USA

In drylands around the world, ephemeral lakes (playas) are common. Dry, wind-erodible playa sediments are potent local and regional sources of dust and PM₁₀ (airborne particles with diameters less than 10 μm). Dust clouds often cause sudden and/or prolonged loss of visibility to travelers on downwind roadways. Lordsburg Playa, in southwestern New Mexico, USA is bisected by Interstate Highway 10. Dust storms emanating from the playa have been responsible for numerous visibility-related road closures (including 39 road closures between 2012 and 2019) causing major economic losses, in addition to well over a hundred dust-related vehicle crashes causing at least 41 lost lives in the last 53 years. In order to improve understanding of the surfaces responsible for the dust emissions, we investigated the critical wind friction velocity thresholds and the dust emissivities of surfaces representing areas typical of Lordsburg Playa's stream deltas, shorelines, and ephemerally flooded lakebed using a Portable In-Situ Wind ERosion Laboratory (PI-SWERL). Mean threshold friction velocities for PM₁₀ entrainment ranged from less than 0.30 m s^- 1 for areas in the delta and shoreline to greater than 0.55 m s^- 1 for ephemerally flooded areas of the lakebed. Similarly, we quantified mean PM₁₀ vertical flux rates ranging from less than 500 μg m^- 2 s^- 1 for ephemerally flooded areas of lakebed to nearly 25,000 μg m^- 2 s^- 1 for disturbed delta surfaces. The unlimited PM₁₀ supply of the relatively coarse sediments along the western shoreline is problematic and indicates that this may be the source area for longer-term visibility reducing dust events and should be a focus area for dust mitigation efforts.

A wind tunnel and field evaluation of various dust suppressants

A series of experiments was designed to assess the relative efficacy of various dust suppressants to suppress PM₁₀ emissions from nepheline syenite tailings. The experiments were conducted in the Trent University Environmental Wind Tunnel, Peterborough, Ontario, and on the tailings ponds at a mine near Havelock, Ontario. Treated surfaces were subjected to particle-free airflow, abrasion with blown sand particles, and particle-free airflow after physical disturbance. Emission rates in the wind tunnel tests were calculated from dust concentration measurements obtained in vertical profile with DustTrak™ II aerosol monitors (model 8530); rates in the field were measured using a Portable In-Situ Wind Erosion Laboratory (PI-SWERL). In the particle-free wind tunnel tests, three of the surface treatments performed well, and PM₁₀ emission scaled inversely with crust strength. Light bombardment of each surface by saltating sand grains increased PM₁₀ emission rates by two orders of magnitude. All treated surfaces emitted significantly more PM₁₀ after physical disturbance. In the field study, plots treated with a commercial dust suppressant were found to release more PM₁₀ than either the control or irrigated plots, although it should be noted that the emission rates were similar in magnitude. As in the wind tunnel experiments, all of the field plots became significantly more emissive after physical disturbance. The field results suggest that the site conditions, inclusive of the potential for dust advection and resuspension, must be taken into account when considering the use of a commercial dust suppressant. Implications: Fugitive dust (PM₁₀) emissions from mining and industrial operations worldwide present significant environmental and human health risks, leaving mine operators challenged to find reliable, durable, and cost-effective mitigation options. Commercial dust suppressants boast unique chemical compositions and commensurate particle binding capabilities, although few side-by-side comparisons exist in the literature. The efficacy of four commercial products to suppress PM₁₀ emissions from mine tailings, before and after physical disturbance, was assessed using robust field and wind tunnel experiments. All surfaces emitted significantly more PM₁₀ after physical disturbance but with considerable variability amongst products. Possible reasons for the differences in relative performance are explored.