The evolution in stockpile dust control practices should account for sustainability, efficiency and take a material science driven approach to the development of the products promoted and used as solutions. Unfortunately, many suppliers or distributors of technology suppliers often promote products without understanding why certain stockpile dust control method are successful – or not. Unsubstantiated assertions and buzzwords that are not backed wih factual data from the laboratory and proven in real world testing environments are actually quite common. At GRT we take the road less travelled in trying to steer up an objective discussion concerning the importance of stockpile dust control from a chemistry perspective. Chemistry is not meant to confuse or complicate the discussions but rather to educate in such a way that the next time one comes across mere statements without factual backing they can be able to discern with understanding reasons why choice of stockpile dust suppressant is grounded in the chemistry and material science of both the stockpile and the dust suppressant itself. The article will highlight the importance of stockpile dust control, different scenarios of stockpile dust control and tie in the applications of different Global Road Technology products used in stockpile dust control. 

Why is stockpile dust control important?

The importance of stockpile dust control to both workplace and community health and safety as well as the environment as dust airborne dust can travel long distances from the source. Emissions create environmental challenges when dispersed on vegetation (and economic impact if horticulture) or when it settles into waterways. Economically, the impact is by the loss of raw materials and energy as ore or coal and the opportunity loss for industries. The deterioration of air quality is an environmental issue that then flows on to become a health issue for staff and surrounding communities. So controlling “emissions” from stockpiles is critical as is understanding factors that affect the success of stockpile control, such as:

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  • Material characteristics such as type and structure (clumps or individual particles)
  • How the material behaves on exposure to moisture (crusting or turning to slush)
  • Material processing sensitivity to additives
  • The availability and quality of the water 
  • Feasibility of installing spray systems 
  • Stockpile turnover frequency, and 
  • The type of stacking and reclaiming method. 

Stockpile control – wanted dead or alive!

The effect of wind erosion on the stockpiles also depends on whether it is being worked on as a live stockpile or at rest as a dead storage. Managing long-term stockpiles (for months or even years at a time) whether in mining or in civil construction is relativity simple when compared to managing live stockpiles. This is because the constant disturbing of stockpiled material to load and reload material makes many long-term solutions not financially viable. Dynamic systems involving cannons or overhead sprays/sprinklers may be more efficient process, as long as the water/material interaction is acceptable. Factors affecting the process of wind erosion include stored materials bulk density, polymer-based surface crusting agent, moisture content, particle size distribution, and pile geometry with the most dominant are wind energy and the available erodible particles. Generally, studies have shown that it is important to locate areas of high windspeed near the pile since it is the most probable place where wind erosion is most likely to occur on the contrary areas where wind erosion is least likely to occur are associated with low wind speed. For stockpiles, the area of maximum wind speed is found to be near the top on the upwind sloping faces and extended toward the sides of the pile whereas the lee sides often have flow separating which results in low-speed recirculation flow. 

Mining Stockpiles – an industry example

In iron ore mining operations from pit to port, the iron ore is delivered mostly by dump trucks to the OHP, processing and conveying to stockpile, loading into transport (rail or road) to the port. Here it is again stored in stockpiles before being shipped to its final destination. Water is most often utilized to effect dust control in stockpiles with its efficacy extending beyond airborne dust but also binding mineral dust at the ore surface. The question which remains is the chemistry of water relative to the ore surface is effective, which also creates a further discussion on frequency of watering and then, whether the process of using water for dust control is sustainable in the greater scheme of things. As we begin to interrogate such critical questions it is important to mention that the common enemy in all this is dust which in its different types can create a health hazard to communities within the vicinity of operations, mine and port workers amongst many other likely victims to the exposure of stockpile dust. Dust lift-off from exposed surfaces such as stockpiles has the potential to reach the pulmonary system and result in acute, accelerated and chronic health-related ailments.  

Stockpiles in quarries

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At quarry operations, overburden stockpiles are prone to wind erosion which result in sandblasting of dust from the stockpile hence there is a need for a durable, wind and rain resistant dust suppressant to fulfil the site requirements. Typically, dust particles that are exposed to the environment pose risks to local water systems and locals within close proximity of the quarry operations. Weather conditions affect the dust shifting off the peak of the stockpile and possibly being transported a long distance away from the source which depends on the wind speed. The onsite challenges associated with overburden stockpile dust control include wind speeds which require improvised positioning of equipment to withstand the winds and accurately applying the dust suppressant onto the overburden stockpile making sure to cover all the areas that are potential sources of dust. Where practicable the best option is always to cover the stockpile with a durable and long-lasting dust suppressant which depends on the chemistry of the interaction between the overburden stockpile and the dust suppressant. The use of waterborne polymers has been popular given their ability to suppress dust with the spread of a crust layer, which is resistant to the effects of wind, rain and other possible causes of dust lift off. From a planning and development perspective some of the measures that can be taken to reduce dust lift-off from stockpiles include positioning of stockpiles taking into account the predominant wind direction which can be even supplemented with meteorological monitoring, revegetation of long-term stockpiles and use of windbreaks around stockpiles. 

An understanding of chemistry is critical when choosing the dust suppressant because the strength of the bond of interaction between the surface and the dust suppressant determines how effective the process of dust control becomes in terms of longevity, susceptibility to other factors such as rain, wind, UV light amongst many others. In mining applications, GRT offers GRT Ore-Loc a robust, liquid polymer that forms surface coating as a result of the polymeric backbone, which through the extended 3D network can be used for all ore and material surface types. The benefits of effective spread owing to its liquid nature combined with the polymeric integrity provides agglomeration, encapsulation and demobilization of fugitive dust. Overburden stockpiles that are susceptible to wind erosion which mainly results in soil lift off can be controlled using GRT Soil-Loc which utilizes specialized long chain polymer technology that enables durability whilst harnessing its dilution with water for thorough mixing and spread ability for effective dust control without limitations of flowability and viscosity. For long-term stockpile requirements/projects, GRT Enviro-Binder provides effective water and wind erosion control for years at a time in both the mining and civil industries. Ultimately the combination of polymer chemistry and material chemistry through use of safe products controls dust preventing it from causes harm to human health and sensitive environments. 

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REFERENCES 

  • Badr, T., and Harion, J.L. 2005. Numerical modelling of flow over stockpiles: Implications on dust emission. Atmospheric Environment. 39. 5576-5584. 
  • Katestone Environmental Pty Ltd. 2015. Air Quality Assessment of the Abbot Point Growth Gateway Project. 
  • Rain Baird Incorporation. 2009. Dust Control at Mining Operations: Valé Iron Ore Facility, Brazil. Site Report. 1-6.
  • Smit, P.P.A. 1980. Dust Concentrations Around Coal Stockpiles. The Science of the Total Environment. 15. 207-216.