What is the importance of stockpile dust control? It offers increased control over fugitive dust particles in stockpiles, improves the safety and health of workers, enables control over respirable and inhalable dust generated from stockpiles by keeping it within allowable limits, prevents self-heating of reserve materials such as coal, controls and reduces the effects of leachates and maintains moisture content and surface crust within acceptable levels. Stockpiles play a crucial role and are a matter of necessity to the mining industry in general. One way or another, keeping large amounts of accumulated and reserve stock will be inevitable. Factors such as height and structure, wind erosion pollution, rain driven contamination and the impact on the ecosystem are important in dust and erosion management and making sure safety and health protocols are adhered to whilst managing your risks. The article will firstly focus on stockpiles in general then specifically evaluate coal stockpiles through understanding the problems faced in coal stockpiling. Finally, why water alone is not enough to achieve coal stockpile dust control including the dangers and hazards of coal dust stockpiling. 

Stockpile Management

Height and structure of stockpile, implications of wind erosion, rain and impacts on the ecosystem are some of the key factors to consider when evaluating the importance of stockpile dust control. The protection and coverage of stockpiles can be limited owing to extreme heights and structure of stockpiles which creates problems with efficacy of dust control. Dislodgement of fines as a result of wind can transport dust particles long distances away from the stockpile possibly triggering health and environmental hazards for communities within the vicinity of the source. Stockpiles of bulk materials such as soil, sand, ores and coal exist as potential sources of pollution owing to water run-off from rain which contributes to the contamination of groundwater, soil and local water bodies. Environmentally speaking, the ecosystem consists of flora and fauna which are susceptible and vulnerable to the effects of dust particles and deposition of sediment especially if wind and rain erosion are rife. All the contributing factors described do not exist in isolation but rather as combinations and in some cases cumulatively which makes process of dust control in stockpiles even more important. 

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Looking at Coal Stockpiling

Coal develops in subsurface environments via incomplete decay of organic matter created from a buildup of ancient plant material decays to pure carbon and simple hydrocarbons. Coal minerology, particle and surface chemistry contributes to its hydrophobic nature which also creates the need for careful consideration of coal dust palliatives to ameliorate coal dust in coal stockpiles. Global Road Technology (GRT) offers coal dust control effective for coal stockpile dust control and its capabilities will be highlighted in a solution-based approach to the importance of stockpile dust control. Coal stockpiles are a mass of coal consisting of heterogenous and porous coal particles with gaseous species like oxygen, water vapor, and gaseous product liberated by oxidation reactions transporting inter-particle channels and the microstructure of coal particles. The condition of the stockpile depends on whether it is being worked (live stockpile) or at rest (dead stockpile). The necessity of coal stockpiles is driven by the need for reserves for coal-fired power plants to meet the demand for electricity generation. However, longer periods of accumulation generate chemical reactions. Self-heating and spontaneous combustion of stockpiled coal is a dynamic thermal hazard which results in loss of coal as a resource and possible caking which creates safety issues related to open fires and production of noxious gases carbon monoxide and nitrous oxide in addition to harmful elements such as arsenic, selenium, mercury and lead. The mechanism of stockpiled coal self-heating mainly is propagated by low temperature oxidation but other exothermic processes such as microbial metabolism, interaction of coal with water and oxidation of pyrite also contribute to the self-heating of coal. 

Coal Dust Generation

Major sources of airborne coal dust in the static storage of coal, are wind exposure, surface layer particle size distribution of the coal, local wind velocity over the stockpile area and the moisture content of the exposed surface. Water has been widely used to achieve coal stockpile dust control however they are challenges associated with using water. Over-watering affects the calorific value of coal and generally each coal type has a critical moisture content which depends on the moisture holding capacity. In addition water is hydrophilic contrary to hydrophobic coal surfaces therefore its efficacy in coal stock pile dust control is very limited given the nature of interactions on the surface. Also water particle size should match the particle size of the smallest dislodged particle from coal stock piles otherwise on application water can actually increase the potential of buoyancy of the smallest size particles which creates further problems. 

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Best Practice Management

The problems associated with coal stockpiles are well documented and there is definitely need for effective and relevant tailor-made solutions to deal with safety, health and environmental hazards associated with coal stockpiles. Global Road Technology offers an effective and adaptable coal dust control solution in their coal targeted GRT Activate UG. This product is designed to make water work therefore the activation of water involves lowering of the surface energy which would be a barrier on using water alone. As a result the water is able to bind even the smallest of particles in addition to adsorption of the fugitive coal dust particles generated from the stockpiles. Coupled with GRT: Ore-Loc (a polymeric binding agent), the incentive for using GRT Activate UG is that it does not alter the burning properties of coal or affect its qualities. Since also wind accelerates the risk of spontaneous combustion and self-heating effective dust control minimizes the fire and environmental hazards associated with stockpiling coal dust. 

Conclusion

The complexity in dust generation from stockpiles involves the interaction of coal specific properties such as particle size, stored coal bulk density, surface crust and moisture content as well as operational factors such stockpile size and height. Natural factors such as wind and rain contribute to the complexity as well including the ecosystem involving flora and fauna that is subject to the prolonged exposure of leachate and coal dust from coal stockpiles. The fight to eradicate coal mine workers pneumoconiosis (black lung) continues and the cooperation of coal mining companies and their due diligence to keeping within the allowable coal dust limits is non-negotiable. Compliance can be supported and maintained effectively through utilizing GRT technologies that have the ability to coat and bind airborne particles forcing them to drop out of suspension in the air. 

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REFERENCES 

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