Statistics project that Australia’s population is set to increase from 24 million to 30 million by 2030. That  6 million population growth will take place and rise the demands for public infrastructure and construction materials. Australia’s growth is better understood from estimations of quarry materials, crushed rock, asphalt, aggregate and concrete that are required for infrastructural development. Each Australian requires 7 tonnes per annum of quarry materials to support the building of roads, houses and infrastructure to service their needs. A kilometre stretch of highways uses up to 25 000 tonnes of crushed rock, a kilometer of suburban roadway requires 5000 tonnes of crushed rock, 750 tonnes of concrete for footpaths, kerbs and gutters and 450 tonnes of asphalt for road surfacing. Furthermore a kilometer of railway requires 2000 tonnes of aggregate and high-rise buildings can use up to 1000 tonnes of aggregate per floor. Construction of a typical house including driveways and landscaping utilizes about 110 tonnes of aggregate and 53 cubic meters of concrete. The figures bring a better perspective to the culmination of demand for construction materials as the population rises in Australia which leads us to the topic of dust that is generated from the sources of the construction materials. The article will seek to highlight where dust is generated in quarries whilst understanding how dust chemistry can lead to dust related pulmonary ailments and completing with evaluating what quarry dust suppression should target from a Global Road Technology approach. 

Different quarrying operations

There are different types of quarries namely natural stone quarries, rock aggregate quarries and just mines in general where heavy construction materials can be sourced. In the case of natural stone quarries, they produce stone blocks through detachment from the bedrock via the processes of drilling, blasting, sawing or wedging. Stone block detachment is performed with the intention to obtain bedrock as intact as possible from the excavation without causing damage. Majority of the dust is generated from drilling at the natural stone quarries. Rock aggregate quarries produce aggregates of various sizes through crushing and sieving . Rock detachment from the bedrock is done via drilling and fed into a crusher feeding bin whilst larger rocks are fragmented with a hydraulic impact hammer before crushing. Bulk of the dust is generated from crushing and sieving with the drilling and blasting contributing to dust emissions as well although to a much lesser extent compared to the former. Mining involves similar processes to rock aggregate quarries with drilling, blasting, hydraulic impact hammering, crushing and sieving. Coal mines for example, the material is sheared from the parent rock with the sheared material refined through grinding and pulverization for further processes. Given the closed nature of refiners’ dust formation is always negligible and post mining processes include chemical phases which create minor dust amounts. 

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In seeking to understand more closely the sources of dust in quarries we evaluate closely the sources of dust and the dust suppression for quarries that have been adopted. Intrusion of the drilling stem into the rock produces dust and usually drills are equipped with dry dust collection systems in open pit quarries. Wet dust suppression is utilized in underground mining for dust suppression. Movement of the jaw or cone during crushing results in rock fragmentation via compressive stress on the rock material in the crusher as grain-jaw/cone and grain-grain contact contributes to bulk of the fugitive dust particles. Dust suppression at this stage is normally controlled using encapsulation and water sprays. The demand for quarry materials is commensurate with infrastructural development and the hauling network becomes the backbone of the infrastructural delivery chain. Hauling of raw materials and products produces significant amounts of dust in open-pit quarries with research showing that haul road dust is mainly formed during other processes in the quarry and the hauling re-entrains the dust in the air. The vehicular movement create grain-grain pressure which causes airflow and lifts dust in the air. Dust control measures that have been employed include water and other water applications which include salts and surfactants, soil cements, bitumens, films just to mention but a few. 

Are environmental regulations, health and safety concerns or potential profit loss a concern right now?

The importance of legislation moving from monitoring to controlling

The Department of Natural Resources, Mines and Energy has been key in fostering guidelines for management of respirable dust. In Queensland, the minerals mines and quarries operate under the Mining and Quarrying Safety and Health Act 1999. The guideline enforces safety and health stating ways to achieve an acceptable level of risk to person arising out of operations which is achieved through identification, analysis and monitoring of risk associated with respirable dust hazards. The need for establishment and maintenance of effective controls related to respirable dust hazards is key to driving dust suppression in quarries and the workers on the frontline of mining activities should be protected through establishment of health surveillance. But why all these legislative measures in fact why is it so important? Let us first understand what respirable dust is. Well, these are very small particles of dust with aerodynamic diameters less than 10 microns which when inhaled there are able to reach the deepest parts of the lungs. Exposure to elevated levels of airborne respirable dust for the mine workers increases risks of developing mine dust lung diseases such as pneumoconiosis, chronic obstructive pulmonary diseases and lung cancer. Pulmonary ailments are influenced by mineral composition and chemistry for example respirable dust may contain inorganic compounds such as crystalline silica which is of a respirable size and gets deposited to the lower parts of the lungs as they penetrate through the respiratory tract. Chemistry of silica becomes carcinogenic owing to the dioxide of crystalline silica in the form of alpha-quart, cristobalite and tridymite. 

Industry Best Practice

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Global Road Technology’s innovative approach to dust suppression at quarries factors in the importance of particle size, chemistry and sustainability of the product employed for quarry dust suppression. Water is still the main form of dust suppression across quarrying operations, however it’s inherent chemical and physical behaviour make it a poor dust control agent. Majority of the fugitive dust particles are hydrophobic in nature that from a chemistry perspective renders them difficult to suppress with just water alone because of its hydrophilic nature. The technique employed to suppress dust particles as well is key as particle size of the dust suppressant should at least match the one of the smallest dust particles because instead the particles will bounce off cause further buoyancy owing to aerodynamic effects. The environment is key to sustainable application of dust suppression at quarries it is important to factor in environmentally friendly products that participate in dust suppression without compromise on Earth Stewardship. For haul roads which generate majority of dust, GRT Haul-Loc consisting of a specially formulated liquid polymer added to the watering trucks binds fugitive dust particles preventing them from being airborne dust with fivefold dust suppressing effects than using water alone while improving surface integrity. Given the chemistries of mineral aggregates it is key to use a product which exhibits both hydrophobic and hydrophilic properties and GRT Activate superactivates water to be able to interact with hydrophobic surfaces of mineral aggregates reducing the repulsion of fine dust particles to use of water alone. 

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REFERENCES 

Cement Concrete & Aggregates Australia. 2017. Inquiry into a National Freight and Supply Chain Priorities. Department of Infrastructure and Regional Development. 

Department of Natural Resources, Mines and Energy. 2020. Guideline for management of respirable dust in Queensland mines and quarries. Mining and Quarrying Safety and Health Act 1999.

Gonzalez, G.M. 2018. Dust Production in Mining, Suppression Measures in Quarry Blasting. Masters Thesis. 

Sairanen, M., Rinne, M., and Selonen, O. 2017. A review of dust emission dispersions in rock aggregate and natural stone quarries. International Journal of Mining, Reclamation and Environment.