A common and frustrating challenge for underground miners to deal with is ensuring that wheel generated dust from underground haul roads is kept under control for the health and safety of the workforce.
Common methods employed to suppress underground haul road dust in South Africa can vary from using fixed overhead sprinkler systems for preventative dust control to applying dust palliatives on the haul roads with specially designed underground water bowsers.
Fixed systems will run the length of the roads beneath the surface, including on declines. These systems generally spray untreated water on the roads to saturate the surface, thus preventing dust particles from becoming airborne when the surface is disturbed.
However, this strategy has limited effectiveness and several drawbacks.
Watering haul roads is only ever really a ‘temporary fix’. Inevitably, the road surface will dry out and will need to be re-watered. This approach consumes enormous volumes of water, especially if sprinklers are not automated. They will either over spray or apply insufficient volumes to effectively suppress dust.
In these conditions it's also common to find that the opposite problem can manifest. Dry and dusty roads that are subject to excessive or poorly distributed spray coverage can quickly become muddy and slippery, thus flooding further into the mine can also occur, resulting in blockage of silt traps. This all adds further to maintenance and operating tasks.
Another limitation with using this method is that sprinkler systems need to be reliable and provide complete coverage of the whole road network. Where spray coverage is patchy or incomplete, underground ventilation systems will pick up any airborne dust particles which are not suppressed. This will cause dust to spread further throughout underground tunnels which can become harmful to the health of workers and lead to unsafe working conditions due to poor visibility.
Patchy or incomplete sprinkler coverage is often a symptom of spray malfunction, damage, or poor maintenance. The systems are prone to damage from underground vehicle impact and if sprinklers are not properly and regularly maintained, they simply do not work as intended. Repairing any such damage takes time and risks the stoppages to hauling and production. This is seldom tolerated and as a result, broken systems are neglected and eventually discontinued.
With all of the above issues with overhead sprinklers, it becomes compelling for mines to look for better strategies that will reduce costs, improve productivity and require less maintenance.
What about spraying underground roads with surfactant-based dust palliatives?
Because dust surfactant chemicals are commonly used for dust suppression in underground transfer points and processing, it is also common to find them being applied to underground roads for dust control. However two major drawbacks occur when using surfactants as a road dust control solution.
Firstly, a surfactant is designed to make water wetter (breaking down the surface tension of water so it saturates material more easily), and without added binding agents to bind surface material there is no lasting dust control. As soon as the road dries the surface material remains loose and prone to accelerated fines and dust generation.
Secondly, what makes a surfactant chemical break down the surface tension in water is its industrial grade detergent properties. So adding a surfactant agent alone to underground roads can increase the risk of making them even more slippery when wet – especially if there is no tight control on product dosing and will do nothing to bind dust when the roads are dry.
Surfactants play an important part in suppressing dust that is already airborne and they are entirely appropriate for material transfer points or crushing, but without an added binding agent formulation they have little benefit for dust control on underground road surfaces.
OK, so what dust control treatment should be used on underground haul roads?
Effective and long lasting dust palliative solutions with binding and road sealing properties, such as DAS Product, can be used to provide much needed binding and road stabilisation and even seal road surface material to prevent fines that otherwise can become airborne.
Once applied, the bitumen contained in DAS Product forms a water-impermeable layer that doesn’t leach into the underlying natural soils, helping to stabilise the wearing course layers of the road.
A further benefit of using binders is the reduced equipment utilisation for respraying and grading of haul roads. When correctly applied, DAS Product can also significantly reduce the presence of airborne dust that risks being further distributed by underground ventilation systems.
How can DAS Product be applied to underground haul roads?
DAS Product can be applied via a series of light dilutions using a water bowser. Once applied over time, repeated and accumulated bitumen applications reduce the need for frequent maintenance. This translates into a significant reduction in water usage, water bowser utilisation and frequency of interactions with maintenance vehicles in the decline.
A switch from an underground sprinkler system to using DAS Product can result in potential savings of 90% less dust and 95+% water savings. Another environmental benefit is the fact that once cured, the bitumen in DAS Product does not leach.
For stabilised and robust haul road surfaces , DAS Product can also be incorporated into the wearing course layer through a process of grading, spraying and compaction. This not only provides excellent dust control properties, but significantly improves the durability and quality of the wearing course layer resulting in even lower ongoing maintenance costs.
Investing in DAS Product during the establishment of new underground haul roads will significantly increase longevity and durability, which is particularly prudent for declines and on embankments surrounding the portal.
Want to learn more about using road binders on your underground haul road network?
We’ll provide you with a detailed cost analysis based on managing the size of your haul road network.
We’ll also provide you with figures showing how soon you’ll break even by engaging our services and how much you will be likely to save on operating costs.