Controlling dust at open cut mines is one of the greatest ongoing challenges for mine operators in Australia.
With so many dust generation points to contend with, from haul roads to tipping points to blasting activity, dust control needs to be treated as a site-wide issue. Because airborne dust comes in different types and sizes throughout an open cut mine, innovative solutions are required for each dust generation point.
In this blog post, we take a look at the sources of dust in open cut mines as well as some of the most effective control measures mine operators should be implementing.
Sources of dust in open cut mines
Dust from haul roads is a particularly prominent concern for environmental and safety managers as well for production and mine services managers. If there’s one thing that every production manager knows it’s this: good roads produce more loads.
Given that wheel generated dust from haul roads is the biggest source of fine dust particles on most mine sites, (contributing on average about 40% of total dust emissions), control measures need to be innovative and highly effective. Airborne dust creates significant visibility issues for haul trucks that need good sight of distance to be able to detect hazards up ahead, react on time to avoid incidents such as potential collisions or ore spillage
Additional sources of dust are generated from transfer and processing points such as tipping at ROM feeds into crushers. Dust generation from tipping is often excessive at ROM bins where no dust control is present, further dust is then generated from crushing, and once the crushed material is put onto a conveyor belt, even more, finer dust particles become airborne.
Without effective control measures in place, the dust generated during the various processes at open cut mines can quickly become widespread and unmanageable.
Traditional dust control measures
Dust control measures in open cut mines typically centre around the use of water carts to wet haul roads as well as low pressure watering systems to pre-wet materials. Even though water itself is sometimes considered to be ‘free’, wetting roads and materials in this way is actually expensive, potentially unsafe and not entirely effective.
To begin with, roads which have been overwatered create a number of safety concerns such as reduction in tyre traction, degradation of road quality and increased risks of collisions. Not to mention that roads never stay wet for long and need to be continuously watered, often leading to washouts and collapsing of fill sections and slopes.
Additionally, low pressure watering systems for pre-wetting materials are only a ‘quick fix’ solution at best and consume enormous volumes of water. These control measures will prevent coarser dust (10 microns and larger) from becoming airborne and will reduce overall dust throughout an open cut mine. However, low pressure watering does not actively subdue dust particles that are already airborne or respirable sized dust particles which are less than 10 microns (PM10 dust).
Long term exposure to PM10 dust is proven to cause many adverse health effects such as asbestosis, silicosis and black lung disease. This is because these respirable dust particles are so small they can penetrate the lower respiratory tract in our bodies.
More innovative solutions for controlling dust include:
- Stabilising haul road surfaces
- Utilising fog cannons for visible dust
- Installing high pressure dust suppression systems
1 - Stabilising haul road surfaces
It is becoming increasingly accepted across the mining industry that the correct use of dust binders and suppression product on haul roads will lead to a significant reduction in wheel generated dust emissions compared to using water alone.
This approach to dust control can be taken one step further by stabilising the design of haul roads to create a more permanent haul road solution.
A stabilised haul road consisting of a 50-75mm bonded wearing course with a bitumen seal layer will ensure less wheel generated dust as well as reduced loss of fines and less water ingress.
DASProduct is a proprietary bitumen emulsion technology, specifically designed and formulated to provide stabilisation of the wearing course layer on permanent haul roads as well as subsequent control of fugitive dust. It can be incorporated into the wearing course layer of a haul road and will actively work to reduce the need to employ water carts by 90+% and reduce operational and respirable dust by 90+% (compared to an untreated road). For other less permanent roads on a mine network, different binding and suppression products may be more effective (link to product landing page on website)
2 - Utilising fog cannons for visible dust
Fog cannons are now a popular dust control measure in open cut mines due to their versatility and innovative technology. They are ideal for use in scenarios where visible dust, rather than respirable sized dust, is a major problem.
These cannons use highly pressurised water which is pumped through a series of jet nozzles, turning the water into mist through atomisation. This fine mist is dispersed through the air by a powerful fan.
A fog cannon required to provide versatile dust control on site will have its own generator and be set up on a skid, allowing it to be moved around as dictated by weather conditions and the type of dust being generated. Once connected to a water source, fog cannons can be strategically placed near sources of dust in open cut mines, such as at dig and dump zones ,near haul roads, stockpiles and sensitive receptors at lease boundaries.
When dust particles collide with the mist, the particles are captured and the water dissipates before ever having had the chance to spread. The cannons can be manually or remotely activated when high levels of dust are generated due to certain weather conditions or periods of high activity.
The key to the successful use of fog cannons is not just about how much water can be blasted from the cannon or how far the water can reach. The spray nozzles need to be carefully selected so the correct sized water droplets are released into the air, to match the dust particle size distribution required for control.
Fog cannons are very effective at suppressing airborne dust and contribute to significant reductions in water usage compared to low pressure watering systems.
3 - Installation of dust suppression systems
Unlike low pressure watering systems, high pressure mist systems (at fixed plants) use low volumes of water at high pressure (above 50 bar) to add humidity/moisture to the air, usually at transfer points such as conveyor belts and tipping areas to capture and subdue dust particles that are already airborne.
These types of systems are ideal for ore that is moisture sensitive and in open pits where it is not practical to pre-wet materials. These systems are also very effective in reducing overall water use and preventing water pooling around plant that reduces safe working areas
The performance of these systems can be further enhanced by dosing with a concentrated surfactant agent like HydroWet to the feed water line. This product lowers the surface tension of water particles and makes it easier for the water and dust particles to agglomerate, particularly when managing hydrophobic materials.
The secret to successful dust control is ensuring that the atomised water droplets and the target dust particles are of equivalent size. Spray nozzles need to be exactly calibrated to the right pressure and angle, depending on the type of material being treated. This allows the water droplets and the dust particles to collide and agglomerate increasing in size thus falling to the ground due to gravity. If the water droplets are too large, the fast-moving airborne dust will simply flow around them
The benefits of high-pressure mist systems in open cut mines include the suppression of airborne PM10 dust by 80+%, minimisation of water usage and the prevention of excessive water pooling.
Want to learn more about innovative dust control measures for open cut mines? Talk to Dust-A-Side Australia.
For more than 40 years, we’ve been world leaders in total dust control management.
To learn more about our cutting edge dust control services, call us on 1800 662 387. Or you can get in touch by clicking here.