Fugitive and nuisance dust from mining must be mitigated and controlled to minimise airborne particles that can cause mechanical, environmental, health and local community issues.
Airborne dust particles can harm a person’s health, those in the local community as well as workers on the mine site. Dust clouds can lead to respiratory issues and some metals that are mined or present as processing reagents are potentially toxic if inhaled or ingested such as lead, arsenic and mercury. Additionally, fibrous minerals such as crocidolite, chrysotile and grunerite can be encountered during exploration and mining.
A well-known example of the hazards of dust is the mining of blue asbestos (crocidolite) in the former Pilbara town of Wittenoom. The dust emitted by the mining process contributed to up to 700 workers contracting the deadly peritoneal mesothelioma disease.
Dust provides poor visibility for those handling machinery – which may lead to an accident. Dust can also affect local flora and fauna, contaminate water supplies and infiltrate moving parts of machinery.
Dust comes from several different activities throughout the mining process, from land clearing, blasting, ground excavation and equipment traffic on-site to dust from processing such as crushing, screening, conveyors, transfer chutes and the loading and unloading of material.
Dust Management Strategies in Mining
It is a mining company’s responsibility to ensure that dust is effectively controlled and managed through the entire value chain to minimise negative impacts on the local community and environment and to mitigate possible negative health impacts. The overall aim is to reduce airborne dust particles to achieve as close to a dust-free operation as possible.
What can be done to effectively mitigate and control dust emissions in mining?
Below we outline four strategies you can implement, with the assistance of a dust management specialist, to keep fugitive and nuisance dust under control at your mine site.
1. Mechanical Extraction
Mechanical extraction via the use of fan-driven dust collection (similar to your vacuum cleaner at home) is probably the most effective at key dust generation points such as transfer points, dry screens and feeders. At these locations, dust hoods cover the area where turbulent materials handling is taking place. Dust is collected via large powerful fans and presented to a dust collector where the collected dust is captured.
Various types of dust collector processes capture dust in dry or wet processing methods. These processes include trapping the dust in dry baghouses or conglomeration of the captured dust for depositing back onto conveyor belts and back into the production process.
Mechanical extraction is capital intensive and requires significant energy and maintenance upkeep. Many sites are littered with dust collectors which aren’t in operation, this can draw the unwanted attention of a regulator.
2. Use of Water
Water is one of the main tools for controlling and mitigating dust as it helps to bind the material together, thereby using gravity to prevent it from becoming airborne.
Water can be sprayed onto a material through the use of mobile irrigators or water cannons equipped with the correct water delivery nozzle. It is important to select the correct water delivery system and determine the correct water pressure, delivery flow rate and water droplet size to ensure that the material is maintained at its optimum moisture content.
Materials handling systems such as crushers, conveyors, transfer points and screen houses produce significant dust during operation. This can be reduced by enclosing transfer points, sealing any gaps where dust may escape and operating equipment at its optimum point to limit the amount of dust escaping into the atmosphere. Before product entering these areas, moisture can be added to limit dust even further. Water is also used to spray directly onto falling material in and around the transfer chutes, feeders, screens and conveyors, entry and exit points of chutes, as well as onto tailings dams and stockpiles.
Water carts are often used to moisten unsealed roads where vehicular traffic creates airborne dust particles.
It is important to note that the excessive use of water can cause the material to become wet and muddy which then sticks to equipment. This can cause problems with the build-up of material in chutes, on conveyor belts, pulleys and screens resulting in potential damage. Excessive moisture can also impact the weight balance of stackers and reclaimers.
3. Use of Chemicals
Often water is not fully effective and the use of chemicals may be appropriate. For example, road surfaces can become slippery when water is added to them creating driving hazards.
When haul roads are designed the correct road surface or chemical treatment for dust reduction is a major consideration for the civil engineering team.
Road construction materials with the correct shrinkage and grading properties will provide the right results without becoming slippery when wet, causing tyre damage, or affecting the moving parts of a vehicle. A common material for haul roads is compacted gravel or gravel and crushed stone mix which is then sealed with bitumen or cement. Once treated and swept regularly it will lead to less ultra-fine dust caused by the regular movement of vehicles over the surface.
Alternative road surface products include brine and other proprietary polymer products that can effectively provide a seal over the dust particles, although these are a temporary solution and need to be reapplied at regular intervals.
Further examples of chemical use are on stockpiles of material which can be sprayed with a chemical veneer when heavy winds are predicted. The amount of chemical veneer used can be identified by the estimated wind speeds, anticipated duration of the weather front and the ambient temperature.
4. Use of Buffer Zones and Windbreaks
When considering the location of a mine site it is always important to consider how the dust will impact neighbouring towns and villages. To minimise dust being blown to these areas buffer zones and windbreaks should be used.
The site should always be located downwind so that prevailing winds do not carry the dust to local towns and villages, or towards the offices and workshops on the mine site. A buffer zone around the mine will further assist with minimising the amount of dust impacting local communities.
Vegetation such as trees, bushes and grasslands will collect the dust in their leaves, slow wind speed and hide the operation from view. Wind fences positioned up-wind can minimise dust problems by directing the wind above and over areas that generate or harbour dust. Fences positioned downwind of a dusty area acts as a dust barrier and can harvest dust that has been picked up by the wind.
Revegetating cleared tracts of land can also assist in minimising dust lift-off from previously mined or cleared areas.
Getting the Right Dust Management Strategy
These are just four ways dust can be controlled and mitigated at a mine site. A dust management consultant will be best equipped to offer advice on all the strategies available to you.
Engenium has dust management specialists on our team who can review your operation, or assist you with planning a new operation, and provide a detailed report on the best options for your businesses operation.
Our specialists can also recommend the correct equipment and optimum moisture content levels throughout your entire value chain, including mining, processing and transportation of the material by road, rail, barge and ship.
Project Manager, Perth WA
Engenium Pty Ltd