Mining and Minerals

Issues encountered during our interventions...

mining and minerals

This section describes dust-generating processes and collection control strategies at various stages of the minerals handling process, including drilling, crushing, screening, conveyor transport, bagging and loading for shipment.

Common Processes / Sources And Hazards

Mined ore grinding / crushing

The mined ore undergoes countless grinding and product sizing operations as it is processed into a marketable commodity. These operations are mechanized and are responsible for most dust emissions. The implementation of controls should reduce workers’ dust exposure and pave the way to eliminating related occupational diseases in the mining industry.

Air-borne particulate propagation

Air-borne particulates range in size from a mere 60 µm (or the thickness of a sewing thread) that are easily conveyed by wind to 2000 µm sized matter that remain suspended in air no higher than one meter (3 feet) before they fall back to the surface. Particles larger than 2000 µm roll along surfaces as they are swept by wind currents. The larger particles irritate the nasal cavities and throat, while smaller particulate enter the bronchial tracts and, depending on their size and shape (spherical or angular), will continue their route meandering in deep to lung alveoli.

Hazards

The permissible threshold value for airborne dust for most substances is 10 mg/m3; however crystalline silica or quartz dust is not tolerated in concentrations exceeding 100 µg/m3. Quartz is the second most abundant mineral in the Earth's continental crust (after feldspar) and since most mining operations involve removal of overburden and ore containing quartz, workers are the first in line to inhale crystalline silica through routine mining activities such as drilling, crushing, sizing and loading. Repeated exposure can have several adverse health consequences, including silicosis, tuberculosis, chronic bronchitis, emphysema and chronic renal disease (NIOSH). Crystalline silica is recognized as a human carcinogen by the International Agency for Research on Cancer IARC, and confirmed with some nuances by the IRSST (Quebec) and the INRS (France).

Risk prevention

Dust collectors adapted for individual processes

Dust collection systems for lowering dust levels are designed to control exposure not only to silica dust, but to other types of dust as well. They are by far the most widely used method in mineral processing facilities. Here are some typical applications:

  • Excavation sites
  • Hammer mills
  • Rock crushing
  • Ball mills
  • Mill conveyor transfer points
  • Coal mining dust processing
  • Bin venting of quarry storage

Local exhaust ventilation (LEV) capture effectiveness

Local exhaust ventilation systems (LEVs) are used to capture dust at their source, before they escape to the surrounding environment. Pursuant to ACGIH recommended practice, hood, chute or enclosure design governs capture effectiveness. An effective hood is a critical part of the system; if the hood does not capture the dust, the rest of the exhaust ventilation system is of little or no use. Properly designed, the hood will create an effective flow rate and pattern to capture dust. The material will then be pneumatically conveyed at low / high velocities through a duct network, channelled through an air-cleaning apparatus and a fan.

Dust collection system advantages

These systems offer distinct advantages:

  • Capture of ultra fine particles not easily controlled with wet suppression techniques;
  • Filtering material not suited to the process and by the same token recycling product of acceptable dimensions back into the process; and
  • Compared to wet suppression techniques, capture and filter efficiency is not impaired by cold weather.

Potential LEV locations

In plant or mill ventilation design, there are three areas that justify LEV installations:

  • Conveyor transfer, where mineral ore falls to another piece of equipment. For example: belt conveyor discharge to another belt conveyor, storage bin or bucket elevator.
  • Processes such as crushing, drying, screening, mixing, blending or bag unloading.
  • Operations involving air movement. For example: bag filling, palletizing or pneumatic silo replenishment.

Dust collector design

Controlling dust from mining equipment at excavation sites, mill transfer points and similar locations represents a challenge. If dust emissions are too high, production schedules may be curtailed to meet EPA requirements. The appropriate design and installation of dust collection equipment will not only reduce emissions, but allow mining equipment to operate for longer intervals and improve mill productivity. For example, AIREX DCCH-SB & Baghouse Series dust collectors have been successfully tested at 0.0003 g/dscf emissions on heavy duty rock crushing (ex. primary jaw crushing, secondary hammer mills).

Rock Products and Glass

Minerals handling: A dirty business

From raw material discharge to finished product loading, handling and processing minerals has and always will be a dirty business.

Dust collector design

Collectors with special media and dilution air ports /controls are normally required to handle the high heat associated with glass melting and manufacture. Good housekeeping in compliance with OSHA and EPA directives may be addressed using AIREX dust collection systems. Indeed, dry rock mineral crushing as well as fugitive dust emissions generated by belt conveying, transfer points, bucket elevators and silo vents may be controlled with AIREX baghouses designed for severe wear and abrasion.

Cement

Dust collectors adapted for individual processes

Cement production requires extensive dust control methods from fugitive dust emission control / venting to process-specific applications. High efficiency fabric filters ranging in size from 1,000 to over 80,000 ACFM are well suited for the following processes:

  • Rotary kilns
  • Clinker
  • Clinker coolers
  • Finish mills
  • Bucket elevators
  • Raw mills
  • Material handling systems
  • Conveyor transfer points
  • Bagging stations
  • Limestone
  • Rail load out
  • Cement kiln dust
  • Gypsum
  • Fly ash & activated carbon

Dust collector design

Concrete / cement dust is a particularly abrasive material that can cause significant wear to equipment and, as such, each process offers a different challenge with respect to material properties, moisture, temperature and dust loading. AIREX baghouses and pleated bag with venturi-assisted reverse pulse jet cleaning can be optimized for your specific application.

  • Glendyne

    (Saint-Marc-du-Lac-Long, Québec)

    Natural slate manufacturer.

    Design, manufacture and installation of a dust collection system to reduce the breathable silica level below the standard maximum exposure.

  • Sitec Canada

    (Charlevoix, Québec)

    Silica mining.

    Installing a dust collector and a plate heat exchanger to recover and recirculate residual energy from the rotary dryer silica stone through the plant.

  • Goldcorp - Mine Éléonore

    (Baie James, Québec)

    Goldmine.

    Manufacture and supply of central dust collection systems.

  • Carrières Miron

    (Montréal, Québec)

    Aggregate quarries.

    Manufacture and installation of centralized dust collection systems.

  • Bellemare

    (Shawinigan, Québec)

    Sand quarry.

    Design, manufacture and installation of a dust collector on the rotary dryer.

  • Béton Fournier

    (Val d’Or, Québec)

    Concrete manufacturer.

    Design, manufacture and installation of a dust collector on the rotary dryer.

  • Graymont

    (Joliette, Québec)

    Lime plant.

    Design, manufacture and installation of a dust collector.

  • Carrières Mathers

    (Saint-Eustache , Québec)

    Aggregate quarries.

    Design, manufacture and installation of dust collector on the aggregates treatment process.

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