For selected air duties, roots blowers for mining and mineral processing must be matched to the material, route and site conditions. Modern mining operations recover and process metallic ores, industrial minerals, mineral fuels, construction materials and chemical feedstocks. Their production chains can include drilling, crushing, screening, grinding, classification, flotation, leaching, dewatering, drying, conveying and storage.
Roots blowers are used in selected mining and mineral-processing operations that require a dependable supply of air or process gas at low or moderate differential pressure. Their positive-displacement operating principle allows them to deliver an approximately constant gas volume as system resistance changes within the permitted operating range.
The strongest roots blower applications are generally found in mineral processing rather than primary rock extraction. Typical duties include froth-flotation air supply, pneumatic conveying, mineral-silo aeration, heap-leach aeration, wastewater treatment and certain specially engineered coal-mine methane extraction systems.
Roots blowers should not be described as universal mining air machines. Drilling equipment, pneumatic tools, filter presses, mine ventilation and high-pressure conveying can require substantially different fan or compressor technologies.
Mining and Mineral-Processing Operations
Mining projects are commonly divided into:
- Surface mining
- Underground mining
- In-situ recovery
- Mineral beneficiation
- Extractive metallurgy
- Tailings and water treatment
- Product storage and transportation
Mineral resources may be grouped broadly as:
- Metallic ores
- Non-metallic industrial minerals
- Mineral fuels
- Construction and aggregate materials
- Chemical and fertilizer minerals
These categories overlap. A limestone operation, for example, can supply construction aggregate, cement raw material or chemical-process feedstock. Equipment should therefore be selected from the actual process rather than the commercial name of the mineral.
Where Roots Blowers Fit
Roots blowers are most suitable where the process requires:
- High volumetric airflow
- Low or moderate differential pressure
- Approximately constant displacement
- Oil-free gas transport
- Pressure or vacuum operation
- Speed-based flow control
- Continuous industrial duty
- Relatively simple mechanical construction
Their typical mining applications can be summarized as follows:
A roots blower should be selected from the required operating point and process conditions, not solely because a mining application requires “air.”
Roots Blowers Are Not Main Mine-Ventilation Fans
Underground mine ventilation is a safety-critical discipline. Its purpose is to deliver fresh air, remove heat and contaminants, dilute methane and other hazardous gases, and maintain safe conditions throughout working areas.
Main and auxiliary mine ventilation is normally provided by purpose-designed axial-flow or centrifugal mine fans. These machines move extremely large air volumes through mine airways at pressure conditions determined by the ventilation network.
A roots blower should not be presented as the standard primary mine-ventilation machine.
This distinction is particularly important in coal mines. Methane can accumulate near a mine roof because it is less dense than air. Under unfavourable airflow and mixing conditions, a buoyant methane layer can form. Its control depends on the complete ventilation system, including:
- Air quantity
- Air velocity
- Airway geometry
- Methane-release location
- Turbulent mixing
- Ventilation controls
- Gas monitoring
- Methane drainage
- Main and auxiliary fan operation
It would be technically incorrect to state that installing a roots blower alone prevents methane layering.
Roots technology can have a legitimate but different role in methane drainage, where methane-rich gas is extracted through boreholes or drainage piping. That duty requires a gas-tight process blower and should be treated separately from mine ventilation.
Operating Principle of a Roots Blower
A roots blower contains two synchronized lobed rotors that turn in opposite directions. Gas enters the inlet, becomes trapped between the rotors and casing, and is transported toward the discharge.
The rotors do not normally contact each other or the casing. Timing gears maintain rotor synchronization, while bearings support the shafts outside the process chamber.
The blower transfers an approximately fixed volume per revolution. It does not independently generate a fixed pressure. Discharge pressure develops when the delivered gas encounters resistance in downstream piping or equipment.
This characteristic is useful in mining processes where airflow must remain stable despite changing:
- Flotation-cell liquid level
- Pipeline solids loading
- Filter resistance
- Heap permeability
- Silo material depth
- Diffuser fouling
- Process-valve position
A blocked or restricted discharge can cause pressure to rise rapidly. Pressure-relief protection and high-pressure shutdown are therefore essential.
Froth-Flotation Air Supply
Froth flotation separates valuable minerals from gangue by exploiting differences in surface chemistry. Finely ground ore is mixed with water and reagents to create a slurry. Air introduced into the flotation cell forms bubbles to which selected hydrophobic mineral particles attach.
The particle-loaded bubbles rise and form a mineral-rich froth that can be removed from the cell.
Airflow affects:
- Bubble size
- Gas dispersion
- Particle-bubble collision
- Froth stability
- Mineral recovery
- Concentrate grade
- Reagent performance
Roots blowers can supply stable, oil-free air for appropriate flotation duties. Their positive-displacement characteristic can be useful when several cells or flotation banks require controlled airflow against changing pressure.
They are not the only suitable technology. Large installations may use rotary-screw, multistage centrifugal or turbo blowers after evaluating capacity, turndown and lifecycle efficiency.
Pneumatic Conveying of Minerals
Pneumatic conveying is used to transfer dry mineral powders, concentrates, additives and prepared materials through enclosed pipelines.
Potential materials include:
- Lime
- Limestone powder
- Mineral concentrates
- Silica
- Alumina
- Soda ash
- Bentonite
- Activated carbon
- Cementitious backfill ingredients
- Dry tailings
- Pulverized coal
- Process additives
In a positive-pressure system, the roots blower is installed upstream of the feeding device and supplies clean conveying air. In a vacuum system, the blower operates downstream of the receiver and filtration equipment.
The mineral must not pass through the blower. Abrasive particles can damage rotors, casing surfaces, bearings and seals.
The conveying system must consider material density, particle size, abrasiveness, moisture, pipeline distance, elevation, bends and required conveying velocity.
Heap-Leach and Bioleaching Aeration
Heap leaching extracts valuable material from crushed or agglomerated ore placed on an engineered pad. A leaching solution percolates through the heap and dissolves the target mineral.
In some heap-leach and bioleaching processes, air is introduced through pipes beneath or within the heap. The supplied oxygen can support chemical oxidation and the activity of microorganisms involved in mineral dissolution.
Glossary
Abrasive solids: Hard particles capable of wearing machine or pipe surfaces.
Concentrate recovery: Fraction of a target mineral recovered into the saleable concentrate stream.
Froth-flotation cell: Vessel in which bubbles carry selected mineral particles to a froth.
Heap leaching: Recovery process in which solution percolates through stacked ore.
Mine ventilation: Large-scale air supply and exhaust used to control underground mine atmosphere.
Ore beneficiation: Processing that increases the concentration or value of useful minerals.
Ore throughput: Mass of mineral-bearing feed processed per unit time.
Tailings: Residual material remaining after mineral recovery.