Coal washing and mineral beneficiation involve pumping abrasive slurries through grinding, classification, separation, and dewatering circuits. These processes remove impurities (ash, sulfur, gangue) from coal and minerals, requiring slurry pumps that handle high solids, abrasive particles, and process chemicals. This guide covers slurry pump selection for coal washing and mineral beneficiation.
Coal Washing Process
- Crushing: Reduce run-of-mine coal to <50mm
- Screening: Separate by size (coarse, fine, ultrafine)
- Heavy media separation: Dense medium cyclone (coal floats, gangue sinks)
- Spirals/jigs: Gravity separation for fine coal
- Flotation: Froth flotation for ultrafine coal (<0.5mm)
- Thickening: Increase solids concentration (tailings and clean coal)
- Filtering/centrifuge: Dewater clean coal product
- Tailings: Dispose of waste (refuse, clay, pyrite)
Mineral Beneficiation
- Grinding: Ball mill/SAG mill to liberate minerals
- Classification: Hydrocyclone (coarse regrind, fine to separation)
- Gravity separation: Spirals, jigs, shaking tables (density difference)
- Magnetic separation: Magnetic minerals (magnetite, ferrosilicon)
- Flotation: Sulfide and oxide minerals (collectors, frothers)
- Thickening/filtering: Dewater concentrate and tailings
Slurry Applications
| Application | Solids % | SG | Abrasion | Particle Size |
|---|---|---|---|---|
| Coal slurry | 20-50% | 1.2-1.5 | Moderate | <50mm |
| Heavy media (magnetite) | 10-30% | 1.4-2.0 | High | <100μm |
| Cyclone feed | 30-50% | 1.3-1.8 | High | <150μm |
| Flotation feed | 20-40% | 1.2-1.6 | Moderate | <100μm |
| Concentrate | 50-70% | 1.5-2.5 | High | <75μm |
| Tailings (coal refuse) | 20-50% | 1.3-1.7 | Moderate | <1mm |
| Tailings (mineral) | 30-60% | 1.4-1.8 | Very high | <150μm |
| Clay slurry | 10-30% | 1.1-1.3 | Low | <10μm |
Pump Type Selection
Horizontal Centrifugal Slurry Pump
- Most common for cyclone feed, heavy media, tailings (high abrasion, large flow)
- Flow: 100-20,000 m³/h, head: 30-200 m
- Large passages, thick volute, hard metal or rubber-lined
- Material: high-chrome iron (HCCI), Ni-hard, or rubber-lined
- Advantages: high flow, handles solids, replaceable wear parts
- For heavy media: rubber-lined (magnetite is abrasive)
Vertical Slurry Pump
- For sumps, tanks, thickener underflow, flotation cells
- Flow: 50-10,000 m³/h, head: 20-100 m
- Submerged or semi-submerged, no priming
- Material: HCCI or rubber-lined
- Advantages: handles variable level, no priming, compact
- For thickener underflow: vertical pump common
Positive Displacement (PD) Pump
- For high-solids concentrate and paste (high viscosity, high pressure)
- Types: piston, peristaltic, progressive cavity
- Flow: 10-300 m³/h, pressure: 20-150 bar
- For paste fill: piston pump (underground placement)
- Advantages: handles high viscosity, high pressure, consistent flow
Chemical Process Pump
- For reagents, flotation chemicals, acid/alkaline solutions
- Flow: 10-500 m³/h, head: 20-150 m
- Material: 316, duplex, or fluoroplastic-lined
- Seal: mechanical with flush or magnetic drive
Material Selection
Wetted Parts
| Service | Casing | Impeller | Shaft | Seal |
|---|---|---|---|---|
| Coal slurry | HCCI/rubber | HCCI | 4140/316 | Expeller/packing |
| Heavy media | Rubber/HCCI | HCCI | 4140 | Expeller/packing |
| Cyclone feed | HCCI/rubber | HCCI | 4140/316 | Expeller/packing |
| Concentrate | HCCI/rubber | HCCI | 4140 | Expeller/mechanical |
| Tailings | HCCI/rubber | HCCI | 4140 | Expeller/packing |
| Reagents | 316/PTFE | 316 | 316 | Mechanical/mag drive |
Heavy Media (Magnetite) Considerations
- Magnetite (Fe3O4): dense (SG 5.2), abrasive
- Used as dense medium in coal washing (SG 1.4-2.0 slurry)
- High SG increases pump power and wear
- Material: rubber-lined (magnetite is fine, abrasive)
- Magnetite recovery: magnetic separators recover and reuse
- Pump must handle high SG without excessive wear
Coal vs Mineral Tailings
- Coal refuse: lower SG (1.3-1.7), moderate abrasion (clay, pyrite)
- Mineral tailings: higher SG (1.4-1.8), very high abrasion (silica, hard minerals)
- For coal: HCCI or rubber-lined (moderate abrasion)
- For mineral: HCCI (very high abrasion, silica)
Design Considerations
Abrasion Resistance
- Mineral slurry: high silica (very abrasive, Mohs 7)
- Coal slurry: moderate (coal is soft, but pyrite and clay are abrasive)
- Heavy media: magnetite (fine, dense, abrasive)
- Wear rate ∝ velocity³ — keep velocity low (1.5-3 m/s)
- Material: HCCI for coarse/hard, rubber for fine particles
- Replaceable wear parts: volute liner, throatbush, impeller, wear plate
- Monitor wear: performance curve shift, vibration, visual
High SG Slurry
- Heavy media: SG 1.4-2.0 (magnetite)
- Concentrate: SG 1.5-2.5 (mineral)
- High SG increases: pump power, bearing load, shaft stress
- Pump: robust design, heavy-duty bearings, large shaft
- Motor: oversized for high SG (power ∝ SG)
Flotation and Reagents
- Flotation reagents: collectors (xanthates), frothers, modifiers
- Mild corrosion, but can affect seal elastomers
- For reagent dosing: diaphragm metering pump
- For flotation feed: slurry pump (HCCI or rubber-lined)
- Air entrainment: flotation slurry contains air (use gas-handling impeller)
- Verify seal elastomer compatibility with reagents
Clay and Ultrafine
- Coal clay: very fine (<10μm), high viscosity, difficult to dewater
- Clay slurry: low abrasion, but high viscosity at high solids
- Use large centrifugal or PD pump (for high solids)
- Flocculants: improve dewatering (add with metering pump)
- For ultrafine coal: flotation and thickening
System Design
Cyclone Feed Circuit
- Cyclone feed pump: high flow, medium head, abrasive
- Material: HCCI or rubber-lined
- Multiple pumps in parallel (match mill capacity)
- VFD: optimize cyclone pressure (classification efficiency)
- Key: reliability, abrasion resistance, pressure control
Heavy Media Circuit
- Magnetite slurry: high SG, abrasive
- Pump: horizontal slurry pump, rubber-lined
- Circulation: maintain media density and flow
- Recovery: magnetic separators recover magnetite
- Key: handle high SG, maintain density, minimize magnetite loss
Tailings Disposal
- Coal refuse: slurry to refuse pond or thickener
- Mineral tailings: slurry to tailings dam or paste fill
- Pump: horizontal slurry pump or vertical
- For paste fill: PD pump (piston)
- Key: handle high solids, reliable, environmental compliance
Common Issues
- Excessive wear: Silica/mineral, high velocity. Use HCCI/rubber, lower velocity, replaceable parts.
- Heavy media wear: Magnetite, high SG. Use rubber-lined, lower velocity, monitor.
- Settling/blockage: High solids, low velocity. Maintain velocity, agitate, flush, large passages.
- High SG power: Magnetite/concentrate. Oversize motor, heavy-duty pump, verify power.
- Air entrainment (flotation): Gas in slurry, cavitation. Use gas-handling impeller, vent, deaerate.
- Clay viscosity: High solids, difficult pumping. Use flocculants, PD pump, heat (reduce viscosity).
- Seal failure: Abrasive/corrosive slurry. Use expeller/double seal, proper flush, monitor.
- Reagent compatibility: Flotation chemicals affect seals. Use compatible elastomers, verify.
Procurement Recommendations
- Provide: material type (coal/mineral), SG, solids %, particle size, reagents, flow, head
- For cyclone feed/tailings: specify horizontal slurry pump, HCCI or rubber-lined
- For heavy media: specify rubber-lined slurry pump (magnetite)
- For high SG concentrate: specify heavy-duty pump, oversize motor
- For sumps/thickener: specify vertical slurry pump
- For paste fill: specify PD pump (piston/peristaltic)
- For reagents: specify diaphragm metering pump or chemical process pump
- Specify material per abrasion/SG (HCCI, rubber, 316)
- Include replaceable wear parts (impeller, volute, throatbush, wear plate)
- For flotation: specify gas-handling impeller if needed
- Include instrumentation: flow, pressure, density, vibration
- Verify supplier has coal/mineral beneficiation references
Related Industries
Coal washing and mineral beneficiation slurry pump principles apply to all mining and mineral processing, power generation (ash handling), cement (raw meal), and wastewater (sludge). The core principle — reliable handling of abrasive high-SG solids-laden fluid with proper materials, wear parts, and heavy-duty design — is consistent across beneficiation applications.