Bauxite refineries (Bayer process) produce alumina (Al₂O₃) from bauxite ore using hot caustic soda (NaOH). Pumps handle highly caustic slurry, hot liquor, and red mud (waste residue). This guide covers pump selection for bauxite and alumina refinery operations.
Bayer Process and Pump Services
| Service | Fluid | NaOH Conc. | Temp | Key Characteristic | Pump Type |
|---|---|---|---|---|---|
| Bauxite slurry (grinding) | Ground bauxite + caustic liquor (50–60% solids) | 150–250 g/L | Ambient–80°C | Very abrasive (bauxite, silica), highly caustic, viscous, large flow, settling | Heavy-duty slurry pump (high-chrome/rubber-lined, caustic-resistant, large passage, expeller seal) |
| Digestion feed (to autoclave) | Bauxite slurry + caustic | 180–250 g/L | 100–150°C (pre-heat) | Very caustic, abrasive, hot, high pressure (pumping to digester), scaling | Multistage high-pressure (316L/duplex, API 610, hot caustic, high pressure) or positive displacement |
| Digester circulation | Caustic bauxite slurry (digesting) | 180–250 g/L | 140–280°C | Extremely caustic (hot), abrasive, very hot, high pressure, scaling (sodalite, cancrinite), hazardous | High-pressure slurry (duplex/super duplex, jacketed, large passage, expeller seal, high temp) |
| Flash tank slurry | Digested slurry (after flash) | 150–200 g/L | 100–150°C | Caustic, abrasive, hot, scaling, large flow | Slurry pump (316L/duplex/high-chrome, large passage, hot, expeller seal) |
| Red mud separation (settler) | Red mud slurry (Fe₂O₃, SiO₂, TiO₂, 30–50% solids) | 100–200 g/L | 90–120°C | Very abrasive (red mud), highly caustic, hot, large flow, settling, environmental | Heavy-duty slurry (high-chrome/rubber-lined, caustic-resistant, large flow, expeller seal) |
| Red mud washing (CCD) | Red mud slurry (diluted, washing) | 50–150 g/L | 80–110°C | Abrasive, caustic, hot, large flow, settling, recovery (caustic) | Slurry pump (high-chrome/rubber-lined, large passage, underflow control) |
| Red mud disposal (tailings) | Red mud slurry (15–30% solids, to pond) | 10–50 g/L | 60–90°C | Abrasive, caustic (mild), large flow, settling, environmental (alkaline tailings) | Heavy-duty slurry (high-chrome, large flow, caustic-resistant, expeller seal) |
| Green liquor (pregnant liquor) | NaAl(OH)₄ solution (Al dissolved, clear) | 150–200 g/L | 90–110°C | Highly caustic, hot, scaling (Al(OH)₃), clean (after filtration), large flow, valuable | 316L/duplex centrifugal (caustic-resistant, hot, large flow, scaling-resistant) |
| Precipitation (Al(OH)₃) | Green liquor + seed Al(OH)₃ (precipitating) | 120–180 g/L | 50–75°C | Caustic, precipitating (Al(OH)₃ crystals), scaling, viscous, large flow, valuable | Slurry pump or 316L/duplex (large passage, scaling-resistant, caustic, gentle) |
| Al(OH)₃ slurry (product) | Aluminum hydroxide slurry (30–50% solids) | 50–120 g/L | 50–75°C | Abrasive (Al(OH)₃ crystals), caustic, viscous, valuable (loss critical), large flow | Slurry pump or peristaltic (gentle, zero leakage, abrasive, caustic) |
| Calcination feed | Al(OH)₃ slurry (to calciner) | 0–50 g/L | 50–100°C | Abrasive, viscous, to filtration/drying, moderate flow | Slurry pump (high-chrome, large passage, abrasive) |
| Spent liquor (caustic recovery) | Spent caustic (after precipitation, NaOH + Na₂CO₃) | 150–200 g/L | 50–80°C | Highly caustic, scaling (Na₂CO₃), clean, large flow, recycling | 316L/duplex centrifugal (caustic-resistant, scaling-resistant, large flow) |
| Caustic make-up (NaOH) | Concentrated caustic (50% NaOH) | 50% (1300 g/L) | Ambient–50°C | Highly caustic, viscous (50% = ~80 cP), corrosive, precise, hazardous | Magnetic drive or screw pump (zero leakage, viscous, caustic-resistant, precise) |
| Lime dosing (causticization) | Lime slurry (Ca(OH)₂, 10–20% solids) | — | Ambient–80°C | Abrasive (lime), scaling (CaCO₃), caustic, viscous, precise | Peristaltic hose pump or screw pump (abrasive, scaling, viscous, self-priming, no valves) |
| Wash water (mud washing) | Hot water/condensate | 0 | 80–100°C | Hot, clean, large flow, low pressure, caustic (mild from carryover) | 316L centrifugal (hot, clean, large flow, caustic-resistant) |
| Wastewater (refinery effluent) | Alkaline wastewater (pH 9–12, Al, Na, sulfate) | 1–10 g/L | 40–70°C | Caustic (mild), scaling, corrosive, environmental, large flow | 316L/duplex or slurry (caustic, scaling, solids) |
Critical: Hot Caustic (NaOH) + Abrasive Slurry
The Bayer process uses hot concentrated caustic — the most demanding combination for pumps:
- Highly caustic: NaOH 150–250 g/L at 90–280°C. Use 316L SS minimum; duplex 2205 or super duplex for hot concentrated caustic (＞150°C, ＞200 g/L). NO carbon steel (caustic embrittlement, stress corrosion cracking). NO 304SS (caustic stress cracking). PTFE/FFKM or EPDM seals (caustic-resistant — NO NBR, NO FKM for concentrated caustic). Post-weld heat treatment (PWHT) to prevent caustic stress corrosion cracking. Jacketed pump (maintain temp, prevent crystallization).
- Abrasive: Bauxite (silica, alumina) and red mud (Fe₂O₃, SiO₂) are highly abrasive. Use high-chrome iron (A532 III) or rubber-lined (natural/butyl for ＜80°C) wetted parts. Large passage open impeller. Reduce tip speed. Expeller seal (no mechanical seal to wear out in slurry). Plan 32 clean water flush (caustic-free). Wear life 3–12 months.
- Scaling: Hot caustic + alumina → sodalite, cancrinite, Al(OH)₃, Na₂CO₃ scale. Large passage. Velocity ＞2 m/s (but ＜3 m/s to reduce erosion). Jacketed pump (maintain temp above crystallization). Flush with hot water/weak caustic on shutdown. Periodic acid wash (5–10% HCl or HNO₃ — but pump is caustic service, use water flush). Open impeller. Smooth surfaces (electropolished 316L resists scale adhesion).
- High pressure/temp (digestion): Digestion at 140–280°C, 10–40 bar. Use multistage BB5 pump (API 610, duplex/super duplex). High-pressure mechanical seal (Plan 53A/B barrier fluid, or Plan 32 flush). Thick casing. High-temp bolts. Thermal expansion. NPSH (hot caustic flashes). N+1 redundancy. Safety instrumented system.
Critical: Red Mud (Very Abrasive + Caustic + Environmental)
- Very abrasive: Red mud (Fe₂O₃ 30–50%, SiO₂, TiO₂) is highly abrasive. Use heavy-duty slurry pump with high-chrome iron (60+ HRC) or rubber-lined. Large passage. Expeller seal. Reduce tip speed. Plan 32 flush. Wear life 3–12 months. Multiple parallel pumps.
- Caustic + environmental: Red mud is highly alkaline (pH 10–13) — environmental hazard. Sealed pump (containment). Leak detection. Secondary containment. Red mud pond liners. Monitoring (pH, flow). Spill response. Caustic recovery (CCD washing) to reduce caustic in tailings. Our slurry pumps can be supplied with sealed configurations.
- Settling + large flow: Red mud settles rapidly. Flooded suction. Large suction lines. Velocity ＞3 m/s. Continuous operation. Flush with water on shutdown. Strainer. Thickener underflow control. Our heavy-duty slurry range handles red mud.
Critical: Al(OH)₃ Precipitation (Valuable Product + Scaling + Gentle)
- Valuable product: Al(OH)₃ (gibbsite) is the product precursor — zero leakage, gentle handling. Use peristaltic hose pump (gentle, no impeller to damage crystals, zero leakage) or slurry pump with large passage open impeller (low shear). Secondary containment. Product recovery (flush lines to product tank).
- Scaling + crystal growth: Al(OH)₃ precipitates and scales on surfaces. Large passage. Velocity ＞2 m/s. Jacketed (maintain 50–75°C). Flush with hot water/weak caustic. Smooth surfaces. Seed crystal control (agitation). Our peristaltic/slurry range handles Al(OH)₃ slurry.
- Caustic + viscous: Green liquor is caustic (120–180 g/L NaOH) and viscous (with crystals). Use 316L/duplex. EPDM/PTFE seals. Jacketed. Flooded suction. Our 316L/duplex range handles caustic liquor.
Material Compatibility
| Material | Hot caustic (150°C, 200 g/L NaOH) | Red mud slurry (100°C, caustic + abrasive) | 50% NaOH (ambient, viscous) | Al(OH)₃ slurry (60°C, caustic + crystals) |
|---|---|---|---|---|
| Carbon steel | NOT (caustic embrittlement, SCC) | NOT | Fair (concentrated caustic passivates, but risk) | NOT |
| 304 SS | NOT (caustic SCC) | NOT | Fair | Fair |
| 316L SS | Good (standard, PWHT) | Fair (abrasion) | Good | Good (standard) |
| Duplex 2205 | Good (hot caustic, PWHT) | Fair (abrasion) | Good | Good |
| Super duplex 2507 | Excellent (very hot caustic) | Good (abrasion + caustic) | Good | Good |
| High-chrome iron (A532 III) | Fair (caustic corrosion) | Excellent (abrasion, standard) | NOT | Good (abrasion) |
| Rubber-lined (natural/butyl) | NOT (temp ＞80°C, caustic attacks some rubber) | Good (＜80°C, fine abrasion) | NOT | Good (abrasion + caustic, ＜80°C) |
| EPDM seals | Excellent (caustic-resistant) | Good | Excellent | Good |
| PTFE/FFKM seals | Excellent (high temp) | Excellent | Excellent | Excellent |
| NBR/FKM seals | NOT (caustic attacks) | NOT | NOT (concentrated caustic) | NOT |
Critical: Hot caustic = 316L minimum, duplex/super duplex for ＞150°C/＞200 g/L, PWHT, EPDM/PTFE seals (NO NBR/FKM, NO carbon steel/304). Red mud = high-chrome/rubber-lined slurry (abrasion) + 316L/duplex (caustic). 50% NaOH = magnetic drive/screw (viscous, zero leakage). Al(OH)₃ = peristaltic/slurry (gentle, zero leakage, scaling). All = flush on shutdown + scaling control + jacketed for hot.
Common Problems and Solutions
Problem 1: Caustic pump cracks (stress corrosion). Carbon steel/304SS pump cracks with hot caustic. Solution: use 316L minimum; duplex 2205 for hot concentrated. PWHT all welds. EPDM/PTFE seals (NO NBR/FKM). Jacketed. Stress-relieve. Our duplex range handles hot caustic.
Problem 2: Red mud pump wears (abrasion). High-chrome impeller wears in 3 months. Solution: use rubber-lined slurry pump (fine red mud ＜150 μm) or high-chrome (coarse). Reduce tip speed. Expeller seal. Plan 32 flush. Monitor wear. Quick-change parts. Our rubber-lined slurry range extends wear life.
Problem 3: Digester pump scales (sodalite/cancrinite). Hot caustic + silica → sodalite/cancrinite scale — flow drops. Solution: large passage open impeller. Jacketed (maintain temp). Flush with hot water/weak caustic on shutdown. Periodic acid wash. Velocity ＞2 m/s. Smooth electropolished surfaces. Our large-passage designs resist scaling.
Problem 4: 50% NaOH pump loses prime (viscous). Concentrated caustic (50%, ~80 cP) is viscous — centrifugal loses prime. Solution: use screw pump or magnetic drive gear pump (positive displacement, self-priming, viscous). Jacketed (maintain ＞20°C — 50% NaOH crystallizes at 12°C). Flooded suction. Large suction. Our screw/magnetic drive range handles concentrated caustic.
Problem 5: Al(OH)₃ pump leaks (product loss). Seal failure loses valuable Al(OH)₃ product. Solution: use peristaltic hose pump (zero leakage, only hose wears). Or sealed slurry with double seal. Secondary containment. Flush lines to product tank. Leak detection. Our peristaltic range handles Al(OH)₃ with zero loss.
Selection Summary
- Bauxite slurry (grinding): Heavy-duty slurry (high-chrome/rubber-lined, very abrasive, caustic, large flow, expeller seal)
- Digestion feed: Multistage high-pressure (316L/duplex, 100–150°C, high pressure, API 610, hot caustic)
- Digester circulation: High-pressure slurry (duplex/super duplex, 140–280°C, very caustic, abrasive, jacketed, expeller seal)
- Flash tank slurry: Slurry pump (316L/duplex/high-chrome, 100–150°C, caustic, large passage)
- Red mud (settler/CCD): Heavy-duty slurry (high-chrome/rubber-lined, very abrasive, caustic, hot, large flow, expeller seal)
- Red mud disposal: Heavy-duty slurry (high-chrome, large flow, caustic, settling, environmental containment)
- Green liquor: 316L/duplex centrifugal (highly caustic, 90–110°C, scaling, large flow, clean)
- Precipitation (Al(OH)₃): Slurry or 316L/duplex (caustic, precipitating, scaling, gentle, large passage)
- Al(OH)₃ product: Peristaltic or slurry (zero leakage, valuable, abrasive, caustic, gentle, NO product loss)
- Spent liquor: 316L/duplex centrifugal (caustic, scaling, large flow, recycling)
- 50% NaOH make-up: Magnetic drive or screw pump (zero leakage, viscous, caustic, jacketed, precise)
- Lime (causticization): Peristaltic or screw (abrasive, scaling, viscous, self-priming, no valves)
- Wash water: 316L centrifugal (hot 80–100°C, clean, large flow)
- Wastewater: 316L/duplex or slurry (alkaline, scaling, environmental)
- Critical: hot caustic = 316L/duplex + PWHT + EPDM/PTFE (NO carbon steel/304/NBR/FKM), red mud = high-chrome/rubber-lined slurry + caustic-resistant, digestion = multistage BB5 + duplex/super duplex + high-pressure seal, Al(OH)₃ = peristaltic (gentle + zero leakage), 50% NaOH = screw/magnetic drive (viscous), all = flush + scaling control + jacketed + N+1
- Our heavy-duty slurry covers bauxite/red mud; multistage duplex covers digestion; peristaltic covers Al(OH)₃/lime; screw covers 50% NaOH. For alumina refinery pump selection, talk to our metallurgy engineers with your bauxite type, caustic concentration, and digestion temperature.