3t/h aluminum electrolyte impurity removal and lithium extraction MVR evaporator

I. Project Background 

With the approaching retirement of new energy vehicles, lithium extraction from aluminum electrolytes (cathode carbon blocks + electrolyte) has become a crucial step in lithium battery resource regeneration. The electrolyte contains soluble salts such as Li₂CO₃ 5–7 g/L, NaF/KF 180 g/L, and Al³⁺ 15 g/L, along with trace amounts of heavy metals (Ni, Co, Mn). Traditional processes employ "multi-effect evaporation + cooling salt precipitation," resulting in high steam consumption, significant lithium entrainment losses, and severe equipment corrosion. The owner plans to construct a 3t/h aluminum electrolyte lithium extraction MVR evaporator in 2024, with the following requirements: Primary concentrate Li₂CO₃ ≥ 60g/L, enrichment ratio ≥ 10; Condensate F⁻ ≤ 10mg/L, reuse rate ≥ 95%; No mother liquor discharge; Power consumption per ton of water ≤ 45kWh; Equipment material resistant to 20% HF and long-term operation at 80℃.

II. Process Route

1. Pretreatment for Impurity Removal

• Using “CO₂ aluminum removal + resin heavy metal removal”:

• CO₂ bubbling at pH 8.5 generates Al³⁺ to form Al(OH)₃ colloid, which, after filtration through a ceramic membrane, yields Al ≤ 5mg/L;

• The chelating resin selectively adsorbs Ni/Co/Mn, with total heavy metal content ≤ 0.1mg/L, preventing subsequent evaporation foaming and catalyst poisoning.

2. MVR Forced Circulation Evaporation Concentration: 

A combination of plate preheating + forced circulation tubular evaporation + centrifugal steam compressor is used. Evaporation temperature: 75℃ (vacuum -0.082MPa), compressor temperature rise: 18℃, compression ratio: 1.7. All secondary steam is reused; only 0.4t of live steam is added during startup. Circulation pump flow rate: 1200m³/h, pipe velocity: 3.5m/s, inhibiting fluoride scaling.

3. Freeze-Heat Melt Salt Separation: Concentrated Li₂CO₃ (60g/L) and NaF (190g/L) solutions enter a 0℃ freeze crystallizer. NaF·KF mixed salt precipitates, is centrifuged, and returned to the front end. The mother liquor is heated to 95℃; Li₂CO₃ crystal purity ≥98.5%, first-pass yield: 88%.

4. Mother Liquor Drying: Lithium-rich mother liquor is fed into a scraper dryer, with a dry solids content of ≤3% water and 0.15 t/d of mixed salts, and then sent to hazardous waste co-processing, achieving zero mother liquor discharge.

III. Key Equipment and Materials

IV. Operating Data (Average over 180 days, April 2024 - October 2024)

• Processing Capacity: 3.2 t/h (Load Rate 107%)

• Electricity Consumption per Ton of Water: 42 kWh (Including Compressor, Circulating Pump, and Drying)

• Steam Makeup: 0.03 t/t of Water (On-Duty Only)

• Lithium Enrichment Ratio: 12 times, Li₂CO₃ Concentration: 62 g/L Lithium recovery rate: 90.5%, NaF mixed salt recovery rate: 93%

• Condensate F⁻: 6mg/L, reuse rate: 96%

• System uptime: 98.2%, unplanned shutdown once every six months

• Cleaning cycle: 90 days (5% citric acid online circulation for 4 hours)

V. Technical Innovations

1. Fluorine corrosion resistant material system: TA10 titanium alloy in the tube side has an HF corrosion resistance rate ≤0.01mm/a, increasing lifespan by 6 times compared to 316L.

2. Low-temperature MVR + high vacuum: Evaporation temperature 75℃, avoiding high-temperature re-dissolution of Li₂CO₃, reducing lithium loss by 70%.

3. Centrifugal compressor titanium impeller: Under conditions of 18℃ temperature rise and 1.7 pressure ratio, the isentropic efficiency reaches 84%, saving 15% more energy than the Roots type.

4. AI anti-scaling algorithm: Real-time monitoring of temperature difference, conductivity, and vibration predicts fluoride scaling trends, providing a 72-hour advance warning, reducing annual cleaning frequency from 12 times to 4 times. 5. Freeze-Melt Salt Separation: Utilizing the solubility difference between NaF and Li₂CO₃, battery-grade Li₂CO₃ (99.2% purity) is obtained in a single process, reducing impurities by 80%.

VI. Environmental and Economic Benefits

Environmental: Annual reduction of 26,000 tons of high-salinity wastewater, 4.2 tons of F⁻ emissions, and 85% reduction of hazardous waste and impurities, successfully passing zero-discharge testing.

Economic: Annual savings of 25,000 tons of primary water and 3,200 tons of live steam, with a byproduct of 1,650 tons of Li₂CO₃. Based on a cost of 150,000 yuan/ton, annual sales revenue is 248 million yuan; operating cost per ton of water is 46 yuan.

Social: The project has attracted technical exchanges from over 40 domestic and international companies.

VII. Conclusion 

The 3t/h aluminum electrolyte lithium extraction MVR evaporator successfully solved the three major challenges of "high fluoride, high salt, and high lithium loss." With "corrosion-resistant titanium material + low-temperature MVR + cryogenic separation" as its core, it achieves high-level lithium resource enrichment and zero wastewater discharge. This case provides the lithium battery recycling industry with a standardized module that is efficient, low-consumption, and has a long cycle time, marking a new stage in the large-scale application of MVR technology in the field of new energy strategic resource extraction.