5t/h electrolyte lithium extraction MVR evaporator

Project Background and Raw Material Characteristics:
A large-scale electrolytic aluminum enterprise produces 500,000 tons of electrolytic aluminum annually. During the electrolyte recycling process, the lithium content continuously accumulates to 3-5%, leading to a decrease in electrolysis temperature and current efficiency. The enterprise is constructing a lithium recovery project with an annual processing capacity of 30,000 tons of lithium-containing electrolyte, employing a process route of "acid leaching purification + MVR evaporation concentration + cooling crystallization" to recover battery-grade lithium carbonate.

Raw Material Characteristics:

Source: Lithium-containing electrolyte acid leaching solution (sulfuric acid system)

Composition: Li⁺ 12-15g/L, Na⁺ 25-30g/L, K⁺ 8-12g/L, Al³⁺ <0.5g/L, SO₄²⁻ 80-100g/L

pH Value: 6.5-7.5 (after purification)

Process Capacity: 50m³/h (continuous feed)

MVR Evaporation System Technical Solution

1. Process Flow Design

Lithium-containing mother liquor → Preheater (plate type) → Falling film evaporator → Forced circulation evaporator (concentration section)

↓ Steam compressor (temperature rise 12℃) ← Secondary steam ← Gas-liquid separator

↓ Concentrated liquid (Li⁺ 45-50g/L) → Cooling crystallizer (40→25℃) → Centrifugal separation → Wet lithium carbonate

↓Condensate (reuse) → Mother liquor reflux → Drying and packaging

2. Core Equipment Parameters

Steam Compressor: Centrifugal, 315kW, 12t/h, compression ratio 1.15

Falling Film Evaporator: Heat exchange area 280m², TA10 titanium material, 6m tube length

Forced Circulation Evaporator: Heat exchange area 180m², circulation volume 800m³/h, axial pump power 75kW

Gas-Liquid Separator: Diameter 2.8m, height 6m, wire mesh demister

Preheater: Plate type, heat exchange area 45m², condensate waste heat recovery

3. Key Operating Control Parameters

Evaporation Temperature: 85±2℃

Concentration Endpoint Density: 1.28-1.32g/cm³

Steam Compressor Speed: 2800-3200rpm

Liquid Level Control: Falling film section 60%, forced circulation section 40%

Crystal Transfer Cycle: Solid content checked every 4 hours, centrifuge started if >15% Technical Challenges and Solutions

Challenge 1: Salt Separation in the Lithium Sulfate-Sodium Sulfate-Potassium Sulfate Ternary System

The electrolyte leachate has high Na⁺ and K⁺ concentrations. During evaporation, sodium sulfate and potassium sulfate preferentially precipitate, affecting the purity of lithium carbonate.

Solution: Adopt a stepwise evaporation strategy: The first stage uses MVR to control the concentration factor at 3-4 times. At this stage, the solubility of sodium sulfate/potassium increases due to the co-ion effect, remaining in the liquid phase. The second stage uses high-temperature flash evaporation to rapidly concentrate to above 45 g/L Li⁺, then transfers to cooling crystallization. The crystallizer is equipped with a washing leg structure to separate large lithium carbonate particles from the sodium and potassium salts entrained in the fine crystals using density differences. A portion of the mother liquor is discharged to the refrigerated denitrification system to control sodium and potassium accumulation.

Challenge 2: Corrosion and Abrasion of Titanium Welds

The sulfuric acid system combined with solid particles causes erosion corrosion at the evaporator inlets. Solution: The heat exchange tubes are made of TA10 titanium (Ti-0.3Mo-0.8Ni), which has better resistance to crevice corrosion than pure titanium. The tube sheet and heat exchange tubes are connected using a double connection of strength expansion and sealing welding to eliminate gaps. A ceramic liner is installed at the inlet of the forced circulation evaporator, reducing the flow velocity to below 1.5 m/s.

Challenge 3: Lithium carbonate crystallization particle size control. The product must meet battery-grade standards (D50 10-30 μm, >100 μm particles <5%). Solution: The cooling crystallizer uses a programmed cooling curve: 80℃→60℃ (rate 2℃/min, inducing nucleation), 60℃→30℃ (rate 0.5℃/min, crystal growth). A fine crystal removal system is configured: the washing liquid at the bottom of the crystallizer is separated into fine crystals by a hydrocyclone, dissolved, and returned to the evaporation system. The stirring paddle speed is 15-25 rpm to control the crystal suspension state and prevent secondary nucleation.

Investment and Return: System investment: RMB 18.5 million (including evaporator, compressor, crystallizer, and automatic control system). Annual operating cost: RMB 4.8 million (mainly electricity). Annual revenue: Lithium carbonate production value of RMB 24 million (based on RMB 120,000/t), saving RMB 3 million in hazardous waste disposal costs. Investment payback period: Approximately 1.1 years.

Technical Summary and Promotion Value: The technology in this case... The core of this technology lies in its customized salt separation strategy and crystallization control for the MVR system, addressing the complex compositional characteristics of lithium extraction from electrolytes. This achieves: High efficiency and energy saving: MVR technology reduces evaporation energy consumption to 20-30% of traditional processes, solving the high-energy-consumption bottleneck of high-salt wastewater treatment. High resource value: Extracting battery-grade lithium carbonate from waste with a lithium recovery rate >90%, resulting in high product added value. System reliability: Titanium material selection and anti-crystallization design ensure annual operating time >8,000 hours. Intelligent control: The DCS system achieves coupled regulation of density, temperature, and vacuum, reducing manual intervention. This process can be extended to fields such as lithium extraction from aluminum electrolytes, lithium spodumene/lepidolite sulfuric acid extraction, and waste battery recycling. It is a key equipment technology for new energy material production and the resource utilization of metallurgical waste.