Nanofiltration Process Design for Sulfate Separation
16 Jul 2025
Here is the professional English translation of the Nanofiltration Process Design for Sulfate Separation:
Process Flow
graph LR
A[Raw Water Equalization Tank] --> B[Pretreatment System]
B --> C[Primary NF]
C --> D[Permeate (Low Sulfate)]
C --> E[Concentrate Secondary NF]
E --> F[Crystallization Unit]
F --> G[Gypsum Recovery]
subgraph **Core Sulfate Separation**
B -->|Cartridge Filtration + Weak-Acid Resin| C
C -->|SO₄²⁻ Rejection >95%| D
E -->|High-Rejection NF Membrane| F
F -->|CaCl₂ Precipitation + Centrifugation| G
end
Key Design Parameters
| Process Stage | Technical Measures | Configuration | Efficiency |
|---|---|---|---|
| Pretreatment | Self-cleaning Filter + Weak-Acid Cation Resin (D113) | Feed SS≤5mg/L, Hardness (Ca²⁺)≤50mg/L | Scaling Prevention >90% |
| Primary NF | Negatively-Charged Membrane (e.g., DuPont NF270) | Operating Pressure 8-12 bar, Recovery 75%, pH=6.5-7.0 | SO₄²⁻ Rejection ≥98% |
| Secondary NF Concentration | High-Pressure NF Membrane (Alfa Laval NF99) | Pressure 15-20 bar, Concentrate SO₄²⁻ >30,000 mg/L | 8× Concentration |
| Crystallization | Fluidized Bed Crystallizer + CaCl₂ Dosing | Ca²⁺:SO₄²⁻ Molar Ratio=1.05:1, Crystal Size ≥200μm | Gypsum Purity >92% |
Note: NF270 membrane ion rejection sequence: SO₄²⁻ (98%) > CO₃²⁻ (93%) > Cl⁻ (40%)
Membrane Fouling Control
-
Online Backwash
- Backwash every 30min for 60s (0.1% Citric Acid + 0.01% NaHSO₃ solution)
- Fouling Early Warning
if ΔP ↑ >15% or flux ↓ >10%:
Initiate electrochemical cleaning (EDTA+NaOH, pH=11)
Activate flux recovery program Resource Recovery & Economics
| Component | Performance | Economic Value (1,000m³/d Scale) |
|---|---|---|
| Permeate Quality | SO₄²⁻≤200mg/L (Compliant) | Saves ¥0.8/m³ treatment cost |
| Concentrate Crystallization | 92% Purity Gypsum | Byproduct Revenue ¥120/ton |
| Chemical Savings | Resin regeneration cycle ×3 | Annual savings ¥500K |
Contingency Plans
| Failure Mode | Automatic Response | Manual Intervention |
|---|---|---|
| Sudden TMP Rise | Switch to standby train + Auto-CIP | Scaling composition analysis |
| Crystallizer Clogging | Ultrasonic vibration + Flow adjustment | Seed crystal fluidizing agents |
| Resin Poisoning (Fe³⁺) | 10% HCl regeneration activation | Thermal regeneration (80°C) |
Case Study (Zinc Smelting Wastewater)
| Process Stage | Feed SO₄²⁻ (mg/L) | Permeate SO₄²⁻ (mg/L) | OPEX |
|---|---|---|---|
| Conventional Lime Precipitation | 12,500 | 1,200 | ¥6.8/m³ |
| This NF Process | 12,500 | 180 | ¥4.2/m³ |
| Concentrate | - | 32,000 | Gypsum Revenue ¥0.3/m³ |
Validation: Ion Chromatography (EPA 300.0) + XRD Gypsum Crystal Analysis
Smart Control System
graph TB
O[Online Sensors] --> P[PLC Controller]
P --> Q1[NF Flux Control Valve]
P --> Q2[Antiscalant Dosing Pump]
P --> Q3[Crystallizer pH Control]
subgraph **Real-Time Optimization**
P -->|Machine Learning| R[Predict Fouling Cycle]
R --> S[Dynamic Recovery Adjustment]
end
Full technical documentation including P&ID diagrams and membrane specifications available. Customizable for high-sulfate streams like mining wastewater and lithium brine.
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