Magnesium Recovery from Nanofiltration Brine by Membrane Distillation Crystallization

Area of Science:

• Environmental Engineering
• Chemical Engineering
• Materials Science

Background:

• Hypersaline brine management is critical for sustainable water treatment.
• Membrane distillation crystallization (MDCr) offers a promising sustainable and cost-effective solution.
• Crystallization of magnesium sulfate (MgSO4) from nanofiltration (NF) brine presents unique challenges.

Purpose of the Study:

• To explore MgSO4 crystallization from synthetic NF brine using MDCr.
• To evaluate the impact of feed temperature and flow rate on MDCr performance.
• To investigate strategies for separating mixed MgSO4 and NaCl crystals.

Main Methods:

• Utilized membrane distillation crystallization (MDCr) with synthetic nanofiltration (NF) brine.
• Tested varying feed temperatures (41.8-64.5 °C) and flow rates (0.7-1.3 L/min).
• Analyzed the solubility of MgSO4 and co-crystallization behavior with other ions (Na+, K+, Cl-).

Main Results:

• Temperature significantly impacts MDCr performance and MgSO4 crystallization more than flow rate.
• Presence of other ions reduces MgSO4 solubility and promotes co-crystallization with NaCl.
• Optimized conditions (64.5 °C feed, 1.3 L/min flow) achieved 65.98% water recovery by delaying MgSO4 crystallization.
• Selective dissolution successfully separated NaCl from MgSO4 crystals.
• Permeate purity remained high (<5 μm/cm) across all tested conditions.

Conclusions:

• MDCr is effective for MgSO4 crystallization from NF brine.
• Higher temperatures enhance MgSO4 solubility, improving water recovery and reducing co-crystallization.
• A selective dissolution method can purify mixed salt crystals, ensuring high permeate quality.