Heavy Metal Removal from Aqueous Solutions Using a Customized Bipolar Membrane Electrodialysis Process

Area of Science:

• Environmental Science
• Water Treatment Technologies
• Analytical Chemistry

Background:

• Contamination of water sources with heavy metals (HMs) poses significant risks to public health and ecosystems.
• Existing water purification methods often struggle with efficient and cost-effective removal of diverse HM pollutants.
• There is a critical need for advanced technologies to ensure safe water availability and mitigate HM-induced diseases.

Purpose of the Study:

• To investigate the efficacy of a customized bipolar membrane electrodialysis (BMED) process for removing heavy metals from aqueous solutions.
• To analyze the influence of operational parameters such as feed ionic strength, electrical potential, and HM type/concentration on BMED performance.
• To elucidate the mechanisms underlying heavy metal removal and membrane interactions during the electrodialysis process.

Main Methods:

• A custom bipolar membrane electrodialysis stack was employed for heavy metal removal experiments.
• Systematic variation of feed ionic strength (NaCl concentration), applied electrical potential, and initial concentrations of Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, and Ni²⁺.
• Analysis of feed solution pH changes, heavy metal speciation, membrane surface analysis (SEM-EDX), and mass balance calculations.

Main Results:

• The BMED process demonstrated effective removal of heavy metals, with removal efficiency influenced by operational conditions.
• Optimal performance was observed at 1.5 g/L NaCl, with HM removal increasing linearly with concentration up to 30 mg/L and applied potential up to 15 V.
• Heavy metal removal order was generally Cd²⁺ > Ni²⁺ > Co²⁺ > Cu²⁺ > Cr³⁺, with evidence of HM sorption onto both cation and anion exchange membranes.

Conclusions:

• The customized bipolar membrane electrodialysis process is an efficient technology for separating heavy metals from water.
• The process exhibits beneficial features including diluate pH adjustment, reduced electrical resistance, and effective multivalent cation removal via anion exchange membranes.
• Heavy metal removal occurs through diffusion, migration, and subsequent sorption onto the electrodialysis membranes.