Recovery of Hydrochloric Acid from Industrial Wastewater by Diffusion Dialysis Using a Spiral-Wound Module

Industrial processes often produce acidic wastewaters containing heavy metals, which pose environmental risks. Prior research has shown that acid recovery is possible using membrane technologies. However, the efficiency of these methods in recovering acid while rejecting metal ions remains unclear. This gap motivated the current investigation into diffusion dialysis as a potential solution. Existing methods struggle with the simultaneous recovery of acid and rejection of transition metals. The solubility of metal chlorides in water complicates separation. No prior work had resolved the issue of selective acid recovery from such complex mixtures. The need for cost-effective and sustainable acid recovery methods is evident. This study addresses the challenge by evaluating a specific membrane configuration.

The study aimed to assess the feasibility of using a spiral-wound diffusion dialysis module for recovering hydrochloric acid from industrial wastewater. The specific problem addressed is the separation of HCl from metal salts like Zn2+, Ni2+, Cr3+, and Fe2+. The motivation stems from the environmental and economic benefits of acid recovery. The researchers sought to determine the efficiency of acid recovery and metal ion rejection. They also wanted to evaluate the membrane's performance under accelerated degradation conditions. The study's goal was to provide a practical solution for industrial acid recovery. The findings could inform wastewater treatment strategies. The focus was on achieving high acid recovery while minimizing metal ion contamination.

The researchers employed a spiral-wound diffusion dialysis module to separate HCl from metal salts in a spent pickling solution. They used an anion-exchange membrane to facilitate acid diffusion. The process involved varying the volumetric flowrate of the stripping medium to assess its impact on acid recovery. The mechanical and transport properties of the FAD-PET membrane were tested under accelerated degradation conditions. The rejection of transition metals was measured to evaluate membrane performance. The study included long-term operational tests to assess durability. Economic analysis was conducted to estimate operational cost savings. The results were compared against established separation methods to determine feasibility.

The study found that diffusion dialysis recovered 68% of free HCl from the spent pickling solution. Increasing the stripping medium's flowrate to a higher value improved recovery to 77%. Transition metals like Fe, Ni, and Cr were rejected by more than 85%. In contrast, Zn showed a lower retention rate of 35%. This difference was attributed to the diffusion of chloro complexes through the anion-exchange membrane. The FAD-PET membrane maintained its mechanical and transport properties under accelerated degradation conditions. Long-term tests confirmed the membrane's suitability for industrial applications. Economic calculations predicted annual OPEX savings of up to 58%, supporting the method's viability.

The authors concluded that diffusion dialysis is a suitable method for recovering hydrochloric acid from industrial wastewater. The study demonstrated that the spiral-wound module effectively separates HCl from metal salts. The high rejection of transition metals supports the method's effectiveness. The lower retention of Zn was explained by the diffusion of chloro complexes. The membrane's performance under accelerated degradation conditions was satisfactory. Long-term tests confirmed the method's durability. Economic analysis favored diffusion dialysis for wastewater treatment. The findings suggest that this approach could be implemented in industrial settings.