Effects of metal ions on diffusion dialysis of inorganic acids

Diffusion dialysis has been studied to investigate the effects of metal species on its performance for recovery of inorganic acids. It was observed that metal–acid complex formation affected the selectivity and flux of the diffusion dialysis operations due to the existence of negatively-charged complexes. In the limited concentration ranges, nearly 90% of HCl, HNO3, and H2SO4 were recovered. Of five metal species investigated, Fe, Ni, Cr, and Cu in the feed solutions were rejected reasonably by the dialysis membrane, while Zn in the HCl solution leaked through the membrane significantly. Moreover, the high Zn content decreased the mobility of the acid in the membrane. Proton release from formation of Fe–F complexes in a HF–HNO3 acid mixture gave the unusual result of a nitric acid recovery exceeding 100%.