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

In the present study, the possibility of using a spiral-wound diffusion dialysis module was studied for the separation of hydrochloric acid and Zn2+, Ni2+, Cr3+, and Fe2+ salts. Diffusion dialysis recovered 68% of free HCl from the spent pickling solution contaminated with heavy-metal-ion salts. A higher volumetric flowrate of the stripping medium recovered a more significant portion of free acid, namely, 77%. Transition metals (Fe, Ni, Cr) apart from Zn were rejected by >85%. Low retention of Zn (35%) relates to the diffusion of negatively charged chloro complexes through the anion-exchange membrane. The mechanical and transport properties of dialysis FAD-PET membrane under accelerated degradation conditions was investigated. Long-term tests coupled with the economic study have verified that diffusion dialysis is a suitable method for the treatment of spent acids, the salts of which are well soluble in water. Calculations predict significant annual OPEX savings, approximately up to 58%, favouring diffusion dialysis for implementation into wastewater management.

Recovery of Spent Sulphuric Acid by Diffusion Dialysis Using a Spiral Wound Module.

In this study, we assess the effects of volumetric flow and feed temperature on the performance of a spiral-wound module for the recovery of free acid using diffusion dialysis. Performance was evaluated using a set of equations based on mass balance under steady-state conditions that describe the free acid yield, rejection factors of metal ions and stream purity, along with chemical analysis of the outlet streams. The results indicated that an increase in the volumetric flow rate of water increased free acid yield from 88% to 93%, but decreased Cu2+ and Fe2+ ion rejection from 95% to 90% and 91% to 86%, respectively. Increasing feed temperature up to 40 °C resulted in an increase in acid flux of 9%, and a reduction in Cu2+ and Fe2+ ion rejection by 2-3%. Following diffusion dialysis, the only evidence of membrane degradation was a slight drop in permselectivity and an increase in diffusion acid and salt permeability. Results obtained from the laboratory tests used in a basic economic study showed that the payback time of the membrane-based regeneration unit is approximately one year.