A review on methods of regeneration of spent pickling solutions from steel processing

The review presents various techniques of regeneration of spent pickling solutions, including the methods with acid recovery, such as diffusion dialysis, electrodialysis, membrane electrolysis and membrane distillation, evaporation, precipitation and spray roasting as well as those with acid and metal recovery: ion exchange, retardation, crystallization solvent and membrane extraction. Advantages and disadvantages of the techniques are presented, discussed and confronted with the best available techniques requirements. Most of the methods presented meet the BAT requirements. The best available techniques are electrodialysis, diffusion dialysis and crystallization; however, in practice spray roasting and retardation/ion-exchange are applied most frequently for spent pickling solution regeneration. As “waiting for their chance” solvent extraction, non-dispersive solvent extraction and membrane distillation should be indicated because they are well investigated and developed. Environmental and economic benefits of the methods presented in the review depend on the cost of chemicals and wastewater treatment, legislative regulations and cost of modernization of existing technologies or implementation of new ones.