Recovery of acid from spent pickling solution by diffusion dialysis with anion exchange membrane

When etching steel, waste products such as spent etching solutions containing free acids and metal salts are formed, and such solutions must be recycled or disposed of. The article shows the possibility of using dialysis to isolate hydrochloric acid from these solutions. The advantage of this membrane method is the compactness of the equipment, the possibility of partial regeneration of wastewater components and the organization of a closed cycle of chemical consumption in production, as well as the possibility of combination with other membrane methods. The process of diffusion dialysis of a model solution containing hydrochloric acid (1.5 mol/dm3) and iron (III) chloride (0.25 mol/dm3) has been studied. The experiment was carried out in a two-chamber countercurrent dialyzer with an anion exchange membrane MA-41 in the recycle mode. The efficiency of separation of the solution components is characterized by such process parameters as acid fluxes through the membrane, separation coefficient, and salt rejection coefficient. The process was carried out in two versions: with the volume ratios of the giving (feeding) and receiving solutions equal to 1:1 (first variant) and 2:1 (second variant). During dialysis of the studied model solution, the following values of the hydrochloric acid/iron (III) salt separation coefficients were obtained for the first and second variants, respectively: 27.2 and 19.2. The volume ratio of the giving and receiving solutions, equal to 2:1, allows us to obtain a hydrochloric acid solution of a given concentration in less time than with a volume ratio of giving and receiving solutions equal to 1:1. The advantage of the first variant of the experiment is the possibility of obtaining a cleaner target product, namely a solution of hydrochloric acid (with a lower content of iron (III) salt).