Experimental investigation and modelling for sulphuric acid recovery by diffusion dialysis

Sulphuric acid is known to be one of the key inorganic acid and has been widely used in chemical reaction and metal industries for surface treatments as in the copper electroplating process. During these processes, large amounts of waste sulphuric acid solution are generally generated, containing high concentrations of metals and acid. The possibility of recover and reuse the sulphuric acid in the process could avoid environmental contamination and reduce costs of the disposal. Among several separation methods, diffusion dialysis (DD) is becoming more and more attractive thanks to the recent important advances in ion exchange membranes (IEMs) field and because of its clean nature and operational simplicity, low installation and operating costs and low energy consumption [1,2]. In the present work, two single-cell diffusion dialysis modules, equipped with commercial anion exchange membranes, with different dimensions, were employed. The first consisted in a laboratory-scale DD unit (10x10cm2) operated in a batch configuration to study the effect of process parameters on the efficiency of H2SO4 recovery. The latter consisted in a large-scale DD unit (80 cm long) operated in a continuous configuration to simulate the process operation at the industrial scale. Acid recovery has been evaluated at different operative conditions. In both the cases, the effect of the presence of copper salt on the acid recovery was also evaluated. In addition, the mathematical model for the DD process, developed and validated with experimental data previously obtained for HCl case [3], has been adapted and validated with experimental data obtained in this work. Membrane behaviors to H2SO4 diffusion were compared with results obtained for HCl [3]. Opposite to the HCl case, H2SO4 diffusion permeability tends to decrease when increasing the solution concentration and the presence of copper reduces sulphuric acid recovery.