Treatment of Spent Pickling Solutions by Diffusion Dialysis Using Anion-Exchange Membrane Neosepta-AFN

This article presents the possibility of using diffusion dialysis for processing spent pickling solution from pickling stainless steels with a mixture of nitric acid and hydrofluoric acid. A counter-current two-compartment dialyzer equipped with an anion-exchange membrane Neosepta-AFN was used to study and compare the diffusion dialysis of model mixture of hydrofluoric acid and ferric nitrate and a real spent pickling solution. The separation efficiency was characterized by the acid recovery yield, the rejection coefficient of the metals, the permeability coefficient of the membrane, and the separation factor. These characteristics were calculated from the data obtained at steady state. For the real spent pickling solution tested, the permeability values of nitrates 1.7 × 10^-6 m s^-1, fluorides 0.4 × 10^-6 m s^-1, and ferric ions 1.1 × 10^-7 m s^-1 were achieved. The separation factor for nitrates/ferric ions was 15.7 and 3.6 for fluorides/ferric ions. Furthermore, the dependencies of recovery yield and rejection for different concentrations of hydrofluoric acid and ferric nitrate were determined.