Hybrid membrane process for the recovery of major components (zinc, iron and HCl) from spent pickling effluents

The separation and recovery of the major components contained in spent pickling effluents, that is, iron, zinc and HCl, is a key issue in the definition of sustainable treatments of this kind of industrial effluents. We propose a hybrid membrane process consisting first of a liquid membrane step that generates a raffinate highly concentrated in iron chloride and a mixture of HCl and zinc chlorides in the stripping phase. Second, diffusion or Donnan dialysis have been applied to the stripped solution in order to further separate the acidic stream in the diffusate from a solution containing zinc chlorides in dialyzate. Industrial effluents with an average composition of 1.2 kmol/m3 of Zn, 1.6 kmol/m3 of Fe, and 6.5 kmol/m3 of HCl were previously used to analyse the kinetics of the metallic separation with the emulsion liquid membranes; this study reports the experimental and theoretical analysis of membrane dialysis of the stripped solution; the influence of operative variables such as concentration of HCl (0.5 to 3.0 kmol/m3) and ZnCl2 (0.25 to 1.0 kmol/m3), type of the anion-exchange membranes, and the basicity of the stripping agent on the dialysis flux and selectivity has been analysed.