Spent pickling liquor as industrial waste recover opportunities

Pickling is one of the essential steps in galvanizing industries in which hydrochloric acid (HCl) is used as the main composition to clean up the steel surface. This HCl lost its pickling efficiency because of decreasing in its concentration as well as increasing metals content because of dissolution processes. Recovery processes could be done to this kind of waste, so circular economics and a nearly zero waste cycle industry can be established. Processing SPL by electrodeposition is possible to recover pure metal from the waste solution. However, the presence of iron in the zinc chloride solution changes the nature and the conditions. It was found that the effect of iron concentration on the polarization curves is complex. Initially it has a negative effect on the generated cathodic current because of the enhancement of hydrogen bubble formation. Further increased iron concentrations may make the composition of the Zn-Fe deposit dominantly in favour of iron, resulting in a hydrogen dominated cathodic mechanism. Controlling the parameters such as Zn and Fe concentration, and the electrolyte's agitation intensity could play essential impacts on the electrodeposition of zinc from chloride media. Nevertheless, separation is still essential; thus, introducing the anion exchange separation to prepare the electrolyte is needed to achieve an acceptable quality of zinc deposition. In the relatively low concentration of HCl, Zn tend to be retained in the resin as its more likely to produce chloro-complex. As in the higher concentration of HCl (>1), Fe(III) distribution fucntion in HCl will increase thus the Fe may retain in the resin. However oxidation state control can be the answer of this problem by reducing Fe(III) to Fe(II) or in order to optimalize the separation process partially precipitation of Fe might be an option.