Reuse of Zinc: from Galvanized Scrap to Galvanized Steel. The Role of Cathodic Plasma Electrolysis

Zinc is the fourth widely consumed metal in the word, with a global refined output of 15 Mt in 2018. Half of the production of zinc is employed to produce galvanized steel, largely used in automotive and construction sector. The strong link between zinc and steel continues also at their end-life cycles, in steel mills employing Electric Arc Furnace (EAF) for the production of secondary, recycled steel from mostly galvanized scraps. The Zn-rich powdery wastes from EAFs (4-8 Mt per year) represent a valuable source for secondary zinc production. Driven by the Circular Economy paradigms, the aim of our current project is to demonstrate the feasibility of a hydrometallurgical process, based on the employment of Cathodic Plasma Electrolysis (CPE), for the direct production of galvanized steel using Zn-containing leachate solutions of the EAF dust. CPE is an electrochemical technique that, while working at atmospheric pressure and temperature, generates at the electrode surface a thin sheath of plasma (Fig. a) that assures peculiar properties to the treated sample. Its application ranges from surface cleaning/pre-treatment to coating deposition.1 In the present talk, some preliminary data will be discussed concerning the employment of CPE for both surface pre-treatment and galvanizing of steel in the form of plate and wire rod. Through a systematic study, electrolyte nature and concentration, temperature and applied potential have been identified as the most affecting operative parameters for both formation and stability of plasma (Fig. b). In optimized conditions, CPE carried out for 10-20 seconds in various blank solutions invariably showed a neat modification of the surface morphology (Fig. 1c) resulting into a neat increase of the surface roughness (from profilometry scans) of the sample, potentially useful to improve the adhesion of the zinc layer to be deposited. Concerning zinc electrodeposition, by exploiting design of experiment approach, many operative parameters were scanned to optimize uniformity, continuity and thickness of the resulting zinc layer (Fig. 1d). Acknowledgements: This work was funded by SIAT-Società Italiana Acciai Trafilati S.p.A and Engitec TECHNOLOGIES S.p.A