Chemical recycling of galvanized steel scrap

Abstract

The chemical recycling of galvanized steel was investigated by preferential dissolution of the galvanized coating (dezincing or degalvanization) in a variety of acidic environments comprising dilute and moderately concentrated nitric, hydrochloric and sulphuric acids. Weight loss immersion tests were conducted for galvanized steel in the various acidic environments. It was generally observed that the more concentrated acids (10% or more) reacted or dezinced much faster with greater inherent attack on the steel substrate while the more dilute acids (2% or less) reacted very slowly with partial or ineffective dezincing. Optimum results were obtained at intermediate (5%) acid concentrations with little or no attack on the underlying steel substrate, except in 5% HNO₃. It was suggested that two competing cathodic reactions, hydrogen evolution and oxygen reduction, simultaneously occurred in this characteristic oxidizing environment (5% HNO₃) leading to high corrosion rates observed, the remedy of which lies in electrolyte deaeration or use of appropriate corrosion inhibitors. These findings were fully supported with optical microscopy. The various factors favouring or hindering the galvanized steel recycling and the scope for possible scrap product utilization were discussed.