Research on neutralization of wastewater from pickling and electropolishing processes

Abstract

Process baths used for electropolishing and pickling of stainless steel have become increasingly contaminated with heavy metal ions over time. There is still lack of research on the neutralization of this type of technological wastewater with high concentrations of metal ions and containing complexing compounds, which significantly hinders their effective treatment. The aim of this paper is to study how the selected methods of heavy metals removal will affect the quality of the treated, industrial post-galvanic sewage from pickling and electropolishing of chromium-nickel steel on a laboratory and technical scale. The research used sodium sulphide or a decomplexing agent based on organic sulphur to neutralize wastewater containing triethanolamine or glycerol. Treatment of electropolishing wastewater poses a challenge. Nevertheless, wastewater with glycerol is easier to neutralize than those containing triethanolamine. In the industrial scale the use of a decomplexing agent is necessary to achieve the required nickel values in the wastewater after treatment below 1 ppm. Even in the case of high concentrations of nickel ions in raw wastewater, the neutralization process of the wastewater originating only from pickling alone was effective. The search for effective methods of neutralization of mixed wastewater is especially important in industrial conditions, where it is not always possible to completely separate these two types of sewage. The paper also presents the results of the composition of post-neutralization sludge, which may be useful in planning further management and disposal of this type of waste.

Keywords

• stainless steel
• heavy metals
• contaminants removal
• nickel
• industrial scale
• electrochemical polishing