Development of electrolyte filtration system for ECM taking into account removal of chromium (VI) ions

• Published in: Precision engineering Vol. 49; pp. 211 - 219
• Main Authors: Zhao, Yonghua, Kunieda, Masanori, Obi, Nobuaki, Watanabe, Shunjiro
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.07.2017
• Subjects: Activated carbon; Chromium removal; Cr(VI) reduction; Electrochemical machining; Electrolyte filtration; Electrolyte treatment; Scrap iron; Chromium removal; Cr(VI) reduction; Electrolyte treatment; Activated carbon; Electrochemical machining; Scrap iron; Electrolyte filtration
• ISSN: 0141-6359; 1873-2372
• DOI: 10.1016/j.precisioneng.2017.02.009

•Cr(VI) in NaNO3 electrolyte can be effectively removed by activated carbon.•Electrolyte purification by activated carbon has on influence on ECM.•Reduction of Cr(VI) in electrolyte is possible using scrap iron as reductant.•The pH of electrolyte solution should be strictly controlled during purification.•A filtration system for electrolyte purification of ECM process is proposed. During the ECM process, the metal workpiece is dissolved and turns into sludge which contaminates the electrolyte. To realize precise ECM with high cost-effectiveness, an electrolyte treatment system which can realize reuse of the electrolyte and maintain the electrolyte quality constant is significantly important and essential. Especially, in the ECM of alloys containing a certain level of chromium, it is very likely chromium dissolves to the toxic carcinogen Cr(VI). Therefore, an electrolyte filtration system is required for removing not only the sludge but also residual toxic ions in the electrolyte for health and environment conservation reasons. In this study, activated carbon and scrap iron, which are low cost and easily available materials, were newly utilized to reduce and remove toxic Cr(VI) ions. Experiments clarified that use of activated carbon has no influence on the machining ability of NaNO3 aqueous solution serving as the electrolyte. By adjusting the pH of the electrolyte to acidic, activated carbon can remove Cr(VI) from the NaNO3 aqueous solution electrolyte to a concentration of less than 0.1mg/L. On the other hand, scrap iron generated from metal cutting processes can be used to reduce Cr(VI) to non-toxic Cr(III). By mixing HNO3 into the electrolyte solution, the reduction efficiency of scrap iron on Cr(VI) improves significantly.