Multistep treatment of a complex electrolyte for removal of heavy metal ions and recycling in electrochemical machining

During electrochemical machining (ECM) of metals, the electrolyte gets polluted by heavy metal ions and compounds. This creates crucial process control problems due to variation in electrical conductivity and is an environmental threat if the solution is discharged without treatment. In this study, an economical, simple multistep treatment system based on ion-exchange was developed to remove metal ions from the polluted electrolyte. We specifically looked at the electrolytic discharge from ECM of copper pieces, which is widely used in biomedical and electronic applications. Three different ion-exchange media were used: (1) a natural zeolite, (2) a special type of adsorbent quantitative filter paper, and (3) a polymer-based synthetic cation-holder resin (Lewatit TP 207) that works well with copper ions. Optimization studies for pH and contact time showed the following: (1) by using zeolite alone, and after 2 h of mixing, 43.2% of Cu²⁺ could be removed; (2) by using the filter paper alone, and after three times of filtration, 90% of Cu²⁺ could be removed; and (3) by using Lewatit TP 207 alone, 100% of Cu²⁺ could be removed. While Lewatit TP 207 allowed for 100% removal of Cu²⁺, its use alone is costly and troublesome due to constraints from service life and multistep regeneration and conditioning with strong acids and bases, respectively. The most simple and economical scheme for removal of Cu²⁺ and recycling the electrolyte for reuse was the three-step zeolite-filter-resin treatment system.