Solvent Extraction of Copper and EDTA in Electroless Copper Plating Wastewater Using a Quaternary Ammonium Salt

Abstract

To separate both copper and 2,2',2'',2'''-(ethane-1,2-diyldinitrilo)tetraacetic acid (EDTA) from the waste electroless copper plating solution by solvent extraction, the liquid–liquid equilibria of the copper-EDTA complex and unbound EDTA ion were experimentally measured. An organic solution of tri-n-octylmethylammonium chloride (TOMACl) was used as solvent. The kerosene solution of TOMACl could extract both copper-EDTA complexes and EDTA ions from the model wastewater. The fractional removal and distribution ratios of both the copper-EDTA complex and EDTA ions decreased as the pH increased. The valence number of the major copper-EDTA complex or EDTA ion in the aqueous phase increased with pH, and the number of TOMA+ cations required to chelate the complexes and ions increased. These complexes and ions had lower reactivity with TOMACl owing to steric hindrance. These effects caused lower removal of both copper and EDTA in a higher pH range, which is a typical condition of waste electroless copper solution.