A Comparison of Liquid and Supercritical Carbon Dioxide as an Extraction Solvent for Plating Bath Treatment

Because of increasing federal regulations, alternative metal recovery methods for spent electroplating baths are needed. Supercritical extraction of waste metals using CO 2 is potential candidate for this process. However, because of the high-cost of supercritical fluid processing equipment, an extraction system modeled on the use of liquid CO 2 rather than supercritical CO 2 may be more economical. For this reason, the use of liquid CO 2 containing β-diketones as an extraction solvent for the removal of Ni 2+ and Zn 2+ from an electroplating solution was investigated and compared to results obtained with supercritical CO 2 . Acetylacetone (ACAC) and its fluorinated analogues were used as the ligands for the extraction of Ni 2+ and Zn 2+ from the electroplating bath. While the fluorinated ACAC showed a potential for a higher extraction efficiency, over 70% of both Ni 2+ and Zn 2+ was extracted using both liquid and supercritical CO 2 using a 100-fold molar excess of ACAC. With isopropyl alcohol as a modifier, extraction efficiency was increased to over 80% for both metals using both phases of CO 2 as the carrier fluid.