Supercritical Fluid Extraction: A Study on Metal Recovery and Regeneration of β‐Diketones and Organophosphorus Extractants

Abstract

For the design of extraction processes that are feasible both environmentally and economically, suitable extractants are required that result in high extraction and that are recyclable. Therefore, the relation between metal‐complex stability and extractant dissociation at standard conditions has been investigated. Complex stability versus dissociation of extractants with non‐coordinating side chains resulted in a linear reference line. This line helps finding extractants optimised for both extraction (of metals) and recovery (of extractants and metals). The solubilities of acetylacetonate complexes with Cu, Zn, Ni, and Co in supercritical CO₂ were determined. Regeneration experiments under supercritical conditions have been carried out using a packed countercurrent column. Metal recovery of Cu, Zn, Ni, and Co from supercritical CO₂ into nitric acid was shown by decomplexation from both a β‐diketone (acetylacetone) and an organophosphorus compound (Cyanex 272).

Keywords:

• Supercritical
• extraction
• metal‐complex
• recovery
• dissociation
• β‐diketone
• organophosphorus

Acknowledgments

We thank Robin J. van Velde for his contribution to this work, Daniela Trambitas‐Popescu for her helpful discussions, and SENTER (Den Haag, NL) for the financial support of the IOP project IZW 97407.