Separation of Copper(II) from Base Metals in an Acidic Synthetic Sulfate Leach Solution Using a Novel 1-Octylimidazole-2-Aldoxime Extractant

Abstract

The design and application of a novel bidentate imidazole-oxime extractant, 1-octylimidazole-2-aldoxime, for the separation of copper from base metals in a solvent extraction system is presented in this report. This extractant was used alongside dinonylnaphthalene sulfonic acid (DNNSA) as a bulky counterion, and an optimized molar ratio of 1:60 for the metal ions to the extractant was used while the DNNSA concentration was 0.020 M. The effective separation of copper from the other base metals was achieved under these conditions with good extraction efficiency in Shellsol 2325 as diluent. The ΔpH 0.5 ≈ 1.05 was obtained for the separation of copper from nickel in the extraction order of Cu²⁺ > Ni²⁺ > Zn²⁺ > Cd²⁺> Co²⁺ as a function of pH. At pH 1.65 the extracted copper from a synthetic mixture of the base metals reached 90.1%, and this method required a two-step extraction process to recover 98.2% copper with negligible nickel and cobalt impurities. The stripping of the copper from the loaded organic phase using TraceSelect sulfuric acid at pH 0.35 yielded 96.6% of the loaded quantity after the second stage of stripping. An investigation of the chemistry involved in this separation system showed that the species formed between the metal ions and the ligand, 1-methylimidazole-2-aldoxime, are isostructural with an octahedral geometry from the evidence of solid-state studies. The second stability constants (log β₂) for the complex formation reactions were of the order; Cu²⁺ (14.9) > Ni²⁺ (14.4) > Zn²⁺ (8.8) > Co²⁺ (8.7), which is the same pH-metric order of the extraction curves. Thus the separation of copper from the other base metals was thermodynamically driven. Therefore, 1-octylimidazole-2-aldoxime, with its bidentate character in coordination, proved useful for application as an extractant of copper from other base metals in a sulfate medium.

Keywords:

• base metals
• imidazole-oxime
• stability constants
• sulfate medium

Acknowledgments

For financial support to carry out this research, we thank the National Research Foundation (South Africa) and Rhodes University (JRC and Mellon Foundation Scholarship). We also thank Shell Chemicals (SA) (Pty) Ltd for supplying Shellsol 2325.