Extraction Behavior and Separation of Precious and Base Metals from Chloride, Bromide, and Iodide Media Using Undiluted Halide Ionic Liquids

Within the framework of metal separations and solvent extraction, chloride media are among the most studied systems. Bromide and iodide media have received much less attention, but can allow a different selectivity during the extraction. In present research, the extraction behavior of several precious and base metal ions, i.e. Pt­(IV), Pd­(II), Rh­(III), Au­(III), Cu­(II), Fe­(III), and Ni­(II), from the different halide media was explored using the undiluted ionic liquid Aliquat 336 chloride and its bromide and iodide analogues. A single-step separation of Pt­(IV) and Pd­(II) from Fe­(III) and Ni­(II) was possible in the iodide system, but it was found to be incompatible with Au­(III) and Cu­(II). The chloride and bromide media showed potential for the separation of Au­(III), Pd­(II), Fe­(III), and Cu­(II), and their performance was subsequently compared. Fe­(III) and Cu­(II) were easily separated from Au­(III) and Pd­(II) via an extraction at low acid concentration followed by scrubbing with water for both systems. However, the stripping showed superior characteristics for the bromide system, where Pd­(II) could be recovered using a 0.2 mol L^–1 ammonia solution and Au­(III) using 1.0 mol L^–1 sodium sulfite. The proposed method for the separation of Au­(III), Pd­(II), Fe­(III), and Cu­(II) can be relevant for the recycling of waste electric and electronic equipment or analytical applications. The results highlight the importance of considering halides other than chloride, as both the extraction and stripping properties of the system can be changed.