Abstract— <p>The work is devoted to the study of the possibility of extraction separation of copper(II) and iron(III) ions from hydrochloric acid solutions using hydrophobic eutectic solvents as extractants. For the first time, new eutectic solvents triisobutylphosphine sulfide/octanol and triisobutylphosphine sulfide/octanoic acid are proposed and characterized. The eutectic solvents have low viscosity (&lt;8 mPa s), which makes them technologically suitable extractants. A comparative analysis of the efficiency of Cu(II) and Fe(III) extraction with eutectic solvents is carried out, where menthol, octanol, and octanoic acid are used as hydrogen bond donors. Of greatest interest is the eutectic solvent based on octanoic acid, which is capable of selectively extracting metal ions in a wide range of aqueous phase acidity. In the absence of hydrochloric acid in the initial solution, β_Fe/Cu amounts to 1432. The regularities of metal ion extraction are established by varying the process conditions: acidity of the aqueous phase, volumetric ratio of the phases, and concentration of the salting-out agent. An assessment is made of the possibility of purifying eutectic solvents from metal ions using different stripping agents. The potential of using the proposed extraction systems for solving the problem of selective extraction of metal ions from process solutions is demonstrated.</p>