Extraction separation of Cu(II) and Fe(III) using a hydrophobic eutectic solvent TIBPS /octanoic acid

Recently, the processing of metals from secondary sources has been actively developing to meet the rapidly increasing demand for metals. The main secondary sources of metals are electronic and electrical wastes. Fe and Cu account for the largest share of the total amount of electronic waste. Therefore, effective separation of Cu and Fe is important in terms of comprehensive e-waste recycling. This problem can be solved via extraction methods using hydrophobic eutectic solvents (HESs). HES is considered a promising alternative to conventional extractants, which are organic extractants (carboxylic acids, oximes, DEHPA, TBP) dissolved in diluents (kerosene, toluene, chloroform). An important advantage of HES is its non-volatility, non-flammability, and the ability to control its properties by changing its composition.

In this work, the extraction of Fe(III) and Cu(II) using a hydrophobic eutectic solvent based on triisobutylphosphine sulfide (TIBPS) and octanoic acid was investigated.

HES was obtained by mixing TIBPS and octanoic acid in a molar ratio of 3:7, respectively. Extraction experiments were carried out at 25 °C and atmospheric pressure by stirring the aqueous and organic phases in a shaker at 45 rpm for 15 minutes.

During the work, the dependence of the extraction efficiency on the acid concentration, the phase ratio, and salting-out agent concentration were established. It was found that HES TIBPS/octanoic acid allows for the separation of metal ions at both low and high concentrations of hydrochloric acid with high separation coefficients (β_Cu/Fe=31.97 at 5 M HCl and β_Fe/Сu=1061.92 at <1M HCl). Cu(II) and Fe(III) can be stripped using aqueous solutions of 0.5 M Na₂S₂O₃ and 0.5 M H₂SO₄, respectively.

The results obtained open up prospects for using HES TIBPS/octanoic acid to develop effective hydrometallurgical processes for recovering Fe and Cu.