Application of Phosphonium Ionic Liquids as Ion Carriers in Polymer Inclusion Membranes (PIMs) for Separation of Cadmium(II) and Copper(II) from Aqueous Solutions

Abstract

Facilitated transport through polymer inclusion membranes (PIMs) is a promising method for simultaneous separation and removal of valuable and toxic metal ions from aqueous solutions. Recently, ionic liquids (ILs) have been used as extracting agents for metal ions due to their unique physicochemical properties. This paper presents research on the facilitated transport of cadmium(II) and copper(II) ions from aqueous chloride solutions through PIMs with phosphonium ILs as new selective ion carriers. Cellulose triacetate membranes containing o-nitrophenyl octyl ether (ONPOE) as a plasticizer and Cyphos IL 101 [trihexyl(tetradecyl)phosphonium chloride] or Cyphos IL 104 [trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate] as the ion carriers have been prepared and applied for investigations. Cd(II) ions were transported preferably from hydrochloric acid solutions containing Cu(II) ions through the PIMs. Higher selectivity coefficient of Cd(II) over Cu(II) (S_Cd/Cu) from 0.1 mol·dm^-3 hydrochloric acid was obtained for PIM with Cyphos IL 104 as the ion carrier. The influence of HCl and NaCl concentrations in the source phase on metal ion transport across PIM doped with Cyphos 104 was studied. It was found that the initial fluxes of Cd(II) and Cu(II) increase with increasing chloride ions concentration in the source phase. The selectivity coefficient for Cd(II) over Cu(II) decreases with increasing HCl concentration in the source phase. The results suggest that the separation system presented in this paper can be useful for the removal of Cd(II) from acidic chloride solutions in the presence of Cu(II).

Keywords: Cadmium(II); Copper(II); Cyphos IL 101; Cyphos IL 104; Polymer inclusion membrane (PIM).

Fig. 1

Extraction efficiency of Cd(II) and Cu(II) as a function of HCl concentration by ILs. a 0.1 mol·dm⁻³ Cyphos IL 101 in toluene; b 0.1 mol·dm⁻³ Cyphos IL 104 in toluene. Aqueous phase: 0.01 mol·dm⁻³ Cd(II) and 0.01 mol·dm⁻³ Cu(II) in HCl solutions

Fig. 2

Logarithm of selectivity coefficient (log₁₀ S _Cd/Cu) of Cd(II) over Cu(II) versus HCl concentration. Aqueous phase: 0.01 mol·dm⁻³ Cd(II), 0.01 mol·dm⁻³ Cu(II) in HCl; organic phase: 0.1 mol·dm⁻³ Cyphos IL 101 and 0.1 mol·dm⁻³ Cyphos IL 104 in toluene

Fig. 3

Plot of ln(c/c _i) versus time for Cd(II) and Cu(II) transport across PIM depending on the kind of ion carrier. PIM: 0.075 g CTA, 2.7 cm³ ONPOE/1 g CTA, 1.5 mol·dm⁻³ ion carrier; the source phase: 0.01 mol·dm⁻³ Cd(II), Cu(II) in 0.1 mol·dm⁻³ HCl; the receiving phase: 1 mol·dm⁻³ H₂SO₄

Fig. 4

Effect of HCl concentration in the source phase on the permeability coefficient (P) of Cd(II) and Cu(II) across PIM with Cyphos IL 104. PIM: 0.075 g CTA, 2.7 cm³ ONPOE/1 g CTA, 1.5 mol·dm⁻³ Cyphos IL 104; the source phase: 0.01 mol·dm⁻³ Cd(II), 0.01 mol·dm⁻³ Cu(II) in HCl; the receiving phase: mol·dm⁻³ H₂SO₄

Fig. 5

Relation of recovery factor [RF (%)] of Cd(II) and Cu(II) after 24 h versus HCl concentration in the source phase. Experimental conditions as in Table 3

Fig. 6

The permeability coefficient (P) of Cd(II) and Cu(II) versus chloride concentration in the source phase from NaCl solutions. PIM: 1.5 mol·dm⁻³ Cyphos IL 104, 2.7 cm³ ONPOE/1 g CTA; the source phase: 0.01 mol·dm⁻³ Cd(II) and 0.01 mol·dm⁻³ Cu(II); the receiving phase: 1 mol·dm⁻³ H₂SO₄

Fig. 7

The selectivity coefficient of Cd(II) over Cu(II) versus NaCl concentration. Experimental conditions as in Fig. 6