The extraction of Fe(III), Ni(II) and Co(II) from a Ni(II)-Co(II) solution containing Fe(III) was analyzed in a chloride medium using a mixed extractant consisting of 50% ( v /v) tributyl phosphate (TBP), 20% (v/v) 2-octanol and 30% (v/v) kerosene. The extraction of 0.5 mol/L Fe(III) in 4 mol/L hydrochloric acid reached 97%, and the consumption of chloride ions was investigated. Nickel(II) ions were not detectably extracted by TBP, with an inclusion of <1.1%. Compared with Fe(III), TBP extracted only a small amount of Co(II). The iron complexes formed by TBP and 2-octanol were [H 2 FeCl 4 · 2TBP] and [H 2 FeCl 4 · 5(2-octanol)], and the possible compositions of Co-containing extracts were [H 2 CoCl 4 · 2TBP] and [H 2 CoCl 4 ] · n[2-octanol]. An industrial process consisting of two-step extraction was designed to achieve the separation of Co(II) and Fe(III), resulting in a decrease in the Fe/Co mass ratio from 0.46 to <3.5 × 10 −4 in the raffinate.
An ion-imprinted polymer (IIP) was synthesized by radical copolymerization for use in the removal of trace Fe(III) ions from Cr(III)-containing solutions. During the synthesis process, Fe(III) ions, acrylic acid and ethylene glycol dimethacrylate were employed as the template ions, functional monomer and cross-linker, respectively. The optimal mole ratio of acrylic acid to Fe(III) ions, which significantly affected the adsorption performance, was determined. The maximum static adsorption capacity of the polymer for Fe(III) ions was 114.25 mg g −1 , with a selective factor ( k ) of 492.18 and a relative selective factor ( k′ ) of 50.87 for Fe(III)/Cr(III). The Fe(III) ions removal efficiency could reach 94.43%, leading to a final Fe(III) concentration of 0.053 mg L −1 in the treated solution. After the removal process, the mass ratio of Cr(III) ions to Fe(III) ions was higher than 26, 000:1 in the solution, with an initial mass ratio of Cr(III) to Fe(III) ions of 1500:1.
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