Application of bidentate N,N'-donor extractants in the hydrometallurgical separation of base metals from an acidic sulfate medium,Application of bidentate N,N'-donor extractants in the hydrometallurgical separation of base metals from an acidic sulphate medium

Abstract

Bidentate imidazole-based extractants, 1-octylimidazole-2-aldoxime (OIMOX) and 1-octyl-2-(2"²-pyridyl)imidazole (OPIM), along with dinonylnaphthalene sulfonic acid (DNNSA) as a synergist, were investigated as potential selective extractants for Cu²⠺and Ni²⠺ respectively from base metals in a solvent extraction system. The study was extended to evaluate the sorption and separation of Ni²⠺ from other base metals in a solid-solution system using microspherical Merrifield resins and nanofibers functionalized with 2,2"²-pyridylimidazole. Copper was effectively separated with OIMOX and DNNSA as extractants from nickel with ΔpH½ ≈1.05 and the extraction order of Cu²⠺ > Ni²⠺ > Zn²⠺ > Cd²⠺> Co²⠺ was achieved as a function of pH. At pH 1.65 the extracted copper, from a synthetic mixture of the base metals reached 90.13(±0.90)%, and through a two-step extraction process 98.22(±0.29)% copper was recovered with negligible nickel and cobalt impurities. Stripping of the copper from the loaded organic phase using TraceSelect sulphuric acid at pH 0.35 yielded 96.60(±0.44)% of the loaded quantity after the second stage of stripping. The separation of Ni²⠺ from the borderline and hard acids; Co²⠺, Cu²⠺, Zn²⠺, Fe2²⠺, Fe²⠺, Mn²⠺, Mg2²⠺ and Ca²⠺ at a pH range of 0.5-3.5 with OPIM and DNNSA was acvieved to the tune of a ΔpH½≈ 1.6 with respect to cobalt from a sulfate and sulfate/chloride media. A three-stage counter-current extraction of Ni²⠺, at the optimized pH of 1.89, from a synthetic mixture of Ni²⠺, Co²⠺ and Cu²⠺, yielded 99.01(±1.79)%. The total co-extracted Cu²⠺ was 48.72(±0.24)% of the original quantity in the mixture, and it was 19.85(±0.28%) for Co²⠺. The co-extracted Cu²⠺ was scrubbed off from the loaded organic phase at pH≈8.5 by using an ammonium buffer, while co-extracted Co²⠺ was selectively and quantitatively stripped with Hâ‚‚SOâ‚„ at pH 1.64. The total recovery of Ni²⠺ by stripping at pH 0.32 was 94.05(±1.70)%. In the solid-liquid system, Ni²⠺ was separated from Co²⠺, Cu²⠺, and Fe²⠺ with the microspherical resins funtionalised with 2,2"²-pyridylimidazole by a separation factor (β) in the range 22-45. Electrospun nanofibers as sorbents yielded high sorption capacity in the range of 0.97 - 1.45 mmol.g⠻¹ for the same metals ions. Thus, 1-octylimidazole-2-aldoxime (OIMOX), and1-octyl-2-(2"²-pyridyl)imidazole (OPIM) can be effectively utilized alongside DNNSA as a co-extractant in the separation of Cu²⠺ and Ni²⠺ respectively from base metals in acidic sulfate medium in a solvent extraction process, and the latter as a selective ligand in the solid-liquid separation of Ni²⠺ from Co²⠺, Cu²⠺, and Fe²⠺.