Mechanism of poisoning hydroxyoximes by cobalt in different organic systems

Abstract

Poisoning of 2-hydroxy-5-nonylbenzaldoxime (Mextral 84H) by cobalt in the presence of neodecanoic acid (Versatic 10) and bis(2-ethylhexyl) phosphoric acid (P204) diluted in aliphatics was comparatively studied. The cobalt-organic extractants species structure and stoichiometry were determined by slope analysis, Fourier transform infrared (FT-IR) spectrometer, visible absorption and cyclic voltammetry. It is found that P204 can significantly inhibit the poisoning of Mextral 84H by cobalt and the poisoning is weakened with the increase of P204 concentration while Versatic 10 has no effect on it. The stoichiometries of adducts formed in the organic phase with Mextral 84H (HL) in the presence of Versatic 10 and P204 (HA) are CoL2 · 2H2O and Co(H2A2L2), respectively. The divalent cobalt in the CoL2 · 2H2O complex is easily oxidized to trivalent cobalt because of its inner-orbital d2sp3 hybridization, resulting in low oxidation potential and the poisoning of Mextral 84H by cobalt in the presence of oxygen. With the addition of P204, the hybridization configuration of the cobalt complex transforms from d2sp3 to the more stable sp3d2, and the oxidation potential of divalent cobalt in the organic phase significantly increases to prevent the Co(H2A2L2) complex from being oxidized, resulting in the significantly inhabitation of the poisoning Mextral 84H by cobalt in the presence of oxygen.