LIQUID – LIQUID EXTRACTION OF VANADIUM (V) FROM PERCHLORIC ACID SOLUTIONS BY TRIOCTYLPHOSPHINE OXIDE

Many inorganic acids lack counter-ions required for the formation of extractable metal species thereby necessitating a continuous search, which has been extended to perchloric acid (HClO4) used in the current work with trioctylphosphine oxide (TOPO) extractant dissolved in purified kerosene to extract vanadium (V). Batch extractions were carried out in a separating funnel mechanically shaken at 120 rpm. The analysis of the V (V) content of the aqueous and organic phases were by UV – visible spectrophotometry based on hydrogen peroxide complex formation method. Various experimental conditions that could affect the percentage V(V) extraction (extraction efficiency, E%) were investigated. With increase in concentration of HClO4 at the studied range (1.0 – 6.0 mol dm-3), the extraction efficiency increased to an optimal value of 43.3 % at [HClO4] = 6.0 mol dm-3 at an ionic strength of [NaClO4] = 0.1 mol dm-3 and extractant concentration of log [TOPO] = - 1.19 mol dm-3, and least (E % = 10.0) at [HClO4] = 5.0 mol dm-3, while an intermediate value of E% = 33.3 was observed at [HClO4] = 3.0 mol dm-3, which was employed for a substantial part of the work to avoid TOPO degradation at higher concentrations. The mixing of other extractants with TOPO was found non synergistic to V (V) extraction. Increased ionic strength was observed to have no appreciable effect on the extraction efficiency. All the added foreign ions increased the E% for V (V), highest with V4+ (E% = 50.0) and Sr2+ (E% = 46.7) compared with E% = 33.3 without added foreign ion. Based on analytical and spectra data, the mechanism of extraction was deduced to be by the formation of two different extractable species VO2ClO4 . TOPO and (VO2ClO4)m . nTOPO (where m >> n) at lower and higher concentrations, respectively. It could be inferred at the studied conditions that TOPO was slightly efficient for the removal of V (V) from HClO4 solutions.