Liquid-Liquid Extraction of Tetravalent Zirconium from Acidic Chloride Solutions Using Cyanex 272

Abstract

The liquid-liquid extraction of zirconium(IV) from acidic chloride solutions was carried out with Cyanex 272 as an extractant diluted in kerosene. An increase of the acid concentration decreased the percentage extraction of metal, which indicates that the extraction follows ion exchange-type mechanism: MO²⁺_(aq) + 2(HA)_2(org) ↔ MO (HA₂)_2(org) + 2H⁺_(aq), where, M = Zr(IV); HA = Cyanex 272. The extraction of Zr(IV) increases with an increase of the extractant concentration. In a plot of log D vs. log[extractant], M is linear with a slope of ∼2, indicating the association of two moles of extractant with the extracted metal species. On the other hand, the extraction decreases with an increase of the H⁺ ion concentration. A plot of log D vs. log[H⁺] gave a straight line with a negative slope of 1.7, indicating the exchange of two moles of hydrogen ions for every mole of Zr(IV). The effect of the Cl^- ion concentration at a constant concentration of [H⁺] did not show any change in the D values. The addition of sodium salts enhanced the percentage extraction of metal, and followed the order of NaSCN > NaNO₃ > Na₂SO₄ > NaCl. The stripping of metal from the loaded organic (L.O) with different acids indicated sulfuric acid to be the best stripping agent. An increase of the temperature during the extraction and stripping stages increases the metal transfer, showing that the process is exothermic. The synergism, regeneration and recycling capacity of Cyanex 272; the extraction behavior of associated elements, such as Hf(IV), Ti(IV), Al(III), Fe(III); and IR spectra of the extracted Zr-Cyanex 272 complex were studied.