3-Phenyl-4-Acyl-5-Isoxazolones as Reagents for Liquid-Liquid Extraction of Tetravalent Zirconium and Hafnium from Acidic Chloride Solutions

Extração líquido-líquido de zircônio e háfnio tetravalentes, a partir de soluções de ácido clorídrico, foi investigada usando-se 3-fenil-4-acil-5-isoxazolonas em xileno, tais como 3fenil-4-benzoil-5-isoxazolonas (HPBI), 3-fenil-4-(4-fluorobenzoil)-5-isoxazolona (HFBPI) e 3-fenil-4-(4-toluoil)-5-isoxazolona (HTPI). A extração de zircônio(IV) / háfnio(IV) mostrou um mecanismo de troca iônica: MO (aq) + 2 HA (org) ↔ MOA 2 (org) + 2 H (aq) , onde M = Zr(IV) / Hf(IV) e HA = HPBI ou HFBPI ou HTPI. A variação dos valores D (razão [MOA 2 ] (org) / [MO] (aq) ; prováveis espécies em equilíbrio durante a extração) com o aumento da concentração ácido/extrator mostrou um gráfico linear com inclinação 2. O efeito da natureza dos diluentes, como tetracloreto de carbono, ciclohexano, n-hexano, benzeno, nitrobenzeno, xileno, tolueno e clorofórmio na extração de zirônio(IV) / háfnio(IV) foi estudado. O comportamento da extração de zircônio(IV) / háfnio(IV) foi também comparado com o de outros íons metálicos, como titânio(IV), alumínio(III) e ferro(III), e pode, genericamente, ser aplicado aos íons metálicos estudados.


Introduction
In analytical chemistry, liquid-liquid extraction (LLE) enjoys a favored position among separation techniques because of its simplicity, speed and wide scope.This method is also frequently used in nuclear chemistry and technology for the separation of various radioisotopes and for the reprocessing of nuclear fuels.Zirconium and hafnium co-exist in nature and are difficult to separate because of similar chemical properties.In order to achieve these objectives, the zirconium and hafnium metals industry needs to separate the title metals from other associated metals like Ti, Fe, Si and Al etc.

Experimental
Reagents HPBI, HFBPI and HTPI were synthesized from 3-phenyl-5-isoxazolone and corresponding acid chlorides according to the method described elsewhere. 9ZrOCl 2 .8H 2 O and HfCl 4 (Fluka, 98%) were used.Working solutions of zirconium(IV)/ hafnium(IV) were freshly prepared and used for the extraction experiments through out the studies.All other reagents used were analytical reagent grade.
The synthesized 4-acyl-3-phenyl-5-isoxazolones was identified by elemental analysis, IR and 1  In the 1 H NMR spectrum of HPBI, a peak at δ 12.2 ppm has been observed corresponding to the enolic -OH.On the other hand, no peak was observed for the -OH in the case of HTPI.However, in the case of HFPBI, a broad peak at δ 3.57 ppm has been noted.This signal did not move on changing the concentration and found to disappear with the addition of D 2 O, thus confirming the existence of HFBPI in the enolic form.The absence of a peak at δ 3.8 ppm corresponding to the methylene proton at the fourth position of the isoxazolone ring, further confirms the existence of various 3-phenyl-4-acl-5isoxazolones in the enolic form.

Apparatus
The concentration of Zr(IV) and Hf(IV) in the aqueous phase was determined by the xylenol orange (XO) method 10 at 535 nm and Ti (IV) by hydrogen peroxide 10 method at 410 nm using a GBC CINTRA 10e UV-Vis-DRS spectrometer.Analysis of Fe(III) and Al(III) was obtained using Perkin Elmer Model A 300 AAS.The NMR spectrum of the extracted solid comlex was recorded with Avance -300 MHz 1 H NMR instrument.The IR spectrum of the solid complexes was recorded with FTIR-Nicolet (USA)-740-spectrophotometer.

General liquid-liquid extraction procedure
Equal volumes (10 mL) of the aqueous phase containing desired concentration of metal and organic phase containing the extractant, were equilibrated for 30 minutes in glass stoppered bottles using a mechanical shaker.Preliminary experiments on the kinetics of metal extraction showed that equilibrium was achieved with in 20 minutes contact.After phase disengagment, the aqueous phase was separated and metal concentrations were estimated by XO method.All the experiments were conducted at room temperature (30 ± 1 o C) and the general agreement with D values obtained was within ± 5%.The distribution ratio, D is calculated as the concentration of metal present in the organic phase to that part in the aqueous phase at equilibrium.

Effect of phase contact time
The effect of phase contact time was studied on the distribution ratio of 0.0005 mol L -1 zirconium(IV)/ hafnium(IV) from 0.1 mol L -1 hydrochloric acid solutions using 0.001 mol L -1 3-phenyl-4-acyl-5-isoxazolones as the extractants.Distribution ratio increases with increasing phase contact time upto 20 minutes and remains constant thereafter (Figure 1).

Extraction equilibrium and species
The extraction equilibrium of zirconium(IV)/hafnium(IV) from acidic chloride solutions with 3-phenyl-4-acyl-5isoxazolones as the extractants may be represented as: Where K ex denotes the equilibrium constant, M is equal to zirconium(IV) or hafnium(IV) and HA refers to HPBI or HFBPI or HTPI.( The extraction of 0.0005 mol L -1 zirconium(IV) or hafnium(IV) with 0.001 mol L -1 3-phenyl-4-acyl-5isoxazolones in xylene as a function of hydrochloric acid has been studied.The extraction behavior shows an inverse dependence on the acidity (Figure 2).The log vs. log plots (Figure 3) for zirconium(IV) and hafnium(IV) gave slopes -2, confirming the formation of simple metal chelates.The results clearly indicate the release of H + ions from the extractant during the extraction process.
The effect of HPBI, HFBPI and HTPI concentrations in the range 4 × 10 -3 to 1 × 10 -3 mol L -1 on the extraction of zirconium(IV) and hafnium(IV) has been studied by keeping the metal (0.0005 mol L -1 ) and hydrochloric acid concentrations (0.1 mol L -1 ) constant.It is clear from the results that the extraction of both Zr(IV) and Hf(IV) increases with increase in concentrations of 3-phenyl-4-acyl-5-isoxazolones (HA).The log vs. log plots gave slopes of 2, indicating extraction of the complex, MOA 2 (M = Zr(IV) or Hf(IV) (Figure 4).
The effect of metal ion concentration on the extraction of zirconium(IV)/hafnium(IV) (0.0001 -0.001 mol L -1 ) from hydrochloric acid solutions (0.1 mol L -1 ) using various 3-phenyl-4-acyl-5-isoxazolones (0.001 mol L -1 ) has been investigated and the results are shown in Figure 5.It has been observed that the extraction of Zr(IV) and Hf(IV) were found to be independent of metal ion concentrations in the studied range.The log-log plots of equilibrium organic phase metal concentrations to the aqueous phase metal concentrations are linear with slopes of unity, indicating the extraction of mononuclear species into the organic phase.

Effect of associated metal ions
The extraction behavior of zirconium(IV), hafnium (IV), titanium(IV), aluminium(III) and iron(III) (0.0005 mol L -1 each) has been investigated as a function of hydrochloric acid concentration using 0.001 mol L -1 HPBI in xylene as an extractant (Figure 6).The results indicate that the percentage extraction of Ti(IV) and Al(III) is quantitative under the present experimental conditions.On the other hand, Zr(IV), Hf(IV) and Fe(III) extraction decreases with increasing acid concentration.

Conclusions
The extraction behavior of zirconium(IV)/ hafnium(IV) has been investigated using 3-phenyl-4acyl-5-isoxazolones such as HPBI, HFBPI and HTPI  in xylene.The present study on LLE of Zr(IV)/Hf(IV) from acidic chloride solutions by HPBI revealed the transfer of metal by cation exchange mechanism.The extraction efficiency of zirconium(IV) / hafnium(IV) with various HPBI reagents follow the order HPBI > HTPI > HFBPI for Zr(IV) and HFBPI > HPBI > HTPI for Hf(IV).Variation of D values with increase of extractant concentration showed linear plots with slope of 2, indicating that the species extracted as MOA 2 (M = Zr(IV) or Hf(IV)).