Liquid-Liquid Extraction of V(IV) from Sulphate Medium by Cyanex 301 Dissolved in Kerosene

The equilibrium of extraction of V(IV) in the V(IV)- SO42- (H+, Na+)-Cyanex 301 (HA)-kerosene system has been studied. Significant extraction occurs above pH 1 within 10 min. CD (extraction ratio at constant pH(eq) and [HA](o,eq)) value is slightly decreased with increasing [V(IV)](ini). CD is found to be directly proportional to [H+]-n (n ≤ 2), [HA] 2 and (1+1.58 [SO42-]). The process is endothermic (DH = 16 kJ/mol). Apparent Kexvalues at 303 K are 10-1.419 and 10-0.94 in 0.10 and 1.50 mol/L SO42- medium, respectively. The loading capacity is calculated to be7.87 gV(IV) per100 g Cyanex 301. Kerosene appears as the best diluent. Stripping to the extents of 100%, 94% and 97.7% are possible in single stage by 1 mol/L H2SO4, HCl and HNO3, respectively. Separations of V(IV) from Cu(II) (at pH 0), Zn(II) (at pH 0.5) and Fe(III) (at pH 1.0) by Cyanex 301 are possible.

Equilibrium of the Extraction of V(IV) in the V(IV)-SO₄^2-(H⁺, Na⁺)—Cyanex 302-Kerosene System

The title system has been investigated from the equilibrium point of view. Significant extraction occurs above pH 2. Equilibration time is 20 min. The extraction ratio (D) remains constant with increasing [V(IV)] of at least 0.50 g/L. It is inversely proportional to [H+]2, [H+] and [H+]0.3 in the lower pH (2;and [SO42-]0 and [SO42-]-1 in the lower [SO42-] (42-] (>1 mol/L) regions, respectively. The apparent extraction equilibrium constant (Kex) in 0.02 mol/L SO42- medium and at 303 K is found to vary from 10-3.447 to 101.508 with increasing equilibrium pH from 2.25 to 4.00. Various sulphated, hydrolyzed, hydrated and mixed sulphated hydrolyzed species of V(IV) have been considered at different extraction conditions to propose the extraction equilibrium reactions to form always [VO(HA2)2] as the extractable species. The system is highly temperature dependent with ?H value of ~90 kJ/mol and ~25 kJ/mol in lower and higher temperature regions, respectively. The calculated loading capacity is low (4.05 g V(IV)/100 g Cyanex 302). Kerosene is a better diluent over CHCl3, Cyclo-C6H12 and CCl4;but much better solvents are C6H6, C6H5CH3, n-C7H16,C6H4(CH3)2, petroleum benzin, 1,2-C2H4Cl2, C6H5Cl. Mineral acids (1 mol/L) are able to strip off V(IV) from the organic phase in a single-stage. Using Cyanex 302, almost complete separations of V(IV) from Cu(II) at pH 1.0 and from Ni(II) at pH(eq) 4.5 are possible in a single-stage of extraction;whereas, its separation from Zn(II) at pH(eq) 2.5, Co(II) at pH(eq) 3.5, Fe(III) at pH(eq) 2.0 and Ti(IV) at pH(eq) 2.5 will require counter-current multi-stage extractions.

Extraction Kinetics of Ni(II) in the Ni²⁺- SO₄<sup style="margin-left:-7px;">2-</sup>-Ac^-(Na⁺, H⁺)-Cyanex 272 (H₂A₂)-Kerosene-3% (v/v) Octan-1-ol System Using Single Drop Technique

The kinetics of extraction of Ni(II) in the Ni2+-SO4 2_AC- (Na+, H+)-Cyanex 272 (H2A2)-kerosene-3% (v/v) octan-1-ol system using the single falling drop technique have been reported. The flux of Ni2+ transfer (F) at 303 K in presence of 3% (v/v) octan-1-ol (de-emulsifier) can be represented as:.Depending on reaction parameters, the activation energy (Ea) and enthalpy change in activation (DH±) varies within 17 - 58 kJ/mol and 17 - 67 kJ/mol, respectively. Entropy change in activation (DS±) is always negative. Based on the empirical flux equation, Ea and DS± values, mechanisms of extractions in different parametric conditions are proposed. At low and [Ac-], and pH, the chemical controlled step is: Ni2+ + A- → NiA+;and this reaction occurs via an SN2 mechanism. But in most parametric conditions, the process is under intermediate control;and at high SO42- and [Ac-], and pH, the extraction process is under diffusion control.