Abstract
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.
Highlights
Vanadium is used for alloying steel and the manufacture of oxidative catalyst
When 0.20 g/L V(IV) existing in the aqueous phase at pH(ini) 4.00 containing 0.02 mol/L SO24 was extracted with 0.15 mol/L H2A2 in kerosene at 303 K and O/A = 1, it was found that the [V(IV)](o) was increased up to phase contact of 18 min
It is found in both cases that the [V(IV)](o) is increased, but the value of D is decreased continuously with increasing [V(IV)](ini). This is contrary to the general principle of solvent extraction chemistry as suggested by Equation (2) which is valid at constant [H2A2](o,eq) and pH(eq)
Summary
Vanadium is used for alloying steel and the manufacture of oxidative catalyst. The rich deposits of its ores, viz. patronite (V2S3), vanadinite (3Pb3(VO4)2·PbCl2), carnotite (K2U2V2O11·3H2O) etc. are rare on the earth’s crust now. It is necessary to develop extraction processes for low grade ores and waste materials (tar sand, waste desulphurization catalyst etc.). Solvent extraction technique is convenient for such purpose. Di-2-ethylhexyl phosphoric acid (D2EHPA) is a promising extractant for V(IV) and V(V) [2,3,4,5,6,7,8]. Vanadium(IV) and (V) have been extracted by EHEHPA (2ethylhexyl phosphonic acid mono-2-ethylhexyl ester) [9]. A recent development in the field of solvent extraction is the use of organophosphinic acid derivatives and their sulphur analogues (Cyanex reagents) introduced by American Cyanamid Company and Cytec Canada Inc. Cyanex 302 and Cyanex 301 are the mono- and disulphide analogues of Cyanex 272 (di-2,4,4-trimethylpentylphosphinic acid). The presence of P-C bonding in Cyanex reagents renders them to be less susceptible to hydrolysis and less soluble in water [14]
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