Extractive recovery of vanadium (V) from hydrochloric acid solutions using alkanols (1-butanol and 1-octanol) dissolved in n-heptane has been investigated by liquid-liquid extraction, propelled by the need to proffering alternatives to the scarce and relatively costly organophosphorous extractants. At the studied pH range (1.0-4.0), with 1-butanol as extractant, the percentage V(V) extraction (extraction efficiency, E%) reached optimum (E% = 63.3) at pH of 0.5, and for 1-octanol, optimum E% was 73.3 at pH 1.0.Increasing concentration of HCl at the studied range (1.0-6.0 mol L -1 ) was found to have an appreciable effect on percentage V(V) extraction. With both extractants, E% peaked at 6.0 mol L -1 HCl with values 86.7 and 70.0% for 1-butanol and 1-octanol, respectively. With increase in the concentration of extractants, both extractants produced a trend of increase/decrease in E% for V(V), suggesting the extraction of two different species. The optimal percentage extraction values were 76.7 and 96.7% observed at log[1-butanol] = 0.81 mol L -1 and log[1-octanol] = 0.49 mol L -1 , in that order. The determined enthalpy change, ΔH, for 1-butanol and 1-octanol systems were -19.9kJ mol -1 and -37.1 kJ mol -1 , respectively, indicating exothermic extraction processes. On the number of required extraction stages, 1-octanol gave a higher extraction efficiency after three consecutive extractions (E% = 99.3) than 1-butanol (E% = 88.6). Recycling experiment showed 1-octanol as more recyclable than 1-butanol (Recycling coefficient R.C. = 1.0 for 1-octanol while R.C. < 1.0 for 1-butanol). All extractants mixed with 1-butanol were found antagonistic. All added foreign ions decreased E% for V(V). From slope analysis, analytical and spectra data, the extracted complexes have been formulated as VO 2 Cl·nROH and (VO 2 Cl) m ·nROH (where m >> n) at low and high concentrations of extractant, respectively. On the whole, 1-octanol could be adjudged a better extractant for vanadium (V) under the prevailing experimental conditions.

Equilibrium study was carried out to determine the optimum conditions required for Mo(VI) extraction from HNO 3 solutions and subsequently, simulated mixed Mo(VI), and V(V) were extracted from HNO 3 (pH ¼ 1.0) and 6.0 mol L À1 HCl solutions with TBP dissolved in n-hexane. The variation of pH (selective extraction) and selective stripping were investigated as methods of separation of Mo(VI) and V(V). The latter method was found inefficient for separations from HNO 3 solutions (pH ¼ 1.0) except supplemented with selective stripping (back-extraction with 2.0 mol L À1 H 2 SO 4 /14.5 mol L À1 NH 4 OH). While from 6.0 mol L À1 HCl, selective stripping was adequate to quantitatively strip in turns the Mo(VI) and V(V) co-extracted into the TBP phase. About 100% of the co-extracted V(V) from the HCl medium was stripped in a two-stage process, in contrast to a single-stage required for Mo(VI) of the same result. The selective stripping method was found to be better because an initial appreciable co-extraction had occurred prior to stripping separation. Based on analytical and spectra data, the extracted complexes from HNO 3 and HCl media were formulated as ((MoO 2 ) 7-8n (VO 2 ) 2n Á (NO 3 ) 16 ) (16-18)n-Á m TBP (where n>m) and (MoO 2 Cl 2 Á VO 2 Cl) Á xTBP, respectively.

The mechanism of extraction of Mo (VI) from diluted HCl and HNO 3 solutions with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-hexane has been investigated. The mechanism of extraction from both acids at pH 1.0 -6.0 was found to be majorly by cation exchange of MoO 2 2+ . The extraction efficiency was maximal at pH 1.0 for both acids, E% = 84.8 and 80.0 for HCl and HNO 3 media respectively. From the method of slope analysis, the number of D2EHPA molecules associated with MoO 2 2+ was found to be two at pH = 1.0.

Further to the previous study on the extractive recovery of V(V) from HCl solution by some alkanols, the extraction of V(V) from HCl solutions by 1-pentanol and 3-methyl -1-butanol (isomers) dissolved in n-heptane were investigated in the present study, still propelled by the need to proffering viable alternatives to the scarce and relatively costly organophosphorous extractants, and also compare the extraction efficiency of straight-and branched-chain extractants. At the studied pH range (0.5-4.0) with 1-penttanol as extractant, the percentage V(V) extraction (extraction efficiency, E%) reached optimum E%= 40.0 at pH of 3.0 and for 3-methyl-1-butanol, optimum E% was 36. respectively, indicating exothermic/endothermic extraction processes. The isomer 3-methyl -1-butanol gave a higher extraction efficiency after a three-stage extraction (E% = 92.5) than 1-pentanol (E% = 83.4). Recycling experiment revealed both to be recyclable. From slope analysis, analytical and spectra data, the extracted complexes have been formulated as VO 2 Cl.nROH and (VO 2 Cl) m .nROH (where m>> n) at low and high concentrations of extractant, respectively. On the whole, 3-methyl-1-butanol was assessed as fairly better as an extractant for vanadium (V) at lower temperature experimental conditions. The effect of methyl branched-chain played an insignificant role on the extraction.