Separation of Simulated Mixed Mo(VI) and V(V) From HNO₃ and HCl Solutions by Selective Extraction and Stripping with Tri-N-Butyl Phosphate as Extractant

Abstract

Equilibrium study was carried out to determine the optimum conditions required for Mo(VI) extraction from HNO₃ solutions and subsequently, simulated mixed Mo(VI), and V(V) were extracted from HNO₃ (pH = 1.0) and 6.0 mol L⁻¹ 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 HNO₃ solutions (pH = 1.0) except supplemented with selective stripping (back-extraction with 2.0 mol L⁻¹ H₂SO₄/14.5 mol L⁻¹ NH₄OH). While from 6.0 mol L⁻¹ 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 HNO₃ and HCl media were formulated as ((MoO₂)_7–8n(VO₂)_2n · (NO₃)₁₆) ^(16–18)n- · m TBP (where n>m) and (MoO₂Cl₂ · VO₂ Cl) · xTBP, respectively.

Keywords:

• extraction
• molybdenum (VI)
• separation
• stripping
• vanadium (V)

Notes

O = organic phase, A = aqueous phase.

Original Mo(VI) conc. = 2399.0 mg L⁻¹.

Original V(V) conc. = 1273.5 mg L⁻¹.

^a  = Mo(VI) conc. left in aqueous phase.

^b  = V(V) conc. left in aqueous phase.

α = separation factor.

[V/Mo] = 0.025 mol L⁻¹; [KCl] = 0.1 mol L⁻¹; [TBP] = 1.098 mol L⁻¹.

^c  = 2nd stage stripping.

^a  = absorption band for Mo (VI).

^b  = absorption band for V(V).

vs = very strong, s = strong, w = weak.