SEPARATION OF VANADIUM (V) AND MOLYBDENUM (VI) FROM NITRIC ACID SOLUTION BY EXTRACTION WITH TRI-N-BUTYL PHOSPHATE AND 1-OCTANOL

Abstract

The separation of V(V) and Mo(VI) from 5 M nitric acid solution by extraction with tri-n-butyl phosphate and 1-octanol has been studied. The study was propelled by the rapid trend of rising global demand and increasing wide spread use of the metals “vanadium and molybdenum” and also to develop an efficient method for their recovery from solutions since their natural sources have become depleted. The effects of various parameters such as contact time, concentration of extractants, temperature, organic to aqueous phase ratio, batch extraction stages, mixing of extractants, foreign ions and stripping agents were investigated. The electronic absorption and infrared spectra of the raffinate, unstripped organic phase, the aqueous and organic phases after stripping with H2SO4 and NH3(aq) and of the extractants, tri-n-butyl phosphate and 1-octanol in n-heptane were measured. On the effect of contact time, 5 and 2 min optimum contact time with separation factors, α = 1.086 and 1.084 were observed for tri-n-butyl phosphate and 1-octanol respectively. On the effect of concentration of extractants, 20% (v/v) of extractants with separation factors of 3.828 and 1.496 for tri-n-butyl phosphate and 1-octanol were observed. The optimum extraction temperature was observed at 43 and 28oC for tri-n-butyl phosphate and 1-octanol respectively. Both extraction processes were endothermic. On phase ratio, the optimum phase volume ratio of 2.5:1 and 2:1 were observed for tri-n-butyl phosphate and 1-octanol respectively. Batch extraction stages with tri-n-butyl phosphate gave a percentage extraction by mass of V(V), (64.4%) and Mo(VI), (65.3%) and 1-octanol gave V(V), (44.7%) and Mo(VI), (46.5%) after six consecutive extractions respectively. The effect of mixing of extractants showed no synergistic effect on the percentage by mass of the analytes extracted, since V(V), (39.5%) and Mo(VI), (37.5%) extracted were lower compared to the mass of analytes extracted by individual extractants on batch extraction stages. In the presence of foreign ions, tri-n-butyl phosphate gave a percentage yield by mass of V(V) and Mo(VI) as 20.0 and 54.2%, 21.6 and 36.5% at 10 and 20% contamination level in that order while 1-octanol gave V(V) and Mo(VI), (37.3 and 64.6%), (22.9 and 30.2%) at 10 and 20% contamination level respectively. The effect of stripping agents showed that, tri-n-butyl phosphate gave a percentage stripping by mass of V(V), (59.2%) and Mo(VI), (55.7%) while 1-octanol gave a higher percentage stripping by mass of V(V) and Mo(VI) each as 58.2%. From analytical and spectra data available, the extracted complexes have been formulated as VO2NO3.nPO(OC4H9)3 and MoO2(NO3)2.nPO(OC4H9)3 for V(V) and Mo(VI) with tri-n-butyl phosphate and VO2NO3.nROH and MoO2 (NO3)2.nROH for V(V) and Mo(VI) with 1-octanol respectively. Selective stripping was found better than selective extraction for the separation of vanadium (V) and molybdenum (VI).