Abstract:
Niobium (V) oxide (Nb2O5) sample was subjected to hydrofluoric acid leaching using acid concentrations varied from 3M-8M and a mixture of 4M HF and 3M-8M H2SO4 and extracted with hexanol and octanol. Niobium was analysed by spectrophotometric determination using thiocynate method at 385nm, infrared (4000-450cm-1) and electronic spectra measurements of organic phases and X-ray fluorescence (XFR) determination of pure tantalite ore. The effects of acid concentration, temperature, mixed extractant, extraction stages and foreign ions on the extraction of niobium (V) from the fluoride leach liquors using hexanol and octanol were investigated. It was found that optimum extraction efficiency (E%) of 78.2% was achieved by hexanol at acid concentration of 4MHF/5MH2SO4 and 59.9% was achieved by octanol at acid concentration of 4MHF/7MH2SO4. Hexanol and octanol had their least extraction efficiencies of 36.0% and 47.3% at acid concentrations of 4MHF/3M H2SO4 and 4MHF/ 6MH2SO4 respectively. On the mixing of extractants, 10% v/v each of octanol, TBP, TRPO, D2EHPA,TOA and 2.5%W/V TOPO separately added to 90%v/v hexanol reduced its extraction efficiency to 39.4%, 31.7%, 40.5%, 28.1%, 44.0% and 63.1% respectively compared with78.2% when it was used alone. Change in temperature produced an irregular variation in the extraction efficiency of the extractants at 301K, 306K, 311K and 316K used, the percentage extraction (E%) using hexanol were 78.2, 41.4, 50.0 and 52.5% respectively while that of octanol were 59.9, 46.7, 52.1 and 50.2% respectively. A concentration of 0.001M or 0.002M each of Mn2+, V5+, Fe2+, Zr4+, Zr2+ and Ta5+ separately added to 0.01M Nb5+ as foreign ions reduced percentage extraction (E%) of Nb5+ using hexanol to 50.5, 27.0, 43.1, 63.0, 58.0 and 43.9% respectively as against the E% of 78.2 when no ion was added. Nb(V) was separated from co-extracted Ta(V) present in the ore leachate by selective stripping of the metal-loaded hexanol or octanol with varied concentration of sulphuric acid. Hexanol has been found
better than octanol as extractant for Nb(V) under the prevailing experimental conditions for both laboratory and field experimental conditions.
