Solvent extraction of tantalum(V) from aqueous sulphate/fluoride solution using trioctyl phosphine oxide in MIBK

Tantalite–columbite with a combined Ta–Nb content of 33% was leached using 20 M hydrofluoric acid. The acidity of the leach was adjusted with sulphuric acid and the tantalum–niobium content was extracted using methyl isobutyl ketone (MIBK) and trioctyl phosphine oxide (TOPO), with kerosene and xylene as diluents. Stripping and precipitation of the extracted species was performed using 30% V/V ammonia solution. Both tantalum and niobium were extracted to different extents, with greater degree of extraction observed for tantalum. The extraction of tantalum was found to be dependent on the concentration of sulphuric acid added. For systems involving TOPO as extractant, kerosene proved to be a better diluent than xylene. Synergism was observed with respect to tantalum extraction when 20 g/l solution of TOPO in MIBK was used as the extractant. The number of extraction stages can be greatly reduced using a TOPO — MIBK blend in place of MIBK or TOPO only.