During the solvent extraction (SX) experiments of tantalum (Ta) and niobium (Nb), the aqueous phase consisted of tantalum- and niobium penta-fluoride (Ta(Nb)F₅), water (H₂O) and sulphuric acid (H₂SO₄), which was contacted with an organic phase. In this study the aqueous phase used during SX was modelled by studying the interactions and resulting reactions of specifically TaF₅ when it is contacted with H₂O and H₂SO₄. Different functional and basis set combinations within density functional theory (DFT) were investigated. From previous modelling it was seen that by increasing the number of water molecules, the reaction energy decreased due to molecule stabilisation (hydrogen bonding) and subsequently a 1:1:10 metal:acid:water ratio were used.

Results showed that the deprotonation of H₂SO₄ was exothermic, leading to the formation of HSO₄⁻. Furthermore, from the various reactions and geometries between TaF₅, H₂SO₄ and H₂O investigated, it was observed that only four species would be available in the aqueous phase during solvent extraction, namely TaF₅·H₂O in water or diluted acid medium, TaF₄·HSO₄ in a concentrated H₂SO₄ medium and TaF₄OH or TaF₃OH·HSO₄ if the aqueous phase was aged. From the results obtained a reaction mechanism that might occur during SX of TaF₅ was predicted.