Molecular modelling of tantalum in an aqueous phase

metals found in the same group (VB) of the periodic table of elements. Owing to their similar chemical and physical properties, they are difficult to separate. Ta and Nb are usually found together in various minerals, of which the most important are columbite ((Fe, Mn, Mg)(Nb, Ta)2O6) and tantalite ((Fe, Mn)(Nb, Ta)2O6) (Agulyanski, 2004). Ta is used in a variety of applications, including capacitors in electronic circuits, rectifiers, pins for bone fixtures, surgical and dental instruments, and in chemical heat exchangers (Krebs, 2006). For many applications, pure Ta is needed; however, increasing purity entails a proportional increase in production cost. One way of ensuring an economically viable process for the production of high-purity Ta is to find a cost-effective way to separate Ta and Nb. Solvent extraction (SX) is used for the separation and purification of various metals, including copper (Bidari, Irannejad, and Gharabaghi, 2013), nickel (Noori et al., 2014), iron (Li et al., 2011), platinum group metals (PGMs) (Kumar et al., 2008), zirconium (Biswas and Hayat, 2002), hafnium (Lee, Banda, and Min, 2015), and Ta, and Nb (Zhu and Cheng, 2011). Ungerer et al. (2014) studied the separation of Ta and Nb (in the form of MF5) by SX using safer and more environmentally friendly chemicals and techniques. Although partial separation was achieved in a sulphuric acid (H2SO4) medium with the extractants diiso-octyl phosphinic acid (PA) and di-(2-ethylhexyl) phosphoric acid (D2EHPA), the main obstacle remained the lack of data on the speciation of Ta and Nb compounds, without which it was not possible to fully explain the separation data obtained. One method that could be used for speciation of the compounds is computational methods for SX, which entails a step-by-step analysis of the extraction process on a molecular level and determination of the molecular reactions occurring during SX from a thermodynamic perspective, which could lead to the development of a new method for the analysis of Ta and Nb separation by SX. Molecular modelling of tantalum in an aqueous phase