Interphase distribution of Ti(IV), rare metal, and rare-earth metal ions in hydrochloric acid solution – bifunctional hydrophobic ionic liquid system

Currently, the processing of titanium from ores that contain considerable amounts of valuable rare and rare-earth metals requires methods ensuring high selectivity of recovery and purification, along with the possibility of obtaining additional products. A promising approach for processing such titanium-bearing sources is a combination of acid leaching and solvent extraction.

In this work, the extraction of Ti(IV), Nb(V), Ta(V) and Y(III) from hydrochloric acid solutions was studied using an ionic liquid based on trioctylmethylammonium chloride (TOMAC) and di(2‑ethylhexyl)phosphoric acid (D2EHPA). The ionic liquid was prepared by mixing and dissolving equal amounts of TOMAC and D2EHPA in kerosene for 15 min, followed by washing the organic phase with alkali to remove chloride ions and to deprotonate D2EHPA. Prior to extraction, the ionic liquid [TOMA][D2EHP] was diluted to the desired concentration, and TBP was added as a modifier. Extraction experiments were carried out at 25 °C and atmospheric pressure (~100 kPa) by stirring the aqueous and organic phases in a shaker at 45 rpm for 15 min. After stirring, the mixture was centrifuged at 2500 rpm for 5 min. The phases were then separated, and the metal ion concentrations in the aqueous phase were determined.

The effects of acid concentration, chloride ion concentration, and extractant concentration on the extraction efficiency were investigated. It was shown that Ti(IV), Nb(V), and Ta(V) can be separated from Y(III): at 9 M HCl, the separation factors reached β_Ti/Y  = 2403, β_Nb/Y = 161, and β_Ta/Y =102. A potential for selective stripping of Ti from the organic phase using a 1 M H₃PO₄ + 1 % H₂O₂ solution was established.

The obtained results open up prospects for employing the ionic liquid [TOMA][D2EHP] in the development of efficient hydrometallurgical processes for the recovery of titanium and rare metals.