A literature review of titanium solvent extraction in chloride media

A number of organic extractants for Ti(IV) solvent extraction from chloride solutions were reviewed, including acidic organophosphorus, neutral organophosphorus and amine extractants. The extraction of Ti(IV) by acidic organophosphorus extractants is via a cation exchange mechanism in low hydrochloric acid concentration solutions, whilst in high hydrochloric acid concentration solutions, it proceeds via a solvating mechanism. The Ti(IV) extraction kinetics with D2EHPA, EHPEHPA and Cyanex 272 is very slow: more than 1 h is required to reach equilibrium in some cases. The Ti(IV) extraction kinetics with Cyanex 301 and Cyanex 302 is fast: only 2–5 min are required to reach equilibrium. The Ti(IV) extraction kinetics with neutral organophosphorus extractants, such as TBP, TOPO and TRPO is also fast: the extraction equilibrium reaches within 5 min. The extraction mechanism with neutral organophosphorus extractants is solvating. Stripping Ti(IV) from loaded acidic organophosphorus extractants including D2EHPA, EHPEHPA, Cyanex 272, Cyanex301 and Cyanex 302 is difficult, requiring H2SO4 solution in the presence of H2O2. In contrast, the stripping of Ti(IV) from neutral organophosphorus extractants is much easier with low acidic solutions.It was found that the practical application of acidic organophosphorus extractants is difficult for Ti(IV) extraction from chloride solutions due to their slow extraction kinetics and difficulty in stripping, and neutral organophosphorus extractants could be used to separate both Fe(III) and Ti(IV) from other impurities or separate Fe(III) from Ti(IV) and all other impurities.

Research Highlights
► Extractants reviewed include acidic and neutral organo-phosphorus compounds, and amine-type compounds.
► The Ti(IV) extraction and stripping behaviours, and the selectivity with the above extractants are compared.
► The effect of diluent on Ti(IV) extraction in chloride media is investigated.
► Further development for more effective solvent extraction systems is recommended.