Optimizing the yield of TiFe intermetallic compound from direct calciothermic reduction of ilmenite sand

The titanium-iron (TiFe) metal hydride system has been identified as particularly suitable for safe, long-duration stationary solid-state hydrogen storage applications. However, the high cost of production of the stoichiometric TiFe intermetallic remains a major challenge to its widespread use. Here, we report experimental investigations into an alternative route to the production of TiFe through the direct reduction of ilmenite mineral sand (FeTiO 3 ), an abundant natural resource. Reduction experiments were conducted in a tube furnace under an argon atmosphere using calcium hydride (CaH 2 ) as the reducing agent. The reduction temperature and hold time were key parameters systematically explored to understand the reduction pathway and maximise TiFe yield. For natural ilmenite, a maximum TiFe yield of ~58 wt.% (from XRD analysis) was achieved after reduction at 800 °C for 9 h, whilst a yield of ~54 wt.% was obtained after reduction at 900 °C for 1 h. However, experiments utilising a high purity synthetic ilmenite feedstock under the same reduction conditions gave a TiFe yield of up to 75 wt.%. In an attempt to bridge this gap, a sodium hydroxide leaching process was used to remove aluminosilicate gangue inclusions from the natural ilmenite. Optimised calciothermic reduction of the leached natural ilmenite then gave an increased TiFe yield of ~73% - comparable to that achieved with high-purity synthetic ilmenite. These results indicate that direct calciothermic reduction of natural ilmenite therefore offers a cost-effective alternative route to produce TiFe-based hydrogen storage material. • A TiFe yield of 58 wt.% from ilmenite sand and 75 wt.% from synthetic ilmenite was achieved. • Titanium was partially lost to an XRD transparent/amorphous oxide phase during reduction. • The amorphous titanium was identified as Ti-Si-O and Ti-O by detailed SEM examination. • NaOH leaching of natural ilmenite almost halved the aluminosilicate gangue content. • Calciothermic reduction of leached ilmenite sand led to an increased TiFe yield of ~73 wt.%.