Extraction of Vanadium from New Zealand Titanomagnetite Sand and Vanadium Recovery Concentrate
This study explores the extraction of the vanadium from titanomagnetite ironsand (IS) from the West Coast of New Zealand, and a vanadium-rich concentrate (VRC) which is formed during the New Zealand steel-making process from this titanomagnetite resource. This extraction first involved an HCl leaching method, with acid concentrations ranging between 1M – 11.5M (concentrated) where the amount of Fe, Ti and V leached/dissolved from the VRC and titanomagnetite materials was determined with respect to leaching time. The concentrations of dissolved Fe, Ti and V in the leachates were measured by ICP-MS, and the solid residues by X-ray fluorescence spectroscopy. The morphology, chemical and individual component characterisation of the solid residues were carried out by X-ray diffraction and scanning electron microscopy and associated energy dispersive elemental and mapping analyses. The leaching results for the VRC showed no selective leaching of Fe, Ti, and V. The amount of Fe, Ti, and V leached increased with increasing HCl concentrations, up to about 50 % of the amount in the original VRC. A different approach was then taken where the VRC material was roasted overnight at two different temperatures (900 and 1200 °C) wherein the V and Mn formed a manganese vanadate phase(Mn2V2O7) and the Fe and Ti formed pseudobrookite (Fe2TiO5) within the VRC. The Mn2V2O7 phase was found to leach much more readily in HCl, while the pseudobrookite phase, which is comparatively acid-resistant, did not leach to any extent. HCl leaching of the roasted VRC thus resulted in selective dissolution of the V (86.89 % amount leached) from the Fe and Ti (~3 % amount leached). This provides a potential new approach for extracting the vanadium from the VRC material.
In order to remove the small amount of Fe and Ti that did leach from the roasted VRC, an attempt to precipitate the dissolved Ti and Fe from the leachate was made. The dissolved Ti was seeded to promote hydrolysis and form TiO2, and the Fe was precipitated by increasing the pH to form an iron hydroxide precipitate. ICP-MS analysis of the resulting filtrate showed a large decrease in the concentrations of Fe, Ti, and V compared to the starting leachate, indicating that the V in solution was removed alongside the Ti and Fe. This was likely caused by the V 5+ forming V2O5 and/or being adsorbed onto the surface of the iron hydroxide precipitate. This method to separate the residual dissolved Fe and Ti in the roasted VRC leachate was deemed unsuitable for the extraction of vanadium. The leaching experiments were repeated with the IS material, and again no selective leaching of Fe, Ti and V was found. Approximately 73 % of these elements were leached. A portion of the IS material was roasted (900 °C overnight) in an attempt to form an acid-soluble manganese vanadium phase similar to the one formed in the VRC roast. Only a small amount of this phase could be identified in the EDS and XRD analyses. HCl leaching of the roasted material similarly resulted in selective dissolution of ii the V (29.26 % amount leached) from the Fe and Ti (~13 % amount leached), although total dissolution for these elements was decreased after roasting. This research has therefore shown that V can be selectively leached from the IS and VRC materials, using a pre-roasting stage to form the manganese vanadate Mn2V2O7 phase which is more readily soluble in HCl than the pseudobrookite Ti- and Fe- containing phase.