Magnesium Removal from TiC-TiB2 SHS-Powders by Controlled Hot Acid Leaching

TiC and TiC–TiB2 powder mixtures obtained directly from titanium (TiO2) and boron (B2O3 or B4C) raw-materials by reduction with magnesium by self propagating high temperature synthesis (SHS) contain, as impurity, large quantities of MgO under its periclase form, together in some cases with unreacted magnesium. Several leaching agents, namely hydrochloric acid, sulphuric acid, acetic acid and EDTA were tested aiming at removal of magnesium from these powders as required characteristic for further work. Several parameters as leachant concentration, pH, reaction time and temperature were evaluated. Alternative leaching methodologies were compared in order to achieve magnesium removal yields over 98% and minimising at the same time the expected high matrix losses due to TiC and/or TiB2 co-solubilisation. As main conclusion it was established that strong hydrochloric acid (6M) is the most efficient medium to remove magnesium from these particular TiC-TiB2 SHS mixtures. The leaching methodology used (controlled hot acid leaching under close conditions) allowed to minimise TiC and TiB2 solubilisation losses. Sulphuric acid is not an effective leaching medium and contaminates the resulting powder mixture with unfriendly sulphur. Using acetic acid, magnesium removal yield is low and titanium losses are considerable. On the other hand, low aggressive EDTA complexant leaves TiC-TiB2 matrix unalterable but residual MgO remains over 6%. The proposed process seems to have potential for application in the general field of semi-micro materials purification.