Template-Free Synthesis of Alkaline Earth Vanadate Nanomaterials from Leaching Solutions of Oil Refinery Waste

Currently, industrial wastes are typically combusted at incineration plants, and the resulting ashes are sent to landfill. This practice raises issues, such as potential toxicity of the leachate to the environment, as well as the loss of valuable metals left in the waste. Therefore, from both economic and environmental standpoints, it is becoming increasingly important to recover valuable metals from industrial waste. In this work, a transformative recovery of vanadium (conversion nearly 100%) from leaching solutions of carbon black waste (metal leaching efficiency > 97%) which originates from oil refineries in Singapore, has been systematically studied. Interestingly, three distinctive alkaline earth vanadate nanomaterials were successfully synthesized from the leaching solutions by a facile hydrothermal process, that is, single-crystal calcium vanadate nanorods (Ca10V6O25) oriented along the [001] direction, strontium vanadate nanorods with ellipsoid-like assembly (Sr10V6O25), and barium vanadate polyhedral nanoparticles (Ba3V2O8). Importantly, we have demonstrated that this facile metal recovery route enables the morphology control of vanadate nanomaterials without templates in the system. Moreover, the vanadate nanomaterials obtained are potential wide band gap semiconductors for electronic devices and semiconducting glasses.