Innovative process intensification route for Gallium recovery from fly ash

Fly ash, a byproduct generated from thermal power plants serves a potential secondary resource for the extraction of critical and strategic elements. These are commonly present in accessory minerals in the form of silicates, carbonates and other compounds. Fly ash represents a strategic secondary resource, containing substantial aluminium reserves (≈50 wt% alumina) alongside critical trace metals with average content including gallium (89 g/t), lithium (375 g/t), and scandium (25 g/t). Extracting Gallium (Ga) from coal fly ash typically relies on hydrometallurgical or pyrometallurgical processes. The fly ash sample contains 59g/ton gallium. The fly ash was characterised by XRD and three major phases were detected i.e. quartz(SiO₂), mullite and haematite(Fe₂O₃). These are in accordance with the ICP-OES results as iron (Fe), aluminium(Al), sodium(Na), calcium(Ca) and silicon(Si) are the major constituents of fly ash. The previous works in literature focusses on direct leaching with acid/ or flash Joule heating which are either high acid consuming or demands high temperature reactions. In this study, a novel two-stage process is proposed, which involves acid baking followed by water leaching, was employed to enhance gallium (Ga) recovery. The pre-treatment step facilitated the activation of alumino-silicate glassy phase into soluble compounds, which helps in further dissolution through hydrometallurgical methods. The effect of parameters like time., temperature and acid-to-feed ratio on the leaching of Ga was investigated. The process achieved an extraction efficiency of gallium exceeding 80%. The process is being further explored for other REMs (Ge) and REEs (La, Ce, Sc, Nd, Y) present in the fly ash. This method demonstrates a sustainable approach towards gallium recovery from various industrial wastes, contributing to resource recycling.