Microwave-assisted preparation of a new esterification catalyst from wasted flint kaolin

- Thermal activation at 850 °C made the flint kaolin more reactive to acid leaching.
- Catalysts prepared using microwaves decreased time and temperature of reaction.
- Metakaolin activated at 400 W by 15 min presented better performance.
- A more efficient and eco-friendly catalyst for production of biodiesel.