Mineral phases synthesized by hydrothermal treatment from biomass ashes

- Zeolitic phases are synthesized from the valorisation of biomass ashes.
- Eco-efficient valorisation is achieved by hydrothermal process in alkaline solution.
- Synthesis of tobermorite by hydrothermal treatment of biomass ashes is optimized.
- Reuse of ashes as pozzolanic addition in cement-based materials is assessed.

The development of mineral phases, analcime, tobermorite and cancrinite, from the valorisation of a waste, is the main objective of this work. The waste considered is a biomass ash (BA) obtained from a fluidized bed forest combustor powered principally by eucalyptus bark residue in a paper company. BA is valorised positively by a hydrothermal treatment (HT) in an alkaline solution. This treatment is an eco-efficient process because it employs low temperatures to activate the BA and implies no emission of CO2 to the atmosphere. Through this HT process, the synthesis of tobermorite is optimized considering the results from different characterization techniques. In addition, the dissolution of chlorides through HT is observed, improving the reutilization of BA in cement-based materials. The results promote the reuse of BA waste and assess its incorporation in cement-based materials due to the high pozzolanic activity shown by the synthesized tobermorite phase (98% of fixed lime at 28 days).