Characterization and utilization of fly ash of heavy fuel oil generated in power stations

• Fly ash of heavy oil fuel is rich with V and Ni metals compared to coal ashes.
• V is accumulated in FA as Mg3V2O8 as confirmed by XRD.
• Based on physicochemical tests, the best utilization of FA is in geopolymers.
• High extraction recoveries of metals were observed using HNO3.
• Stable geopolymers containing high dosages of FA were prepared.

Unlike coal fly ash, fly ash of heavy fuel oil has received much less attention in the literature. In this work, detailed physicochemical characterization of heavy fuel oil fly ash (FA) is provided. The ash has a carbonaceous matrix and contains V, Ni, Zn, Cr, Cu, and Pb with variable amounts. V was the most abundant heavy metal with enrichment factor of 277 in the FA. The presence of V in the FA is attributed to the formation of Mg3V2O8 oxides at high combustion temperature as confirmed by XRD. Particle size distribution showed that the mean particle diameter of the FA was 70.5 μm. Extraction recovery up to 85% of metals was achieved using 1.0 M HNO3 and at room temperature. Standard metal-leaching tests confirmed that the elution of the toxic metals and the level of eluted Zn were much higher than the regulated value for the solid residues. Five stable geopolymers GPs containing 41.7 wt.% FA were prepared. All GPs showed high compressive strength and low water absorption which support their application as lightweight construction composites. Most importantly, adding FA to GP had significantly reduced metal migration into the environment as confirmed by the synthetic precipitation leaching procedure.