Salt roasting of suncor oil sands fly ash

Abstract

Fly ash samples from 25 years of Suncor’s oil sands upgrading operations were tested to determine the effects of time, temperature, and salt addition on vanadium recovery by salt roasting and water leaching. The optimum roasting conditions for “carbon-free” ash were determined to be 2 to 3 hours roasting at 850 °C to 900 °C with NaCl additions of 20 to 30 pct that resulted in vanadium extractions of 75 to 85 pct for all samples tested. Leach solutions contained less than 150 mg/L Al, Fe, Ni, Si, and Ti and typically analyzed 12–20 g/L V, 0.3 to 0.6 g/L Mo, 3.2 g/L K, and 10 g/L Na. Sodium carbonate (100 g/L) was also a selective lixiviant for vanadium and produced 2 to 7 pct higher extractions than water leaching. Characterization tests showed that most of the mineral matter in the Suncor fly ash is initially present as a poorly crystalline aluminosilicate glass, but crystallizes on heating with NaCl to form distinct aluminosilicate (albite and hauyne) and iron-titanium (pseudobrookite and hematite) phases. Water-soluble vanadium and molybdenum compounds are likely formed by reacting with NaCl during this crystallization. These tests indicate that insoluble vanadium and molybdenum are associated with the aluminosilicates and that nickel is associated with the iron-titanium minerals.