Functional speciation and leachability of titanium group from industrial fly ash

Functional speciation and leachability of titanium group from industrial fly ash were investigated by using sequential extraction. Fractions: soluble in water and exchangeable, soluble in acids (pH 5), oxide, pseudosulfide and residual were characterized. Results of the fractions analyses were compared with the total content of metals in ash: Ti - 0.48%, Zr - 85.8 mg kg−1, Hf - DL. Two parameters were defined for the evaluation of leachability of metals from ashes: the accumulation of metal in the soluble fraction (a = mass of soluble fraction metal/mass of the soluble fraction of ash) and the parameter of metal leaching from ash (w = mobility of metal (%)/solubility of ash (%)). Accumulation of titanium group (mg kg−1) was found in fractions: oxide (43.4 Ti), pseudosulfide (5.3 Ti; 4.3 Zr), residual (2378 Ti; 22.8 Zr) and not-digested residue (8862 Ti, 167.6 Zr). The oxide fraction was characterized by low parameter of leachability (0.01 Ti, 0.05 Zr), while the residual was high parameter of leachability (0.50 Ti, 0.25 Zr). It is possible to apply new defined parameters for the evaluation of leachability of metals from ashes in relation to the mass solubility of ash.