Investigations of chemical fraction of Co and Ni in industrial fly ash and mobility of metals in environmental conditions

The quantitative evaluation of chemical fraction of Co and Ni in the industrial fly ash by methods of five step sequential extraction was carried out in order to characterize metal mobility in environmental conditions. The research involved (i) water-soluble (pH = 7), (ii) acid-soluble (pH = 5), (iii) oxide, (iv) sulfide and (v) residue metal fractions. It was discovered, that the total extraction of the studied metals from fly ash to solutions take place in the following quantities Co – 35.5 and Ni – 153.0 mg kg−1. The investigations of chemical fractions proved that the subject metals occur mainly in fly ash as: oxide (Co – 7.0, Ni – 28.5 mg kg−1) and residue (Co – 11.5, Ni – 42.5 mg kg−1) as well as sulfide (Co – 8.5, Ni – 46.5 mg kg−1). Low concentrations of metals for water-soluble fraction (Co – 0.7, Ni – 1.2 mg kg−1) and acid-soluble fraction (Co – 4.5, Ni – 23.5 mg kg−1) were observed. The fractions of Co and Ni leachable from the ash in environmental conditions contain: 24.0% (Co) and 23.3% (Ni) of metal total amount in the industrial fly ash. The obtained mobility parameter of Co and Ni can be applied to estimate the concentration increase of mobile and hardly mobile forms of these metals in soil polluted with the ash.