Heavy metal concentrations in different kinds of Finnish fly ash and bottom ash with respect to the new limit values for materials used as an earth construction agent

摘要

The total concentrations of Cd, Cu, Pb, Cr, Mo, Zn, As, V and Ba in bottom ash and fly ash from the thermal power plants of Oulun Energia and Laanilan Voima Oy were lower than the Finnish limit values for materials used as an earth construction agent, which came into force in July 2006. Furthermore, a leaching study also confirmed that these ashes can be used as an earth construction agent because the amounts of leachable heavy metals were lower than the maximal allowable concentrations for leachable metals. However, the total concentrations of Cd, Cr, Zn and Ba in fly ash (i.e. cyclone fly) from the municipal district heating plant of Keminmaan Energia Oy exceeded the new Finnish limit values. The enrichment factor (EF), which is the ratio of the heavy metal concentration in fly ash to that in bottom ash, varied between 0.4 and 41 for different elements. Due to the elevated heavy metal concentrations in the cyclone fly ash, it cannot be used as an earth construction agent. However, the limit values do not apply if the ash is utilized as landscaping material in dumping sites, which is therefore an alternative use for cyclone fly ash.