Acidic extraction and precipitation of heavy metals from biomass incinerator cyclone fly ash

Biomass incineration is increasingly used for the generation of heat and/or electricity. After incineration two ash fractions remain. Bottom ashes (the coarser ash fraction) can usually be used as fertilizing agent on fields as it contains valuable elements for soils and plants and only minor concentrations of heavy metals. Fly ashes (the finer ash fraction) are in most cases disposed as their heavy metal concentrations are too high for a usage as soil enhancer. In this study highly heavy metal contaminated fly ash has been cleaned through extraction with hydrochloric acid. The heavy metals were removed from the extract by precipitation with sodium hydroxide. After the cleaning procedure the ash can be pelletized and be returned to the soils.