title: Alkali activation of recovered fuel-biofuel fly ash from fluidised-bed combustion: Stabilisation/solidification of heavy metals.
abstract: Recovered fuel-biofuel fly ash from a fluidized bed boiler was alkali-activated and granulated with a sodium-silicate solution in order to immobilise the heavy metals it contains. The effect of blast-furnace slag and metakaolin as co-binders were studied. Leaching standard EN 12457-3 was applied to evaluate the immobilisation potential. The results showed that Ba, Pb and Zn were effectively immobilised. However, there was increased leaching after alkali activation for As, Cu, Mo, Sb and V. The co-binders had minimal or even negative effect on the immobilisation. One exception was found for Cr, in which the slag decreased leaching, and one was found for Cu, in which the slag increased leaching. A sequential leaching procedure was utilized to gain a deeper understanding of the immobilisation mechanism. By using a sequential leaching procedure it is possible fractionate elements into watersoluble, acid-soluble, easily-reduced and oxidisable fractions, yielding a total 'bioavailable' amount that is potentially hazardous for the environment. It was found that the total bioavailable amount was lower following alkali activation for all heavy metals, although the water-soluble fraction was higher for some metals. Evidence from leaching tests suggests the immobilisation mechanism was chemical retention, or trapping inside the alkali activation reaction products, rather than physical retention, adsorption or precipitation as hydroxides.
authors.affiliation: Fibre and Particle Engineering Laboratory, P.O. Box 4300, University of Oulu, 90014, Finland. Electronic address: juho.yliniemi@oulu.fi.
authors.forename: Juho
authors.initials: J
authors.lastname: Yliniemi
authors.affiliation: Department of Chemistry, P.O. Box 3000, University of Oulu, 90014, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Pesonen
authors.affiliation: Department of Chemistry, P.O. Box 3000, University of Oulu, 90014, Finland.
authors.forename: Minna
authors.initials: M
authors.lastname: Tiainen
authors.affiliation: Fibre and Particle Engineering Laboratory, P.O. Box 4300, University of Oulu, 90014, Finland.
authors.forename: Mirja
authors.initials: M
authors.lastname: Illikainen
mesh_terms: D001464:Barium / Q000737:chemistry; D056804:Biofuels; D005591:Chemical Fractionation; D060729:Coal Ash / Q000032:analysis / Q000737:chemistry*; D017745:Incineration; D007854:Lead / Q000737:chemistry; D019216:Metals, Heavy / Q000032:analysis / Q000737:chemistry*; D012037:Refuse Disposal / Q000379:methods; D017640:Silicates / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D015032:Zinc / Q000737:chemistry
chemical_list: D056804:Biofuels; D060729:Coal Ash; D019216:Metals, Heavy; D017640:Silicates; D001464:Barium; D007854:Lead; C005691:sodium silicate; D015032:Zinc
keywords: Alkali activation; Fluidized bed combustion; Fly ash; Immobilization; Recovered fuel; Sequential leaching procedure