Journal of Hazardous Materials 196 (2011) 86–92 Contents lists available at SciVerse ScienceDirect Journal of Hazardous Materials j our na l ho me p age: www.elsevier.com/locate/jhazmat Geopolymers prepared from DC plasma treated air pollution control (APC) residues glass: Properties and characterisation of the binder phase Ioanna Kourti a , Amutha Rani Devaraj a,b , Ana Guerrero Bustos c , David Deegan d , Aldo R. Boccaccini b,e , Christopher R. Cheeseman a,∗ a Department of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, UK b Department of Materials, Imperial College London, London SW7 2BP, UK c Institute of Construction Science Eduardo Torroja (CSIC), C/Serrrano Galvache, 4, 28033 Madrid, Spain d Tetronics Ltd., South Marston Business Park, Swindon, Wiltshire SN3 4DE, UK e Institute of Biomaterials, Department of Materials Science and Engineering University of Erlangen-Nuremberg, Cauerstr. 6, 91058 Erlangen, Germany a r t i c l e i n f o Article history: Received 14 February 2011 Received in revised form 30 August 2011 Accepted 31 August 2011 Available online 6 September 2011 Keywords: Geopolymers Plasma Incineration Energy Waste APC residues a b s t r a c t Air pollution control (APC) residues have been blended with glass-forming additives and treated using DC plasma technology to produce a high calcium aluminosilicate glass (APC glass). This has been used to form geopolymer–glass composites that exhibit high strength and density, low porosity, low water absorption, low leaching and high acid resistance. The composites have a microstructure consisting of un-reacted residual APC glass particles imbedded in a complex geopolymer and C–S–H gel binder phase, and behave as particle reinforced composites. The work demonstrates that materials prepared from DC plasma treated APC residues have potential to be used to form high quality pre-cast products. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The air pollutions control systems at energy from waste (EfW) plants burning municipal solid waste (MSW) produce granular air pollution control (APC) residues. These are a hazardous waste with an absolute entry in the European Waste Catalogue (19 01 07*), and they contain fly ash, excess lime, carbon, relatively high concentrations of volatile heavy metals and soluble salts, particu- larly leachable chlorides. They also contain trace levels of organics including dioxins and furans. DC plasma technology provides a sustainable treatment for APC residues that meets the aims of the EU waste policy as it is a recy- cling/recovery option higher in the waste management hierarchy than alternative options [1,2]. In the DC plasma treatment pro- cess APC residues are combined with glass-forming additives and melted to produce inert APC glass [2]. There is increasing interest in developing sustainable construc- tion products which contain recycled materials. Reuse of APC glass would have significant economic and environmental benefits, and ∗ Corresponding author. Tel.: +44 207 594 5971; fax: +44 207 823 9401. E-mail address: c.cheeseman@imperial.ac.uk (C.R. Cheeseman). would help to make DC plasma treatment of APC residues com- mercially attractive. Previous work has investigated the use of APC glass in glass-ceramics [3,4] and sintered ceramic tiles [5]. Geopolymers are synthetic alumino-silicates consisting of sil- ica (SiO 4 ) and alumina (AlO 4 ) tetrahedra, linked by shared oxygen atoms [6]. Their formation is based on the chemistry of alkali- activated inorganic binders and involves the chemical reaction of geopolymeric precursors, such as alumino–silicate oxides with alkali poly-silicates, to form polymeric Si–O–Al bonds [7]. The negative charge of Al 3+ in four-fold coordination is balanced by the presence of positive ions such as Na + , K + and Ca 2+ in framework cavities [8]. The empirical formula of geopolymers is therefore: M n (–(SiO 2 ) z –AlO 2 ) n ,wH 2 O (1) where M is a cation such as Na + , K + or Ca 2+ , z is 1, 2 or 3, and n is the degree of poly-condensation. Geoploymers are associated with low CO 2 emissions compared to Portland cement [9]. Using APC residue glass to form a geopoly- mer would provide a low-carbon emission reuse option that does not involve thermal processing. The microstructure and properties of geopolymers are deter- mined by the raw materials used, and they can have high early 0304-3894/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2011.08.081