Journal of Hazardous Materials 176 (2010) 623–628 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat The role of open and closed curing conditions on the leaching properties of fly ash-slag-based geopolymers Maria Izquierdo a,c,∗ , Xavier Querol a , Charles Phillipart b , Diano Antenucci b , Mark Towler c a Institute of Environmental Assessment and Water Research, Jordi Girona 18, 08034-Barcelona, Spain b Institut Scientifique de Service Public (ISSeP), 200, rue du Chéra 200, BE-4000 Liège, Belgium c Clinical Materials Unit, Materials and Surface Science Institute, University of Limerick, Limerick, Ireland article info Article history: Received 13 May 2009 Received in revised form 9 November 2009 Accepted 12 November 2009 Available online 18 November 2009 Keywords: Fly ash Blast furnace slag Geopolymers Curing conditions Leaching Compressive strength abstract This study deals with the synthesis of geopolymers from co-fired fly ash and blast furnace slags. Geopoly- mer bodies were simultaneously synthesized in open and closed curing conditions in order to elucidate the role of this parameter on their resultant properties. Open curing conditions produce solid bodies characterized by high porosity, low compressive strength and exacerbated leaching of certain oxyan- ionic metalloids. By contrast, protected curing promotes the binder development, giving rise to higher strength and less porous systems. This imposes physical restrictions to leaching which decreases and/or retards releases of oxyanionic metalloids in comparison to open curing conditions. Fly ash-slag-based geopolymers may immobilize a number of trace pollutants such as Be, Bi, Cd, Co, Cr, Cu, Nb, Ni, Pb, REE, Sn, Th, U, Y and Zr, regardless of the curing conditions. Due to geopolymers displaying weak assimilation capacity for oxyanionic species, their successful regarding oxyanionic retention is strongly dependent on porosity and therefore on curing conditions applied. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Over 40 million tonnes of fly ash are produced annually in Europe [1]. European Union regulations are focused on the recy- cling of pulverised coal combustion (PCC) fly ash into added-value products. One method of addressing this is the synthesis of geopoly- mer binders; economically and environmentally low-cost materials which offer cementing properties close to those of ordinary Port- land cement [2]. The term ‘geopolymer’ was first used in the early 1970s to describe inorganic materials with polymeric Si–O–Al bonds, obtained from the chemical reaction of alumino-silicate oxides with alkali silicates [3]. The network is composed of SiO 4 and AlO 4 tetrahedra linked alternately by sharing all the oxygens. The Al 3+ in IV-fold coordination creates a local charge deficit that must be bal- anced with counter ions. According to Davidovits [2] the empirical formula of geopolymers or poly (sialates) may be written as follows (1): M n {-(SiO 2 ) z - AlO 2 } n · wH 2 O (1) ∗ Corresponding author at: Materials and Surface Science Institute, University of Limerick, Limerick, Ireland. Tel.: +353 061 234170. E-mail address: maria.izquierdo@ul.ie (M. Izquierdo). where M is a cation such as K + , Na + or Ca 2+ ; n is the degree of polycondensation and z is 1, 2 or 3. Other cations such as Li + , Ba 2+ , NH 4 + and H 3 O + may be also present. Studies on geopolymer green-chemistry have resulted in the development of alternative cements based on natural materials or industrial wastes; particularly coal combustion fly ash [4–14]. The geopolymerization of fly ash offers environmental benefits, such as lower consumption of natural resources and a decrease in the net production of CO 2 ; around 17% of that emitted by the Portland cement industry [15]. Geopolymers have other properties that make them attractive for cementation such as fast hardening, high and early compres- sive strength, optimal acid resistance and long term durability [16]. Geopolymer matrices have been proven to stabilize, solid- ify and encapsulate metallic and radioactive wastes and industrial wastewater [17–20]. A number of studies have focused their attention on the microstructure, chemistry and mechanical properties of fly ash- based geopolymers, but less attention has been paid to their leaching behaviour. Furthermore, the leaching properties have been assessed mainly under acidic conditions, on pulverised mate- rial and based mostly on Cd, Cr, Cu and Pb mobility [3,8–11,21], while other leaching conditions and elements of environmental concern in PCC fly ash have been overlooked. It is for these rea- sons that, for environmental applications, the leaching behaviour of fly ash-slag-based geopolymer binders needs to be addressed more comprehensively. 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.11.075