Coal fly ash-slag-based geopolymers: Microstructure and metal leaching

• Published in: Journal of hazardous materials 2009-07, Vol.166 (1), p.561-566
• Main Authors: Izquierdo, Maria, Querol, Xavier, Davidovits, Joseph, Antenucci, Diano, Nugteren, Henk, Fernández-Pereira, Constantino
• Format: Article
• Language: English
• Subjects: Adsorption; Applied sciences; Carbon - chemistry; Chemical engineering; Coal; Coal Ash; Crystallization, leaching, miscellaneous separations; Environmental Pollutants - isolation & purification; Exact sciences and technology; Fly ash; Geopolymers; Hazardous Waste - prevention & control; Leaching; Metals, Heavy - isolation & purification; Other industrial wastes. Sewage sludge; Particulate Matter - chemistry; Pollution; Polymers - chemistry; Trace pollutants; Wastes; Water Purification - methods
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2008.11.063

This study deals with the use of fly ash as a starting material for geopolymeric matrices. The leachable concentrations of geopolymers were compared with those of the starting fly ash to evaluate the retention of potentially harmful elements within the geopolymer matrix. Geopolymer matrices give rise to a leaching scenario characterised by a highly alkaline environment, which inhibits the leaching of heavy metals but may enhance the mobilization of certain oxyanionic species. Thus, fly ash-based geopolymers were found to immobilise a number of trace pollutants such as Be, Bi, Cd, Co, Cr, Cu, Nb, Ni, Pb, Sn, Th, U, Y, Zr and rare earth elements. However, the leachable levels of elements occurring in their oxyanionic form such as As, B, Mo, Se, V and W were increased after geopolymerization. This suggests that an optimal dosage, synthesis and curing conditions are essential in order to obtain a long-term stable final product that ensures an efficient physical encapsulation.