Encapsulation of Solid Waste Incinerator Ash in Geopolymer Concretes and Its Applications

The current study examines chemical and mechanical behaviors resulting from the gradual incorporation of incinerator fly ash (IFA) into an alkaline-activated coal fly ash (CFA) matrix, such as: 1) the incinerator ash is chemically stabilized; and 2) the resulting mixture provides fresh and hardened properties adequate for the production of commercially viable precast components. This paper presents the results of an extensive chemical characterization of IFA and CFA, including particle size distribution (PSD), X-ray fluorescence (XRF), and inductive coupled plasma (ICP) methods. Geopolymer concretes and grouts made from IFA, CFA, and four IFA-CFA blends were subjected to leachability tests, as well as extensive mechanical and rheological testing, including compressive strength, elastic modulus, Poisson's ratio, and setting time. Preliminary results are encouraging, suggesting that toxicity levels of the leachate can be reduced by up to two orders of magnitude. Reduction in leaching levels of heavy metals was observed for Al, Cr, Ni, Zn, Se, Mo, Ba, Tl, Pb, and Th in geopolymer samples. Furthermore, the resulting mixture is workable and yields a mechanical strength of up to 41 MPa (6000 psi). PSD analysis showed CFA was 8% smaller than IFA. PSD plays a vital role in contributing to geopolymerization, as finer particle sizes involved in geopolymerization lead to a dense microstructure. This indicates that while geopolymerization could be viewed as an effective approach for treating IFA, immobilization of heavy metals by forming stable zeolites provides an additional mechanism for encapsulation of heavy metals. The use of IFA in beneficiation applications is expected to result in significant cost reduction to operators of municipal waste incinerators, eliminating costly transportation and landfill expenditures.