Effects of Aluminum Dosage on Gel Formation and Heavy Metal Immobilization in Alkali-Activated Municipal Solid Waste Incineration Fly Ash

Abstract

This work attempts to investigate the effects of aluminum dosage on the immobilization of heavy metals in alkali-activated municipal solid waste incineration fly ash-based pastes to manage hazardous threats in it. A variable proportion of metakaolin is used to achieve different aluminum dosages in the synthesized pastes. Structure, composition, morphology, and mechanical property of the prepared pastes are studied by employing X-ray diffraction, 29Si NMR, scanning electron microscopy, and compressive strength measurements. The results showed that a 5% metakaolin-composed paste exhibited the highest compressive strength (10.94 MPa). The addition of the aluminum dosage-converted soluble chloride salt into Friedel’s salt, subsequently, improved the immobilization of heavy metals. The toxic characteristic leaching procedure test showed that a small amount of aluminum can improve immobilization dominantly because of the effective encapsulation ability of the pastes. The molecular modeling and simulation analysis illustrated that because of the presence of Na+ in it, sodium–alumino–silicate–hydrate (N–A–S–H) gel possesses the most stable molecular orientation.

Characterization of Slag Reprocessing Tailings-Based Geopolymers in Marine Environment

“…NMR spectroscopy is an excellent analytical method for characterizing the short-range ordering and molecular structure of silicates [23,24]. It employs Gaussian peak deconvolution to overcome the lack of spectra resolution and separate and quantify Q n (mAl) species (0≤ m ≤ n ≤4, m, n = integer).…”

Review on Geopolymers as Wellbore Sealants: State of the Art Optimization for CO2 Exposure and Perspectives

“…However, the use of alkali carbonates and alkali aluminates has also been reported . The major roles of alkali reactants are (a) to provide high pH conditions required for the activation of the raw aluminosilicate precursors and (b) to provide alkali cations that can balance the negative charges induced when AlO 4 tetrahedra are incorporated into the cross-linked 3D network structure of the GPs. ,,,,, …”

“…They can be produced by mixing a liquid activator (i.e., hardener), such as solutions of K 2 SiO 3 , Na 2 SiO 3 , NaOH, KOH, Na 2 CO 3 , and K 2 CO 3 , with various sources of (solid) reactive aluminosilicate precursors. The precursors most considered are fly ash, metakaolin, blast furnace slag, naturally occurring rocks, natural soil, biomass ash, rice husk ash, red mud, mine tailings, and glass product waste. − Some of the major benefits of GPs over OPC-based binders are their environmental and economic merits, low Ca content, simple synthesis process, lower chemical shrinkage, rapid strength development, low matrix permeability, resistance to fire and acid attack, and the potential to immobilize toxic materials. ,− However, these properties can vary significantly depending on the mix design of the slurry and the minerology of the GPs.…”

Gel Evolution of Copper Tailing-Based Green Geopolymers in Marine Related Environments

“…For further characterization of the nanostructure change in the geopolymers with different exposures, NMR spectroscopy was used to characterize the short-range ordering and molecular structure of the geopolymer [6,36]. It employs Gaussian peak deconvolution to overcome the lack of spectra resolution and to separate and quantify Q n (mAl) species (0≤ m ≤ n ≤ 4, m, n = integer).…”

“…Although Davidovits defended that geopolymers differ from alkali-activated materials (AAMs) in chemistry, molecular structure, long-term durability, etc., plenty of works use the term geopolymer when dealing with AAMs, even in high-calcium alkali-activated systems [2,3]. Geopolymers are mainly studied in the application of green concrete materials for the replacement of ordinary Portland cement (OPC) material [4][5][6], although there are other particular applications of geopolymers that are also interesting, for example, the synthesis of waste-based materials into marine concrete geopolymers [7][8][9].…”