Use of Ladle Furnace Slag and Other Industrial By-Products to Encapsulate Chloride in Municipal Solid Waste Incineration Fly Ash

Abstract

Municipal solid waste incineration fly ash (MSWIFA) is a hazardous by-product of waste incineration. The objective of this research is to encapsulate the chloride in MSWIFA and to develop a utilizable construction material using MSWIFA, ground granulated blast-furnace slag (GGBFS), ladle furnace slag (LFS), and gypsum. A secondary objective of the work is to explain the hydration and encapsulation mechanisms in this material system using isothermal calorimetry (IC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and ion chromatography (IC). The predominant hydration products are ettringite, Friedel’s salt, and C-S-H gel, with Friedel’s salt and C-S-H dominating in systems high in LFS and ettringite and C-S-H gel dominating in systems low in LFS. The chloride encapsulation showed a strong correlation with the Friedel’s salt amount; however, some encapsulation was also likely due to physical binding in the C-S-H gel. In a system with 30% MSWIFA (by mass), the optimal amount of LFS for strength and chloride encapsulation is 20%–40% (by mass).

Optimal Mixture Designs for Heavy Metal Encapsulation in Municipal Solid Waste Incineration Fly Ash

“…While the specific systems studied here have not been investigated in the past, the hypothesis is in line with the literature which suggests that the use of such slags will favor the formation of hydrates and microstructures that will result in enhanced immobilization of heavy metals [22]. This work is part of a larger study on sustainable by-product binders and results on chloride binding and hydration in some of the systems studied here have been already published [21].…”

“…The LFS has a large amount of Al 2 O 3 and a negligible amount of SiO 2 . This composition is somewhat different from other LFS materials found in the literature and appears to be because Al bars were used in process of extraction and purification of steel [20,21]. MSWIFA contains considerable amounts of Cl, SO 3 , K 2 O, Na 2 O and a large amount of CaO.…”

“…Table 1. Chemical composition (mass %) and Blaine fineness (m 2 /kg) of the raw materials [21]. When considering the chemical composition, GGBFS and LFS both contain high CaO contents.…”

“…Although the composition and crystalline phase in LFS tend to be variable, a commonly found crystalline phase in LFS is mayenite (C 12 A 7 ). In our previous work, we have investigated mayenite reactions and found that it can form Friedel's salt when it reacts with the chloride that is commonly present in MSWIFA [21]. Friedel's salt is a layered double hydroxide (LDH) material, with interesting anion-exchange properties which leads to a potential for high heavy metals encapsulation [21].…”

“…In our previous work, we have investigated mayenite reactions and found that it can form Friedel's salt when it reacts with the chloride that is commonly present in MSWIFA [21]. Friedel's salt is a layered double hydroxide (LDH) material, with interesting anion-exchange properties which leads to a potential for high heavy metals encapsulation [21]. Due to these characteristics and potential hydrates that are formed with LFS, its use for heavy metal encapsulation warrants further study.…”