# Optimal Mixture Designs for Heavy Metal Encapsulation in Municipal Solid Waste Incineration Fly Ash
## 2 Materials and Methods  
### Materials  
The MSWIFA was obtained from a local municipal waste incineration plant in Beijing, China. The FGD gypsum and GGBFS were obtained from Xingtai, China. The LFS was collected from Liuzhou, China. The GGBFS is classified as Grade S95 according to GB/T 18046-2008 [13]. Grade S95 slags provide compressive strength values at 7 days of at least 75% of a control mixture, and 28-day values of at least 95% of the control mixture. A Type I ordinary Portland cement (OPC) was also used in this study. The chemical compositions of all materials were determined using X-ray fluorescence (XRF), following procedures similar to ASTM C 114-18. ASTM C204-18 was used to determine the Blaine fineness of all materials. The fineness and chemical composition are shown in Table 1.  
When considering the chemical composition, GGBFS and LFS both contain high CaO contents. GGBFS contains a moderate amount of Al\({}_{2}\)O\({}_{3}\) and a large amount of SiO\({}_{2}\). 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.  
The reactivity of the slags and MSWIFA was assessed and the results suggest that the GGBFS and the LFS are latent hydraulic materials and the MSWIFA is an inert material [15]. The LFS however causes strength reductions when used in cement paste, likely because the mayenite causes sulfate imbalance [15].  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Material** & **CaO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **MgO** & **Fe\({}_{2}\)O\({}_{3}\)** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** & **SO\({}_{3}\)** & **Cl** & **Blaine Fineness** \\ \hline GGBFS & 46.54 & 29.78 & 12.18 & 6.00 & 1.22 & 0.45 & 0.41 & 0.36 & 0.02 & 420 \\ \hline LFS & 55.86 & 0.73 & 36.91 & 3.40 & 1.16 & 0.00 & 0.01 & 0.40 & 0.09 & 400 \\ \hline MSWIFA & 43.82 & 3.80 & 1.09 & 2.64 & 4.53 & 5.75 & 7.63 & 8.56 & 17.4 & 913 \\ \hline Gypsum & 48.13 & 2.62 & 0.96 & 1.48 & 0.48 & 0.08 & 0.21 & 44.03 & 0.43 & 373 \\ \hline Cement & 64.05 & 22.87 & 4.47 & 2.46 & 3.48 & 0.52 & - & 2.44 & 0.011 & 341 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition (mass %) and Blaine fineness (m\({}^{2}\)/kg) of the raw materials [21].  
X-ray diffraction (XRD) patterns of all materials are shown in Figure 1. The procedure followed for XRD is similar to that described in detail in Section 2.3. As expected, the GGBFS is mostly amorphous, though it does show minor amounts of jaffeite and fukalite. The LFS is also largely amorphous, but it shows substantial amounts of mayenite. On the other hand, the MSWIFA is largely or completely crystalline. It shows the presence of numerous crystalline phases, including calcium sulfates, sodium sulfate, sodium chloride, etc. The crystalline phases detected in the tested materials are in agreement with findings from the literature [15; 23; 24]. However, we note here that MSWIFA can be a very variable material in terms of its bulk oxide composition and crystalline phases, and generalizations regarding its chemistry should be done with caution.  
The phase composition of the cement as provided by the manufacturer is C\({}_{3}\)S: 56.54; C\({}_{2}\)S: 20.87; C\({}_{3}\)A: 6.22; C\({}_{4}\)AF: 10.31 (all amounts in mass %). Further details on the raw materials and their characterization are provided elsewhere [15; 21].