**2. Materials and Methods**

The process presented in Figure 1 consists of three stages of dry molding, roasting and alkaline leaching. First, according to the content of Al element, SAD was mixed with a certain amount of alkali. The mixture was dry pressed under a constant pressure to produce cylindrical samples. Then, the clinkers were roasted at a high temperature and leached in alkaline solution to obtain NaAlO2 solution, which can be used to produce alumina. During the roasting process, AlN was decomposed into harmless N2, while the chlorate was separated and recovered after volatilization into the gaseous phase.

First, the thermodynamic analysis was carried out. Then, the roasting and leaching experiments were conducted to investigate the phase transition and to optimize the recovery efficiency. The leaching kinetics and the apparent activation energy of the NaAlO2 leaching process were discussed. The developed extraction process described here has several innovations, some of which are as follows:

(1) The roasting process can achieve the sustainable treatment and extraction of the valuable Al element from SAD without any pretreatment. (2) Dry pressing was applied to avoid the generation of harmful ammonia and liquid waste and to decrease the energy consumption of the roasting process. (3) The reaction exhibited a high yield and was simple and sustainable. (4) The chlorate in the SAD was volatilized in the roasting process and could be recovered after condensation.

#### *2.1. Materials*

The SAD used in this study came from an aluminum remelting plant in Guangxi, China. The X-ray diffraction (XRD) analysis of the SAD showed that the aluminum-containing phases included the metallic aluminum, α-Al2O3, γ-Al2O3, AlN and MgAl2O4, as shown in Figure 2. These were the products of the reactions of the molten aluminum with the O2, N2 and Mg impurities during the formation and remelting of the SAD. Additionally, some impurity oxides (Fe2O3 and SiO2) and salts, including chlorides (NaCl) and fluorides (CaF2), were present in the SAD. The salts were added as a flux during the melting process to facilitate the heat transfer and reduce the oxidation of the molten aluminum. The chemical analysis of the SAD is presented in Table 1. Nearly 40 wt.% of the sample was made up of

Al element, indicating that the SAD was a solid waste with a high utilization value. All the nitrogen was transformed into the phase of AlN with a content of 19.62 wt.%.

**Figure 2.** XRD pattern of the SAD sample.

**Table 1.** Chemical composition of SAD.

