2.2. Experimental Process

Experiments were performed in a high-purity alumina crucible with a capacity of 1000 g, an internal diameter of 100 mm, and a height of 150 mm. Before the liquation experiments, the zinc metal was placed into the alumina crucible and heated to 1223 K in a resistance furnace. The refined coarse Al–Si alloy was added to the zinc, and stirred slowly until all the coarse Al–Si alloy melted into the zinc to form a Zn–Al–Si–Fe alloy [18,19]. Afterwards, the alloy was slowly cooled to 823–1023 K and maintained at that temperature for 30 min. Some semi-solidified solid alloy, i.e., slag, separated out from the melt and collected under the melt. The semi-solidified solid slag was an Fe- and Si-rich Zn–Al–Si–Fe alloy, and the melt was a Zn–Al alloy. After the liquation process, vacuum distillation experiments were performed in a vacuum furnace. In the distillation process, the Zn was distilled from the Zn–Al alloy and the Zn–Al–Fe–Si alloy, aluminum, and an Al–Si–Fe alloy were obtained [20,21]. Most of the aluminum was extracted from the coarse Al–Si alloy by selective liquation and vacuum distillation.

The composition of alloys and slag was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES, iCAP 6500, Thermo Fisher Scientific, Waltham, MA, USA). The phases and microstructure of the products were identified by X-ray diffraction analysis (XRD, Bragg–Brentano mode, X Pert ProMPDDY2094 (PANalytical B.V., Almelo, The Netherlands), 2θ: 5–90°, step size: 0.015°/0.1 s, Working voltage: 40 kV, Working current: 40 mA) and scanning electron microscopy (SEM, Ultra Plus-43-13, Zeiss, Oberkochen, German). The yield of the Zn–Al alloy of the selective liquation process was calculated by Equation (1) and the Al extraction efficiency was calculated by Equation (2):

where ηAl is the Al extraction efficiency (%); ηZn−Al is the Zn–Al alloy extraction efficiency (%); mZn−Al is the weight of the Zn–Al alloy (g); ms is the weight of slag (g); ωZn is the content of Zn in the Zn–Al alloy (wt%); and MAl−Si is the weight of the coarse Al–Si alloy (g).