*2.1. Experiment on Arsenic Removal from Roasting Iron Ore*

The composition of mixed ore used in the test is listed in Table 1.

**Table 1.** Composition and proportion of roasting ore.


Note: "/" Represents "the chemical composition is not determined".

The mixed ore can be obtained by mixing 90% iron ore with 10% arsenopyrite. Mixed ore was crushed by an F77-1 sealed sample grinder for 1 min, then screened by a 75 mesh sieve. The ore powder larger than 75 mesh was crushed again until all powders were less than 75 mesh, and then the crushed powder was mixed. Mixed ore was blended with water to make iron ore balls with a diameter of 10 ± 2 mm. Furthermore, the iron ore balls were heated in an oven at 110 ◦C for 3 h, until they were completely dry. Then, the balls were taken out and reserved for further experiments.

The roasting test was carried out in a horizontal resistance furnace with 60 mm i.d. quartz tube, and the constant temperature zone of the resistance furnace was controlled using a thermocouple. The experiments were carried out in an air atmosphere and nitrogen atmosphere (1 L·min−1, STP), respectively. The roasting temperature was 700, 800, 900, and 1000 ◦C, respectively, and the roasting time was 60 min. The porcelain boat loaded with the ore ball was put into the constant temperature zone of the tube furnace. When the roasting time was over, the power was turned off, and the sample was cooled down to room temperature and analyzed by various techniques. The schematic illustration of the roasting method is shown in Figure 1.

Gas inlet Resistance furnace Thermocouple Beaker

**Figure 1.** Schematic illustration of roasting test.

#### *2.2. Experiment on Recovery of Arsenic by Roasting Dust Ash*

The composition of dust ash of roasting iron ore from an iron plant is shown in Table 2. After adding 10% As2O3 chemically pure powder to the dust ash, the XRD pattern of the mixed dust ash powder is shown in Figure 2.


**Table 2.** Composition of dust ash from roasted iron ore.

The arsenic recovery experiment by roasting was carried out in two different atmospheres with 10% As2O3 powder in the dust ash. The experiment was carried out in a horizontal resistance furnace with a 60 mm i.d. quartz tube. The dust ash was first placed in the constant temperature zone of the quartz tube. When the roasting experiment was carried out under an anaerobic atmosphere, the quartz tube was evacuated and washed with high-purity nitrogen 3 times before heating up the furnace. The test process was protected by 100 mL/min of high-purity nitrogen. The dust ash was heated to 600 ◦C and then cooled to room temperature after an hour of constant temperature. The experimental steps of roasting in a reducing atmosphere with 2% graphite powder as raw material are the same for the anaerobic atmosphere. When the roasting time was over, the sample was cooled down to room temperature and analyzed by the following various tests.

**Figure 2.** XRD spectra of the mixed dust ash powder.
