**1. Introduction**

Arsenic content in the earth's crust is up to 5 mg·kg<sup>−</sup>1, and more than 300 arsenic species occur in nature. Arsenic is mainly associated with minerals such as pyrite, arsenopyrite, or enargite [1,2]. In most cases, arsenic is an unfavorable element in metallurgical processes. For example, arsenic reduces the quality of raw materials, affects the extraction of metal, interferes with the purity of the product, and poses serious environmental hazards [1]. Arsenic has an adverse effect on steel; for instance, the surface hot shortness increases, and the reduction of area and impact toughness decrease with the increase of arsenic content in steel [3–6]. Under the hot rolling or welding conditions, the arsenic in the steel leads to the increase in the content of arsenic at grain boundaries and the expansion of welding cracks [4,7–9]. Moreover, as the oxidability of arsenic is less than that of iron, it is difficult to remove arsenic by oxidation in the ironmaking or steelmaking process. It is theoretically possible to remove arsenic from molten iron by using excessive Al and Ca–Fe alloys or rare earth elements, but it also needs deep deoxidation and desulfurization before arsenic removal can be achieved, so the cost of arsenic removal is too high to be feasible in realistic production [10]. However, the price of arsenic-bearing iron ore is cheaper than that of high-grade iron ore. Moreover, the total amount of high-grade iron ore is

decreasing greatly in the earth, and arsenic-bearing ore needs to be comprehensively utilized through ore blending. Some metallurgical enterprises at home and abroad, such as Peru, Chile, Philippines, France, Mexico, and China, have adopted some arsenic-bearing ore in the metallurgical industry [11]. When these arsenic-bearing ores are used, they are faced with the problem of arsenic removal from ores and the problem of arsenic-bearing dust treatment from the point of view of environmental protection.

Arsenic can be removed from arsenic-bearing ore by a roasting or sintering method due to the volatile nature of arsenic and its compounds [12]; thus, some scholars have explored the appropriate arsenic removal conditions by performing roasting or sintering experiments. Yin et al. and Lu et al. studied arsenic removal from copper–silver ore using a roasting method [13,14], and the impact of different parameters (e.g., temperature, atmosphere, and roasting time) on the arsenic removal ratio was also evaluated. Lu et al. investigated arsenic removal from arsenic-bearing iron ore during the sintering process [15,16]. The effects of temperature, bed depth, gas pressure, and coal ratio on arsenic removal during the sintering process were studied, and the reasonable technical parameters were obtained. In addition to the arsenic removal tests by roasting and sintering methods, a number of scholars also carried out thermodynamic calculations on arsenic removal, and discussed the arsenic-bearing products and suitable conditions for arsenic removal. Chakraborti and Lynch analyzed the As–S–O vapor system [17] and further identified the importance of bed depth in the rapid release of arsenic from arsenical materials under an oxidizing atmosphere. Contreras et al. evaluated the impact of various factors, such as trace element concentration, flue gas composition, temperature, and pressure, on the equilibrium composition based on the arsenic interactions in the co-combustion processes [18]. Nakazawa et al. and Zhang et al. studied the thermodynamics of arsenic removal from arsenic-containing copper ore during roasting [19] and arsenic-bearing iron ores during sintering [20–23], respectively, and obtained the equilibrium components containing arsenic and the arsenic removal rate.

The arsenic removed by roasting is mixed in the dust ash. For arsenic existing in dust, chemical adsorption of gaseous arsenic by CaO or CaCO3 can effectively control arsenic content in flue gas and prevent arsenic pollution [24–26], but arsenate is easy to remain in dust, which is not conducive to the use of dust ash as raw material for sintering or roasting ore. Therefore, recovery of As2O3 is another feasible method.

Although arsenic removal experiments and thermodynamic calculations have been carried out by many scholars [12–23], and the volatilization behavior of arsenic in the process of roasting has also been explored [13,22], the mechanism of arsenic removal by roasting has never been reported. Exploration of the mechanism of arsenic removal by a roasting process and investigation of the residual form of arsenic in the roasted ore are important for controlling the arsenic removal efficiency and the arsenic component. Moreover, it is important to recover arsenic from dust ash to prevent further mobilization of arsenic and arsenic contamination. Therefore, these problems were attempted in this research.
