*3.6. Selectivity for Hg2+ Removal from Binary Solution System*

Considering the field application of FA48, the selectivity for Hg2+ adsorption is one of the critical parameters in this study. Therefore, the effect of coexisting ions on the adsorption capability of Hg2+ is shown in Table 6. In our study, Na<sup>+</sup> , Mg2+, K<sup>+</sup> , Ca2+ , Ni2+, Cu2+, Zn2+, Sr2+, and Cd2+ were used as the components of the binary solution system, as these ions are ubiquitous in the water environment [48,49]. In this study, the removal percentage of Hg2+ using FA48 in a single solution system was approximately 14.0% whereas, the removal of Hg2+ in the binary solution system was over 11.4% (except for Na<sup>+</sup> and K<sup>+</sup> ), and the removal of other cations was significantly lower. A similar trend was reported in a previous study [6]. In addition, previous studies reported that the radius of the hydrated ion and/or the electronegativity of the adsorbate (Hg2+ in this study) strongly and directly influenced the adsorption capability in aqueous media [48,49]. Therefore, similar phenomena were observed under our experimental conditions. Finally, our results show that FA48 is useful for the selective removal of Hg2+ from aqueous media. Moreover, the Minamata Convention on Mercury was adopted by the Intergovernmental Negotiating Committee in 2017. Therefore, the development of removal techniques for Hg2+ in wastewater from anthropogenic activities such as the steel industry is very important for establishing a sustainable society. Thus, FA48 could be applied for wastewater purification including Hg2+ such as the steel industry.


**Table 6.** Adsorption capacity of Hg2+ in binary solution system.
