3.2.1. The Effects of the Sorbent Dosage

The influence of sorbent dosage on Hg removal has been investigated to find out the appropriate dosage of sorbents as a basis for subsequently study. The sorbent dosage determines the sorption capacity of sorbents for a given concentration of Hg2<sup>+</sup> because it controls the sorbent-sorbate equilibrium of a system [37]. The effects of sorbents dosage on Hg sorption were studied in the dosage range of 5−60 mg in 50 mL Hg2<sup>+</sup> solution. The results of AC, SAC, and FeS dosage are presented in Figure 2, and all experimental data are performed in triplicate. The Hg sorption capacity of AC first increased and then decreased as the Hg removal efficiency increased, due to the increment of AC dosage would provide more sorption active sites to take up Hg in a fixed Hg2<sup>+</sup> initial concentration. The SAC and FeS showed a similar tendency as AC. Based on the result, the suggested optimum dosages for AC, SAC and FeS at a fixed initial concentration of Hg2<sup>+</sup> were 30, 10, and 10 mg, respectively. Owning to Hg removal efficiency may be affected by both the properties and dosage of sorbents, the normalization and comparison of different types sorbents in the same mass benchmark were

needed. Therefore, the appropriate dosage of sorbents was determined as 20 mg for the subsequent experiments in this research.

**Figure 2.** Effect of (**a**) AC; (**b**) SAC; (**c**) FeS dosage on Hg removal efficiency.
