Removal and Recovery of Gaseous Elemental Mercury Using a Cl-Doped Protonated Polypyrrole@MWCNTs Composite Membrane

Abstract

Due to the restrictions on mercury mining, recovering the mercury from mercury-containing waste is attracting increasing attention. This study successfully achieved the removal and recovery of gaseous elemental mercury (Hg0) by using membrane technology. A novel composite membrane of Cl-doped protonated polypyrrole-coated multiwall carbon nanotubes (Cl-PPy@MWCNTs) was fabricated in which MWCNTs acted as the framework to support the active component Cl-PPy. The morphology, structure, and composition of the prepared membranes were determined by field emission scanning electron microcopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, etc. The composite membrane exhibited an excellent performance in Hg0 removal (97.3%) at a high space velocity of 200,000 h–1. The dynamical adsorption capacity of Hg0 was 3.87 mg/g when the Hg0 breakthrough reached 10%. The adsorbed Hg0 could be recovered/enriched via a leaching process using acidic NaCl solution; meanwhile, the membrane was regenerated. The recovered mercury was identified in the form of Hg2+, with a recovery efficiency of over 99%. Density functional theory calculations and mechanism analysis clarified that the electrons of Hg0 transported to the delocalized electron orbits of protonated PPy and then combined with Cl– to form Hg2Cl2/HgCl2. Finally, we first demonstrated that the analogous protonated conductive polymers (e.g., polyaniline) also possessed good Hg0 removal ability, implying that such species may offer more outstanding answers and attract attention in future.

Spontaneous adsorption–oxidation of gaseous elemental mercury via a conjugated unit –NH+˙–Cl*: creation and mechanisms

“…S6 † and 5c, where the decrease in zNH +from 0.30 to 0.15, namely the conversion from -NH + cto -NH-, conrmed the electron transfer from Hg 0 to -NH + c-, consistent with our previous conclusion that -NH d+in Cl-PPy + @MWCNTs predominates for Hg 0 removal. 26 Furthermore, the current study claried a key point that the functional unit -NH d+is -NH + c-, which is useful in terms of Hg 0 removal. In addition, their different adsorption energies conrm the above conclusions.…”

“…In order to show the difference in the structures of the various PANI forms, two types of PANI were synthesized. Additionally, the current study still used the previous fabrication method 26 (Fig. S2 †), which was convenient to exhibit the unique advantages and properties of PANI for Hg 0 removal.…”

“…Given the above drawbacks, we speculated that if a novel lightweight material that possesses a high removal efficiency, large adsorption capacity, good regeneration ability, and low regeneration energy consumption could be designed, the costeffective removal of Hg 0 could be realized. Further, in our previous work 26 we synthesized a novel ultralight organic composite material, namely Cl-doped protonated polypyrrolecoated multiwall carbon nanotubes (Cl-PPy@MWCNTs), and conrmed that it could realize the removal and recovery of Hg 0 from simulated tail gas. So we put proposed a mechanism for the spontaneous adsorption-oxidation of Hg 0 , whereby the Hg 0 could spontaneously transfer its electrons to the delocalized electron orbits of the protonated PPy and then combine with Cl − to form Hg 2 Cl 2 /HgCl 2 .…”

Simultaneous Adsorption of Gaseous Hg0 and Hg(II) by Regenerable Monolithic FeMoSx/TiO2: Mechanism and its Application in the Centralized Control of Hg Pollution in Coal-Fired Flue Gas

“…4 Hence, controlling Hg 0 emissions is essential to control Hg emissions from CFG. 6 There are two mainstream technological paths to control Hg 0 emitted from CFG. 3,4 One path is to convert Hg 0 to Hg(II) using selective catalytic reduction (SCR) catalysts, which are then removed by WFGD.…”

“…Hg p is removed by electrostatic precipitators (ESPs) with particulate matter, and Hg­(II) is removed by wet flue gas desulfurization (WFGDs) because of its water solubility . Hence, controlling Hg 0 emissions is essential to control Hg emissions from CFG …”