Multimedia Mercury Recovery from Coal-Fired Power Plants Utilizing N‑Containing Conjugated Polymer Functionalized Fly Ash

To recover multimedia mercury from coal-fired power plants, a novel N-containing conjugated polymer (polyaniline and polypyrrole) functionalized fly ash was prepared, which could continuously adsorb 99.2% of gaseous Hg⁰ at a high space velocity of 368,500 h^–1 and nearly 100% of aqueous Hg²⁺ in the solution pH range of 2–12. The adsorption capacities of Hg⁰ and Hg²⁺ reach 1.62 and 101.36 mg/g, respectively. Such a kind of adsorbent has good environmental applicability, i.e. good resistance to coexisting O₂/NO/SO₂ and coexisting Na⁺/K⁺/Ca²⁺/Mg²⁺/SO₄^2–. This adsorbent has very low specific resistances (6 × 10⁶–5 × 10⁹ Ω·cm) and thus can be easily collected by an electrostatic precipitator under low-voltage (0.1–0.8 kV). The Hg-saturated adsorbent can desorb almost 100% Hg under relatively low temperature (<250 °C). Characterization and theoretical calculations reveal that conjugated-N is the critical site for adsorbing both Hg⁰ and Hg²⁺ as well as activating chlorine. Gaseous Hg⁰ is oxidized and adsorbed in the form of Hg_XCl_X(ad), while aqueous Hg²⁺ is adsorbed to form a complex with conjugated-N, and parts of Hg²⁺ are reduced to Hg⁺ by conjugated-N. This adsorbent can be easily large-scale manufactured; thus, this novel solid waste functionalization method is promising to be applied in coal-fired power plants and other Hg-involving industrial scenes.