Sustainable Biochar Sorbents for Elemental Mercury Capture From Flue Gas: Review and Prospects

ABSTRACT

Elemental mercury (Hg ⁰ ), as the most dominant form of airborne mercury, is extremely hard to be captured because of its high volatility, aqueous insolubility, and thermal stability. Hg° capture from coal combustion, metallurgical, and incineration flue gases is still challenging due to lack of cost‐efficient sorbents. Recently, biochar, as a sustainable and cost‐effective sorbent, has been extensively employed for Hg° capture due to its low price, natural abundance, renewability, carbon neutrality, and variety diversity. This review outlines the recent progress of Hg° capture by biochars in terms of biochar production, chemical activation, surface modification, and reaction mechanisms. Pristine biochar holds a lower Hg ⁰ adsorption activity. Chemical activation and surface modification can effectively reinforce the performance of the biochar due to improved porosity and augmented active species. Generally, the optimal mass ratio of activators to biomass is 2:1. Molten salt activation combined with sulfide modification or H ₂ S plasma treatment is proposed as a prospective pathway to prepare high‐performance biochars. Mercury capture mechanisms of the biochars could likely be unraveled using theoretical calculation based on density functional theory (DFT).