A review on coal fly ash-based adsorbents for mercury and arsenic removal

Emissions of mercury and arsenic from flue gas and water have become a great public concern due to their hazards to human health and the ecosystem. Many removal methods have been developed to capture mercury and arsenic from flue gas and water. Adsorption is the most potential one based on simple equipment, low energy consumption, and low corrosiveness. However, due to huge demand, inactivation or consumption, the cost of adsorbents is quite high, limiting the large-scale applications of adsorption technologies. Coal fly ash (CFA) is a kind of solid waste generated from coal combustion. Its emissions and accumulation have resulted in severe environmental consequences and disposal challenges. Recently, CFA has been identified as a suitable adsorbent to capture mercury and arsenic from water and flue gas due to its abundant supply, good pore structure, and low cost. Hence, the use of CFA as adsorbents/precursors to prepare mercury and arsenic adsorbents has great practical significance as it cannot only reduce their capture cost but also ameliorate problems associated with solid waste disposal. This comprehensive review provides the state-of-the-art of mercury and arsenic capture using adsorbents prepared from CFA. It is intended to advance our fundamental understanding of this emerging research field and outline directions to spur future research and development of sustainable and cost-effective mercury/arsenic adsorption technologies based on CFA re-utilization. • Cost of activated carbon for mercury removal is very high, and its price is up to 1190 $/ton. • Fly ash is likely to achieve zero cost due to a very wide range of sources. • Fly ash has low surface area (mostly below 20 m 2 /g), but can reach 8–12 times of original after activation. • Hg removal efficiencies are only 11–66% for raw fly ashes, and are up to 44–100% for modified fly ashes. • Using fly ash to prepare adsorbent can reduce Hg/As capture costs and ameliorate disposal problem.