Mercury adsorption from South African coal fired power plants using modified and unmodified fly ash.

Abstract

Mercury can be classified as a global pollutant due to its ability to travel vast distances atmospherically, be deposited on land, and enter water sources. It poses significant environmental, human, and animal risks, especially when converted to methylmercury (any toxic compound containing the complex CH3Hg) (Merriam-Webster, 2024). One of the primary anthropogenic sources is from coal-fired power stations. Therefore, effective control measures need to be employed. Fly ash provides a practical, cheap solution by acting as an adsorbent The fly ash can be enhanced by modification with metallic salts such as CuCl2, FeCl3, ZnCl2, and CuSO4. Two South African fly ash samples obtained from Camden and Majuba power stations show excellent adsorption capacity for mercury when modified by CuCl2 and FeCl3. Fly ash characterisation revealed that the two fly ash samples have very similar chemical compositions. However, the pH differs, with the Camden (dark) ash having a lower pH of 8.62 and Majuba (light) ash having a pH of 10.35. The fly ash samples successfully adsorb Hg0 whilst in the presence of CO2, which competes for the active sites available for adsorption. The emission control technology is costly, so power stations should meet a specific eligibility criterion. The fly ash adsorption process can be operated as a single pollutant system or a part of sequential pollution systems with co-benefits. The environmental impact should be an essential consideration when operating the pollution control system as the waste generated is classified as hazardous according to NEM: WA (2008).