Copper slag as a catalyst for mercury oxidation in coal combustion flue gas

Copper slag is a byproduct of the pyrometallurgical smelting of copper concentrate. It was used in this study to catalyze elemental mercury (Hg⁰) oxidation in simulated coal combustion flue gas. The copper slag exhibited excellent catalytic performance in Hg⁰ oxidation at temperatures between 200 °C and 300 °C. At the most optimal temperature of 250 °C, a Hg⁰ oxidation efficiency of 93.8% was achieved under simulated coal combustion flue gas with both a high Hg⁰ concentration and a high gas hourly space velocity of 128,000 h^-1. Hydrogen chloride (HCl) was the flue gas component responsible for Hg⁰ oxidation over the copper slag. The transition metal oxides, including iron oxides and copper oxide in the copper slag, exhibited significant catalytic activities in the surface-mediated oxidation of Hg⁰ in the presence of HCl. It is proposed that the Hg⁰ oxidation over the copper slag followed the Langmuir-Hinshelwood mechanism whereby reactive chlorine species that originated from HCl reacted with the physically adsorbed Hg⁰ to form oxidized mercury. This study demonstrated the possibility of reusing copper slag as a catalyst for Hg⁰ oxidation and revealed the mechanisms involved in the process and the key factors in the performance. This knowledge has fundamental importance in simultaneously reducing industrial waste and controlling mercury emissions from coal-fired power plants.