Catalytic Synergistic Removal of Nitrate, Sulfate, and Trace Metals from Wet-Oxidation Denitrification Wastewater

Abstract

Wet oxidation denitrification of flue gas enables ultralow NOx emissions and is increasingly adopted at coal-fired power plants. However, the process discharges wastewater enriched in nitrate and sulfate with minimal heavy metals. Conventional limestone and magnesium hydroxide treatments reliably remove sulfate but are ineffective for nitrate control. To bridge this gap, we propose a catalytic approach that selectively targets high nitrate while concurrently removing sulfate and trace metals. Waste heat from the plant is recovered to heat the wastewater, after which ferrous oxalate is dosed. This initiates a catalytic cycle among oxalate, Fe2+, and nitrate, generating Fe3+ in situ while consuming H+. The resulting pH rise triggers a secondary crystallization–precipitation sequence wherein Fe3+ precipitates sulfate as jarosite, coprecipitating trace Cu and Cr and releasing H+ back into the wastewater. Under optimized conditions at 95 °C, nitrate was reduced by 98% to 1.1 g/L and sulfate fell below the detection limit, allowing the treated wastewater to be directly reused in the wet oxidation process for flue gas purification. This approach uses simple equipment under atmospheric conditions and offers adaptive operational strategies for water recycling and sustainable wastewater management in coal-fired power plants.