Simultaneous NOx and SO2 removal during wet flue gas desulfurization, using copper smelter slag slurry combined with yellow phorphorus

The study of copper slag has attracted the attention of scholars from both China and around the world. But few have paid attention to its applications in the simultaneous removal of SO2 and NOx in wet flue gas desulfurization (WFGD), becasue WFGD technique is inappropriate for directly treating NOx owing to the low solubility of NO. This work aims to improve NOx removal efficiency in WFGD technology using copper slag slurry associated with the oxidation of NOx by yellow phosphorus. Different operating conditions, including dispersion of P-4, solid-liquid ratio, initial pH value of copper slag slurry, reaction temperature, oxygen content, and gas flow rate, were compared regarding the efficiency of SO2 and NOx simultaneous removal. The characterizations were carried out on the liquid and solid part of fresh and spent copper slag slurry after filtration. The results indicated that a great amount of metals ions, such as Fe3+ and Zn2+, were leached by reacting with produced acids (H2SO4, HNO3, and H3PO4), which had a liquid-phase catalytic oxidation on S-IV species (SO32-/HSO3-), leading to promotion in absorption for SO2. The copper slag played a significant role in dispersing the yellow phosphorus and promoting ozone generation, thus improving NOx removal efficiency. The reaction pathway can be divided into three parts: (a) ozone generation induced by yellow phosphorus, (b) the oxidation of NO by O-3 and then dissolution in aqueous solution, and (c) the dissolution of SO2 and the liquid-phase oxidation for SO2 through metal ions produced by the reaction between acid and copper slag.