Nitric oxide removal by combined persulfate and ferrous–EDTA reaction systems

Abstract

Nitric oxide (NO) removal from simulated flue gas is investigated using combined aqueous persulfate (Na2S2O8) and ferrous ethylenediaminetetraacetate (Fe2+–EDTA) systems. The results at 23–70°C showed significant improvement in NO removal using the optimally obtained molar ratio of 1:1 for the Fe2+ and EDTA compared with temperature-only and combined temperature-Fe2+ activated persulfate systems with 0.1M Na2S2O8 and 0.01M Fe2+ in the absence of EDTA. Almost 100% NO conversion can be achieved at 70°C (flue gas treatment inlet temperature generally at 50–70°C) compared to temperature and Fe2+-activated persulfate systems which require ⩾90°C for such high removal efficiency. The percentage increases in NO removal were dependent on temperature, 25–30% and 5–10% at the lower (<40°C) and higher (>40°C) temperatures, respectively. A very high concentration of Fe2+–EDTA appears to negatively impact NO removal. However, this process operates at an optimal NO removal pH of near neutral (∼6.5) with efficiency decreasing at very low or high pH. This should reduce the use of auxiliary chemical for pH adjustment and help mitigate the important technological hurdle of undesired ferric product formation associated with Fe2+-only activated persulfate and other Fenton-like systems at pH (>3.5). The material balance on iron species (Fe2+, Fe3+ and Fe2+–EDTA) was determined to better understand the chemistry of persulfate with Fe2+–EDTA for NO removal. The results demonstrate the feasibility of near complete NO removal at relatively lower temperatures (with the advantage of reduced energy usage), and sustained longtime high NO absorption capability.