In this study we demonstrate both laboratory and pilot scale results for NOx ozonation of the simulated and real flue gases from the NPK fertilizer production plant. The off-gases from phosphate rock digestion process contain nitrogen oxides NOx, H2O vapor, hydrogen fluoride (HF) and silicon tetra-fluoride (SiF4). The usefulness of the pre-ozonation as a method for the intensification of NOx removal was proved. The required molar ratio O-3/NOx together with the residence time and the influence of water vapor were determined. The O-3/NOx ratio turned out to be around 1 for the industrial process. The presence of water vapor enhances the conversion rate from 5% to 63% for residence time lower than 1 s. We had confirmed for the first time that the pre-ozonation of flue gases from phosphate rock digestion process is a viable solution for the NOx removal. (C) 2016 Elsevier B.V. All rights reserved.