The researchers studied a method to remove harmful SO2 gas from flue gas using a semi-dry desulfurization process. They tested different factors like SO2 concentration, temperature, and sorbent amount to see how they affected the removal efficiency. They found that the initial SO2 concentration had the biggest impact on removal efficiency. Adding a specific amount of HNO3 to the sorbent slurry improved removal efficiency, but adding too much decreased it. The optimal amount of HNO3 was 200 mmol.