The wet limestone process is one of the standard processes for the cleaning of SO2 containing flue gases in industry. In order to reduce capital and operating costs an increasing separation efficiency and the quality of the gypsum are very important. The absorbent material has great influence on the above mentioned criteria. Experiment with chalkstone, calcium hydroxid and limestones of different purity and grain size have been performed. Results differ in a wide range. Limestone dissolution and therefore Ca2+ availability influence the performance of the flue gas desulphurization. The fundamental influencing factors on the limestone dissolution are pH, the absobent material, CO2 concentration in the flue gas, the concentration of different ions in the slurry and the particle size distribution of the limestone. This study deals with the influence of particle size distribution and the different absorbent materials. Results show that finer particles dissolve faster than the coarser ones. In addition the separation efficiency was way better with calcium hydroxide and also chalkstone did show a better desulphurization performance compared to standard quality limestone.