Process for the production of reactive composition particles comprising at least 60% by weight of sodium carbonate and having a BET specific surface of at least 4 m2/g, according to which particles based on sodium bicarbonate and/or sodium sesquicarbonate having a median particle size D50 of less than 35 μm are brought into contact with a stream of hot gases having a temperature of at least 100° C. in order to convert the sodium bicarbonate into sodium carbonate by calcination, the stream of hot gases comprising calcined particles subsequently being subjected to a separation stage in order to obtain, on the one hand, the reactive composition particles and, on the other hand, a separated stream of hot gases comprising CO2 and steam, the separated stream of hot gases being at least partly recycled upstream of the separation stage.