Abstract: Waste gas is contacted with a solution of a salt from a pollutant of the gas. This solution is obtained from another stage of the process used for cleansing or purifying the gas. The resulting mixture of gas and solution is subjected to vaporization so as to obtain a dry gaseous substance constituted by the waste gas and the evaporated solvent for the salt. The gaseous substance thus formed contains crystals of the salt as well as the pollutant present in the original waste gas. The salt crystals and other solid particles are removed from the gaseous substance in the form of a dry solids mixture. The gaseous substance is subsequently mixed with an absorption fluid such as an ammonia solution in order to wash out and redissolve any salt crystals which may remain in the gaseous substance and in order to remove the pollutant present in the original waste gas from the gaseous substance.