Abstract: A process is disclosed for the absorption of gaseous or liquid ammonia in acid solutions or slurries, including an ammonia absorption zone separated from a water vapor generation zone disposed at a higher level. A pressure difference is created between the two zones, so that the ammonia absorption takes place completely in the neighborhood of the point of inflow of the ammonia, with a temperature increase localized only near to said inflow point, and thus without giving rise to the generation of water vapor which therefore takes place in a liquid-vapor separation zone located at a higher level with respect to the ammonia absorption zone. The acid solutions or slurries to be neutralized may consist essentially of solutions of phosphoric acid, sulphuric acid, nitric acid, solutions resulting from the nitric acid attack on phosphorites, acid slurries resulting from nitric acid attack or sulphonitric acid attack on phosphorites, or mixtures thereof.