Limestone and slaked lime influence physical and chemical modelling on the mixed mineral fertilizers components activity

A binary systems’ components mutual influence thermodynamic assessment containing limestone or slaked lime in a mixture with nitrogen-containing, potassium-containing and phosphorus-containing mineral fertilizers has been carried out. The systems under study the following indicators were taken into account: the Gibbs system energy, the corresponding components chemical potentials, the solution components amount, the evolved gases amount, the solution pH, and the system redox potential. The results obtained made it possible to conclude an increase in the oxygen chemical activity in systems containing limestone and slaked lime. At the same time, the slaked lime introduction gives an increasing oxygen activity significantly greater effect than the limestone introduction. The maximum effect concerning an increase in oxygen activity is achieved with the limestone and slaked lime introduction in doses of approximately 2 t/ha in the mixed mineral fertilizers’ composition. The phosphorus activity increases with calcium carbonate and calcium hydroxide increasing amounts in mixtures. The potassium activity is lower than that of phosphorus. Nitrogen has the lowest activity, which is possibly due to the low-activity gaseous nitrogen present in the system, although, as shown by the simulation results, there is its transformation thermodynamic probability into a nitrate ion. Binary mixtures based on calcium carbonate have a higher oxidation potential in comparison with calcium hydroxide.