Mutual solubility of salts in a triple NH4HCO3-(NH4)(2)SO4-H2O system was studied in the temperature range of 293.15-323.15 K. The tests were performed using the isothermal solution saturation method. The obtained results provided a basis for a graph depicting the partial solubility polytherm and for the determination of solubility plane equations for the studied system. The obtained experimental results and knowledge related to qualitative and quantitative relationships in a three-component system are required in order to specify the direction of further work on disposal methods of gypsum waste via carbonization. The obtained experimental results provide a physico-chemical basis for planning of separation and crystallization processes in the chemical industry.