Phase Diagrams of Na₂SO₄–MgSO₄–CO(NH₂)₂–H₂O System at 25 °C and Their Application

Bloedite (Na2SO4·MgSO4·4H2O) is an important natural chemical resource. So far, it has not been developed and utilized effectively because of its separation difficulties. To develop a new technology to produce Na2SO4 and Mg–N compound fertilizers by a CO(NH2)2 salting-out method to separate bloedite, the mutual solubilities of the ternary system Na2SO4–CO(NH2)2–H2O and the quaternary system Na2SO4–MgSO4–CO(NH2)2–H2O at 25 °C were measured, and the phase digrams of these two systems were investigated. According to the phase diagram analysis, it indicates that, by using the CO(NH2)2 salting-out method, Na2SO4 and MgSO4 in bloedite can achieve better separation and anhydrous sodium sulfate can be directly obtained. The yield of Na2SO4 was 90.98 % in the case of the mother solution without cycling and utilizing. Adding a certain amount of CO(NH2)2 into the mother solution after Na2SO4 separation, MgSO4·CO(NH2)2·2H2O can be obtained. After separating MgSO4·CO(NH2)2·2H2O from the solution, the remain mother solution was recycled to dissolve bloedite. The new technology can get stable recycle production.

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