Phase Diagrams of the Quaternary System Na+, Mg2+, NH4+//SO42−-H2O at 288.15K and Their Application

Abstract

In order to process and utilize the astrakanite resources comprehensively, the technology of (NH4)2SO4 salting-out method was proposed. On the base of the salt-water system phase equilibrium theory, The phase equilibrium solubilities of the quaternary system Na+, Mg2+, NH4+//SO42−-H2O and its subsystems at 288.15K were determined by isothermal method, and the phase diagrams were drawn. The results showed that the phase diagram of Na+, Mg2+, NH4+//SO42−-H2O system at 288.15K exists three co-saturation points and five crystallization fields, which the largest crystallization field is MgSO4·(NH4)2SO4·6H2O. The technique of processing astrakanite was proposed. The Mg–N compound fertilizer can be yielded with astrakanite and (NH4)2SO4 as the raw materials at 288.15K, and then Na2SO4·10H2O would be obtained when the remaining mother liquor was cooled to 273.15K. The method can separate and process astrakanite effectively with the advantages of simple operation, energy saving, environmental protection and so on, and can realize recycling production.

Keywords

• Astrakanite
• Phase equilibrium
• Salting-out method
• Mg–N compound fertilizer
• Na2SO4·10H2O