Bloedite (Na2SO4 center dot MgSO4 center dot 4H(2)O) is a kind of abundant natural resources. So far, it has not been developed and utilized effectively. In order to process and develop bloedite, a new technology to produce Na2SO4 and Mg-N compound fertilizers by a (NH4)(2)SO4 salting-out method to separate bloedite was proposed, the phase equilibrium of the quaternary system Na2SO4-MgSO4-(NH4)(2)SO4-H2O at 25 C was studied. The solubilities of the quaternary system Na2SO4-MgSO4-(NH4)(2)SO4-H2O were measured using isothermal method, and the phase diagram of this system was investigated. According to this phase diagram, there are six solid phases crystalline zones, which correspond to MgSO4 center dot 7H(2)O, MgSO4 center dot Na2SO4 center dot 4H(2)O, Na2SO4 center dot 10H(2)O, Na2SO4 center dot(NH4)(2)SO4 center dot 4H(2)O, (NH4)(2)SO4 and MgSO4 center dot(NH4)(2)SO4 center dot 6H(2)O respectively. MgSO4 center dot(NH4)(2)SO4 center dot 6H(2)O has the largest crystalline zone among these crystalline zones, which indicates that the double salt MgSO4 center dot(NH4)(2)SO4 center dot 6H(2)O is the most easily to crystallize out. Based on the analysis and calculation of the phase diagrams, a new technology to produce Mg-N compound fertilizers and Na2SO4 center dot 10H(2)O using bloedite and (NH4)(2)SO4 as raw materials shows the advantage of non-evaporation of water and low energy consumption. (C) 2014 Elsevier B.V. All rights reserved.