【Abstract】 In order to establish the theortetical basis and optimize the production conditions for the separation process of the H₃BO₃-MgSO₄ mixed solution by using Mg（NO₃）₂ as the salting out agent.The phase diagrams of H₃BO₃─MgSO₄─Mg（NO₃）₂─H₂O system at 25℃ and 100℃ were studied.The results show that there appear MgSO₄·7H₂O,MgSO₄·6H₂O,Mg（NO₃）₂·6H₂O and H₃BO₃ three crystallization regions in the phase diagram at 25℃,and three crystallization regions of MgSO₄·H₂O,Mg（NO₃）₂·2H₂O,and H₃BO₃ at l00℃.When the temperatures rise from 25℃ to 100℃,the crystallization regions for magnesium sulfate hydlates grow larger and while that of H₃BO₃ get smaller.Only MgSO₄·4H₂O could be crystallized out alone,if evaporating the H₃BO₃─MgSO₄ solution in the presence of Mg（NO₃）₂.On cooling the MgSO₄ mother liquor,H₃BO₃ can be separated alone without any addition of water.更多还原