Study On Phase Equilibrium Of The Quaternary Systems Mg²⁺,NH₄⁺//Cl^-,SO₄^2--H₂O And NaCl-MgCl₂-NH₄-Cl-H₂O

The Qarhan salt lake is enriched with abundant potish resource, and the utilization of its resource mainly focuses on the preparation of potassium chloride and sodium choride at present. However, the byproduct magnesium chloride after extracting potassium chloride from the sea-lake brine is not adequately used. In view of the above, a new technology to produce Mg-N compound fertilizers by MgCl2 and（NH₄）2SO₄ was proposed, and a new idea to produce ammonium carnallite by MgCl2 and NH₄ Cl was raised. According to this,the high efficient utilization of MgCl2 and NaCl in salt lakes was realisead.The solubilities of the quaternary systems Mg2+, NH₄+//Cl^-, SO₄^2--H2 O at 25℃ and 0℃were measured using isothermal method, and the phase diagrams of the systems were investigated. By analysing the saturation points and the crystalline regions in these phase diagrams, we find that MgSO₄·（NH₄）2SO₄·6H₂O has a largest crystalline zone, and NH₄ Cl has a respectable crystalline zone too. It indicates that MgSO₄·（NH₄）2SO₄·6H₂O can be formed by the reactaion of MgCl2 and（NH₄）2SO₄, and NH₄ Cl is easy to crystalize from the mother liquid after extracting Mg-N compound fertilizers. On the basis of the phase diagrams of the quaternary systems Mg2+, NH₄+//Cl^-, SO₄^2--H2 O at 25 ℃ and 0 ℃, We analyse the new technology to produce Mg-N compound fertilizers by MgCl2 and（NH₄）2SO₄. At the same time, The solubilities of the quaternary systems NaCl^-MgCl2-NH₄Cl^-H2 O at 25℃ and 0 ℃ were measured using isothermal method, and the phase diagrams of the systems were investigated. The saturation points and the crystalline regions in the phase diagrams were analysed. According to the phase diagrams obtained, we find that MgCl2·NH₄Cl·6H₂O can be formed by the reactaion of MgCl2 and NH₄ Cl, when NH₄ Cl was added into the ternary system NaCl^-MgCl2-H2 O, the salt has a large crystalline zone. Based on it, we proposed a new technology to separate NaCl and MgCl2 by adding NH₄ Cl into the mixed solution of NaCl and MgCl2 to form ammonium carnallite.The extended Pitzer model of system was derived and applied into the systems which were studied in the paper and its sub-systems from the literature data. The activity of the equilibrium solid phase will not change at the same reaction time, base on it, the Pitzer parameters can be calculated. Then we put the parameters and the experimental dates intothe Pitzer model of the quaternary systems. By using the Date Processing Software 1stopt,we get the calculated dates. The results show that the calculated values were consistent with experimental date well.