Study On The Processing Of Bloedite By Ammonium Sulfate (Urea) Salting Out At 60?

Bloedite(Na₂SO₄·MgSO_4·4H₂O)is stored largely in China.However,it is difficult to realize rational development and comprehensive utilization of bloedite using the traditional processes of physical and chemical methods and crystal precipitation method.In order to separate and process bloedite comprehensively,new technologies were proposed,which has a very important practical significance in exploiting bloedite.The solubilities of the quaternary system Na₂SO₄-MgSO₄-?NH₄?₂SO₄-H₂O at 60?were measured by isothermal method and the phase diagram was plotted.The analysis of phase diagram shows that MgSO₄·?NH₄?₂SO₄·6H₂O and Na₂SO₄ crystalline fields are larger than other crystalline fields,which indicates that MgSO₄·?NH₄?₂SO₄·6H₂O and Na₂SO₄ can be crystallized out easily.Combined with the ternary system Na₂SO₄-?NH₄?₂SO₄-H₂O at 60?,a technology was designed to produce Mg-N compound fertilizers and Na₂SO₄ using?NH₄?₂SO₄ as salting-out agent to separate bloedite,which is easy to operate,fast to reach phase equilibrium and can gain anhydrous Na₂SO₄ directly.ThesolubilitiesoftheternarysystemNa₂SO₄-CO?NH₂?₂-H₂Oand MgSO₄-CO?NH₂?₂-H₂O and the quaternary system Na₂SO₄-MgSO₄-CO?NH₂?₂-H₂O at60?were measured by isothermal method,and the corresponding phase diagrams were studied.The analyses show that there are larger crystalline fields of Na₂SO₄ and MgSO₄·CO?NH₂?₂·4H₂Oinphasediagramofthequaternarysystem Na₂SO₄-MgSO₄-CO?NH₂?₂-H₂O.New technologies were proposed to produce Na₂SO₄ and Mg-N compound fertilizers using CO?NH₂?₂ as salting-out agent directly,which is fast to reach phases equilibrium and can gain anhydrous Na₂SO₄ and Mg-N compound fertilizers with high yield.New technologies of processing bloedite using?NH₄?₂SO₄ and CO?NH₂?₂ as salting-out agent to produce Mg-N compound fertilizers and Na₂SO₄ can provide theoretical basis for comprehensive utilization of bloedite.On the basis of Pitzer electrolyte solution theory,the phase equilibrium solubilities of the quaternary system Na₂SO₄-MgSO₄-?NH₄?₂SO₄-H₂O and the quaternary system Na₂SO₄-MgSO₄-CO?NH₂?₂-H₂O and its sub-systems at 60?were calculated.The interaction parameters of ion-ion and paticals were regressed and used to calculate the solubilities of liquid-solid phase equilibrium of every system.The results show that the calculated values are well consistent with the experimental results.The phases equilibrium time,production yield and mother solution circulation were determined by experiments.The analyses show that phase equilibrium at 60?is in the shortest reaction time,and the new technologies at 60?can gain anhydrous Na₂SO₄ with low mother solution circulation.Combined with the analyses of phase diagrams of producing Mg-N compound fertilizers at 60?,25?and 35?,the mother solution entainment in wet solid phase crystal of Mg-N compound fertilizers was studied by experiments.The result shows that the mother solution entainment at 60?is lower than other temperatures.Washing method of saturated MgSO₄ can improve the quality of the Mg-N compound fertilizers obviously,and the dissolved washing method of saturated MgSO₄ is superior to the traditional washing method.