Multi-temperature phase diagram of lithium-sodium-magnesium coexistence sulfate system and its application
In order to solve the problem of lithium separation caused by high ratio of sodium to lithium and high ratio of magnesium to lithium in sodium sulfate subtype salt lake brine,the multi-temperature phase diagram of lithium-sodium-magnesium coexistence sulfate system was studied to obtain the action relationship and crystallization precipitation law of lithium-sodium-magnesium sulfate.It is applied to guide the process design of reducing the content of sodium and magnesium in brine.The solid-liquid phase equilibria for the quaternary systems Li+,Na+,Mg2+//SO2-4-H2 O at 303.2 and 318.2 K were studied by using isothermal dissolution equilibrium method.The solid phases of invariant points were verified by X-ray diffraction method(XRD).The crystal structure,crystal morphology and thermal analysis of the double salts were analyzed by X-ray diffraction method(XRD),scanning electron microscope(SEM)and thermogravimetric analysis(TG-DSC).The results show that both these systems are complex systems,and their phase diagrams contain 4 quaternary co-saturation points,9 univariate curves and 6 crystallization regions.The crystallization regions of the phase diagram of the system at 303.2 K is Na2 SO4,Na2 SO4·10H2 O,Li2 SO4·H2 O,MgSO4·7H2 O,Na2 SO4·MgSO4·4H2 O,Li2 SO4·3Na2 SO4·12H2 O;318.2 K is Na2 SO4,MgSO4·7H2 O,Li2 SO4·H2 O,Na2 SO4·MgSO4·4H2 O,Li2 SO4·Na2 SO4,Li2 SO4·3Na2 SO4·12H2 O.By comparing the multi-temperature phase diagrams of the quaternary system at 288.2,298.2,303.2,318.2 and 323.2 K,it is found that the effect of temperature on the system is mainly manifested in the crystallization form of hydrated salts and lithium-containing double salts and the change of crystallization areas of each salts.Combined with the crystallization rules of lithium-containing double salts(Li2 SO4·Na2 SO4,Li2 SO4·3Na2 SO4·12H2 O),astrakhanite(Na2 SO4·MgSO4·4H2 O)in quaternary system and the crystallization rules of salts in ternary system Na+,Mg2+//SO2-4-H2 O,some suggestions for the separation and processing of sodium sulfate subtype salt lake removal sodium(magnesium)and astrakhanite separation process were given.
phase equilibriasolutionsolubilityastrakhanitelithium-containing double salt
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