Phase Equilibria Of The Quaternary Systems Containing Lithium And Potassium At 15?

Vast lakes,which contain abundant of inorganic salt,such as Li+,K+,Mg2+,borate,are distributed widely in China.Therefore,study of salt lake brine has theoretical value and guiding significance for the comprehensive utilization of salt lake brine resources.Using the method of isothermal evaporation and the method of isothermal solution equilibrium,the metastable phase equilibria of the ternary system Li2SO4-LiBO2-H2O,the stable phase equilibria of the quaternary system Li+,K+//Cl-,SO42-H20 at 15? and the stable phase equilibria of the quaternary system Li+,K+,Mg2+//SO42--H2? at 15? were researched respectively.The solubilities of the equilibrium liquid phase and the physicochemical properties including density,refractive index,and pH values in the systems were determined.Be based on experimental results,the metastable phase diagram of the ternary system,the dry-salt phase diagrams,water-phase diagrams of the quaternary systems and the physiochemical properties versus composition diagrams were plotted.There are one eutectic for(Li2SO4-H2O + LiBO2·8H2O),two univariant curves,and two crystallization fields corresponding to two single salts Li2SO4·H2O and LiBO2·8H2O in the ternary system Li2SO4·LiBO2·H2O at 15?.And the area of crystallized zone of LiBO2·8H2O is much larger than that of Li2SO4·H2O.The physicochemical properties(density,refractive index and pH)change regularly with the increasing of Li2SO4 concentration.Using the empirical equations,it can be found that the calculated values of density and refractive index agree well with the experimental values,which density maximum deviation is 0.28%and refractive index maximum deviation is 0.25%,which is favorable.Compared with stable phase diagrams for the ternary system at 15?,it can be found that the solid phase numbers and exist minerals are the same,but the crystallized region of Li2S?4·H2O is increased while that of LiBO2·8H2O is decreased obviously.There are three invariant points,seven invariant curves,and five crystallization regions corresponding to the lithium sulfate monohydrate(Ls),lithium chloride monohydrate(Lc),arcanite(Ar),sylvite(Sy),potassium lithium sulfate(Db).The crystallization phase field of arcanite is the largest,whereas the crystallized area of lithium chloride monohydrate is the smallest.No solid solution was found in the quaternary system.The physicochemical properties of the stable equilibrium solution change regularly with the increase of J(K22+),such as density and refractive index,and the invariant points exist singularity changes in the system.Compared with the stable equilibrium system Li+,K//Cl-,SO42--H2O at 25 ?,50? and 75?,it was found that the solid phase numbers and the minerals exsited are the same from 15?,25?,50? to 75?.With the increasing of temperature,the crystallized areas of potassium lithium sulfate and lithium sulfate monohydrate are increased,and the phase zone of arcanite,sylvite,and lithium chloride monohydrate are decreased.It shows that the salt of lithium chloride has an ever-increasing strong salting-out effect possibly.There are three invariant points,seven invariant curves,and five crystallization regions corresponding to the lithium sulfate monohydrate(Ls),arcanite(Ar),epsomite(Eps),potassium lithium sulfate(Db),schoenite(Pic)in the quaternary system Li+,K+,Mg2+//SO42-H2O at 15?.No solid solutions were discovered.With the increasing concentration of magnesium sulfate,the physicochemical properties of the stable equilibrium solution change regularly,such as density and refractive index.Compared with the stable system at 25 ? and 35?,the numbers of crystalline regions are the same and there are no new crystallized areas formed and no old phase zones disappeared.With the increasing of concentration,the crystallized zones of lithium sulfate monohydrate,schoenite and potassium lithium sulfate increased,whereas,the phase zones of arcanite and epsomite decreased.