Study On The Stable Equilibrum Of Systems Containing Lithium, Sodium, Ammonium And Strontium

There are abundant groundwater and oilfield brine resources in Western China,especially in Nanyishan Section of the Qaidam Basin,China,in which the high concentration of lithium,potassium,ammonium and strontium was found in the oilfield.Phase equilibrium and phase diagram is the important theoretical basis for the separation and purification of the salt minerals in the brine.Therefore,the study of the phase equilibrium for the relative oilfield systems is of great significance to the development and utilization for the valuable oilfield resources in the region.In this paper,the stable equilibria of some subsystems for the system Li⁺,Na⁺,K⁺,NH₄⁺,Sr²⁺//Cl^--H₂O were studied with isothermal dissolution method.The ternary and quaternary subsystems include five ternary systems NH₄Cl-Li Cl-H₂O（288K）,Na Cl-NH₄Cl-H₂O（288K）,NH₄Cl-Sr Cl₂-H₂O（298K,308K,323K）,Na Cl-Sr Cl₂-H₂O（308K）,KCl-Sr Cl₂-H₂O（308K）,and three quaternary systems Na Cl-NH₄Cl-Sr Cl₂-H₂O（288K）,Li Cl-NH₄Cl-Sr Cl₂-H₂O（288K）and Na Cl-KCl-Sr Cl₂-H₂O（308K）.According to the experimental data,the phase diagrams of the ternary and quaternary systems were plotted.The equilibrium solid of the ternary system Li Cl-NH₄Cl-H₂O at 288K is Li Cl·2H₂O and NH₄Cl.which can be used to separation of Li Cl·2H₂O and NH₄Cl.The solid salts existed in the ternary system Na Cl-NH₄Cl-H₂O at 288K are Na Cl and NH₄Cl,respectively.And the liquid concentration of the invariant point is w（NH₄Cl）=14.07%,w（Na Cl）=16.78%,w（H₂O）=69.15%.The solid minerals of the ternary system NH₄Cl-Sr Cl₂-H₂O at 298,308,323K are all NH₄Cl and Sr Cl₂·6H₂O.Thus,the temperature effect can be used to separate the NH₄Cl and Sr Cl₂·6H₂O.The solid minerals of the ternary systems Na Cl-Sr Cl₂-H₂O and KCl-Sr Cl₂-H₂O at 308K are Na Cl+Sr Cl₂·6H₂O and KCl+Sr Cl₂·6H₂O,respectively.And the phase diagrams of the two systems at 288 K and 308K have been compared.No double salt and solid solution was found in all above ternary systems.The solid minerals in the invariant point of the quaternary system Na Cl-NH₄Cl-Sr Cl₂-H₂O at 288K is NH₄Cl+Sr Cl₂·6H₂O+Na Cl,and the crystallization region is corresponding to NH₄Cl、Sr Cl₂·6H₂O and Na Cl.The quaternary system Li Cl-NH₄Cl-Sr Cl₂-H₂O at 288K has two invariant points E₁and E₂.The point E₁is cosaturated with Sr Cl₂·6H₂O+Sr Cl₂·2H₂O+NH₄Cl,while E₂is cosaturated with Li Cl·2H₂O+Sr Cl₂·2H₂O+NH₄Cl.The solid salts existed in quaternary system Na Cl-KCl-Sr Cl₂-H₂O at308K are KCl,Na Cl and Sr Cl₂·6H₂O.