Phase Equilibria Of The Quinary System(Li⁺,Na⁺,Ca²⁺,Sr²⁺//Cl^--H₂O)and Its Subsystems At 273.15 K

In this thesis,the phase equilibria of the oil-field brines containing lithium,sodium,calcium and chloride was investigated by the isothermal dissolution equilibrium method,and the studies were mainly focused on the phase equilibria of the ternary systems(LiCl+SrCl2+ H2O),(LiCl+CaCl2+H2O),(CaCl2+SrCl2+H2O)and the quinary system(Li+,Na+,Ca2+,Sr2+//Cl--H2O)at 273.15 K.On the basis of Pitzer model,the Pitzer mixing parameters and solubility equilibrium constants of equilibrium solid salts for the ternary systems were acquired.The chemical models,which combined the Pitzer parameters and the solubility equilibrium constants,were constructed.The comparions between the experimental solubilities and calculated data showed the models are reliable.The ternary system(LiCl+SrCl2+H2O)at 273.15 K belongs to the hydrate ? type.There are no double salt and solid solution in this system.The phase diagram of the system consists of two invariant points,three univariant solubility curves and three crystallization areas corresponding to LiCl·2H2O,SrCL2·2H2O and SrCl2·6H2O.The concentration of LiCl decreases while the concentration of SrC12 increases,which shows that LiCl has an obvious salting-out efect on SrCl2.The ternary system(LiCl+CaCl2+H2O)at 273.15 K belongs to complex ternary system containing an incongruent double salt(LiCl·CaCl2·5H2O).There are no solid solution in this system.The phase diagram of the system consists of three invariant points,four univariant solubility curves and four crystallization areas corresponding to LiCl·2H2O,LiCl·CaCl2-5H2O,CaCl2·4H2O,and CaCl2·6H2O.It shows that LiCl has an obvious salting-out efect on SrCl2 from phase diagram.The ternary system(CaC12+SrCl2+H2O)at 273.15 K belong to the type of solid solution,and no double salt formed in this system.There is no invariant point,one univariant solubility curve saturated with solid solution,and one crystallization field of the solid solution(Ca,Sr)Cl2·6H2O in the phase diagrams,formed in this system.The phase diagram of the quinary system(Li+,Na+,Ca2+,Sr2+//Cl--H2O)at 273.15 K consit of three unvariant points,seven univariant solubility curves and five crystallization fields corresponding to(Ca,Sr)Cl2·6H2O,LiCl·CaCl2-5H2O,LiCl·2H2O,CaCl2·4H2O and SrCl2·2H2O.The crystallization field of(Ca,Sr)Cl2·6H2O is much large than SrCl2·2H2O,which is more easily separated in the aqueous solution.On the basis of Pitzer ion-interaction theory for electrolyte solution,the Pitzer parameters of three ternary systems were obtained,meanwhile,the chemical model was constructed,and the predicted results agreed well with the experimental results.