Metastable Phase Equilibria for Quinary System Contained with Lithium and Isothermal Evaporation of the Zabuye Old Brine

Author:Feng Shan

Supervisor:Ceng Ying

Database:Doctor

Degree Year:2015

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Pages:107

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In accordance with the composition of the Zabuye old brine,the metastable phase equilibria of the quinary system Li+,Na+,K+ // Cl-,borate-H2 O and two quaternary systems Li+,Na+,K+ // Cl--H2 O and K+ // Cl-,CO32-,SO42--H2 O were studied at 273 K using an isothermal evaporation method.The densities of the solution and the composition of solid phase and liquid phase at equilibrium in the above systems were also determined.Based on the measured data,the phase diagrams,the water content diagrams and the diagrams of densities vs composition in the quaternary systems and quinary system were all plotted.The isothermal evaporation experiment were carried out at 273 K and 288 K on the Zabuye old brine,273 K isothermal evaporation experiments after freezing at 268 K on Zabuye old brine was aslo done.The quaternary system Li+,Na+,K+ // Cl--H2 O belongs to simple eutectic type,without solid solution or double salt formed at 273 K.The metastable phase diagram consists of one invariant point,three crystallization zones,and three univariant curves.The solubilities of the salts in the system decrease in the order of Li Cl·H2O > Na Cl > KCl.Salt Li Cl has strong salting out effect on Na Cl and KCl.The quaternary system K+ // Cl-,CO32-,SO42--H2 O belongs to simple eutectic type,without solid solution or double salt formed at 273 K.The metastable phase diagram consists of one invariant point,three crystallization zones,and three univariant curves.The solubilities of the salts in the system decrease in the order of K2CO3·3/2H2 O > KCl > K2SO4.Salt K2CO3 has strong salting out effect on K2SO4 and KCl.The reciprocal quinary system Li+,Na+,K+ // Cl-,borate-H2 O belongs to a simple type,without solid solution or double salt formed at 273 K.The space phase diagram of the quinary system consists of one commensurate invariant point,two incommensurate invariant points,six crystallization zones,ten univariant curves.With a view to the crystallization zones,salt Li Cl·H2O has the smallest crystallization zone,which means that it has the largest solubility among the salts at 273 K;salt Li2B4O7·3H2O has the largest crystallization zone,which means that it has the smallest solubility.Under the condition of KCl saturated,the solubility of salts increase in the order of rease in the order of Li2B4O7·3H2O < Na2B4O5(OH)4·8H2O < K2B4O5(OH)4·2H2O < Na Cl < Li Cl·H2O;under the condition of Li2B4O7 saturated,the solubility increase in the order of Na2B4O5(OH)4·8H2O < KCl < K2B4O5(OH)4·2H2O < Na Cl < Li Cl·H2O.Results show that borate only formed single salts in equilibrated solution,salts Li2B4O7·3H2O and Na2B4O5(OH)4·8H2O precipitate easily due to the larger crystallization fields,thus they can be separated by isothermal evaporation method.Salts Li Cl·H2O and K2CO3·3/2H2 O have the larger solubility,corresponding crystallization zone are smaller,thus it is difficult to obtain them only by evaporation method.This feature is very important to extract lithium,potassium and borate from the salt lake brine.The precipitation sequence during 273 K isothermal evaporation was Na Cl → KCl → Li2CO3 → Na2CO3·10H2O;the precipitation sequence during 288 K isothermal evaporation was Na Cl → KCl → Li2CO3 → Na2CO3·10H2O → Na2SO4·10H2O;the precipitation sequence during 273 K isothermal evaporation experiments after freezing at 268 K was Na Cl → KCl → Na2CO3·10H2O + Na2SO4·10H2O → Li2CO3.Study results show that: in the process of old brine evaporation,the higher the temperature,the more conducive for Na Cl,Li2CO3,Na2CO3·10H2O to precipitate.Under the 273 K isothermal evaporation process,Na Cl,Li2CO3,Na2CO3·10H2O precipitated when the evaporation ratio reaches 13.96 %,68.15 % and 83.32 %,respectively;Under the 288 K isothermal evaporation process,Na Cl,Li2CO3,Na2CO3·10H2O precipitated when the evaporation ratio reaches 12.65 %,60.46 % and 72.16 %,respectively.The lower the temperature,the relatively sooner for KCl to precipitate,under the 273 K isothermal evaporation process,KCl precipitated when the evaporation ratio reaches 20.99 %;under the 288 K isothermal evaporation process,KCl precipitated when the evaporation ratio reaches 40.88 %.After freezing at 268 K,the relatively sooner for Li2CO3 to precipitate when the evaporation ratio reaches 82.83 %,the relatively advance for Na2CO3·10H2O + Na2SO4·10H2O to precipitate when the evaporation ratio reaches 65.88 %.