Study on the Mechanism and Key Factors of Separation and Extraction of Lithium from Salt Lake Brine by TBP Extraction System

Author:Li Hui Fang

Supervisor:li wu li li juan


Degree Year:2019





Lithium is a strategic resource critical to national defense and energy safety.Lithium resources from salt lake account for more than 80%in China.Separation and extraction of lithium from salt lake brine has been a subject of research focus.Solvent extraction has shown excellent performance in selective separation of lithium and magnesium and efficient utilization of resources.Therefore,much attention has been paid to investigation of lithium extraction by the solvent extraction method.The extraction system of TBP-FeCl3 is the typical extraction system using the solvent extraction,which has high selectivity on lithium extraction and favorable industrial production economics.However,there remain two main issues in extracting lithium from salt lake when using TBP-FeCl3 extraction system,as follows:(1)Research around the key factors and extraction mechanism of extraction lithium is less thorough;(2)The third phase would occur in extraction when the TBP is low.In this paper,the extraction kinetics and the key factors on extraction lithium were investigated.The law of lithium mass transfer during extraction was demonstrated,while understanding of extraction mechanism and extraction kinetics was also improved.The cause and mechanism of a third phase formation were studied,clarifying the role of each component in organic phase and providing an effective way to eliminate the third phase.The interaction between the extraction system and common ions in brine was revealed through preliminary modeling.The application research of TBP-DIBK-FeCl3 extraction was initiated to provide a theoretical basis for industrial practices.The main contents and results were as follows:(1)The extraction kinetics of TBP-FeCl3 was studied by interfacial area cell method.The results hinted the mass transfer resistant zone was in aqueous phase,the extraction reaction occured in interfacial area and the extraction reaction was controlled by mixed mode.The extraction kinetic equation can be obtained.The results of extraction thermodynamics indicated the extraction process was spontaneous exothermic reaction.(2)The effect of key factors of TBP-FeCl3 extraction system on extraction efficiency was studied.The effect of different aqueous phase suggested FeCl4-complex anion was determined to be the key to the extraction system.Formation of FeCl4-complex anions was limited by the source of Cl-in the aqueous phase.The order of difficulty of binding different metal ions with FeCl4-and TBP in aqueous phase was determined:Ca2+>Li+>Mg2+>Na+>K+by investigating the influence of different metal chlorides as the source of aqueous phase Cl-on extraction efficiency.It was determined that the increase of MgCl2 concentration was conducive to the extraction of lithium by investigating the influence of MgCl2,which was the main component in brine.The influence of Cl-was greater than that of Mg2+.It was determined that Fe3+and Cl-were the optimal central ions and ligands for the formation of monovalent anions with high selectivity for lithium by investigating the influence of FeCl3 on lithium extraction.(3)The cause of the third phase appearance in extraction process was studied.The results showed that the third phase was a result of the solubility of extraction in kerosene by poor.EA,DIBK,BA and MIBK four kinds of organic reagents were added to the TBP extraction system,four kinds of organic solvent to join not only improved the separation of organic phase and aqueous phase,but BA,MIBK and DIBK in mixed extraction process also had the effect of the synergistic extraction.In addition,DIBK had better solubility for extracted complex.Studies on the solubility of extraction agents showed that DIBK was less soluble in both aqueous and saline solutions.(4)Appliedωb97XD method of density functional theory at the def2-TZVP level with Gaussian 16 software.The structure of FeCl3 and FeCl4-were optimized under vacuum conditions,and the theoretical Raman spectra of FeCl3 and FeCl4-were calculated for the first time.The structures of extraction complexes which formed by cations in brine,FeCl4-and the extractant TBP were optimized.The property parameters of structure,bond length and interaction energy were obtained.The calculation results of complexes suggested the stability of extracted complexes is H+>Li+>Na+>K+.(5)DIBK was added to the TBP extraction system which had less soluble and the good dissolve capability.The mixed extraction system was applied in Xitai brine for extracting lithium.The process parameters of the extraction section,scrubbing section,reextraction section and regeneration section were determined by experiment investigation.On the basis of experiment,the whole process had been carried,after ten cycles,lithium extraction percentage can reached 99.90%,the separation factor of Li+/Mg2+(βLi/Mg)was 5.215×104,the separation factor of Li+/K+(βLi/K)was2.159×103,the separation factor of Li+/Na+(βLi/Na)was 3.659×102 and the separation factor of Li+/Ca2+(βLi/Ca)was 3.104×102.The extracted complex was determined LiFeCl4×2TBP×0.2317DIBK by slope method,and the mechanism of the whole process was described.