Novel Co-extraction System For Lithium Recovery From High Mg/Li Ratio Salt Lake Brine

With the increasingly exhaustion of solid lithium mineral resources,the effectively exploitation and utilization of lithium in salt lake brine has already become the hotspot of research.In order to separate and extract lithium from high Mg/Li ratio salt lake brine,we developed a novel co-extraction system TBP-KPF6 in this thesis.The influence factors for lithium extraction by this system were investigated in details,by which the optimum extraction conditions were finally obtained.Meanwhile,the mechanism and thermodynamics for lithium extraction by this system were further studied.Main conclusions presented in this thesis were summarized as following:(1)The novel co-extraction system TBP-KPF6 was established after the screening of co-extraction and diluent.Subsquently,the technological parameters for lithium extraction from high Mg/Li ratio salt lake brine were optimized.The single extraction rate for Li+ and Mg2+ were 81.88%and 4.41%with the separation factor ?MgLi reached to 114.87 at the optimum extraction conditions TBP%= 100%,n(PF6/Li)= 2,T= 25?,phase ratio R(O/A)=1.2.Meanwhile,the single back-extraction rate of Li+ was 95.48%by back-extraction with 1 mol/L HCl and 3 mol/L NaCl mix-solution at 25 ? and phase ratio R(O/A)= 1,by which the Mg/Li ratio in brine was decreased from 33.42 to 2.33.(2)The mechanism for lithium extraction by TBP-KPF6 system was investigated using fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance spectroscopy(NMR).The results showed that there had't obvious chemical shifts in the 1H NMR spectrum of TBP befoe and after extraction,while it shifted to downfield for 31P spectrum and there presented a P peak of PFe6-after extraction.The IR,1H NMR and 31P NMR spectrums of the extracted organic phase showed that the lone pair electrons in P=0 of TBP conbined with the unoccupied orbital of P(V)in PF6-to form[PF6·nTBP]-.Subsequently,it bonded with Li+ by ion bond to generate[LiPF6·nTBP],and then extracted into organic phase.The extraction complex was finally proved to be LiPF6-2TBP by the slope method at 25 ?.(3)The thermodynamics for lithium extraction by TBP-KPF6 system was carried out using BT 2.15 micro calorimeter.The heat flow-time curves during the extraction of lithium from high Mg/Li ratio brine and the heat of extraction reaction at 25 ?,35? and 50?were obtained.The results showed that the extraction reaction was an exothermic process.The thermodynamic parameters for the extraction were studied using Friedman equal conversion method,and the relationship between reaction progress,reaction rate,activation energy,pre-exponential factor and time at different temperatures were also obtained.Furthermore,the relationship between reaction progress and time within the temperature range of 0?-70? was predicted based on the Non-isothermal Conditions module,by which it has important significant to guide the industrial production.