| With the rapid development of portable electronic devices and electric vehicles,the application of lithium in the field of new energy materials has become apparently increased,and its development and utilization has also been highly concerned.In China,lithium resources are abundant in salt lake brines which lithium reserves account for 71%.However,due to the high ratio of magnesium to lithium in salt lake brines,it is difficult to separate them,and the cost of existing lithium extraction technologies are high,which leads to a heavily reliance on the imported lithium ores for lithium salt production in China.As lithium extraction from ores has many drawbacks such as large amount of waste discharge,serious pollution and high cost,it is urgent to develop new cost effective and clean technology in China to efficiently use lithium resources in salt lake brines.Compared to the existing lithium extraction process,solvent extraction has obvious advantages.It can selectively extract lithium from salt lake brines containing a large amount of Mg,Na,K,B and other impurities in one cycling process with the advantages of simple process,low cost,less fresh water consumption and less solid waste.The solvent extraction system of TBP-FeCl3 has been widely studied and applied in industry due to its high lithium extraction rate(99.1%)and lithium magnesium selectivity(SLi/Mg=1.87×105).However,in this system,the use of high concentration TBP causes serious damage of the equipment.High stripping acidity is easy to cause equipment corrosion and TBP degradation.At the same time,the organic phase needs to consume a large amount of alkali to neutralize the acid before it can be recycled,and the refining process of lithium products is complex,resulting in the high cost of lithium recovery.In order to solve above mentioned problems,our research group developed a new ternary synergistic solvent extraction system TBP/P507-FeCl3 to selectively extract lithium from high magnesium content salt lake brines.In this system,the efficient stripping of lithium with water was realized by controlling the coordination of Fe3+ in the process of extraction and stripping.The organic phase can be directly recycled without regeneration,and the process of lithium recovery is simplified.The new system successfully overcomes the serious drawbacks caused by high acid stripping and the technical bottleneck of difficult recovery of lithium from stripping solution,which greatly reduces the production cost,and is expected to be widely used in large-scale industrial application of lithium extraction from high magnesium content salt lake brines.In this dissertation,the mechanism of TBP-FeCl3 system was studied firstly.On this basis,the fundamental and application research on the lithium recovery using new ternary synergistic solvent extraction system TBP/P507-FeCl3 was carried out.Main results obtained were as follows:(1)The extraction competitive relationship of Li+and H+in TBP-FeCl3 system was intensively studied.The results showed that the compositions of the two extraction species were[Li(TBP)2][FeCl4]and[H(TBP)2][FeCl4],respectively.The extraction of H+by TBP was significantly stronger than that of Li+,and the apparent equilibrium constants of their extraction reactions at room temperature(25?)were KH=799.8 and KLi=120.6,respectively.When they were extracted simultaneously by TBP,the distribution ratio of H+was 4?6 times that of Li+and KH/KLi was also close to 4?6.Therefore,the calculated apparent equilibrium constant can be used to quantitatively determine the competitive relationship between Li+and H+,which lays a foundation for the study of the influence of important acidity parameters on the extraction of lithium in the new extraction system.(2)The mechanism of lithium extraction from high magnesium content salt lake brines with the new ternary synergistic solvent extraction system of TBP/P507-FeCl3 was studied.The results showed that TBP was still used as extractant to extract Li+,and Li+in organic phase mainly existed in the form of[Li(TBP)2][FeCl4],and P507 was not involved in the extraction.When the loaded organic phase was stripped with water,the Fe3+was synergistically extracted by P507 and TBP synergisms to formed the extraction species of FeCl2L·(HL)·2TBP,resulting in the destruction of the complex structure of[Li(TBP)2][FeCl4].Therefore,Li+was effectively stripped,while Fe3+remained stable in the organic phase.Compared with TBP-FeCl3 system,the new system uses water as the stripping agent instead of high concentration HCl,which greatly improves the economy and green sustainability of the process.(3)The new system TBP/P507-FeCl3 was applied to extract lithium from Dongtaijinaier salt lake concentrated brine(Li+,5.02 g/L)in Qinghai Province.Under the optimized extraction conditions:the organic phase containing 40%TBP-30%P507-30%kerosene loaded with 14 g/L Fe3+was mixed with brine at O/A ratio of 4:1,20?,shaking for 20 min.The extraction rates of each element were as follows:Li,84.5%;Fe,99.2%;Mg,2.6%and B,20.9%.After three-stage simulated countercurrent extraction,99.8%of Li+in the brine was recovered;after three-stage simulated countercurrent stripping,the stripping liquor contained(g/L):Li,20.9;Mg,2.2;B,1.6;H,0.3,with slight loss of Fe3+in the strip liquor.At the same time,the stripped organic solution could be directly recycled without further treatment.(4)The thermodynamic of lithium extraction from Dongtaijinaier salt lake concentrated brine and its stripping was simulated using numerical regression method with TBP/P507-FeCl3 system.By fitting the experimental value with the calculated value,the empirical value of equilibrium constant of each reaction in the system was optimized,and the thermodynamic calculation model of lithium extraction and stripping in the system was established.The concentration of each species in the organic phase was calculated by the model,which further confirmed that Li+mainly existed in the organic phase in the form of[Li(TBP)2][FeCl4],and there was a small amount of[Li(TBP)][FeCl4].When the stripping process was carried out at a low O/A ratio,Fe3+was mainly maintained in the organic phase in a form of FeCl2L·HL·2TBP.With the increase of O/A ratio,the concentration of FeCl2L·HL·2TBP decreased,leading to a change that Fe3+existed mainly to a form of[H(TBP)2][FeCl4].The mechanism of lithium extraction with the new system was further improved by this thermodynamic simulations.(5)In TBP/P507-FeCl3 system,a multi-component enhanced extraction system was constructed by using ESD instead of kerosene to extract lithium from Xitaijinaier salt lake concentrated brine(Li+,1.69 g/L).Under the optimized extraction conditions:the organic phase containing 40%TBP-20%P507-40%ESD loaded with 15 g/L Fe3+was mixed with brine at O/A ratio of 1:1.The concentration of each element in the loaded organic phase were(g/L):Li,1.24;Fe,14.98;Mg,1.43 and B,0.17,respectively.Compared with the system without ESD,the load capacity of Li+was increased by 50%.After seven-stage simulated countercurrent stripping,the stripping liquor contained(g/L):Li,31.3;Mg,0.02;B,0.04 and Fe,0.06.The concentration of lithium in the stripping solution was highly enriched,and the stripping organic phase can be directly recycled without regeneration.The multi-component enhanced extraction system can greatly improve the utilization rate of organic phase,meet the high yield demand of lithium extraction industrialization,and has broad application prospects. |
PDF Full Text Request