Extraction Of Lithium From Geothermal Water By FPO/KNiFC Ion Pump Technique

As a new-type liquid lithium resource,the development of lithium in geothermal water is of great significance for the sustainable development of lithium in China.In this thesis,the experimental studies on lithium extraction from geothermal water were conducted by using the FePO4/K2NiFe(CN)6(FPO/KNiFC)electrochemical ion pump technology.Based on the establishment of an accurate determination method of lithium in complex matrix,we synthesized three kinds of ferrocyanide compounds and then prepared corresponding electrodes.Meanwhile,the extraction performance of FPO/KNiFC was improved by the regulation and modification of LiFePO4 electrode.Through these experiments,main conclusions obtained are summarized as follows:(1)High concentrations of Na+,K+,Ca2+,and Mg2+ co-existing ions in the sample will cause serious interference with the accurate determination of Li+ by ICP-OES.The interference caused by NaCl,KCl and MgCl2 with a total amount of no more than 40 g/L was successfully solved by improving the traditional matrix matching method and synchronously adding 10 g/L NaCl to the samples and standard solutions.Moreover,when the concentration of Ca2+ in the samples was no more than 1.8 g/L,the results of determination were reliable.(2)Three kinds of ferrocyanide compounds(K2NiFe(CN)6,K2CuFe(CN)6,K2CoFe(CN)6)were synthesized and used to prepare corresponding electrodes.The electrochemical performance tests showed that K2NiFe(CN)6 has obvious advantages.When K2NiFe(CN)6 and FePO4 were used to compose an electrochemical ion pump for Li+recovery from geothermal water,the single insertion capacity was 11.2 mg/g(3 h)at 0.8 V potential,and the electrode materials kept good stability after 5 cycles.In order to solve the problem that insertion and desorption Li+ could not be carried out simultaneously,the connection method of ion pump was improved through parallel connection,and its feasibility was verified by experiment.(3)FePO4 was synthesized by the liquid phase precipitation method,and the feasibility for the direct use of FePO4 as the Li+insertion material was investigated.Meanwhile,in order to improve Li+extraction performance by the FPO/KNiFC ion pump system,the LiFePO4 material was modified using different carbon sources.The experimental results showed that the FePO4 synthesized by the liquid phase precipitation method could not effectively insert Li+,while the composite LiFePO4/C synthesized with carbon nanotubes as the carbon source has good Li+desorption/insertion properties and cycling stability,and the single insertion capacity was 14.9 mg/g(2 h)in geothermal water.In order to solve the problem of low single extraction capacity,a electrochemical device for continuous extraction of lithium was finally designed.