Studies On Electrochemical Ion Extraction Techenology

Brine is rich in lithium resources,which is an important source of lithium.The precipitation method used in brine extraction of lithium is time-consuming,complex and influenced by environmental factors.Lithium hexafluorophosphate（Li PF₆）has become an indispensable electrolyte salt for lithium electricity due to its excellent comprehensive properties.Its synthesis process is sensitive to temperature,humidity and impurity components,etc.Conventional HF solvent method has a negative impact on product quality.As one of the inorganic chemical industries,chlor-alkali products sodium hydroxide（Na OH）and chlorine gas（CI₂）have become essential substances in production and life.The ionic membrane used in the production of chlor-alkali has high cost and strict requirements on the raw materials of sodium chloride.All the above three substances belong to the category of ionic compounds,which are synthesized by electrochemical ion extraction technology.Electrochemical ion extraction technology is based on the electrochemical active materials as the medium,through the electrooxidation/reduction reaction to achieve the ion in the active materials embedded/out,along with the ion transfer in different media,so as to achieve the preparation of substances.The method can not only extract single ion from mixed ion solution,but also prepare compounds composed of simple ions.The extraction of lithium,Li PF₆and chlor-alkali from brine accord with the application of electrochemical ion extraction.Therefore,we can use electrochemical ion extraction technology to achieve the preparation of the above compounds.The specific contents are as follows:1.Electrochemical ion extraction technology is used to extract lithium resources from brine.At present,the extract lithium from the high magnesium lithium brine is more time-consuming,complicated and the environment is more disturbed,so it is urgent to find a new lithium extraction technology suitable for high magnesium lithium brine.In this work,we used Li Mn₂O₄electrode for Li⁺electrode,polyaniline electrode（PANI）as CI^-electrode,simulated brine as electrolyte,and constructed PANI/brine/Li_xMn₂O₄（0<x<1）and Li Mn₂O₄/recovered liquid/PANI·PF₆two-electrolytic cell electrochemical system to study the feasibility of the extraction of Li⁺from brine.The results show that Li Mn₂O₄electrode has excellent selectivity to Li⁺in mixed ion solutions of Li⁺,K⁺,Na⁺and Mg²⁺.In addition,when the current density of lithium extraction in brine simulated by PANI/Li_xMn₂O₄system is 0.5m A cm^-2,the average energy consumption of extraction of 1 mol of lithium is 3.95Wh mol^-1,and the ultimate concentration of Li⁺can be achieved by this system is 3mmol l^-1.2.Electrochemical ion extraction technology was applied to the preparation of high purity Li PF₆.The synthesis of traditional Li PF₆often leaves trace HF,which seriously affects the cycling performance of the battery.Therefore,the development of new methods to clean and avoid HF synthesis is the key to improve the quality of Li PF₆.To this end,we used Li Mn₂O₄electrode as Li⁺electrode,polyaniline electrode（PANI）as PF₆^-electrode,Li CI salt as Li⁺source,KPF₆salt as PF₆^-source,and cationic extraction membrane as membrane to study the electrochemical extraction and synthesis technology of Li PF₆by constructing the electrochemical system of PANI/KPF₆/cationic extraction membrane/Li CI/Li_xMn₂O₄and Li Mn₂O₄/Li PF₆/PANI·PF₆electrolysis cell.The results show that Li⁺and PF₆^-can be successfully extracted by electrochemical technology and Li PF₆can be formed by electrochemical process.The cyclic stability of commercial Li Fe PO₄anode and graphite anode in the synthesized Li PF₆electrolyte and the commercially available electrolyte is basically the same,indicating that the performance of Li PF₆synthesized by PANI/Li_xMn₂O₄system can basically meet the commercial requirements.3.Electrochemical ion extraction technology used in the preparation of chlor-alkali.In order to overcome the problems existing in the ionic membrane extraction method in the chlor-alkali industry,such as the cationic extraction membrane is expensive,susceptible to pollution and the use of high-purity Na CI solution,so the development of membrane-free and pure chlor-alkali technology has become a hot issue.Here,we used Na_0.44Mn O₂electrode for Na⁺storage,Ag electrode for CI^-storage,air electrode for oxygen reduction,graphite as chlorine evolution electrode,Na CI salt as Na⁺and CI^-source,and studied the feasibility of Na_0.44Mn O₂/Na OH/air electrode,Ag/Na CI/Na_0.44-xMn O₂and Ag CI/HCI/graphite electrolytic cell electrochemical system in the preparation of chlorine alkali.The results show that the fitting results of electrode potential of three-electrolytic cell meet the electrochemical requirements of ion extraction and release,and the generation of pure Na OH and Cl₂can be achieved successfully.In addition,under the condition of current density of50m A cm^-2,the average energy consumption of simulated preparation of chlor-alkali is 50.3 Wh mol^-1.Therefore,this electrochemical ion extraction technology can achieve the generation of high purity and low energy chlor-alkali.