Study On System Construction And Performance Of Lithium Extraction From Seawater

Lithium is widely used in new energy,manufacturing,medicine,nuclear military and other fields,and lithium extraction is essential to meet its increasingly strong market demand.The reserves of lithium resources in seawater are huge,more than 10,000 times the total lithium resources on land.However,the concentration of lithium in seawater is low（only 0.17 mg/L）and coexists with sodium,magnesium and other ions,so the extraction technology is difficult.In this study,supercapacitor activated carbon（SAC）and metal-organic framework compounds were used as precursors to prepare Co NC@SAC electrode to investigate their supercapacitive performance;three-dimensional self-supporting porous Mn₃O₄ nanowall arrays were grown in situ on carbon cloth（CC）,and further theλ-Mn O₂@CC lithium ion sieve electrode was prepared by chemical lithiation,and its lithium ion adsorption-extraction performance was studied.An electrochemical lithium extraction system from seawater was constructed withλ-Mn O₂@CC electrode and Co NC@SAC electrode,and its extraction performance for lithium ions was investigated.The main conclusions are as follows:（1）The study of Co NC@SAC supercapacitor electrode shows that the carbonization temperature has a great influence on the morphology of the Co NC@SAC material.As the carbonization temperature increases from 850°C to 900°C,the surface of the activated carbon becomes rougher and the number of nanoparticles decreases,the formation of carbon nanotubes increased.The supercapacitive properties of Co NC@SAC electrode prepared at different carbonization temperatures were investigated.The results show that Co NC@SAC electrode have pseudocapacitive characteristics.Compared with SAC electrode,the specific capacitance and potential window are greatly improved under both alkaline and neutral conditions,and it has higher charge-discharge efficiency and better cycle stability.（2）The study onλ-Mn O₂@CC Li-ion sieve electrode shows that the Mn₃O₄ film prepared by cathodic deposition on carbon cloth is composed of nearly vertically aligned 2D nanowalls,the surface particles of theλ-Mn O₂@CC lithium ion sieve electrode formed after chemical lithiation and delithiation are dense and uniformly distributed,and the morphology is basically unchanged,showing a good spinel structure.The research on Li⁺intercalation-deintercalation performance ofλ-Mn O₂@CC electrode shows that it has good Li⁺intercalation-deintercalation performance for 1.04 mg/L,183.24 mg/L and 1.344 g/L Li Cl,and the adsorption-desorption capacity increases with the increase of Li⁺concentration;The intercalation-deintercalation of Li⁺onλ-Mn O₂@CC electrode is less affected by common coexisting ions in seawater such as Na⁺,Mg²⁺,K⁺,Ca²⁺,which indicates that the electrode has excellent selectivity for Li⁺;Theλ-Mn O₂@CC electrode can maintain stable Li⁺intercalation-extraction performance for 30 cycles.（3）Usingλ-Mn O₂@CC electrode and Co NC@SAC electrode to construct electrochemical seawater lithium extraction system,and investigate the effects of applied current and solution properties on lithium extraction performance.In 1.04 mg/L Li Cl solution,the Li⁺adsorption rate of the system is 57.2%when the external current is 0.5 m A/cm²,while the Li⁺adsorption rate is only 34.4%when the external current is not applied,which indicates that the electrically driven adsorption plays an important role in the extraction of Li⁺from the system.When the simulated seawater was used as the lithium extraction stock solution（the applied current was0.5 m A/cm²）,the adsorption rate of Li⁺in the system was further increased to 77.21%,which may be due to the coexistence of multiple ions improving the conductivity of the solution and promoting the transfer of Li⁺migrate to the lithium ion sieve.