| As the lightest alkali metal element,lithium was widely used in batteries,ceramic glass,lubricants,polymers and other products.The massive use of raw materials has led to the risk of shortage of global lithium resources.How to maximize the production and recovery of lithium resources have become an urgent problem to be solved.In the process of lithium production and recovery,a lot of lithium-containing high-salt wastewater was often generated,correct recycling of these lithium-containing solutions will greatly alleviate the risks faced by the shortage of lithium resources,improve production efficiency,reduce environmental pollution,and maximize economic and environmental protection.Membrane separation technology is an advanced chemical mass transfer and separation technology,which uses concentration difference and potential difference as the driving force to separate,desalt and concentrate ions of different components in the solution.Electrodialysis is a membrane separation process with an ion exchange membrane as the carrier and the potential difference as the driving force.In this paper,the bipolar membrane electrodialysis（BMED）technology was developed for the resource recovery of the lithium salt solution produced during the production and used of the lithium industry.First of all,the sodium sulfate waste salt containing lithium produced in the preparation of lithium carbonate by sulfuric acid roasting method in industry are recycled and then the low-concentration lithium solution generated in the process of lithium extraction from salt lakes,lithium-ion battery recovery,and lithium ore mining was recovered to recover lithium resources.While recovering lithium resources,a new process for lithium hydroxide production was developed.The main conclusions of this study are as follows:BMED was used to recover a large amount of low-value sodium sulfate waste salt produced in the process of preparing lithium carbonate by roasting with sulfuric acid.The effects of feed salt concentration,current density,flow rate and volume ratio on desalting performance were studied.The conversion rate of sodium sulfate was close to 100%under all experimental conditions.The best feed salt concentration was 0.2-0.3 mol/L,the best current density was 30 m A/cm2,the best flow rate and volume ratio were 500 m L/min and 1:2,respectively.Under the optimum experimental conditions,the energy consumption was 1.4 k Wh/kg Na2SO4.The purity of sulfuric acid and sodium hydroxide reached 98.32%and 98.23%respectively.The total process cost of BMED was estimated to be 0.705$/kg Na2SO4 under optimal process conditions,successfully converted low-value sodium sulfate to high-value sulfuric acid and sodium hydroxide.And both can be used as raw materials for upstream processes.The closed-loop production technology of lithium carbonate was realized.The low-concentration lithium solution produced in the process of lithium extraction from salt lakes,the recovery process of lithium ions batteries,and the mining process of lithium ore was recovered.Recovery by phosphate precipitation was an effective method.Then lithium phosphate was converted to lithium hydroxide and phosphoric acid by bipolar membrane electrodialysis.The effects of solubility of lithium phosphate,current density and phosphoric acid concentration on BMED performance were studied.In the experiment,the recovery rate of lithium is up to 99%.The higher the solubility of lithium phosphate in the phosphoric acid solution,the better the performance of the BMED in converting lithium phosphate.As the current density increases from 20 to 60 m A/cm2,the current efficiency gradually decreases to 45%,while the energy consumption gradually increased to 28 k Wh/kg Li OH.The optimal current density should be selected 30 m A/cm2.And when the concentration of phosphoric acid gradually increases,the effect of BMED conversion to lithium phosphate became significantly better.Under optimal experimental conditions,the BMED process economy was 2.941$/kg Li OH.It not only solved the problem of low concentration lithium recovery,but also developed a new lithium hydroxide production process,which provided a reference for industrial production. |
