Synthesis Of Ion Sieve And Its Adsorption Of Lithium In Sodium Aluminate Solution

During the alumina production process,80%～85%of lithium will enter the sodium aluminate solution from the bauxite and then all enter the product during the seed precipitation process,resulting in an increase of the lithium content in the alumina product.The lithium accumulation will adversely affect the subsequent aluminium electrolysis.At present,there are few researches on lithium recovery in sodium aluminate solution.This work draws on the idea of extracting lithium from salt lake brine,using lithium ion sieve to adsorb lithium in sodium aluminate solution to achieve purification of sodium aluminate solution and recovery of lithium simultaneously.Because the sodium aluminate solution is strongly alkaline and unstable,the synthesized lithium ion sieve needs to selectively adsorb lithium ions in the strong alkaline sodium aluminate solution without affecting the stability of the solution.The lithium ion sieve with good adsorption performance was produced by controlling different synthesis conditions and different modification conditions.The effects of lithium source,material ratio,calcination temperature and calcination time on the structure and adsorption effect of lithium ion sieve during the synthesis process were systematically investigated.The influence of the acid type,acid concentration and pickling time during the modification process on the structure and adsorption effect of the lithium ion sieve was also investigated.The process conditions affecting the adsorption effect of the lithium ion sieve in the sodium aluminate solution were studied,as well as the cyclic adsorption effect of lithium ion sieve in sodium aluminate solution.Finally,the adsorption mechanism of lithium ion sieve in sodium aluminate solution was studied by the adsorption kinetic model.The research results showed complete structure and good stability of the obtained lithium ion sieve precursor after calcination at 750°C for 4h.Li₂CO₃ showed better adsorption effect when used as the lithium source,compared to Li OH and Li NO3.The adsorption effect of Li2Ti O3 type precursor in sodium aluminate solution after modification is better than that of Li4Ti5O12 type precursor.The acid washing effect of hydrochloric acid is better than that of sulfuric acid and citric acid during modification.The lithium elution rate of the precursor can reach the maximum value of 93.88%after 6h of pickling in 7.3g/L hydrochloric acid solution.The temperature of the solution during pickling was only found to promote the elution rate of lithium,while no obvious effect on the efficiency of lithium elution was observed.The adsorption effect of lithium ion sieve in sodium aluminate solution is mainly affected by the temperature of the solution.When the temperature is lower than 85°C,the sodium aluminate solution undergoes hydrolysis after adsorption for about 2h.The stability of the solution increases with increasing the temperature of the solution,and thus the time for hydrolysis to occur gradually increases as well.Specifically,within2g/L of lithium ion sieve added under 100°C,the sodium aluminate solution can maintain stability for up to 3.5h during the adsorption process,with a corresponding lithium ion adsorption rate of 66.95%.After that the stabilization time will no longer extend even with further increased solution temperature.And there is no obvious promotion on the adsorption effect of the lithium ion sieve under this circumstance.Through adsorption kinetic fitting,it was found that the adsorption process was controlled by chemical reaction and internal diffusion,which conforms to the pseudo second-order kinetic equation model.Under a liquid-solid ratio of 25:1（m L/g）and 9g/L of hydrochloric acid,after multistage desorption,with a corresponding lithium concentration of 1.43g/L in the solution.The adsorption effect is significantly reduced when the ion sieve is desorbed.The adsorption efficiency was only 15.77%.The cyclic adsorption performance is reduced due to the destruction of the structure of the lithium ion sieve.