Recovery Of Lithium Ion From Exchanged Mother Liquids Of Li-LSX Zeolite

Lithium which is called "the 21st century's energy metal" has been widely applied in the fields of glass, ceramics, metallurgy, textiles, rubber, lubricating materials, medical treatment and other traditional areas. At present, the demand of lithium in high-tech fields such as aerospace, nuclear power generation, high-energy batteries and light-weight high-strength alloys is increasing day by day. Therefore, the recycling research of lithium has a very important practical significance.Li-LSX zeolites have an extensive application in gas separation with the advantages of large nitrogen/oxygen separation faction, high nitrogen adsorption capacity and easiness in desorption. So that, Li-LSX zeolites have been widely used in the process of PSA (pressure swing adsorption). Li-LSX zeolites were prepared from Na-LSX zeolites via ion-exchange method. In the industrial preparation of Li-LSX zeolites, ion-exchange method in aqueous media is generally used, due to mild exchange condition and simple operation. However, there are many disadvantages, such as low lithium utilization efficiency, difficulty in reaching high ion-exchange degree and recovery of lithium. With the increase of lithium price, the cost of this method has become higher, which therefore restricts its application.Recently, a new preparation method of Li-LSX zeolites has been reported by our group, which shared with advantages of the ion-exchange method in aqueous media and in solid phase together. This method could raise the ion-exchange degree of lithium and decrease the usage of lithium salt at the same time. In order to further develop this method and reduce the preparation cost of Li-LSX zeolites, the recycle possibility of lithium ion from exchanged mother liquids (including Li+, Na+, Cl-) were investigated in detail.Below were the main results of the research contents:1. By use of tri-n-butyl phosphate (TPB) with 200# gasoline as mixed solvent, the extraction process of lithium ion from exchanged mother liquids of Li-LSX zeolites was studied in the presence of ferric chloride as cooperation agent. Effects of procedure parameters, such as temperature, contact time, pH value, phase ratio, concentration of extractant, the ratio of [Fe3+]/[Li+] and concentration of Cl- , on the extraction technology were investigated. Meantime, the△H profile of extracting reaction was calculated. The results showed that TBP solvent was a very suitable extractant of lithium ion and the extraction rate could reach up to 85%, on the other hand, the extracting procedure belonged to exothermic reaction. The ratio of [Fe3+]/[Li+], concentration of Cl- and pH value had a significant influence on extraction process. The optimal extracting conditions at room temperature were found as follow: contact time was during the period of 10～15min; pH value was around 2～3; phase ratio was about 1:1; TBP volume fraction was 40～60%; [Fe3+]/[Li+] molar ratio was around 2.5～4; concentration of Cl- was 6～8mol/L.2. The anti-extraction of lithium ion from TBP by hydrochloric acid was also studied. The effects of phase ratio, hydrochloric acid concentration and temperature on the anti-extraction technology were analyzed in detail. It was shown that hydrochloric acid concentration had a significant influence on anti-extraction process. The anti-extraction rate could reach up to 85% under the optimal anti-extraction conditions at room temperature, as follow: phase ratio was about 1:1; hydrochloric acid concentration was more than 5mol/L.3. The recycling of extractant was investigated preliminarily and it was found that: when using the recycled extractant (TBP) and solvent (200# gasoline), the Li+ extraction rate increased, however the anti-extraction rate decreased. Since the content of the decreasing around 26% was more obvious than that of increasing about 4%, the overall recycling rate decreased a bit. For the sake of high overall recycling rate, the organic phase must be added timely, particularly, for the multilevel extraction technology. Furthermore, the industrial prospect of this method has been discussed briefly.