Font Size: a A A

Design,Preparation And Performance Studies Of High Lithium Selective Adsorption Materials

Posted on:2018-02-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:X XuFull Text:PDF
GTID:1311330518493637Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
The primary lithium resources are mainly found in salt-lake brines and seawater on earth, hence lithium ion-sieves (LISs) with high lithium separation efficiency are considered as promising lithium adsorbents for recovering lithium from aqueous solution. Correspondingly, the "LISs technology" has become a hot research field recently. In order to solve the problems of LISs (both Mn-type and Ti-type) such as poor chemical stability, low lithium adsorption capacity and low regeneration performance, several improved methods were proposed in this dissertation, which were based on the ?-MnO2 spinel type and layered H2Ti03-type LISs. The main research results are lists as follows:(1) In order to improve the lithium uptake capacity of Mn-type LISs, the PS microspheres template was applied for preparing porous ?-MnO2 LISs.The specific surface area increased from 16.31 m2 ·g-1 to 90.17 m2·g-1 after PS microspheres template modification, and the lithium uptake capacity increased to 37.75 mg·g-1 correspondingly, which is 94.3% of the theoretical lithium uptake capacity. Besides, the lithium uptake capacity fading rate was only 16.4% after 8 cyclic lithium adsorption-desorption regeneration tests.(2) The doping method was proposed for inhibiting Mn dissolution of Mn-type LISs. The Cr-doped LiMn2O4 spinels were obtained by using sol-gel methods. The results suggested Cr3+ replaced Mn3+ in spinel lattices and the Cr-doped LiMn2O4 samples exhibited typical spinel frameworks. The lithium intercalation rates decreasde with Cr contents increased in pickling process, implying the lithium intercalation process fits for the "redox mechanism". Meanwhile, the dissolution rates of both Mn and Cr were the lowest when the apparent Cr doping amount was 0.2(Cr-LMO-0.2), the dissolution rates of both Mn and Cr were extremely high when the apparent Cr doping amount were higher than 0.4. The lithium capacity of Cr-MO-O.4 was 18.4 mg·g-1, and the Mn dissolution was only 4.9% in 5 cyclic regenerations in the environment of pH 12,25?, which is far less than the un-doped sample (14.6%).(3) The electrochemical assisted lithium recovery process was proposed for improving the Li adsorption/desorption rates. The LIS was loaded on the electrode by using organic binder. Studies showed that the lithium intercalation into/de-intercalation from spinel lattices on electrode confirmed with "the diffusion control mechanism", namely, the rate-control step is the diffusion process of Li+ ions in electrolyte. In electrochemical-assisted lithium recovery process, the optimal current density should be set as 100 mA·g-1, the energy consumption calculation results showed that the average energy consumption was between 4.08 and 4.16 Wh when 1mol lithium ions were recovered.(4) In order to further improve electrochemical assisted lithium recovery performance, the self-supporting ?-MnO2 arrays electrode was designed.It was prepared through hydrothermal lithiation of a cathodic deposited Mn304 arrays followed by potentiostatic treatment. The ?-Mn02 arrays electrode was coupled with Ag electrode, and the electric capacity tests clearly demonstrated the electric capacity of the lithium recovery system with ?-Mn02 arrays electrode was 114.0/121.3 mAh·g-1, which is higher than the electric capacity of the lithium recovery system with ?-Mn02 powder electrode (89.8/97.6 mAh-g-1) at current density of 20 mA·g-1.After 100 cycles' charging-discharging tests, 91% of lithium capacity was remained for the ?-Mn02 arrays electrode system while only 76% of lithium capacity was remained for the ?-Mn02 powder electrode system.The lithium enrichment experimental results showed that when using?-MnO2 arrays electrode system, the lithium enrichment amount was 25.3 mM, which is 82.6% of theoretical lithium capacity in 100 cycles. In addition, the energy consumption results showed that only about 4.14 Wh was required for recovering one mole of lithium ions by using self-supported ?-MnO2 arrays electrode. The fine electrochemical assisted lithium recovery performance of ?-MnO2 arrays electrode system was attributed to the binder-free structure and without using conductive agents.(5) Removing lithium from the Bayer liquor for ensuring alumina product quality demands a special LIS (LIS) with good stability in strong alkaline medium. In this study, a three-dimensional porous H2Ti03-type LIS prepared by PS colloidal microspheres template was applied to adsorb Li+from the strong alkaline Bayer liquor. The results confirm fine stability of H2Ti03-type LIS in strong alkaline medium. In addition, the specific area of porous H2TiO3-type LIS was 94.14 m2·g-1 , and the lithium adsorption processes o fit the pseudo-second-order model, the adsorption rate k2 was 0.02357 g-mg-1·h-1 and the equilibrium adsorption capacity was 76.3 mg·g-1. The lithium removal effect in simulation Bayer liquor of the porous H2Ti03-type LIS was proven to be more efficient as compared with that of the bare H2Ti03-type LIS.(6) In order to improve the recycling rate of the Ti-type LIS with powder form, the PVC, DMF, and layered H2Ti03-type LIS (HTO) were used as binder, solvent and active lithium adsorbent to prepare PVC-HTO composite membrane. The results showed that the optimal mechanical property was obtained when the mass ratio PVC: DMF: HTO was 3:12:5,the film thickness was400 nm. The equilibrium time was about 18 h and the equilibrium lithium capacity was 1384 mg·m-2 at room temperature in lithium-containing solution (pH=12, initial lithium concentration 100 ppm). In addition, regeneration tests results showed about 99.5%recycling rate was remained for the PVC-HTO composite membrane in 5 cyclic regeneration tests (from 98.62 g·m-2 to 98.14 g·m-2), which is far higher than the recycling rate of the HTO powder (about 22.5%).
Keywords/Search Tags:Lithium ion sieves, Lithium uptake capacity, Spinel stability, Electrochemical-assisted lithium recovery process, self-supporting ?-MnO2 arrays, porous H2TiO3-type lithium ion sieves, PVC-HTO composite membrane
PDF Full Text Request
Related items