| Lithium and its compounds have become important strategic resources for national economy and national defense construction.With the continuous growth of market demand,solid lithium mineral resources have been far from meeting the demand,and salt lake lithium has become a hot topic.Ion sieve adsorption method is considered to be an ideal brine extraction method for lithium due to its simple process,high recovery rate,high selectivity and low cost.But the development of ion sieve with selective adsorbability is the key to extracting lithium by adsorption.Al-based lithium adsorbent is an ideal screen for extracting lithium ions because of its advantages of easy preparation,green environmental protection and application to high magnesium lithium brine.However,currently developed aluminum-based lithium adsorbent is mostly in powder form with poor fluidity and permeability,which is not conducive to its industrial utilization.The immobilization of ion sieve can effectively solve the above problems,but after immobilization,the active sites of lithium ion sieve are easy to be coated,resulting in its adsorption performance is reduced.In this paper,in view of the problems faced by the immobilization of lithium ion sieve,the aluminum-based lithium adsorbent was coated in the PVDF ultrafiltration membrane with full sponge pore structure,which could not only realize the dispersion of the adsorbent,but also reduce its dissolution loss,and realize the efficient separation and utilization of lithium ions in brine.(1)First,the adsorbent was prepared by coprecipitation method and the four main factors in the preparation process were optimized by orthogonal experiment.the results show that the best preparation conditions for control of reaction temperature of 75?,adjust pH value of reaction end point 6-7,Al/Li mole ratio was 1.25:1,NaOH drops of accelerating at a rate of 3 ml/min.The adsorption performance study showed that the adsorption capacity was up to 8.66 mg/g at the adsorption temperature of 45?,the original pH of the mother solution was 7 and the adsorption time was 2 h.After 8 times,the adsorption capacity can still maintain the first 91.5%.The adsorption process of adsorbent to Li+is more in line with the Langmuir isothermal adsorption equation.(2)Then,in order to immobilize the adsorbent and disperse it effectively in the membrane pore,PVDF ultrafiltration membrane with full sponge pore structure was prepared.The results show that the phase separation system with water as the non-solvent,the instantaneous phase is easy to occur and develop into finger-like holes;In the phase separation system with ethanol or DMAc as non-solvent,delayed phase separation promoted the development of sponge pore structure.The membrane section shows the transition from the coexistence of a small number of droplets and cavernous pores to the full sponge pores,and the full sponge pore structure PVDF membrane is obtained.Considering the structure and performance of the membrane,the membrane formula was finally determined to be 16 wt%PVDF-84 wt%DMAc.Under the condition that the coagulation bath group at 15? was divided into 30 wt%etoh-70 wt%H2O,the membrane flux was 138.71 L/(m2·h).(3)Finally,the dynamic adsorption/desorption performance of hybrid membrane was investigated by combining LiCl·2Al(OH)3·nH2O with PVDF ultrafiltration membrane with full sponge pore structure under the optimal conditions.The results show that,under the condition of membrane scraping thickness of 250?m,the adsorption capacity of hybrid membrane is basically saturated after 2 h dynamic cyclic adsorption,and when the adsorption time is 1 h,the adsorption capacity is up to 280 mg/m2,which is 93%of the maximum adsorption capacity.When the desorption time was 120 min,the desorption capacity was basically stable.After 10 times of dynamic cyclic adsorption and desorption,the adsorption capacity of hybrid membrane can still maintain 85.3%of that of the first time,indicating that hybrid membrane has good cyclic durability. |
PDF Full Text Request