Study On Preparation And Properties Of Lithium Manganese Oxide Spinel Ion-sieve Blend Membrane

Li1.6Mn1.6O4 is an ideal adsorbent for extracting lithium from salt lake,which has high selectivity,larger adsorption capacity.Polyphenysulfone(PPSU)is used to membrane process due to its characteristics of acid and alkali resistance,solvent resistance,good mechanical strength and outstanding heat resistance.The preparation of Li1.6Mn1.6O4/PPSU blend membrane can not only immobilize the ion sieve but also improve the life of blend membrane.At present,lithium ion sieve is immobilized in finger-like structure membrane,which is easily lost at high operation pressure.So it's necessary to prepare sponge-like structure membrane to coat lithium ion sieve.Firstly,PPSU ultrafiltration membranes were prepared via non-solvent induced phase separation(NIPS)method.The influence of PPSU concentration,coagulation bath conditions(temperature and composition)was studied and disgussed based on phase diagram.From ternary phase diagram of PPSU/NMP/non-solvent system,ethanol is considered weak non-solvent for membrane formation and facilates the formation of sponge-like pores,while water can be seen a strong non-solvent and results finger-like structures formation.In the fromation of membrane process,microvoids were formed with the elevation of temperature,which caused the flux and pore size decreased.As addition of NMP in the coagulation bath,sponge-like pores replaced finger-like structures from membrane bottom gradually.When the concentration of NMP reached to 70 wt%,there were drop-like pores nearby the membrane surface.The best condition of membrane formation is that the composition of cast solution is 16 wt%PPSU-84 wt%NMP under the coagulation bath composition of 70 wt%NMP-4 wt%EtOH-26 wt%H2O at 8?.In this case,full sponge-like structure PPSU membrane was obtained and the pure water plux is 43.44 L/(m2·h),contact angle is 59.12°.Then,PEG 1000 and PVP as non-solvet additive were added into castiong solution to inprove membrane hydrophily and flux.Under the 70 wt%NMP-30 wt%H2O of coagulation bath,the results of orthogonal tests indicated that the order of primary and secondary factors influencing membrane flux was concentation of PPSU,PEG molecular weight and PEG concentation.The best membrane composition is 16 wt%PPSU-8 wt%PEG 1000-76 wt%NMP.Finger-like structures were increased by the addition of PVP.And under the 70 wt%NMP-4 wt%EtOH-26 wt%H2O of coagulation bath at 8?,The best membrane composition was obtained namely 16 wt%PPSU-8 wt%PEG 1000-4 wt%PVP-62 wt%NMP.In this case,the pure water plux is 88.0 L/(m2·h).Finally,lithium ion sieve was blended to the best PPSU casting solution composition with sponge-like pores and high flux.The desorption/absorption capacity of PPSU/Li1.6Mn1.6O4 blend membrane was investigated.The result shows that the best desorption/absorption time is respectively 30min and 24h.Increase of membrane thickness and Li1.6Mn1.6O4 concentration can cause the increase of dissolution loss,which is disadvantage of absorption process.The absorption capacity of membrane still have 82.73%through 10 times cycle,which confirmed good circulation stability of the prepared blend membrane.