Preparation Of Composite Nanofiltration Membrane Based On Biaminoguanidine Salt Monomer And Study On Separation Performance Of Magnesium And Lithium Ions

Lithium resources are widely used in various industries,and the separation of magnesium and lithium from salt lake brine is of great significance for lithium production.The extraction technology of lithium in salt lake brine in foreign countries is relatively mature,but the ratio of magnesium to lithium in salt lake brine in China is much larger than that in foreign salt lake brines.The foreign lithium extraction technology cannot be effectively used as a reference for our country.The composite nanofiltration membrane separation technology has developed well in recent years,showing broad application prospects.Combined with the selective separation of ions by the composite nanofiltration membrane,it has unique advantages in the separation of magnesium and lithium.Low-pressure composite nanofiltration membranes have low energy consumption during operation,which is an important focus of current preparation of composite nanofiltration membranes.Therefore,in this paper,a new type of aqueous monomer 1,3-diaminoguanidine hydrochloride was selected as the aqueous phase monomer for reverse phase interfacial polymerization to prepare a composite nanofiltration membrane,and the retention and separation properties of magnesium and lithium were studied at a lower pressure.First,the structure of NF90 membrane and the separation performance of magnesium and lithium were characterized.The structure of the membrane was characterized by Zeta potential and SEM,and the retention properties of LiCl,MgCl₂,and MgSO₄ were investigated.The results showed that the retention rates of the NF90membrane for the three salts were 39.88%,36.88%,and 15.84%,respectively.Secondly,a composite nanofiltration membrane was prepared by using Ps20 as the base membrane,1,3-diaminoguanidine hydrochloride as the water phase monomer,and trimesoyl chloride?TMC?as the oil phase monomer.The effects of monomer concentration,types of additives,heat treatment temperature and time on the structure and separation performance of the composite membrane were investigated.The results showed that the optimal preparation conditions for increasing the composite nanofiltration membrane potential were 1,3-diaminoguanidine concentration of4.8wt%,trimesoyl chloride concentration of 0.1wt%,and the addition of 1 wt%triethylamine to adjust the concentration of the aqueous solution.The interfacial polymerization time was 1 min,and the post-treatment time was 50?,15 min.The rejection rates of the composite nanofiltration membranes prepared under the optimal conditions for 2g/L salt solutions of LiCl,MgCl₂,and MgSO₄were 13.12%,19.37%,and 16.45%,respectively.Finally,under the optimal preparation conditions,the effect of oil-phase solvents on the separation performance of the composite nanofiltration membranes was discussed.Ps20,porogen-added polysulfone-based membrane,and porogen-free polysulfone-based membrane were used as supporting layers,and n-hexane was mixed with 20 wt%,30 wt%,40 wt%,and 50 wt%n-dodecane as the oil phase Under the optimal preparation conditions,the solvent was used to prepare a composite nanofiltration membrane by reverse phase interface polymerization.The experimental results show that blending the n-dodecane concentration has an effect on the retention and separation performance of the composite nanofiltration membrane.When Ps20 is used as the support layer,the composite nanofiltration membrane has the best lithium ion retention effect when mixed with 20 wt%n-dodecane in the oil phase solvent,which is 59.95%.When the porosity-added polysulfone-based membrane was used as the support layer,the composite nanofiltration membrane had the best lithium ion retention effect when mixed with 40 wt%n-dodecane in the oil phase solvent,which was 75.13%.The retention effect of the porosity-free polysulfone composite nanofiltration membrane at the same n-dodecane blending concentration was not as good as that of the porosity-added polysulfone composite nanofiltration membrane.The composite nanofiltration membrane prepared by mixing n-dodecane in an oil phase solvent improves the retention effect of lithium ions.