Preparation Of Graphene Oxide Modified Nanofiltration Membrane And Its Application In Ionic Rare Earth Leaching Tailings

Ionic rare earth is a national strategic resource,and its special extraction method determines that after normal mining,the tail water from the mountain still contains ammonia nitrogen and rare earth ions.On the one hand,it pollutes the environment.On the other hand,it results in the loss of rare earth.Therefore,it is of great significance to study the treatment of tailings and recover rare earth elements.Compared with the conventional in situ leaching method,the nanofiltration membrane can not only achieve a good treatment effect,but also can enrich and recover rare earth ions in the tailing water.In this paper,the self-made nanofiltration membrane modified by graphene oxide was applied to the treatment of tail water and the recovery of rare earth.It is innovative and practical.The main results are as follows:?1?Graphene oxide?GO?,was prepared by Hummers method.Graphite was oxidized by concentrated sulfuric acid?H₂SO₄?and KMnO₄,the interlayer force of graphite was destroyed,and the graphite layer was completely oxidized and stripped.The microstructure and chemical structure of graphene oxide showed that graphene oxide has thin flake structure and overlapping folds on the edge.The appearance of these folds could increase the water transport channel of nanofiltration membrane and improve the permeability of graphene oxide.The hydrophilic functional groups such as carboxyl group?-COOH?,hydroxyl group)?-OH?in graphene oxide made it hydrophilic,and the carbon oxide of the graphene oxide was hydrophilic.The results showed that the regularity of graphite has been destroyed in the oxidation process,and the graphite lamellar has been successfully oxidized and stripped.These properties of graphene oxide provide a basis for the hydrophilic modification of nanofiltration membranes.?2?The nanofiltration membranes were prepared by interfacial polymerization using polysulfone ultrafiltration membrane?PSF?as base membrane,piperazine?PIP?in aqueous phase and pyrobenzoyl chloride?TMC?in organic phase as active monomers.At the same time,the nanofiltration membrane was modified by adding graphene oxide in the aqueous phase.The microstructure,chemical structure and permeability of the nanofiltration membrane were characterized by the addition of graphene oxide.The results showed that the surface bulge of nanofiltration membrane was increased and the roughness of nanofiltration membrane was decreased by the addition of graphene oxide.When the amount of 0.07wt%GO was added,the bulge formed agglomeration and the roughness increased.After modification,the nitrogen content increased,the hydrophilic functional group increased,the water contact angle decreased,and the water contact angle decreased.The hydrophilicity was enhanced and the negative property of the membrane was stronger than that of the unmodified nanofiltration membrane under different pH conditions.With the increase of the amount of graphene oxide,the salt retention rate decreased,and the membrane water flux increased gradually.When the amount of graphene oxide was0.06wt%,the water flux reached the maximum,98.2L/?m²·h?,when the addition amount was higher than 0.07wt%GO,the water flux reached the maximum,and when the content was higher than 0.07wt%GO,the water flux reached the maximum.The flow of water has fallen.Comprehensive analysis showed that the preparation of nanofiltration membrane modified by graphene oxide was successful and the permeability of the membrane was better when the content of graphene oxide was 0.04⁰.06wt%.?3?The modified nanofiltration membrane with 0.06wt%graphene oxide and the unmodified nanofiltration membrane were used to treat the tail water respectively.La,Y,Nd,Pr and Ce in the tailing water were prepared into 0.0013 mol/L solution.The results showed that the enrichment of rare earth ions is the best when the feed flow rate is 5⁶L/?m²·min?,the operating pressure is 0.6MPa⁰.8 MPa,pH,the operating pressure is 4.5⁵.0,and the temperature is 25?³0?.And the enrichment effect of modified nanofiltration membrane on rare earth solution is better than that of unmodified nanofiltration membrane.Under the optimum conditions,both of the modified nanofiltration membrane have better enrichment effect on rare earth solution.The intercepted water fluxes were 23.3⁴8.3L/?m²·h?and 15.5³7.35L/?m²·h?,respectively.The recoveries of rare earth ions were 82.3%and 73.4%,99.2%,73.4%and 89.6%,respectively.In the anti-pollution test,the pure water flux recovery rate of the modified nanofiltration membrane was 78.5%,and the pure water flux recovery rate of the modified nanofiltration membrane was 95.1%,after 16 hours of retention,the recovery rate of the pure water flux of the modified nanofiltration membrane was78.5%.The results showed that the nanofiltration membrane modified with graphene oxide has better anti-fouling performance.