▎ 摘　　要

NOVELTY - Composite film comprises ultrafiltration support layer and modified polyamide layer, where the modified polyamide layer is prepared by interfacial polymerization reaction between nanoparticle, piperazine monomer and acid chloride monomer. The nanoparticle comprises graphene oxide and/or reduced graphene oxide. The carboxy density on the surface of the composite film is 0.20-15/nm2, and the carboxy density on the surface of the composite film is obtained through quantitative analysis by toluidine blue staining. The nanoparticle includes graphene oxide. USE - The composite film is useful in separating and selecting monovalent and divalent ions, preferably separating and selecting magnesium and lithium in high-magnesium-lithium ratio salt lake brine (claimed). ADVANTAGE - The composite film effectively realizes separation of high magnesium-lithium ratio salt lake brine magnesium lithium and efficient extraction of lithium, ensures high yield of lithium in the separation process, improves the salt lake lithium resource recycling effect, and can effectively relieve the film pollution problem in the process of extracting lithium from brine. It has excellent anti-pollution performance, and improves the service stability of the composite film, reduces the film cleaning times and the use of chemical cleaning agent in the cleaning process, effectively reduces the energy consumption and cost of the film separation process, and also has good environment-friendly effect and high economical efficiency. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for separating and selecting magnesium and lithium in high magnesium-lithium ratio salt lake brine by composite film.