Adsorption Investigation Of PVDF Separation Membrane Modified By The Ethylenediamine Tetramethylenephosphonic Acid Toward Nickel Ion From Wastewater

In this research, using the combined process of the solution blending and phase inversion techniques, ethylenediamine tetramethylenephosphonic acid, tetrabutyl orthotitanate, and polyvinylidene fluoride(PVDF) were employed to prepare the modified PVDF-based membrane aiming for removal of Ni(Ⅱ) in different forms from wastewater.The optimal components of the cast solution used to prepare the membrane were optimized by the orthogonality experiment.Then the influence of membrane breakthrough curve was investigated by dynamic adsorption tests.The modified PVDF-based membrane was characterized by Field-Emission Scanning Electron Microscope(SEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS), Nuclear Magnetic Resonance Spectrometer(NMR) and Thermo Gravimetric Analyzer(TGA) techniques and the ion exchange capacity, zero charge point, porosity, moisture content and pure water flux of the membrane were also measured. Effects of the initial pH, temperature and contact time, initial Ni(Ⅱ) concentration on the adsorption performance of the membreane were investigated. Also, influences of the coexisting Pb(Ⅱ), Cd(Ⅱ), Ca(Ⅱ), Fe(Ⅲ), citrate,nitrilotriacetic acid(NTA) and ethylenediaminetetraacetic acid(EDTA) on the Ni(Ⅱ) uptake of the membrane were investigated. Isotherms and kinetics of the modified membrane toward Ni(Ⅱ) were elucidated. The adsorption/desorption properties of the modified PVDF separation membrane were also studied. Furthermore, the contineous filtration experiment was also conducted.The results show that the modified PVDF separation membrane has a microporous structure and exhibits an excellent thermal stability. The phosphoramidate groups for chealtion have been blended into the PVDF membrane successfully.The zero charge point,and the ion exchange capacity of the separation membrane are 5.4, and 0.60 mmol/g. The four coexistent cations interfere with the Ni(Ⅱ) adsorption in the order of Pb(Ⅱ) > Cd(Ⅱ) >Ca(Ⅱ) > Fe(Ⅲ). The disturbance of the organic acids is in the order of EDTA > NTA >Citrate. Adsorption isotherms and adsorption kinetics are fitted to the Langmuir and the Lagergren second-order models, respectively. D-R plots indicate that the adsorptionprocess is an ion exchange reaction. The thermodynamic parameters ΔG0 < 0, ΔH0 < 0,ΔS0 > 0, demonstrate the spontaneous and exothermic nature of the adsorption. The adsorption/desorption experiment indicates that the separation membrane exhibits an excellent property of reuse. The dynamic adsorption process demonstrates that with the increase of flow velocity, breakthrough time, exhaustion time will be shortened. For the breakthrough curve of Ni(Ⅱ) uptake, the mass transfer rate Ka derived from the BDST model follows the order: Fe(Ⅲ) < Ca(Ⅱ) < Cd(Ⅱ) < Pb(Ⅱ); those of complexing reagents follow the trend: citrate < NTA < EDTA. Furthermore, the bed sorption capacity N0 on unit volume of membrane is in the order of Pb(Ⅱ) < Cd(Ⅱ)< Ca(Ⅱ) < Fe(Ⅲ); N0 of the three complexing reagent coexisting systems follows the sequence of EDTA < NTA < citrate.