Preparation Of PVDF Antifouling Membranes And The Study Of The Treatment Of Radioactive Wastewater By Membranes

As one of the the most promising high-tech in late20th century to mid21stcentury, membrane seperation technology has been widely used in the field of food,medicine, environmental protection, petrochemical, energy, water treatment,etc. Dueto the characteristics of different membrane material, there are a lot of problems in theapplication process of membrane separation technology, one of which ismembrane fouling. Membrane fouling restricts the development of membraneseparation technology. Therefore, modification on membrane material for theimprovement of membrane performance is particularly important.Hydrophilic monomer of N-vinyl pyrrolidone was grafted to poly(vinylidenefluoride)(PVDF) powders using the pre-irradiation induced graft polymerizationtechnique. The effects of reaction time, monomer concentration and absorbed dose onthe degree of grafting were investigated, and the grafted PVDF powders werecharacterized by Fourier transform infrared spectroscopy, X-ray photoelectronspectroscopy, thermogravimetric analysis and differential scanning calorimetry. Thegrafted PVDF powders were also cast into microfiltration (MF) membranes via thephase-inversion method. The contact angle, water flux and water uptake weremeasured. The surface and cross-section morphology of the membranes was studiedby scanning electron microscopy. The antifouling property was determined throughmeasurements of the recovery percentage of pure water flux after the MF membraneswere fouled with bovine serum albumin solution. The results confirmed that theexistence of poly(N-vinyl pyrrolidone)(PVP) graft chains improved thehydrophilicity and antifouling property of the MF membranes cast from PVDF-g-PVPpowders.PVDF-g-PVP powders and PVDF/PVP blends with different PVP content werecast into microfiltration (MF) membranes via the phase-inversion method. Theinfluence of grafting and blending on the structure and property of the membraneswas investigated. The results confirmed that the existence of PVP improved thehydrophilicity of the MF membranes cast from PVDF-g-PVP grafted powders and PVDF/PVP blends, although the thermal stability of PVDF-g-PVP and PVDF/PVPmembranes was slightly reduced compared to PVDF membrane. Because of differentroles of PVP in PVDF-g-PVP and PVDF/PVP membranes, PVDF/PVP membraneshad lower N content, more pores, higher water flux and lower hydrophilicity, incomparison with PVDF-g-PVP membranes with the same PVP content in the castingsolution. In order to obtain membranes with better separation performance, a certainamount of pore forming agents, such as PVP and PEG, can be added to the castingsolution of grafted powders, improving the structure of membranes.Based on the preparation of PVDF-g-PVP antifouling membranes, andcombining the need of working assignments, the application of membrane technologyin the treatment of radioactive wastewater was studied. According to thenuclide species in low-level radioactive wastewater from TMSR, strontium (Sr2+) waschosen as the experimental object. The performance of nanofiltration (NF) fortreatment of strontium-containing radioactive wastewater was investigated using NF90, NF270and XN45membranes. The effects of the initial strontium concentration,solution pH, ionic strength and complexation phenomena on strontium removal weredescribed. The results indicated that the strontium rejection increased with decreasinginitial strontium concentration and ionic strength. In addition, an increase in thesolution pH reduced strontium rejection until pH=5, at which point a further increasein pH increased strontium rejection. In the presence of a complexing agent (PAA orEDTA-2Na), the strontium rejection was generally higher than those obtained withouta complexing agent. The fouling experiments indicated that the three kinds ofmembranes used in the experiments have good antifouling performance when treatingstrontium-containing simulated radioactive wastewater.