Performance evaluation of polyamide nanofiltration membranes for phosphorus removal process and their stability against strong acid/alkali solution

In this study,a quantitative performance of three commercial polyamide nanofiltration(NF) membranes(i.e.,NF,NF90,and NF270) for phosphorus removal under different feed conditions was investigated.The experiments were conducted at different feed phosphorus concentrations(2.5,5,10,and 15 mg·L~(-1)) and elevated pHs(pH 1.5,5,10,and 13.5) at a constant feed pressure of 1 MPa using a dead-end filtration cell.Membrane rejection against total phosphorus generally increased with increasing phosphorus concentration regardless of membrane type.In contrast,the permeate flux for all the membranes only decreased slightly with increasing phosphorus concentration.The results also showed that the phosphorus rejections improved while water flux remained almost unchanged with increasing feed solution pH.When the three membranes were exposed to strong pHs(pH 1.5 and 13.5) for a longer duration(up to 6 weeks)it was found that the rejection capability and water flux of the membranes remained very similar throughout the duration,except for NF membrane with marginal decrement in phosphorus rejection.Adsorption study also revealed that more phosphorus was adsorbed onto the membrane structure at alkaline conditions(pH 10 and 13.5) compared to the same membranes tested at lower pHs(pH 1.5 and 5).In eonelusion,NF270 membrane outperformed Nf and NF90 membranes owing to its desirable performance of water flux and phosphorus rejection particularly under strong alkali solution.The NF270 membrane achieved 14.0 L·m~(-2)·h~(-1) and 96.5% rejection against 10 mg·L~(-1) phosphorus solution with a pH value of 13.5 at the applied pressure of 1 MPa.     

Optimal design of nanofiltration system for surface water treatment☆

Both reverse osmosis (RO) and nanofiltration (NF) membranes have been increasingly used for water purification and desalination. However, the salt rejection of NF membranes is quite different from that of RO membranes, which makes a significant distinction in their process designs. This work started from the performance investigation of a single NF membrane element and then focused on the process design of the NF system for surface water treat-ment. In experimental tests, it was found that the observed rejection of the NF element becomes nearly constant when the concentrate flow is large enough, while the membrane flux of the NF element is quite stable regardless of the water flow across the membrane surface. These findings can be used to instruct the process design of the NF system for surface water treatment. In process design, a two-stage arrangement is sufficient for the NF system to reach the highest water recovery, while the RO system requires a three-stage arrangement.     

Preparation and properties of hollow fibre nanofiltration membrane with continuous coffee-ring structure

Polyamide(PA)hollow fibre composite nanofiltration(NF)membranes with a coffee-ring structure and beneficial properties were prepared by adding graphene oxide(GO)into the interfacial polymerization process.The presentation of the coffee-ring structure was attributed to the heterogeneous,finely dispersed multiphase reaction system and the“coffee-stain”effect of the GO solution.When the piperazine concentration was 0.4 wt-%,the trimesoyl chloride concentration was 0.3 wt-%,and the GO concentration was 0.025 wt-%,the prepared NF membranes showed the best separation properties.The permeate flux was 76 L·m^?2·h^?1,and the rejection rate for MgSO4 was 98.6%at 0.4 MPa.Scanning electron microscopy,atomic force microscopy,and attenuated total reflectance-Fourier transform infrared spectroscopy were used to characterize the chemical structure and morphology of the PA/GO NF membrane.The results showed that GO was successfully entrapped into the PA functional layer.Under neutral operating conditions,the PA/GO membrane showed typical negatively charged NF membrane separation characteristics,and the rejection rate decreased in the order of Na2SO₄>MgSO₄>MgCl₂>NaCl.The PA/GO NF membrane showed better antifouling performance than the PA membrane.     

Effect of ethylene vinyl acetate content on the performance of VMD using HDPE co-blending membrane

Membranes were fabricated with high-density polyethylene(HDPE) and ethylene vinyl acetate(EVA) blend through thermally induced phase separation and were then used for vacuum membrane distillation(VMD).The membranes were supported by nonwoven polyester fabric with a special cellular structure. Different membrane samples were obtained by adjusting the polymer concentration, HDPE/EVA weight ratio, and coagulation bath temperature. The membranes were characterized by scanning electron microscopy(SEM) analysis, contact angle test, and evaluation of porosity and pore size distribution. A series of VMD tests were conducted using aqueous NaCl solution(0.5 mol·L~(-1)) at a feed temperature of 65 ℃ and permeate side absolute pressure of 3 kPa. The membranes showed excellent performance in water permeation flux, salt rejection, and long-term stability. The HDPE/EVA co-blending membranes exhibited the largest permeation flux of 23.87 kg·m~(-2)·h~(-1) and benign salt rejection of ≥99.9%.     

纳滤/反渗透膜处理重金属废水的性能

The performance of different nanofiltration （NF） and reverse osmosis （RO） membranes was studied in treating the toxic metal effluent from metallurgical industry. The characteristics and filtration behavior of the processes including the wastewater flux, salt rejection and ion rejection versus operating pressure were evaluated. Then the wastewater flux of RO membrane was compared with theoretical calculation using mass transfer models, and good consistency was observed. It was found that a high rejection rate more than 95% of metal ions and a low Chemical Oxygen Demand （COD） value of 10 mg·L^-1 in permeate could be achieved using the RO composite membrane, while the NF rejection of the salt could be up to 78.9% and the COD value in the permeate was 35 mg·L^-1. The results showed that the product water by both NF and RO desalination satisfied the State Reutilization Qualification, but NF would be more suitable for large-scale industrial practice, which offered significantly higher permeate flux at low operating pressure.     

Potential use of nanofiltration like-forward osmosis membranes for copper ion removal

The discharge of industrial effluent containing heavy metal ions would cause water pollution if such effluent is not properly treated. In this work, the performance of emerging nanofiltration(NF) like-forward osmosis(FO)membrane was evaluated for its efficiency to remove copper ion from water. Conventionally, copper ion is removed from aqueous solution via adsorption and/or ion-exchange method. The engineered osmosis method as proposed in this work considered four commercial NF membranes(i.e., NF90, DK, NDX and PFO) where their separation performances were accessed using synthetic water sample containing 100 mg·L~(-1) copper ion under FO and pressure retarded osmosis(PRO) orientation. The findings indicated that all membranes could achieve almost complete removal of copper regardless of membrane orientation without applying external driving force.The high removal rates were in good agreement with the outcomes of the membranes tested under pressuredriven mode at 1 MPa. The use of appropriate salts as draw solutes enabled the NF membranes to be employed in engineered osmosis process, achieving a relatively low reverse solute flux. The findings showed that the best performing membrane is PFO membrane in which it achieved N 99.4% copper rejection with very minimum reverse solute flux of 1 g·m~(-2)·h~(-1).     

添加剂和凝结剂温度对用无溶剂致相位分离法生产高性能PVDF/聚醚F127混合中空光纤膜的影响(英文)

Poly(vinylidene fluoride)(PVDF) has become one of the most popular materials for membrane prepara-tion via nonsolvent induced phase separation(NIPS) process.In this study,an amphiphilic block copolymer,Plu-ronic F127,has been used as both a pore-former and a surface-modifier in the fabrication of PVDF hollow fiber membranes to enhance the membrane permeability and hydrophilicity.The effects of 2nd additive and coagulant temperature on the formation of PVDF/Pluronic F127 membranes have also been investigated.The as-spun hollow fibers were characterized in terms of cross-sectional morphology,pure water permeation(PWP),relative molecular mass cut-off(MWCO),membrane chemistry,and hydrophilicity.It was observed that the addition of Pluronic F127 significantly increased the PWP of as-spun fibers,while the membrane contact angle was reduced.However,the size of macrovoids in the membranes was undesirably large.The addition of a 2nd additive,including lithium chlo-ride(LiCl) and water,or an increase in coagulant temperature was found to effectively suppress the macrovoid for-mation in the Pluronic-containing membranes.In addition,the use of LiCl as a 2nd additive also further enhanced the PWP and hydrophilicity of the membranes,while the surface pore size became smaller.PVDF hollow fiber with a PWP as high as 2530 L?m?2?h?1?MPa?1,a MWCO of 53000 and a contact angle of 71° was successfully fabricated with 3%(by mass) of Pluronic F127 and 3%(by mass) of LiCl at a coagulant temperature of 25 °C,which shows better performance as compared with most of PVDF hollow fiber membranes made by NIPS method.     

Effects of Sn residue on the high temperature stability of the H_2-permeable palladium membranes prepared by electroless plating on Al_2O_3 substrate after SnCl_2–PdCl_2 process: A case study

The stability of composite palladium membranes is of key importance for their application in hydrogen energy systems. Most of these membranes are prepared by electroless plating, and beforehand the substrate surface is activated by a SnCl_2–PdCl_2 process, but this process leads to a residue of Sn, which has been reported to be harmful to the membrane stability. In this work, the Pd/Al_2O_3 membranes were prepared by electroless plating after the SnCl_2–PdCl_2 process. The amount of Sn residue was adjusted by the SnCl_2 concentration, activation times and additional Sn(OH)_2coating. The surface morphology, cross-sectional structure and elemental composition were analyzed by scanning electron microscopy(SEM), metallography and energy dispersive spectroscopy(EDS), respectively. Hydrogen permeation stability of the prepared palladium membranes were tested at450–600 °C for 400 h. It was found that the higher SnCl_2 concentration and activation times enlarged the Sn residue amount and led to a lower initial selectivity but a better membrane stability. Moreover, the additional Sn(OH)_2coating on the Al_2O_3 substrate surface also greatly improved the membrane selectivity and stability.Therefore, it can be concluded that the Sn residue from the SnCl_2–PdCl_2 process cannot be a main factor for the stability of the composite palladium membranes at high temperatures.     

Effect of silver-nanoparticles generated in poly(vinyl alcohol)membranes on ethanol dehydration via pervaporation

Pervaporation is an important membrane separation method of chemical engineering. In this work,silver-nanoparticles-poly(vinyl alcohol) nanocomposite membranes(AgNPs-PVA) are produced for the sake of improving its potentials for pervaporation of ethanol–water mixture so that the usual opposite trend between membrane selectivity and permeation can be reduced. The nanocomposite membranes are fabricated from an aqueous solution of poly(vinyl alcohol) with silver nanoparticles via the in-situ generation technique in the absence of any reducing agent. Successful generation of the nano size silver is measured by the UV–vis spectrum showing a single peak at 419 nm due to the plasmonic effect of silver nanoparticles. Our nanocomposite AgNPs-PVA membranes are characterized using scanning electron microscope(SEM), Fourier-transform infrared(FT-IR) spectroscopy, X-ray diffraction and thermogravimetric analysis(TGA). The pervaporation tests of our new AgNPs-PVA membranes show good results since at a higher temperature and higher ethanol concentration in the feed, the prepared membranes are highly permeable for the water having stable selectivity values and therefore our membranes show better performance compared to that of the other PVA-based nanocomposite membranes.     

Effect of adding a smart potassium ion-responsive copolymer into polysulfone support membrane on the performance of thin-film composite nanofiltration membrane

Thin-film composite (TFC) nanofiltration (NF) membranes were fabricated via the interfacial polymerization of piperazine (PIP) and 1,3,5-benzenetricart)oiiyl trichloride on polysulfone (PSf) support membranes blended with K^+-responsive poly(N-isopropylacryamideco- acryloylamidobenzo-15-crown-5)(P(NIPAM-co- AAB15C5)). Membranes were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscope, scanning electron microscope, contact angle, and filtration tests. The results showed that:(1) Under K^+-free conditions, the blended P(NIPAM-co-AAB15C5)/PSf supports had porous and hydrophilic surfaces, thereby producing NF membranes with smooth surfaces and low MgSO4 rejections;(2) With K^+ in the PIP solution, the surface roughness and water permeability of the resultant NF membrane were increased due to the K^+-induced transition of low-content P(NIPAM-co-AAB15C5) from hydrophilic to hydrophobic;(3) After a curing treatment at 95℃, the improved NF membrane achieved an even higher pure water permeability of 10.97 L·m^-2·h^-1 - bar1 under 200 psi. Overall, this study provides a novel method to improve the performance of NF membranes and helps understand the influence of supports on TFC membranes.     

四元体系（Li+， Mg2+//Cl-， borate-H2O）308.15 K相平衡与相图研究

采用等温溶解平衡法,开展四元体系Li⁺, Mg²⁺//Cl^-, borate–H₂O固液相平衡与相图研究,测定平衡溶液的液相组成、密度、折射率和pH。该四元体系相图中存在的盐类矿物为：LiCl·H₂O、Li₂B₄O₇·3H₂O、 MgCl₂·6H₂O、Mg₂B₆O₁₁·15H₂O和锂光卤石LiCl·MgCl₂·7H₂O,其中锂光卤石LiCl·MgCl₂·7H₂O是异成分复盐,溶液中MgCl₂存在下章氏硼镁石（MgB₄O₇·9H₂O）不稳定,转化为多水硼镁石（Mg₂B₆O₁₁·15H₂O）。多水硼镁石结晶区最大,表明镁硼酸盐易于结晶析出,而锂光卤石结晶区最小。采用Pitzer热力学模型对该四元体系的溶解度进行理论预测,计算相图与实验相图吻合较好。该四元体系的稳定相平衡与相图研究,可为含锂硼盐湖老卤中锂、镁、硼产品开发及其综合利用提供理论依据。     

多组分氯盐体系镁锂分离规律初探

以Na₂CO₃为沉淀剂,初步研究了多组分氯盐混合体系（0.6 mol MgCl₂+1.1 mol LiCl+3.2 mol NaCl）中选择性沉镁的工艺规律。结果表明：在25~80 ℃,总C与总Mg物质的量比[n（C_T）/n（Mg_T）]为 0.8~1.1时,25 ℃形成针状MgCO₃·3H₂O,40 ℃以上形成Mg₅（CO₃）₄（OH）₂·4H₂O不规则片状团聚微球,其中40~50 ℃形成的片状物较为分散且粒径较小,导致固液分离困难。40 ℃时沉镁率最低。温度越高,Li₂CO₃越易形成,沉锂率越大。n（C_T）/n（Mg_T）越大沉镁率和沉锂率越高。室温（25 ℃）、n（C_T）/n（Mg_T）=1.0时,沉镁率达98%以上,且沉锂率<0.1%,镁锂分离效果最好。     

Novel polyethyleneimine/TMC-based nanofiltration membrane prepared on a polydopamine coated substrate

Most commercial NF membranes are negatively charged at the pH range of a typical feed solution. In order to enhance the removal of cations (such as Mg²⁺ or Ca²⁺), we utilized polyethyleneimine (PEI) and trimesoyl chloride (TMC) to perform interfacial polymerization reaction on a polydopamine coated hydrolyzed polyacrylonitrile substrate to obtain a positively charged nanofiltration membrane. Effects of polydopamine coating time, PEI concentration, TMC reaction time and concentration on the membrane physicochemical properties and separation performance were systematically investigated using scanning electron microscopy, streaming potential and water contact angle measurements. The optimal NF membrane showed high rejection for divalent ions (93.6±2.6% for MgSO₄, 92.4±1.3% for MgCl₂, and 90.4±2.1% for Na₂SO₄), accompanied with NaCl rejection of 27.8±2.5% with a permeation flux of 17.2±2.8 L·m⁻²·h⁻¹ at an applied pressure of 8 bar (salt concentrations were all 1000 mg·L⁻¹). The synthesized membranes showed promising potentials for the applications of water softening.     

258.15 K下五元体系Li+,Na+,Mg2+//SO42-,Cl--H2O相平衡研究

中国含锂盐湖大部分位于青藏、新疆等干旱少雨、冬季寒冷且漫长的地区。为指导低温提锂工艺的开发和设计、利用冬季冷能进行目标离子的富集及明确含锂盐湖在低温下的析盐规律,采用等温溶解平衡法对258.15 K、二水氯化钠饱和条件下的交互五元体系Li⁺,Na⁺,Mg²⁺∥SO₄^2-,Cl^--H₂O相平衡关系进行研究并构建等温平衡相图。结果表明,相图中有4个共饱点、6个两盐结晶区(NaCl·2H₂O+Na₂SO₄·10H₂O、NaCl·2H₂O+MgCl₂·8H₂O、NaCl·2H₂O+MgSO₄·7H₂O、NaCl·2H₂O+Li₂SO₄·H₂...     

氨基化氧化石墨烯界面聚合制备超薄复合纳滤膜

采用氨基化氧化石墨烯（NGO）为界面聚合水相单体,制备了超薄复合纳滤膜。研究采用傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）、透射电子显微镜（TEM）、扫描电子显微镜（SEM）、原子力显微镜（AFM）表征了NGO以及复合纳滤膜的化学组成和形貌。系统考察了水相单体浓度、有机相单体浓度对于制备的超薄复合纳滤膜性能的影响。该超薄复合膜在低压（0.2 MPa）下纯水通量可达27.8 L·m^-2·h^-1,对小分子染料有较高的截留率（甲基橙截留率74.8%,橙黄钠截留率96.0%,刚果红截留率98.5%,甲基蓝截留率99%）,对于无机盐的截留率较低（Na₂SO₄截留率21.4%,MgSO₄截留率10.7%,NaCl截留率5.3%,MgCl₂截留率1.5%）,展现出优异的染料/盐分离性能。同时制备的复合纳滤膜展现了较好的长周期稳定性以及抗污染特性。     

PAN-H1.6Mn1.6O4锂离子筛膜的制备及在卤水中吸附性能

采用亲水的PAN为成膜材料,制备了掺杂H_1.6Mn_1.6O₄的PAN-H_1.6Mn_1.6O₄锂离子筛膜。通过SEM、Li⁺静态吸附实验、（NH₄）₂S₂O₈对锂的洗脱实验和卤水中吸附实验,研究了锂离子筛的添加量对PAN-H_1.6Mn_1.6O₄锂离子筛膜结构、Li⁺吸附-洗脱性能的影响。结果表明,PAN浓度为10%（质量）,H_1.6Mn_1.6O₄的添加量为50%（质量）时,PAN-H_1.6Mn_1.6O₄离子筛膜的吸附量为17.45 mg·g^-1,达到粉末状吸附量的88.0%。以（NH₄）₂S₂O₈为洗脱剂,当浓度为0.3 mol·L^-1、液固比为600:1、时间为12 h时,锂洗脱量为17.23 mg·g^-1,锰溶损率仅为1.14%。在含有Na⁺、K⁺、Mg²⁺和Ca²⁺的罗布泊老卤卤水中,锂离子筛膜对Li⁺有很高的选择性。在卤水中进行10次吸附与解吸循环,吸附量从11.64 mg·g^-1下降到10.94 mg·g^-1,吸附容量仅损失6.0%。总体结果表明亲水性载体对H_1.6Mn_1.6O₄吸附容量影响较小,温和的洗脱剂对锂离子筛膜的化学稳定性有利。     

Spray-drying assisted layer-structured H2TiO3 ion sieve synthesis and lithium adsorption performance

A spray-drying assisted solid-state method to prepare spherical layer-structured H₂TiO₃ ion sieve (LSTIS) particles is reported herein. The effects of synthesis parameters (calcination temperature, calcination time, and the lithium-titanium molar ratio) on adsorption–desorption performance (the delithiation ratio, titanium dissolution loss, and the adsorption capacity) were investigated. The as-prepared LSTIS exhibited an equilibrium adsorption capacity of 30.08 mg·g^-1 (average of 25.85 mg·g^-1 over 5 cycles) and ultra-low titanium dissolution loss of less than 0.12% (average of 0.086% over 5 cycles). The LSTIS showed excellent selectivity toward Li⁺ in Na⁺, K⁺, Mg²⁺, and Ca²⁺ coexisting saline solutions where its adsorption capacity reached 27.45 mg·g^-1 and the separation factors of Li⁺ over the coexisting cations exceeded 100. The data suggests that the LSTIS is promising to competitively enrich Li⁺ from saline solutions.     

锂铝层状吸附剂超低品位卤水提锂冲洗和解吸过程

锂铝层状氢氧化物对Li⁺具有高吸附选择性,能够有效地从高镁锂比（质量比）盐湖卤水中进行锂资源提取,具有工艺简单、经济环保等特点。本文使用球形锂铝层状吸附剂GLDH作为吸附柱填充物,系统研究了流速、温度和Li⁺初始浓度对铝盐锂吸附剂盐湖提锂工艺中冲洗、解吸的影响。试验结果表明,低温快速冲洗能有效降低冲洗过程中的Li⁺损失率。当冲洗液中Li⁺的浓度为200mg/L,冲洗液以12.0BV/h的速度在0℃下通入吸附柱时,Li⁺损失率可降低到17.8%。在解吸过程中,高温、低速和低初始Li⁺浓度的条件有利于Li⁺从吸附剂中脱出。但鉴于吸附剂的循环稳定性,采用初始Li⁺浓度为300mg/L的解吸液以2BV/h的流速在40℃下对吸附柱进行解吸,3BV时停止解吸,此时锂解吸量可达3.76mg/g,解吸液中Li⁺的平均浓度为590.83mg/L,Mg/Li比仅为0.13,可有效实现镁锂分离和锂元素集浓。循环30个周期后吸附剂的吸附容量没有明显下降,表明锂铝层状吸附剂GLDH具有良好的循环稳定性。     

Preparation and characterization of lithium λ-MnO2 ion-sieves

Lithium λ-MnO₂ ion-sieves were prepared from spinel LiMn₂O₄ via treatment with nitric acid. The LiMn₂O₄ was synthesized by a solid state reaction between LiOH·H₂O and MnO₂. The effects of the calcination time and temperature on the preparation of the LiMn₂O₄ precursor and the lithium ion-sieve were investigated. In addition, the Li⁺ extraction ratio, the Mn²⁺ dissolving ratio and the adsorption properties of the lithium ion-sieve were all measured. The lithium ion-sieve had a high exchange capacity and was selective for Li⁺. Specifically, at pH= 13, the ion exchange capacity of Li⁺ was 30.9 mg/g in 10 mmol/L LiCl solution and the lithium extraction ratio and manganese dissolving ratio were 95% and 25%, respectively.