膜技术在盐湖提锂中的进展和展望

随着新能源产业的快速发展,卤水锂资源开发已成为世界范围战略性新兴产业发展的重要内涵。膜分离技术,因其优异的一/二价离子分离性能、良好的环保和经济性,已成为中国高镁锂比盐湖卤水提锂的主流工艺。归纳分析了膜分离技术在卤水体系中的分离机理、研究进展及未来发展方向。新型高性能锂离子分离膜的持续研究发展,必将加速提升中国卤水锂资源的开发水平。     

纳滤膜对高镁锂比盐湖卤水镁锂分离性能研究

纳滤作为一种新兴的膜分离技术,在高镁锂比盐湖卤水镁、锂分离领域具有非常好的应用前景。研究了不同镁锂比、原料液循环流量对镁锂分离过程的影响,并对膜分离过程中的分离机理进行分析。结果表明原料液镁锂比对膜通量影响较小,镁、锂离子截留率及镁锂分离效果均随原料液镁锂比的增加而降低。当原料液循环流量为225 L/h时,镁离子截留率为95%,锂离子截留率为-66%,透过液镁锂比降低至1.2。膜分离传质机理研究表明,镁离子在分离过程中受到较强的介电排斥效应与尺寸筛分效应。纳滤技术能够有效降低高镁锂比盐湖卤水的镁锂比,为后续高纯锂盐的制备提供基础。     

高镁锂比盐湖镁锂分离与锂提取技术研究进展

随着锂离子电池在电动汽车、便携式电子设备、电动工具及电网储能中的用量持续增加,锂资源需求量快速增长。我国盐湖集中分布在青藏高原地区,青海盐湖普遍具有高镁锂比、低锂含量的特征。高镁锂比盐湖提锂是世界性难题。本文综述了高镁锂比盐湖卤水镁锂分离与锂提取技术的最新研究进展,包括萃取法、吸附法、反应/分离耦合技术、膜法和电化学法。从各技术原理、特点、性能等方面分析了各方法特征和适用性。在现有技术中,吸附法更适合高镁锂比卤水;萃取法可用于锂浓度较低的卤水;新发展的反应/分离耦合技术能实现高效提锂与镁锂资源综合利用;以纳滤、电渗析、双极膜为代表的膜法具有能耗较低和模块化的优点;电化学法具有装置简单的优势,但仍需进一步优化系统。我国盐湖锂资源提取需提高总收率,提升提锂后资源综合利用程度,发展锂产品高值化、多元化利用途径,加强盐湖提锂的工程化技术研究,突破并掌握核心技术与装备,实现盐湖资源高效、综合、可持续利用的目标。     

溶剂极性响应型丁基-环四联吡啶提锂分子的合成及性能研究

盐湖卤水提锂已逐渐成为我国锂及锂产品的生产途径之一,而我国盐湖卤水高镁锂比的特点导致锂离子提取难度大。传统溶剂萃取提锂过程中需使用大量协萃剂和高浓度酸,产品纯度低、危险度高。设计合成了一种具有溶剂极性响应性分子结构“异构互变”的丁基-环四联吡啶提锂分子,实现极性条件下“络合”锂,非极性条件下“释放”锂。核磁共振氢谱和高分辨质谱证实了目标分子结构的准确性,通过对比Li⁺和Mg²⁺存在时目标分子的光谱性质表明丁基-环四联吡啶分子对锂离子具有较强的选择性。此外,支撑液膜的离子跨膜传输结果进一步表明,丁基-环四联吡啶分子在不同极性溶剂条件下可以实现对锂离子的高选择性提取。     

纳滤法用于盐湖卤水镁锂分离的初步实验

膜分离技术是一门新兴的分离方法。为提取盐湖卤水中的锂资源,采用商业可得的DK纳滤膜对稀释的盐湖卤水进行分离操作,以验证纳滤法对卤水中镁锂分离的可行性。实验结果表明,以3种不同组成的卤水为原料,分别进行单级操作,膜的镁锂分离因子均小于0.1,镁锂质量比分别由原料水中的48.50、42.31、28.30降至渗透水中的4.04、3.21、1.86,证明纳滤法可将卤水中的锂提取分离,同时卤水中几乎全部的钙离子、硫酸根及至少73.81%的硼被有效拦截在浓缩水中。渗透水和浓缩水可分别用于相应无机盐的提取,纳滤法可为盐湖卤水的综合利用提供技术上的支持。     

膜法分离一/二价阳离子的研究进展

各类工业过程如水质软化、食用盐纯化、盐湖卤水提锂、酸和重金属资源回收等对一/二价阳离子高效分离的需求日益增长,近年来,针对上述分离体系的膜材料的研究取得了诸多进展。本文详细总结了针对一/二价阳离子分离的选择性阳离子交换膜、纳滤膜、支撑液膜和离子印迹膜的研究进展,重点梳理了相关膜材料的离子选择性优化思路和机理,对比分析了上述膜过程的特点和适用场景。基于此,作者认为,离子筛分精细化是膜分离技术的重要发展方向。在分子尺度明晰分离层的形成和演化机理,对于提高界面聚合反应可控度,实现在亚纳米尺度膜结构的精细调控至关重要。通过在膜基体内可控构建目标离子的特异性识别位点和传质通道,有望实现高选择性离子筛分。此外,具有本征规则孔道结构的新型分离膜材料,如MOFs、COFs、二维层状结构膜等,在精细筛分方面具有良好的发展潜力。     

膜技术分离稀土金属元素的研究进展

稀土金属元素是我国重要的战略资源,因其在高精尖产品中的独特作用,稀土金属元素的分离纯化显得格外重要。膜分离技术是一种高效率、低能耗、环境友好的分离手段,在众多领域应用广泛,将其用于稀土金属分离可明显提升分离效率,降低稀土工业对环境的破坏,但目前的研究尚处于起步阶段,将面临较多挑战。本文介绍了膜技术分离稀土金属的三种策略,包括离子印迹膜、聚合物包合膜和液膜,总结了膜材料的制备方法和分离性能,分析比较了膜技术细分类型的特点和利弊。本文还指出离子印迹膜的选择分离性优势巨大,但在吸附容量上仍有提升空间,也是未来几年膜分离技术的研究重点;聚合物包合膜和液膜分离技术,可根据萃取剂类型和用量灵活调整活性位点种类和数量,在膜技术分离稀土金属的工业化应用方面具有较大潜力。     

钛系锂离子筛盐湖提锂的研究进展

随着新能源行业的迅速发展,带动了锂需求量的显著增长,锂提取技术近年来受到广泛关注。中国是盐湖锂资源大国,盐湖锂储量约占全国锂总储量的78%。但是,中国的盐湖锂资源镁含量高,不易分离提取高纯度锂工业产品;因此,研究开发盐湖提锂技术,具有非常重要的应用价值。在众多的盐湖提锂技术当中,锂离子筛吸附提锂,因其选择性好,对镁的分离效果好,适用于镁锂比高的盐湖卤水体系,这对解决盐湖提锂问题有重要指导意义。选择近年来发展比较热的钛系锂离子筛,从提锂机理、制备方法和应用等方面的研究对钛系离子筛进行一个综述,最后对钛系离子筛的未来研究方向进行展望。     

荷电高分子分离膜研究进展

本文对压力驱动膜过程中所用到的荷电高分子分离膜的分离机理、制备方法、表征手段以及影响荷电膜分离性能的因素进行了综述。     

乳液液膜法对水中对氨基苯甲酸分离富集的研究

用以磷酸三丁脂(TBP)为流动载体的乳液液膜体系对水中的对氨基苯甲酸(PABA)的分离富集进行了研究,考察了影响液膜分离富集PABA的各种因素,同时对PABA在不同pH值水溶液中的存在形态、PABA在液膜分离富集中的传质机理等进行了分析讨论。结果表明在适宜的乳液液膜操作条件下,对含有500mg/L对氨基苯甲酸的料液,经过一级液膜提取分离,对氨基苯甲酸的提取率可达99%,提取分离效果良好。     

离子筛吸附与陶瓷膜耦合用于盐湖卤水提锂

将锰系离子筛吸附与陶瓷膜耦合,用于高镁锂比盐湖卤水的提锂研究。采用水热法制备了高效锂离子筛H_1.6Mn_1.6O₄,考察离子筛用于卤水提锂效果和陶瓷膜的分离性能。结果表明：制备的离子筛粉体粒径分布在100～500 nm之间,平均粒径为160 nm,用于察尔汗盐湖卤水中对Li⁺吸附容量达到31.44 mg·g^-1;孔径50 nm的陶瓷膜对离子筛的截留率达到100%,膜渗透通量大于150 L·m^-2·h^-1;反冲操作可有效维持吸附-膜分离过程的稳定性,吸附与陶瓷膜的耦合过程对盐湖卤水中的锂提取率超过97%,盐酸和双氧水清洗可有效恢复膜渗透通量。研究结果为高镁锂比盐湖卤水提锂提供了新方法。     

腐殖酸聚集体对膜蒸馏过程膜污染的作用机理

膜污染是膜蒸馏过程应用于工业水处理中遇到的主要问题之一。选取水体中具有代表性的有机物（腐殖酸）、微溶无机盐（碳酸钙）作为典型污染物,研究有机腐殖酸聚集体对于膜蒸馏过程膜污染进程的影响规律,探讨天然有机物-无机微溶盐混合水体中腐殖酸聚集体对于无机盐结晶过程的控制机理。结果表明：膜蒸馏通量的衰减大致可分为由滤饼层的形成造成的不可恢复部分以及由浓差极化、膜孔“半润湿”而造成的可部分恢复的通量降低。Ca²⁺通过加速腐殖酸分子的聚集过程,使表面负电性降低的腐殖酸聚集体率先吸附在聚偏氟乙烯中空纤维膜内表面,形成有机基质污染层;碳酸钙在有机腐殖酸聚集体的诱导下在膜内表面异相成核,最终成长为稳定的晶体。腐殖酸聚集体为无机盐晶体在疏水性膜内表面的生长提供了异相成核的基础。可通过控制污染水体中有机物的含量控制微溶碳酸钙在膜内表面成核及生长,实现控制其在膜内表面附着进而诱发疏水膜发生亲水化的过程。     

疏水性PTFE微孔膜处理含Cr(Ⅲ)稀溶液的实验研究

废水中的三价铬在自然环境中容易转化为毒性更强的六价铬。控制并回收废水中的三价铬可达到节约资源和降低污染的目的,用减压膜蒸馏(VMD)分离装置,实验探讨了不同平均孔径大小的聚四氟乙烯(PTFE膜对处理含铬(Ⅲ)溶液的膜通量、截留率等影响,研究了进料浓度、进料温度对分离性能的影响。实验结果表明,对于膜孔径较小的膜,膜内的传质阻力成为主要因素,膜内的传质是VMD过程的控制步骤。     

疏水亲油分离膜的润湿性研究进展

疏水亲油分离膜通过透过油相、截留水相而实现油水分离过程,它具有绿色、高效、易于工业放大等特点,在环境保护、水处理、有机液体分离与回收等领域具有广阔的应用前景,已成为膜科学与技术领域的研发热点。本文回顾了润湿方程的发展历史,介绍了表面润湿性和孔径的协同作用对膜分离过程的影响,讨论了疏水亲油分离膜的设计策略,包括在低表面能材料的表面构建粗糙或微纳米结构和使用低表面能材料对粗糙表面进行疏水改性。最后,对疏水亲油分离膜的发展趋势进行了展望,今后需进一步完善表面浸润理论,开发易于工业生产的制膜方法,探究疏水亲油分离膜对复杂油水混合物（如高黏度、多组分）的分离效果。     

Optimization of structure and properties of polyphenylene sulfide porous membrane by controlling the process of thermally induced phase separation

Polyphenylene sulfide (PPS) porous membranes were successfully prepared from miscible blends of PPS and polyethersulfone (PES) via thermally induced phase separation followed by subsequent extraction of the PES diluent. The morphologies, crystalline structures, mechanical properties, pore structures and permeate fluxes of the PPS porous membranes obtained from different phase separation processes were characterized and are discussed. During the phase separation in the heating process, PPS and PES mainly underwent liquid–liquid phase separation, and then a nonhomogeneous porous structure with a mean pore size of 100 μm and a honeycomb‐like internal structure formed on the membrane surface. The phase separation of PPS/PES occurring in the cooling process was easier to control and the related pore diameter distribution was more regular. In the process of direct annealing, as the phase separation temperature decreased, the pore size distribution became more homogeneous and the mean diameter of the pores also decreased gradually. When the phase separation temperature decreased to 200 °C, PPS membranes with a network structure and a uniform as well as well‐interconnected porous structure could be obtained. In addition, the maximum permeation flux reached 1718.03 L m^–2 h^–1 when the phase separation temperature was 230 °C. The most probable pore diameter was 6.665 nm, and the permeate flux of this membrane was 2.00 L m^–2 h^–1; its tensile strength was 17.07 MPa. Finally, these PPS porous membranes with controllable pore structure as well as size can be widely used in the chemical industry and energy field for liquid purification. © 2020 Society of Chemical Industry     

Effects of pre-oxidant (KMnO4) on structure and performance of PVDF and PES membranes

The structure and performance of membrane materials are very important to the efficient and stable operation in membrane drinking water purification technology. Potassium permanganate (KMnO₄), which can change the characteristics of organic matters and control membrane surface fouling, has been widely used as pre-oxidant in the front of membrane drinking water process. This study investigates the evolution of membrane surface structure and performance when polyvinylidene fluoride (PVDF) and polyethersulfone (PES) were exposed to 10, 100 and 1000 mg·L^-1 KMnO₄ solution for 6 and 12 d, respectively. The aged membrane physicochemical characteristics such as membrane surface morphology, chemical composition, hydrophilicity, porosity and zeta potential were evaluated by modern analytical and testing instruments. The anti-fouling property of membrane surface was also investigated by the filtration-backwash experiment. The results indicated that the different concentrations and exposure time of KMnO₄ led to a different variation on PVDF and PES membrane surface structure and performance, which could further affect the membrane separation performance and the membrane fouling behaviors. The membrane surface pore size and porosity increased due to the dislodgment and degradation of membrane additive (PVP), which improved membrane permeability and enhanced the adsorption and deposition of pollutants in the membrane pores. With the increase of exposure time, the membrane surface pore size and porosity reduced for the reactions of chain scission and crosslinking on membrane materials, and the backwashing efficiency declined, leading to a more serious irreversible fouling. Compared with PVDF membranes, the formation of sulfonic group for PES membranes increased the negative charge on membrane surface due to the oxidation of KMnO₄. The present study provides some new insights for the regulation of the pre-oxidant dose and the selection of the membrane materials in KMnO₄ pre-oxidation combined with membrane filtration system.     

Factors controlling surface morphology of porous polystyrene membranes prepared by thermally induced phase separation

A special device for preparing porous polymer membranes through a thermally induced phase separation (TIPS) process was designed and machined; it included a solution container, a membrane‐forming platform, a coldplate, a temperature‐decreasing system and a temperature‐supervising system. Polystyrene was selected as the model polymer from which to prepare porous membranes using the device due to its better understood TIPS and good biocompatibility with cells. The major factors controlling surface morphology and cell size, ie volume fraction of polystyrene (ϕ₂), quench rate and solvent‐removing methods, were studied. Fixing the coldplate temperature, when ϕ₂ is as low as 0.045, provokes the formation of round pores on both the bottom and top surfaces of the membrane; when ϕ₂ = 0.16 no pores are formed on either surface; when ϕ₂ = 0.087 pores form on the top surface, but not on the bottom surface. When ϕ₂ = 0.087 the cell size is very small or no pores are formed on the bottom surface, whereas the top surface shows a regular decrease of the pore sizes and an increase of the pore number and pore area, along with a decrease of the coldplate temperature. The side near the coldplate is dense, and the dense layer aligns along the coldplate, while the side away from the coldplate is like a porous foam, the shape of which is isotropic and the surfaces are interconnected with each other three dimensionally. On the top surface of a membrane obtained by ethanol extraction, the cell size is enlarged and the cell number reduced, but the surface morphology and the whole area remained almost the same when compared to samples obtained by freeze drying in the same membrane‐forming conditions. The isotropic, uniformly distributed and round pores suggest that the mechanism of phase separation is a spinodal liquid–liquid decomposition under our research conditions. © 2000 Society of Chemical Industry     

γ-Al_2O_3纳米孔膜截留镁离子机理的研究

纳米孔膜的过滤类似于反渗透和超滤,均属于压力驱动的膜过程,但其传质机理却有所不同。根据实验数据用作图的方法得出膜的真实截留率,进而求出膜面浓度。通过实验发现,细孔模型中对特征参数σ和ω的计算与实验值有一定的出入,主要是由于在细孔模型中只考虑了结构尺寸对截留率的影响,而在道南效应决定膜对盐的截留性能的情况下,截留性能主要依赖于离子和膜之间的静电相互作用,电荷因素不容忽略,因此细孔模型用于描述纳米孔膜的分离机理时,其准确性不高。