基于UHMWPE纤维的海水提铀吸附材料制备及铀吸附性能研究

Uranium is an important, rare and strategical resource for sustainable development of nuclear energy. The total amount of uranium in ocean is 4.5 billion tons, which is equivalent to 1000 times of that in terrestrial reserve. Owing to the significant global increase in demand of nuclear energy, stable supply of nuclear fuel is a key issue for many countries, scientists of many countries (e.g. Japan, USA, India, South Korea) have refocused on the extraction of uranium from seawater in recent years. However, since the uranium concentration is only 3.0 ppb in seawater, the collection of uranium from seawater is more difficult than uranium mining. To realize the uranium collection from seawater in large scale, advanced adsorbent with good perfomance and low cost has to be developed. Unlike hydrous titanium oxide powder investigated decades ago, functionalized fiber or non-woven fabrics are believed to be favorable material for uranium collection from seawater. Radiation grafting technique is usually applied for the modification of such fiber materials...In this project, we will develop a new adsorbent utilizing radiation graft polymerization for uranium collection from seawater. Ultra-high molecular weight polyethylene (UHMWPE) fiber will be used as a base material for radiation-induced graft polymerization. The choice of UHMWPE fier is due to its high tensile strength and excellent corrossion resistance in seawater. The amidoxime group modified UHMWPE fiber will be prepared by radiation-induced graft polymerization of acrylonitrile (with the co-monomer of acrylic acid) onto UHMWPE fiber in mixed solvent and followed amidoximation. The behaviors of adsorption and desorption of uranyl ion of the UHMWPE fiber adsorbent will be carefully investigated in order to elucidate the mechanism of adsorption and desorption process. The performance of adsorption against uranyl ion and the service life of the adsorbent will be evaluated in simulated and real seawater in laboratory at ambient temperature,in an attempt to achieve the adsorption capacity of 3 mg/g and service life of 5 cycles at the uranium concentration of 3 ppb (a period of 30 dasy).

铀是一种重要的稀有战略资源，为确保核燃料稳定供应、实现核能可持续发展，海水提铀技术近年重新受到国际关注。海洋中铀的储量约45亿吨，但铀的浓度仅为3.0 ppb，从海水中富集铀的技术难度远高于铀矿开采，因此开发高性能、低成本的吸附材料是实现规模化海水提铀的关键。本项目拟利用辐射接枝技术研发一种新型铀酰离子纤维吸附剂。选择高强度且耐海水浸泡的超高分子量聚乙烯（UHMWPE）纤维为基材，使用辐射技术引发丙烯腈单体与UHMWPE纤维发生接枝聚合反应，再通过肟氨化反应将氰基转化为偕肟胺基，获得偕肟胺基UHMWPE纤维吸附剂。研究该吸附剂对铀酰离子的吸附-脱附行为，阐明吸附-脱附机理；利用模拟海水和天然海水在实验室评估偕肟胺基UHMWPE纤维对铀酰离子的吸附性能和使用寿命。通过优化实验条件，筛选出在3 ppb铀浓度下(30天)吸附容量超过3 mg/g且能重复使用5次以上的偕肟胺基UHMWPE纤维材料。

本项目在执行期间，利用预辐射接枝方法制备了UHMWPE-g-(PAN-co-PAA)纤维，并通过氨肟化反应成功获得UHMWPE纤维海水提铀吸附材料。系统地研究了接枝反应条件对接枝率的影响和氨肟化反应条件对吸附材料上偕胺肟基密度的影响，优化了吸附材料制备工艺，实现吸附材料的稳定制备；建立了吸附材料铀酰离子吸附性能的快速评价方法和低浓度铀酰离子的表征方法，开展了实验室铀酰溶液、模拟海水、真实海水的静态和动态吸附实验，利用ICP-AES、SEM、STXM、EDX、EXAFS等表征手段对铀酰离子吸附过程中铀吸附量、吸附材料形貌、化学结构变化以及活性官能团与铀酰的配位结构进行表征，并通过DFT计算方法加深对吸附机理的理解，阐明了吸附材料的吸附行为和机理；尝试了新的制备工艺，制备了UHMWPE-g-P(GMA-co-MA)-EDA-AO纤维吸附材料，尽可能多的保留了UHMWPE纤维的力学性能，进一步提高了吸附材料的铀/钒吸附选择性。UHMWPE纤维海水提铀吸附材料的接枝反应优化工艺条件为UHMWPE纤维吸收剂量50 kGy，反应液配比64%的丙烯腈、16%的丙烯酸、20%二甲基甲酰胺、莫尔盐2.7×10-4 mol/L，反应温度60 °C，接枝率控制在100%-200%。氨肟化反应优化条件为：5%盐酸羟胺、水与二甲亚砜1:1的混合溶剂、反应液pH=7、反应温度70 °C、反应时间5小时。EXAFS实验与分子模拟DFT计算结果显示在铀酰-配体复合物中偕胺肟基与铀酰以η2双齿模式结合；AO确实能在海水提铀过程中取代碳酸铀酰离子中的碳酸根；U-O(AO)和U-N(AO)键的形成主要源于铀的5f/6d轨道与氮或氧的2p轨道相互作用的结果；根据铀酰与配体反应的相对结合自由能计算结果AO-(CH2)4-AA为最适宜结构。通过本项目的研究，制备了一种高吸附容量、高选择性的UHMWPE纤维基海水提铀吸附材料，系统研究了材料的制备工艺和材料性能，为海水提铀吸附材料批量制备提供技术参考；吸附机理研究深化了对偕胺肟基吸附铀酰离子的理解，为吸附材料的设计提供了理论指导。