放射性核素在氧化物、磷酸盐和黏土矿物表面吸附：热力学和微观结构认识

本文主要以放射性核素在氧化物、磷酸盐和黏土矿物表面上吸附研究为例,概括了放射性核素在固液界面上吸附行为研究的系统方法。主要分为以下7个步骤进行介绍:(1)吸附剂结构、形貌、拓扑性质的表征;(2)吸附剂表面电荷性质表征;(3)表面质子化和去质子化反应的平衡常数;(4)pH、离子强度、吸附质浓度和天然有机质等对放射性核素在固液界面吸附影响;(5)放射性核素在固液界面上的微观形态和空间结构等信息;(6)利用表面配位模型探讨放射性核素在固液界面的吸附机理;(7)采用先进光谱表征技术和量子计算技术对所得吸附机理进行分子或原子水平上的论证。     

氯化钠-乙酸钠水溶液中放射性核素在粘土矿物和沸石上吸附机理的研究

一、前言 放射性核素在各种屏障材料上吸附分配比的测定及吸附机理的研究,是当前环境放射化学中的重要研究课题之一。放射性核素在硅酸盐矿物上的吸附机理,通常看作是阳离子交换反应。根据离子交换平衡理论,在水相pH值恒定及含有大量钠离子的条件下,放射性核     

放射性核素在花岗岩上的吸附行为

综述了放射性核素在花岗岩上吸附作用的研究现状和进展。相关研究表明:(1)花岗岩的物化性质(包括形貌、化学组成及表面酸碱特性)对放射性核素的吸附有一定的影响;(2)放射性核素在花岗岩表面的吸附速率普遍较快,吸附可在较短时间内完成;(3)各种环境因素如pH值、离子强度、温度、地下水中的主要离子、天然有机质、低氧条件等对放射性核素在花岗岩表面吸附的影响因吸附质离子不同而变化各异;(4)建立在基本吸附数据基础上的表面配位模型可以用于间接探讨相应的吸附机理,拓展了研究核素迁移的思路;(5)采用先进光谱表征技术如XPS可对放射性核素在花岗岩上的吸附机理进行分子或原子水平上的论证。     

放射性核素锶的吸附法研究进展

放射性核素⁹⁰Sr是核工业生产过程中最常见的污染核素,吸附法是处理放射性核素⁹⁰Sr污染的重要方法。本文介绍了常用的吸附⁹⁰Sr的方法,如离子交换法、络合/螯合吸附法、静电吸附法、表面与多孔吸附法等,并比较了各自的优劣,以期对采用吸附法处理放射性核素的工艺过程提供参考。     

无机吸附材料处理放射性废水中铀的研究进展

核能与核工业的发展不可避免地会产生大量的含铀放射性废水。随着材料科学的发展,新型吸附材料不断出现,吸附法处理放射性废水近年来得到了特别关注。目前研究的无机吸附材料可分为无机矿物、金属氧化物、碳基材料等。通过接枝、交联、等离子体、复合等技术处理,在吸附材料表面修饰含氧官能团或含氮官能团,可提高对铀的吸附性能和选择性。铀的吸附机理多表现为离子交换和表面络合作用。本文主要介绍了无机吸附材料处理放射性废水中铀的研究进展,并对今后的研究方向提出了建议。     

序言

正随着核电的快速发展,在核能利用的各个环节中,如核燃料开采、加工、发电和乏燃料后处理,部分长寿命放射性核素特别是锕系元素和裂变元素会不可避免地释放到环境中,给生态环境和人类健康造成重大危害。因此,放射性污染的治理具有重要意义,特别是放射性核素的分析、毒性、环境行为研究对于探讨长寿命放射性核素的化学行为尤为重要。在放射性污染治理中,天然的黏土矿物和氧化物等在放射性核素的固定方面具有重要作用,但是天然材料由于其吸附能力低的特点,在放射性核素的吸附富集方面有一定的     

氧化石墨烯对U(Ⅵ)的吸附

氧化石墨烯由于具有高比表面积和大量含氧功能基团，在放射性核素的高效富集方面引起广泛的关注。利用自制的氧化石墨烯作为吸附剂，研究了不同实验条件下对放射性废水中U(Ⅵ)的吸附行为，研究了pH、离子强度、温度和氧化石墨烯浓度对U(Ⅵ)吸附的影响。结果表明，氧化石墨烯对U(Ⅵ)的吸附主要是形成内层表面络合物，具有很强的去除能力，是目前所有材料中对U(Ⅵ)吸附能力最强的材料之一。吸附后的石墨烯经强酸处理后可以实现循环利用，而且吸附能力没有明显降低，但是弱酸处理不能使吸附的铀从石墨烯表面解吸。随着未来技术的发展，氧化石墨烯能够低成本大量制备后，在放射性废水处理中将具有重要的应用前景。     

中国近海海域环境放射性水平调查

总结中国在过去40年中对近海海域环境放射性的调查结果，介绍了中国近海海域中天然和人工放射性核素的水平，海洋生物对放射性核素的吸收与累积，以及海洋沉积物对放射性核素的吸附。     

Cs~+和Yb~(3+)在方解石、高岭石、蒙脱石、绿泥石和海绿石上的吸附实验研究

用静态平衡批试法和放射性示踪技术研究了Cs^ 和Yb^3 共存条件下，在方解石、高岭石、蒙脱石、绿泥石和海绿石等5种矿物上的吸附行为。结果表明，在相同实验条件下（液相初始酸度、液固相比和金属离子初始浓度），按单位质量矿物的吸附量计，蒙脱石对Cs^ 和Yb^3 的吸附能力明显强于其它矿物，而其它矿物对Cs^＋的吸附能力的差异相对不大。Cs^ 和Yb^3 的吸附率，均随金属离子初始浓度的增大呈现减小趋势，但Yb^3 的变化趋势更大。所有吸附等温线均符合Freundlich等温式方程。在实验所用溶液酸度条件下，Cs^ ,Yb^3 在高岭石、蒙脱石和绿泥石中的吸附作用有可能以离子交换反应为主。     

用自射线照相技术研究放射性核素在岩石和矿物上的吸附

应用自射线照相和岩相照相技术联合图象法研究了锕系元素和长寿命裂变产物在岩石和矿物上的吸附行为，直接观察到不同矿物和化学成份对核素的吸附。应用这个方法，研究了＾２３９Ｐｕ、＾２４１Ａｍ在花岗岩上的吸附，＾９０Ｔｃ在辉锑矿、锑赭石和脆硫锑铅矿上的吸附以及＾１２５Ｉ在灰硒汞矿上的吸附，得到了一些有价值的结果。     

Sorption and Desorption of Radionuclides on the Structural Materials of a Nuclear Power System as Applied to Nuclear Power Plants with RBMK Reactors during Shutdown

The sorption and desorption of radionuclides on structural materials are studied as a function of the content of corrosion-activating ions, oxygen, hydrogen peroxide, and corrosion inhibitors in water. The strongest desorption is observed in aerated water containing chloride ions and the weakest desorption in a deaerated medium. The amount of desorbed radionuclides is correlated with the rate of corrosion of metals – it is highest on perlite steel (No. 20 steel) and lowest on zirconium alloys. Anode inhibitors prevent the corrosion of steel and transfer of radionuclides into the coolant.The sorption of radionuclides depends on the sample material. The highest sorption is observed on perlite steel and the lowest on zirconium alloy. Adding an inhibitor to the contaminating solution counteracts the effect of sorption, depending on the type of the structural material and radionuclide, and decreases it manyfold.     

Isolation and identification of bacteria able to form biofilms from deep subsurface environments

Migration radionuclides in an underground environment are one of the major concerns in the safety assessment of a geological repository. Biofilms can have an impact on the transport of radionuclides in several ways: (1) by acting as a barrier to radionuclide sorption onto geological surfaces, or (2) by providing a sorption site for radionuclides, or (3) by trapping many things, including radionuclides. Little is known about bacterial effects on the biofilm formation deep underground. In this study, we isolated bacterial strains from deep groundwater and evaluated the biofilm formation abilities of these strains by crystal violet assay. Bacterial strains were isolated from ground-water collected at –140 m in the 07-V140-M01 borehole at the Horonobe Underground Research Center, Japan. The crystal violet assay showed that 98% of the isolated strains had biofilm formation abilities under tested conditions. This result suggested that biofilm formation must not be neglected in the study of migration radionuclides in nuclear waste repositories. The isolated strains produced differential amounts of biofilm, although they were identified as the same Pseudomonas species, suggesting that biofilm formation abilities varied at different strain levels. These results support the conclusion that the assessment of biofilm impact on the transport of radionuclides in a geological repository must consider the variation in biofilm formation as a function of strain level.     

Sorption Behavior of Selenium(—II) on Rocks under Reducing Conditions

The sorption of radionuclides on rocks is an important factor for performance assessment of geologic disposal of radioactive wastes. Batch sorption experiments under reducing conditions were carried out to investigate the sorption behavior of selenium onto granodiorite, sandy mudstone, tuffaceous sandstone, and their major constituent minerals and accessory minerals. Rock cores and groundwater employed in the experiments were sampled with special care to avoid exposing the cores and groundwater to air to minimize their oxidation. Selenium was spiked as HSe^? and Se₄ ^2- in the experimental solutions, and reducing conditions were maintained throughout the sorption periods. Distribution coefficients, Kd (m³ kg^?1), were obtained in the ranges of 2.2 × 10^?4 to 4.0 × 10^?3 m³ kg^?1 for granodiorite, 3.3 × 10^?2 to 5.6 × 10^?2 m³ kg^?1 for sandy mudstone, and 2.9 × 10^?2 to 8.2 × 10^?2 m³ kg^?1 for tuffaceous sandstone at pHs 8.5 to 11.5. The dominant sorbent minerals for selenium over a neutral to alkaline pH range were determined to be biotite for the granodiorite samples and pyrite for the sandy mudstone and tuffaceous sandstone samples.     

Incident Angle Dependence of Residual Defect in Silicon Surface Barrier Detector

The fate of radionuclides produced in a light water moderator was investigated by assaying with a Ge(Li) detector sampled coolant water and the waste water produced by regeneration of resins, measuring the radiation dose rates along the surface of the resin column length with TLDs, and studying the sorption of radionuclides to resins in dynamic experiments. The buildup concentrations of short-lived radionuclides, produced by activation in the reactor core water and the amounts of radionuclides sorbed on the resin bed, as estimated from a compartment model, are reported. A method for estimating the production rate of soluble radionuclides with long half-lives in the core water has been developed. Changes in the radiation dose rates along the resin column length recorded during reactor operation and after shut-down, showed that the sorbed radionuclides did not migrate downward, as expected from the chromatography theory, rather they were decreased by the decay process. Moreover, the slopes of the dose rates on both sides of the resin surface were almost identical. These results show the behavior and distribution of radionuclides in the light water moderator of a research reactor.     

Analytical modeling for colloid-facilitated transport of N-member radionuclides chains in the fractured rock

A precious analytical model for N-member radionuclide decay chains has been extended to include the ef- fect of radionuclide sorption with groundwater colloids.Published distribution coefficients were employed in the nu- clide decay chain to illustrate the present model.The colloid concentration was assumed constant in time and space owing to equilibrium between colloid generation and sedimentation by chemical and/or physical perturbations.Fur- thermore,the diffusion of colloids into the rock matrix was ignored because the diameter of colloid is relatively large and colloids and fracture surfaces are like-charged.The results indicated that colloids could facilitate the transport of radionuclides and the large adsorbability of nuclides with colloids enlarged the effect of acceleration by colloids.The influence of colloids on the radionuclide transport was expected to be crucial to the actinides with large adsorbability; however,the present results revealed that the low-adsorbing nuclides whose parent nuclides have large capability of sorption could be also facilitated significantly by colloids indirectly.Therefore,the role of colloids played in the transport of the radionuclides decay chain should be assessed carefully in the radioactive waste disposal.The analyti- cal method presented herein is helpful to verify/validate further complex far-field models.     

Development of a web-based sorption database (KAERI-SDB) and application to the safety assessment of a radioactive waste disposal

Sorption plays a key role in a retardation of radionuclide migration in various geological environments. Hence sorption of radionuclides onto geological media is one of the important factors for the safety assessment of radioactive waste disposal. A web-based radionuclide sorption database program named KAERI-SDB has been developed to provide a database for the sorption of radionuclides onto geological media at various geochemical conditions. The KAERI-SDB is designed to determine the distribution coefficient (K_d) of a radionuclide and evaluate sorption properties by easily accessing an internet web-site (http://sdb.kaeri.re.kr). The KAERI-SDB provides a useful output and search result as a scatter plot chart or an index chart. The KAEI-SDB was designed to show the search results in a statistical way by representing the mean K_d value at 95% of confidence as a function of major geochemical indices. Several case studies were carried out to demonstrate the applicability of the KAERI-SDB and the result showed a successful applicability of the KAERI-SDB to various radionuclide sorption cases.