Three-dimensional diffusion of non-sorbing species in porous sandstone: computer simulation based on X-ray microtomography using synchrotron radiation

The diffusion pathways of porous sandstone were examined by a three-dimensional (3-D) imaging technique based on X-ray computed tomography (CT) using the SPring-8 (Super Photon ring-8 GeV, Hyogo, Japan) synchrotron radiation facility. The analysis was undertaken to develop better understanding of the diffusion pathways in natural rock as a key factor in clarifying the detailed mechanism of the diffusion of radionuclides and water molecules through the pore spaces of natural barriers in underground nuclear waste disposal facilities. A cylindrical sample (diameter 4 mm, length 6 mm) of sandstone (porosity 0.14) was imaged to obtain a 3-D image set of 450(3) voxels=2.62(3) mm(3). Through cluster-labeling analysis of the 3-D image set, it was revealed that 89% of the pore space forms a single large pore-cluster responsible for macroscopic diffusive transport, while only 11% of the pore space is made up of isolated pores that are not involved in long-range diffusive transport. Computer simulations of the 3-D diffusion of non-sorbing random walkers in the largest pore cluster were performed to calculate the surface-to-volume ratio of the pore, tortuosity (diffusion coefficient in free space divided by that in porous rock). The results showed that (i) the simulated surface-to-volume ratio is about 60% of the results obtained by conventional pulsed-field-gradient proton nuclear magnetic resonance (NMR) laboratory experiments and (ii) the simulated tortuosity is five to seven times larger than the results of laboratory diffusion experiments using non-sorbing I(-) and Br(-). These discrepancies are probably attributed to the intrinsic sample heterogeneity and limited spatial resolution of the CT system. The permeability was also estimated based on the NMR diffusometry theory using the results of the random walk simulations via the Kozeny-Carman equation. The estimated permeability involved an error of about 20% compared with the permeability measured by the conventional method, suggesting that the diffusometry-based NMR well logging with gradient coils is applicable to the in-situ permeability measurement of strata. The present study demonstrated that X-ray CT using synchrotron radiation is a powerful tool for obtaining 3-D pore structure images without the beam-hardening artifacts inevitable in conventional CT using X-ray tubes.     

土壤-植物系统中的碘与碘缺乏病防治

碘是人和动物必需的微量元素之一。碘缺乏将导致甲状腺肿、克汀病等疾病的发生。文章综述了土壤中碘的来源，碘质量分数和形态，影响土壤碘有效性的因素，植物体内碘的质量分数和分布，不同形态的碘对植物生长的影响，碘毒害等方面的研究进展；最后提出防治碘缺乏病的有效措施。     

催化分光光度法测定环境样品中微量碘

本文介绍一个简单而灵敏的催化分光光度法,用于测定环境样品中微量碘,本法系基于亚硝酸根存在时微量碘离子催化还原硫氰酸铁络含物,并以分光光度计测量该红色络合物的减弱强度,在一定温度时,该络合物的分解速度正比于磺的含量.在给定的实验条件下,磺离子的浓度在0.001-0.024毫克/升之间服从比尔定律. 本法已成功地应用于天然水、土壤、海底泥和海生物中微量磺的测定,结果良好.     

超声激发碘自由基降解水中磺胺嘧啶

以H2O2和KI作为分子碘(I2)的来源,研究超声/H2O2/KI体系对磺胺嘧啶(SD)的降解效果.考察超声/H2O2/KI体系中溶液初始pH值、H2O2和KI添加浓度等因素的影响.采用碘自由基抑制剂甲硫咪唑对体系中的活性物质进行分析.结果表明,超声/H2O2/KI体系显著提高了磺胺嘧啶的降解效果,磺胺嘧啶的去除率随溶液初始pH值(2.6~5.2)的升高而降低; H2O2和KI的添加浓度对磺胺嘧啶的去除率影响较大,磺胺嘧啶的去除率随其初始浓度的增大而降低.碘自由基(I·和I2-·)是超声/H2O2/KI体系降解磺胺嘧啶的主要活性物质.HPLC图谱表明,磺胺嘧啶降解的同时生成4种产物,磺胺为降解产物之一.     

Removal of elemental mercury by iodine-modified rice husk ash sorbents

Iodine-modified calcium-based rice husk ash sorbents(I2/CaO/RHA) were synthesized and characterized by X-ray diffraction,X-ray fluorescence,and N2 isotherm adsorption/desorption.Adsorption experiments of vapor-phase elemental mercury(Hg0) were performed in a laboratory-scale fixed-bed reactor.I2/CaO/RHA performances on Hg0 adsorption were compared with those of modified Ca-based fly ash sorbents(I2/CaO/FA) and modified fly ash sorbents(I2/FA) .Effects of oxidant loading,supports,pore size distribution,iodine impregnation modes,and temperature were investigated as well to understand the mechanism in capturing Hg0.The modified sorbents exhibited reasonable effciency for Hg0 removal under simulated flue gas.The surface area,pore size distribution,and iodine impregnation modes of the sorbents did not produce a strong effect on Hg0 capture effciency,while fair correlation was observed between Hg0 uptake capacity and iodine concentration.Therefore,the content of I2 impregnated on the sorbents was identified as the most important factor influencing the capacity of these sorbents for Hg0 uptake.Increasing temperature in the range of 80-140°C caused a rise in Hg0 removal.A reaction mechanism that may explain the experimental results was presumed based on the characterizations and adsorption study.     

高温热水解-催化分光光度法测定植物样品中的痕量碘

建立了测定植物中痕量碘的高温热水解-催化分光光度法。设计了预处理程序以使植物样品能够稳定、彻底地进行热水解。通过正交实验优化了样品预处理的热水解参数:样品质量0.5g、氧气流量100mL/min、吸收液的NaOH浓度0.2mol/L、温度1100℃和热水解时间20min。为提高催化分光光度法测定吸收液中痕量碘的灵敏度,碘催化砷铈氧化还原反应的条件优化为:反应温度45℃、反应时间35min。该方法的检测限和定量下限分别为0.3ng/g和0.9ng/g,满足植物样品中痕量碘的分析要求。对国家标准植物样品的分析结果表明该方法准确度高、精密度好。由于使用的仪器都很常用、便宜,并具有测试费用低廉,检测限低、准确度和精密度高等优点,该方法易于推广使用,适合于植物样品碘含量的日常分析。     

红外光谱技术结合聚类分析用于海洋绿藻分类研究

利用傅里叶红外光谱研究了10种南极绿藻和6种浒苔,结果显示,傅里叶变换红外光谱主要由蛋白质、脂类化合物及多糖的振动吸收带组成。通过比较两类绿藻原始谱图,发现它们极为相似,在2000～500 cm-1范围内,即多糖吸收区有较小的差别。选取2000～500 cm-1范围的一阶导数进行系统聚类分析。10种南极绿藻、6种浒苔按其红外一阶导数的内在数理统计规律划归两类,南极绿藻为一类,浒苔为一类。傅里叶变换红外光谱技术结合化学统计学方法,为海洋藻类的分类研究提供一种新的方法。     

Assessment of the degree of rancidity on reused oils in university cafeterias,and public awareness

In this study, reused sunflower cooking oil was investigated for rancidity. Three student cafeterias at the University of Dodoma (UDOM) were used for this particular study. Oil samples were analyzed at the University of Dodoma laboratories. Results showed that all parameters were beyond permissible limits by WHO/FAO standards. Acid values ranged between 0.841 and 4.319 mg KOH/g oil, which is beyond the allowable limits by WHO/FAO (0.6 mg KOH/g oil). Peroxide values were found to be 19.5 mill eq O₂/kg oil (minimum), and 62 mill eq O₂/kg oil (maximum), which are both above the recommended limits by WHO/FAO (10 mill eq O₂/kg oil). Iodine values were found to be from 102.87 to 48.26-g I₂/100 g oil, and were all beyond the recommended limits by WHO/FAO, of between 118- and 141-g I₂/100 g oil. The study has further revealed that the number of customers that are saved by the three cafeterias exceeds the capacity of the cafeterias. This study also found out that many students (almost 74%) are not aware on general knowledge about rancidity, including health effects of using rancid oils. It is therefore recommended to the national regulatory authorities to formulate strict regulations to guide and control oil rancidity.     

高级氧化技术去除水中碘代X射线造影剂研究进展

碘代X射线造影剂在医学上的大量使用导致其在水环境中普遍存在,对生态系统和人体健康构成巨大威胁.传统的污水处理技术对碘代X射线造影剂去除效果不佳,应用高级氧化技术去除水中碘代X射线造影剂成为研究热点.本文系统分析了水环境中碘代X射线造影剂的理化性质、来源、危害及污染现状.综述了声化学氧化、光催化、过硫酸盐活化、芬顿和电化...     

离子电极连续测定食醋中的碘氟

采用柠檬酸－KOH为离子强度调节剂,用碘电极、氟电极直接测定食醛中碘氟的量。方法简便、快速。本方法碘氯 的最低检出限分别为4.3ug/L和24ug/L.