Kinetics of selenomethionine disappearance from reclaimed coal mine soils of Wyoming, U.S.A.

 Selenomethionine (SeM) is an organic toxicant that is present in seleniferous environments. No kinetic data is yet available regarding SeM reactions in coal mine environments, where selenium (Se) toxicity is a potential concern. A kinetic study was conducted on two reclaimed coal mine soils (Typic Torriorthents) from Wyoming having sandy and clayey textures. Four levels of SeM treatments (0, 50, 100 μM, and plant amendment from the mine vegetation) were reacted with the soils for 4, 7, 14, 28, 42, 56, and 84 days to characterize the kinetic behavior of overall SeM disappearance from soil solutions. Detection of SeM in soil solutions at the control level (0 μM SeM) indicated occurrence of indigenous SeM in the soils. In the plant-amended soil solutions, much greater concentrations of SeM were observed as compared with the soil-only systems. This indicated the plant material was a more potential source of SeM than the mine soils. A time-dependent loss in solution SeM concentrations was observed for both soils under 0, 50, 100 μM SeM treatments. For the soil-plant mixtures, the solution SeM concentration increased initially, reached a maximum after 14 days, and then decreased thereafter. In the plant-amended soil solutions, SeM concentrations at all time intervals were higher for the sandy as compared to the clayey soil. At 50 and 100 μM SeM treatments, the solution pH was linearly related to the percentages of SeM disappeared from the solutions; greater percentage of SeM was removed from solutions at comparatively lower pH levels, which was ≥90% at pH 7.7 for both soils. Solution SeM concentrations decreased exponentially with time following first-order kinetic reactions. Under all applications (except for the control), C ₀ (SeM concentration at t=0) values for the sandy soil were greater than those determined for the clayey soil, indicating higher solution SeM availability for the former and more SeM retention by the latter at t=0. Comparison of C ₀ in controls (0 μM SeM addition) suggested greater indigenous SeM in the clayey soil. For both soils, C ₀ values under different treatments followed the order, (soil+100 μM)>(soil+50 μM)>(soil+0 μM). The specific reaction rate constants (K _r) of SeM for both soils were similar (0.031 and 0.029 day^–1 for sandy and clayey soils, respectively); low K _r values indicated that SeM loss from our reclaimed coal mine soil solutions would follow rather slow kinetics. The half-life (t _0.5) of SeM varied from 15 to 55 days depending on treatment level. The knowledge obtained from this study should contribute in developing time-based Se reclamation strategies in coal mine environments. Received: 18 September 1995 · Accepted: 28 December 1995     

南极臭氧洞研究综述

本文根据迄今为止对南极臭氧洞研究的成果,综述了南极臭氧洞形成的诸种原因。研究表明人类排放到大气中的污染物氟里昂,通过发生在极地平流层云表面上的非均相化学反应所分解出的活跃的氯基,经过光化学反应过程大量分解臭氧是出现南极臭氧洞的内部原因;太阳活动、大气长波辐射及大气环流造成南极平流层环极涡旋中出现的极地平流层云,可能是形成南极臭氧洞的外部条件。南极臭氧洞的闭合很可能是南半球春季逐渐增强的行星波活动往南极平流层输送的臭氧增多的结果。同时讨论了南极臭氧洞未来的可能趋势,估计南极臭氧洞可能会持续下去,并随着大气环流的波动,其程度和范围也会出现波动。     

A review of the synthesis and characterisation of pillared clays and related porous materials for cracking of vegetable oils to produce biofuels

This paper presents an overview of the modification of clay minerals by propping apart the clay layers with an inorganic complex. This expanded material is converted into a permanent two-dimensional structure, known as pillared clay or shortly PILC, by thermal treatment. The resulting material exhibits a two-dimensional porous structure with acidic properties comparable to that of zeolites. Synthetic as well as natural smectites serve as precursors for the synthesis of Al, Zr, Ti, Fe, Cr, Ga, V, Si and other pillared clays as well as mixed Fe/Al, Ga/Al, Si/Al, Zr/Al and other mixed metal pillared clays. Biofuels form an interesting renewable energy source, where these porous, catalytically active materials can play an important role in the conversion of vegetable oils, such as canola oil, into biodiesel. Transesterification of vegetable oil is currently the method of choice for conversion to biofuel. The second part of this review focuses on the catalysts and cracking reaction conditions used for the production of biofuel. A distinction has been made in three different vegetable oils as starting materials: canola oil, palm oil and sunflower oil.     

EK-Fenton process for removal of phenanthrene in a two-dimensional soil system

Feasibility of electrokinetic (EK) process combined with Fenton-like reaction was investigated for the removal of phenanthrene in a two-dimensional cell. Sandy soil and bentonite were selected as a model soil and a filling material to inhibit the leak of electrolyte solution within the electrode reservoirs into the soil by hydraulic pressure difference, respectively. The effects of parameters including current, electroosmotic flow (EOF), electrolyte pH, and moisture content on the removal efficiency were examined under constant voltage.

At the end of operation for 21 days, the concentration of phenanthrene near the anode was lower than the other positions of soil specimen and increased gradually towards the cathode because hydrogen peroxide solution was supplied from anode to cathode region following the direction of EOF. The concentration of phenanthrene at the bottom soil was lower than that at the top soil. Because capillary attraction in the sandy soil with high porosity was too low to maintain appropriate moisture at the top of the cell, EOF moved through the bottom soil with higher moisture content. Overall removal efficiency at 140 V was 81.6%, which was higher than 68.9% at 100 V because total EOF increased by a factor of 1.5 upon increase of the voltage from 100 to 140 V. In addition, power consumptions at 100 and 140 V were 7.2 and 19.4 kWh, respectively.     

纳米镍-铁去除四氯乙烯的影响因素

氯代烃是地下水中最常检出的有机污染物之一,传统的处理方法需要很长时间与大量经费。本文利用批实验的研究方法以四氯乙烯(PCE)为目标污染物,研究纳米镍铁在去除PCE过程中的影响因素。实验结果表明,暴露后的纳米镍铁脱氯速率比不暴露时速率降低约4倍;反应温度是影响反应速率的重要因素之一,每升高10℃,反应速率常数kSA提高2～3倍;在一定范围内,镍/铁质量比越高,越利于脱氯反应的快速进行,镍/铁的质量比为8%左右时,对氯代烃脱氯速率最快;反应液中的溶解氧不利于纳米颗粒对氯代烃的降解。     

反应条件指数及其与饱和指数的关系初步探讨

反应条件指数(RCI)和饱和指数(SI)都是建立在热力学基础上说明水中物质溶解与沉淀作用的水文地球化学参数。饱和指数能够客观地反映水文地球化学作用发生的方向和状态,反应条件指数综合了水文地球化学状态条件和水文地球化学作用边界条件的信息,它不仅能反映水文地球化学作用发生的方向和状态,而且可以反映其发生的条件及原因。根据反应条件指数和反应条件边界值的概念,运用热力学基本原理和质量作用定律对反应条件指数与饱和指数的关系进行了论证,结果表明两者呈线性函数关系。这对认识和解决生产、科研中存在的水文地球化学问题具有重要指导意义。     

递增变质作用研究中的科学问题

递增变质带广泛出露于全球元古代至新生代的众多造山带中，但递增变质作用的成因尚不完全清楚。本文归纳了典型递增变质带的研究成果，讨论了如下几个悬而未决的科学问题：递增变质带的热源、变质反应与变质作用P- T- t轨迹特征、流体来源与作用、变质与变形耦合关系、花岗岩及混合岩化作用、递增变质带的折返/隆升机制，以及递增变质作用的构造成因等。本文综述了上述科学问题研究进展，探讨了递增变质作用的可能成因。     

实验室模拟研究大气二次有机气溶胶的形成

二次有机气溶胶（SOA）是大气中重要的气溶胶组分,主要由挥发性有机物（VOCs）经化学转化形成,对天气、气候、大气环境和人体健康有重要影响,但至今其确切的化学成分和形成机制还十分不清楚。研究SOA的方法主要采用实验室单个物种或多物种的化学过程的模拟研究,野外实际大气的SOA化学成分、源汇和多尺度分析的观测研究,以及大气中SOA形成的数值模拟的回报和预报研究。实验室研究是对SOA形成过程中获取基础数据和推究SOA生成机制的最主要手段。在过去的几十年中,特别是近五年,SOA的研究取得了较大的进展,其中包括SOA前体物、SOA形成机制及影响因子的进一步理解。本文就这些方面展开了概要性的综述,重点强调了我国研究人员所做的研究工作。在采用实验室烟雾箱系统模拟研究SOA方面,首先简述了烟雾系统的发展以及表征,讨论了跟烟雾箱箱体相关的壁效应问题,重点综述了萜烯类、芳香烃类、小分子类等化学物种转化形成SOA的研究进展。在采用流动管和其他反应器类模拟研究SOA方面,重点讨论了挥发性有机物在颗粒物表面或在液相中所形成的SOA的主要化学成分及其可能的作用。     

Influence of Atmospheric Particulate Matter on Ozone in Nanjing,China:Observational Study and Mechanistic Analysis

Particulate matter with diameters of 2.5 μm or smaller(PM_(2.5)) and ozone(O_3) are major pollutants in the urban atmosphere. PM_(2.5) can affect O_3 by altering the photolysis rate and heterogeneous reactions. However, these two processes and their relative importance remain uncertain. In this paper, with Nanjing in China as the target city, we investigate the characteristics and mechanism of interactions between particles and O_3 based on ground observations and numerical modeling.In 2008, the average concentrations of PM_(2.5) and O_3 at Caochangmen station are 64.6 ± 47.4 μg m~(-3) and 24.6 ± 22.8 ppb,respectively, while at Pukou station they are 94.1 ± 63.4 μg m~(-3) and 16.9 ± 14.9 ppb. The correlation coefficient between PM_(2.5) and O_3 is -0.46. In order to understand the reaction between PM_(2.5) and O_3, we construct a box model, in which an aerosol optical property model, ultraviolet radiation model, gas phase chemistry model, and heterogeneous chemistry model,are coupled. The model is employed to investigate the relative contribution of the aforementioned two processes, which vary under different particle concentrations, scattering capability and VOCs/NOxratios(VOCs: volatile organic compounds;NOx: nitric oxide and nitrogen dioxide). Generally, photolysis rate effect can cause a greater O_3 reduction when the particle concentrations are higher, while heterogeneous reactions dominate O_3 reduction with low-level particle concentrations.Moreover, in typical VOC-sensitive regions, O_3 can even be increased by heterogeneous reactions. In Nanjing, both processes lead to O_3 reduction, and photolysis rate effect is dominant. Our study underscores the importance of photolysis rate effect and heterogeneous reactions for O_3, and such interaction processes should be fully considered in future atmospheric chemistry modeling.     

Mechanical Behavior and Shape Optimization of Lining Structure for Subsea Tunnel Excavated in Weathered Slot

Subsea tunnel lining structures should be designed to sustain the loads transmitted from surrounding ground and groundwater during excavation. Extremely high pore-water pressure reduces the effective strength of the country rock that surrounds a tunnel, thereby lowering the arching effect and stratum stability of the structure. In this paper, the mechanical behavior and shape optimization of the lining structure for the Xiang’an tunnel excavated in weathered slots are examined. Eight cross sections with different geometric parameters are adopted to study the mechanical behavior and shape optimization of the lining structure. The hyperstatic reaction method is used through finite element analysis software ANSYS. The mechanical behavior of the lining structure is evidently affected by the geometric parameters of cross- sectional shape. The minimum safety factor of the lining structure elements is set to be the objective function. The efficient tunnel shape to maximize the minimum safety factor is identified. The minimum safety factor increases significantly after optimization. The optimized cross section significantly improves the mechanical characteristics of the lining structure and effectively reduces its deformation. Force analyses of optimization process and program are conducted parametrically so that the method can be applied to the optimization design of other similar structures. The results obtained from this study enhance our understanding of the mechanical behavior of the lining structure for subsea tunnels. These results are also beneficial to the optimal design of lining structures in general.