Role of magnetite and humic acid in radionuclide migration in the environment

Sorption of ¹³⁷Cs, ⁹⁰Sr, ¹⁵⁴Eu and ¹⁴¹Ce by magnetite has been studied at varying pH (4 to 11) in the presence and absence of humic acid. The sorption studies have also been carried out at varying ionic strength (0.01 to 0.2 M NaClO₄) and humic acid concentration (2 to 20 mg/L). Percentage sorption of ¹³⁷Cs and ⁹⁰Sr was found to be pH dependent, with the sorption increasing with increasing pH of the suspension. At any pH, the percentage sorption of ⁹⁰Sr was higher than that of ¹³⁷Cs. The results have been explained in terms of the electrostatic interaction between the positively charged metal ions and the surface charge of the magnetite which becomes increasingly negative with increasing pH. On the other hand, ¹⁵⁴Eu and ¹⁴¹Ce were found to be strongly sorbed by the magnetite at all pH values, with the sorption being independent of pH. The strong sorption of trivalent and tetravalent metal ions suggests the role of complexation reactions during sorption, apart from the electrostatic interactions. However, in the case of ¹⁴¹Ce surface precipitation of Ce(III) formed by reduction of Ce(IV) in the presence of magnetite cannot be ruled out. Presence of humic acid (2 mg/L) was found to have negligible effect on sorption of all metal ions.     

安全验收评价的体系构建与实践探索

从完善我国安全评价工作的角度出发,提出建设安全验收评价体系的构想;在项目建设安全验收评价实践中,又提出如何进一步加大力度,认真考量建设项目的本质安全度与在安全验收评价时更加关注"人"的安全性。该项目的研究与实践是以科学技术来支撑安全生产监管成效的重要举措,对工程项目的安全验收评价提供了依据和有益参考。     

地震勘探引起植被棋盘式分布分析

通过高分辨率卫星遥感数据和实地调研,发现黄河三角洲的很多区域因胜利油田地震勘探而引起植被棋盘式分布。地震勘探引起植被群落斑块扩展,就其生态作用来说,与当前黄河三角洲生态恢复、保护和重建植被这一目标相吻合。此种植被群落的扩展,无须额外经费投入,对此进行深入研究,寻找使其从自发状态转变为通过人工协调可在适宜区域最大限度扩展的对策,将有助于更好地协调油田开发和湿地生态保护之间的矛盾。     

Assessing field-scale migration of radionuclides at the Nevada Test Site: “mobile” species

Many long-lived radionuclides are present in groundwater at the Nevada Test Site (NTS) as a result of 828 underground nuclear weapons tests conducted between 1951 and 1992. In conjunction with a comprehensive geochemical review of radionuclides (³H, ¹⁴C, ³⁶Cl, ⁹⁹Tc and ¹²⁹I) that are presumably mobile in the subsurface, we synthesized a body of radionuclide activity data measured from groundwater samples collected at 18 monitoring wells, to qualitatively assess their migration at the NTS over distances of hundreds of meters and over timescales of decades. Tritium and ³⁶Cl showed little evidence of retardation, while the transport of ¹⁴C may have been retarded by its isotopic exchange with carbonate minerals in the aquifer. Observed local reducing conditions (either natural or test-induced) will impact the mobility of certain redox-sensitive radionuclides (especially ⁹⁹Tc) that were otherwise soluble and readily transported under oxidizing conditions. Conversely, strongly oxidizing conditions may impact the mobility of ¹²⁹I which is mobile under reducing conditions. The effect of iodine speciation on its transport deserves further attention. Indication of delayed transport of some “mobile” radionuclides (especially ⁹⁹Tc) in the groundwater at the NTS suggested the importance of redox conditions of the natural system in controlling the fate and transport of radionuclides, which has implications in the enhanced performance of the potential Yucca Mountain repository, located adjacent to the NTS, to store high-level nuclear wastes as well as management of radionuclide contamination in legacy nuclear operations facilities.     

三峡库区万州塘角1号滑坡滑带特征研究

三峡库区顺坡向缓倾角滑坡灾害频发,万州塘角1号滑坡具有该种滑坡的典型特征。在对该滑坡详细调查研究、GPS观测及深部位移监测数据分析的基础上,通过钻探工程,探井开挖及大型现场剪切试验对该滑坡的滑带特征及力学性质进行了综合分析。研究结果表明:滑坡体表现为持续蠕滑,前缘比中部和后缘变形要大,其方向为NNW向,滑带埋深在10～21m,滑面呈波状起伏。探井揭露滑体中碎块石排布具有定向性和分段性特点,该滑坡存在多层次级滑动,认为在5.0～8.0m范围内存在一规模较大连续性较差的次级滑动带,受主滑带控制。滑坡各区的力学强度表现为不均一性,在滑坡前缘滑带土剪切强度比中部大,这主要是因为在中部地下水相比前缘要丰富,加上滑带土主要为粘土矿物,遇水膨胀软化致使强度降低。     

发展西部经济的有效途径之一——开发盐湖资源

西部地区最广泛的资源是盐湖,这是一种极其重要的盐类资源、特异生物资源和旅游资源,大力开发盐湖资源是发展西部经济的有效途径。     

煤层气勘探中的生态环境影响及保护对策

煤层气勘探开发不仅可以消除煤层气对矿井和矿工带来的危害,还可以为社会提供一种洁净、使用方便的新能源和作为化工工业的优质原料。本文通过对山西晋西北煤田煤层气勘探过程进行分析,针对煤层气勘探活动的特点和可能造成对生态环境的影响和破坏,提出了减缓这些影响和破坏的综合防治对策。     

纵波横波联合地震勘探在城市地质调查中的应用

在城市地质调查中,物探方法的选择要结合地质背景,充分考虑地球物理前提和地质勘查目的,注重方法的可行性、有效性和适宜性。本文结合杭州市城市地质调查中浅层地震勘探,在第四系厚覆盖区,针对查明基岩埋深、确定松散沉积层的分层。在基岩埋深不同,松散沉积结构不同时选择有效的勘查手段、数据采集时的震源及参数选择等方面进行了探讨。     

北京城市声环境自动监测系统监测点位布设方法初探

噪声自动监测相对手工监测而言,更能真实反映城市声环境质量,随着噪声自动监测技术的不断完善,自动监测替代手工监测已成为必然趋势.但目前我国城市声环境自动监测系统正处于起步阶段,国内还没有对声环境自动监测系统的点位布设提出成熟、合理的方案.文章结合北京市声环境自动监测系统建设的实际工作情况,对监测系统总体框架、自动监测点位布设的原则及方法等进行了阐述并提出近期需要解决的问题.     

深圳市政污水排海工程排污混合区范围的确定

应用全场数学模型模拟了深圳排海的市政污水中悬浮物、化学需氧量、无机氮、活性磷酸盐及大肠菌群5个污染因子在海域大潮和小潮时对海域面积的影响。指出在不同水文条件和23m^3/d排放量下，不同质量浓度的活性磷酸盐和大肠菌群超过Ⅲ类海水水质标准的影响面积在大潮时分别为0.04km^2和7.72km^2，小潮时分别大于0.08km^2和6.16km^2；无机氮由于海水本底值较高，使得这一指标在全海域内超过Ⅲ类海水水质标准；而化学需氧量和总悬浮物质量浓度符合Ⅲ类海水水质标准。通过将现场监测资料用数模计算，提出排海污水混合区面积为1.5km^2。同时还引用部分国外的计算公式，对几种混合区允许范围进行了估算。