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首页> 外文会议>2001 conference of Waste Management (WM);Annual Waste Management Symposium >STUDY ON THE FEASIBILITY OF REMOVING 137Cs FROM BIKINI ISLAND SOILS
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STUDY ON THE FEASIBILITY OF REMOVING 137Cs FROM BIKINI ISLAND SOILS

机译：从比基尼岛土壤中去除137Cs的可行性研究

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摘要

Bikini Island soils are contaminated with 137Cs from fallout during weapons tests. It was introduced intornthe soil either by direct deposition or as a result of rainfall-associated washout and deposition and presentsrna significant radiation exposure through plant uptake and subsequent appearance in the food chain. Thisrnstudy was to provide insight into the adsorption processes of cesium on the surface soils in order to assessrnthe potential for reducing the availability of 137Cs to plants grown in Bikini Island soils. Specifically, therngoal was to reduce the concentration of 137Cs by thirty-fold, equivalent to removing 97 percent of itsrnactivity from the soils.rnThe study plan consisted of four experiments: (1) determination of the fraction of 137Cs, associated withrnsoil organic carbon, that is removable by acid pretreatment, typically used to remove cations that interferernwith organic carbon extraction by base; (2) determination of extraction efficiency of acids and saltsrnrepresenting an acidic medium and/or ion-exchange potential; (3) determination of the extractionrnefficiency of bases and salts that provide a basic medium and/or exchange potential and might effectivelyrnremove 137Cs associated with organic material without acid pretreatment; and (4) determination of 137Csrnactivity by particle-size distribution, which might reveal an approach to remediation by particle-sizernseparation.rnThe following conclusions are drawn from this feasibility study: (1) no extracting solutions selected forrnExperiments 2 or 3 (acid, base, salt, or a combination of acid or base with salt) were successful inrnachieving a thirty-fold decrease in 137Cs concentration (97 percent removal efficiency), even after arntreatment period of 21 days. The maximum removal was 47 percent using 0.5M hydrochloric solution. Itrnis not likely that any of the solutions would approach the extraction goal, even under optimal conditionsrnand particularly under those conditions encountered in in-situ extraction technology (soil flushing); (2) Thernresults of Experiment 2 also illustrates the exceptional reactivity of soil material with acid extractants --rnaddition of acid solutions readily dissolved the carbonate soil matrix; (3) During Experiment 1, selected tornextract organic material with sodium hydroxide, most of the soil matrix was dissolved by the requiredrnaddition of acid. The remaining solids represented less than nine percent of the original soil massesrntreated; the two aliquots examined had a 137Cs concentration of 476 and 554 pCi/g, both from soil aliquotsrnwith less than 70 pCi/g. Very little 137Cs was extracted by the acid or base solution: less than 15 percent ofrnthe total activity was found in the acid supernatant, and less than six percent was found in the basernsupernatant; (4) Most of the soil particles in the sample, approximately 72 percent, were collected in thern+200mesh-size fractions during the performance of Experiment 4. The fraction containing the highestrnconcentration of 137Cs is the -200 fraction, 345 pCi/g. It represents about 17 percent of the soil by weightrnbut over 75 percent of the total cesium activity in the soil. Since the -8/+50 fraction represents 44 percentrnof the soil sample but the 137Cs concentration is only 5 pCi/g, removal of the remaining 66 percent couldrnleave a soil fraction with a concentration of only 5 pCi/g. Mixing the remaining 44 percent with clean soilrn(soil with background concentrations of 137Cs and with complement nutrient and particle characteristics)rnwould dilute the effect of the 137Cs concentration and might bring the concentration to less than 2.5 pCi/g;rn(5) Particle-size separation indicated that most of the 137Cs activity is associated with a fine black soilrnfraction, however, most is not extractable although acid solution dissolves over 90 percent of the soilrnmatrix. Like the particle-size separation procedure, the procedure designed to extract organic materialrnfrom soils left a fine black solid containing much of the radionuclide activity.
机译：在武器测试期间，比基尼岛的土壤被辐射中的137 Cs污染。通过直接沉积或降雨相关的冲刷和沉积将其引入土壤，并通过植物吸收和随后出现在食物链中而表现出显着的辐射暴露。这项研究旨在深入了解铯在表层土壤上的吸附过程，以评估降低137 Cs对在比基尼岛土壤中生长的植物的可利用性的潜力。具体来说，目标是将137Cs的浓度降低30倍，相当于从土壤中去除其97％的活性。研究计划包括四个实验：（1）确定与土壤有机碳有关的137Cs的比例，可通过酸预处理除去，通常用于除去干扰碱萃取有机碳的阳离子； （2）确定代表酸性介质和/或离子交换电位的酸和盐的萃取效率； （3）确定可提供基本介质和/或交换潜能，且可在不进行酸预处理的情况下有效去除与有机材料相关的137C的碱和盐的提取效率； （4）通过粒度分布确定137 Csrn活性，这可能揭示了通过粒度分离进行修复的方法。rn从该可行性研究得出以下结论：（1）对于实验2或3（酸，碱），没有选择萃取溶液。 ，盐，酸或碱或盐与盐的混合物）成功地实现了137Cs浓度降低30倍（去除效率为97％），即使经过21天的精炼处理也是如此。使用0.5M盐酸溶液的最大去除率为47％。即使在最佳条件下，尤其是在原位提取技术（土壤冲洗）中遇到的那些条件下，任何解决方案也不大可能达到提取目标； （2）实验2的结果也说明了土壤材料与酸提取剂的特殊反应性-添加酸溶液容易溶解碳酸盐土壤基质； （3）在实验1中，选择用氢氧化钠提取有机物，通过添加所需的酸将大部分土壤基质溶解。剩余的固体含量不到处理过的原始土壤质量的百分之九；来自土壤等分试样的两个等分试样的137 Cs浓度分别为476和554 pCi / g，均小于70 pCi / g。酸或碱溶液提取的137Cs很少：在酸上清液中发现的总活性不到总活性的15％，在上清液中发现的总活性不到6％。 （4）在进行实验4的过程中，样品中的大多数土壤颗粒约占72％的颗粒收集在rn + 200目级分中。含有最高137Cs的级分是-200级分，即345 pCi / g。它按重量计约占土壤的17％，但占土壤总铯活性的75％以上。由于-8 / + 50分数代表土壤样品的44％，而137Cs浓度仅为5 pCi / g，因此除去剩余的66％可能留下土壤分数仅为5 pCi / g。将剩余的44％与干净的土壤（背景浓度为137Cs且营养成分和颗粒特征互补的土壤）混合会稀释137Cs浓度的影响，并可能使浓度降至2.5 pCi / g以下； rn（5）颗粒-大小分离表明，大多数137Cs活性与细小的黑色土壤馏分相关，但是，尽管酸溶液溶解了90％以上的土壤基质，但大多数都无法提取。像粒度分离程序一样，从土壤中提取有机物的程序也留下了细小的黑色固体，其中含有很多放射性核素活性。

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