Diffusion of an alkaline fluid through clayey barriers and its effect on the diffusion properties of some chemical species

This work, which lies within the scope of the European project ECOCLAY II, focuses on the effects of an alkaline solution on the diffusion of solutes in clay barriers. The solids investigated here were a mudrock of the Bure site (Meuse/Haute-Marne, France) extracted from the Callovo-Oxfordian layer and a compacted MX-80 bentonite, as an example of a clay used for engineered barriers. The alkaline solution was a synthetic “evolved” cement water, controlled by portlandite dissolution (pH˜12.5).Through-diffusion tests with HTO, K⁺, Ca²⁺, Na⁺, Cs⁺ and Cl⁻ were performed in the presence of the alkaline solution. Diffusion properties of HTO, K⁺ and Ca²⁺ were also evaluated under site conditions (i.e., without cement water). Conclusions to date are as follows: The D_e values of calcium and potassium, which were the two major cations present in excess in cement water compared to site water, are higher when diffusion occurs with the alkaline fluid than when the migration of these species is determined under site conditions. The HTO effective diffusion coefficient decreases over a 12-month period when one face of the clay sample is in contact with cement water. Such a behaviour could be caused by clogging of voids. For a given clayey material, D_e values of the considered cations have the same order of magnitude, but D_e(Cl) is one to two orders of magnitude lower. Such a difference is attributed to anionic exclusion processes that occur in argillaceous media. It is thus concluded that assigning a single diffusion coefficient to all the dissolved species when modelling an alkaline plume spread in a clayey material is a debatable hypothesis.     

Investigation of a basic dye removal from aqueous solution onto chemically modified Unye bentonite

The adsorption behavior of crystal violet (CV⁺) from aqueous solution onto magnesium-oxide coated bentonite (MCB) sample was investigated as a function of parameters such as initial CV⁺ concentration, contact time and temperature. The Langmuir, and Freundlich adsorption models were applied to describe the equilibrium isotherms. The Langmuir monolayer adsorption capacity of MCB were estimated as 496 mg/g. The pseudo-first-order, pseudo-second-order kinetic and the intra-particle diffusion models were used to describe the kinetic data and rate constants were evaluated. The values of the energy (E_a), enthalpy (ΔH^≠) and entropy of activation (ΔS^≠) were 56.45 kJ/mol, 53.90 kJ/mol and −117.26 J/mol K, respectively, at pH 6.5.     

膨润土水泥浆的研制及应用

用钠膨润土、防窜降滤失剂配制成了膨润土水泥浆，用于百色油田３口油气井的固井施工，效果良好，提高了油层、水层及油水同层的封固质量。本文介绍了配方研究、性能测试结果及现场应用概况。     

膨润土对山西石灰性土壤钾素有效性的影响

室内培养试验结果表明 :山西石灰性土壤在田间持水量条件下 ,加入不同浓度的外源钾后 ,经过一段时间培养 ,土壤释钾量随加入外源钾浓度的增加而增加 ,施加膨润土后土壤释钾量明显高于未施加膨润土的土壤 .在干湿交替过程中 ,土壤固钾能力增强 ,其固钾量随加入外源钾浓度的增加而增加 ,施加膨润土后土壤固钾量明显降低     

Microstructure and micro/macro-diffusion behavior of tritium in bentonite

Diffusion of tritium water, HTO, in bentonite clay is investigated. The method provides a sequential procedure of microscopic characterizations of the clay by a confocal laser scanning microscope (CLSM), the molecular dynamics (MD) simulation and the micro-/macro-analysis by the homogenization analysis (HA) method in which the results of the microscope characterizations and the MD simulations are used. The diffusion properties of HTO calculated by HA agree with the experimental data. Then we simulate the diffusion behavior of HTO in the barrier system of high-level radioactive waste management.     

膨润土制备A型分子筛的实验研究

以膨润土为基础原料 ,用低温水热合成技术合成A型分子筛。探讨了残存膨润土、碱度、晶化温度、晶化时间对反应的影响。     

膨润土干燥剂的制备、测试及吸湿机理的研究

本文介绍了膨润土干燥剂的制备工艺、测试方法,并用测试结果与现行传统的硅胶干燥剂进行了性能数据经济价格上的对比兮析,指出了膨润土干燥剂的开发应用前景。最后作者分析了膨润土干燥剂的吸湿机理。     

Hydrothermal alteration of “La Serrata” bentonite (Almeria, Spain) by alkaline solutions

Bentonite and concrete are considered as backfilling and sealing materials in a deep geologic repository of high-level radioactive waste (HLRW). The pH of the pore waters leached during concrete degradation is >11 for a long period of time. Under these alkaline conditions, bentonite is susceptible to dissolution–precipitation reactions. The aim of this work is to study mineralogical changes in bentonite in contact with synthetic pore waters of cements. The temperature effect has been taken into account in order to consider the thermal impact of radioactive decay.The bentonite used comes from “La Serrata de Níjar” (Almería, Spain) and is mainly composed of montmorillonite. Bentonite was submitted to alkaline solutions at 35, 60 and 90 °C up to 365 days. Alkaline solutions were similar to the pore waters leached in the first stage of cement degradation.The zeolite crystallization and the increase of magnesium in a non-exchangeable form in the smectitic clay fraction are the main mineralogical changes detected in the bentonite. Both processes are enhanced with the duration time and temperature of reaction.     

A new method for identifying Wyoming bentonite by ATR-FTIR

Bentonites are important for numerous industrial applications. The properties of bentonite vary depending on their genesis. Wyoming bentonites often behave in a special way with respect to industrial applications; therefore, these bentonites are of special economic interest.Bentonites of different origin differ in their mineralogical composition, chemical composition of individual minerals, surface properties, rheology, and texture. However, the analysis of these parameters is time-consuming. The aim of this study is to propose an accurate and fast analytical tool for the differentiation of bentonite products of unknown origin, particularly of Wyoming bentonites.For this purpose infrared spectroscopy with the attenuated total reflection (ATR) technique is used which allows the fast and reproducible measurement of IR bands of octahedral sheets of smectites. The extinctions and positions of these bands are quantified by fitting procedures. The attention was focused on the OH-bending region, where the position of the AlMgOH band and also the intensity ratio I_{(AlMgOH/(AlAlOH + AlFeOH + AlMgOH))} proved to be characteristic for Wyoming bentonites.In total 60 bentonites were analysed as standards with known origin, 13 of which are from Wyoming while the remaining 47 are from 19 other districts. To eliminate disturbing bands of typical admixtures (carbonates and illite/mica), which can influence the intensity and the position of the octahedral bands of smectites, each sample was treated with HCl and smectites were enriched by centrifugation.Applying this fast pre-treatment procedure, the AlMgOH band occurs at significantly higher wave numbers (10 cm^− 1) in Wyoming bentonites than in other bentonites.In order to verify this technique, 41 products of unknown origin were analysed. Six were identified as Wyoming bentonites. Analysis of the ratio of exchangeable cations Na/(Ca + Mg + Na), which is specifically high for Wyoming bentonites, confirms the IR identification.