Simulations of THM processes in buffer-rock barriers of high-level waste disposal in an argillaceous formation

The main objective of this paper is to investigate and analyse the thermo-hydro-mechanical (THM) coupling phenomena and their influences on the repository safety. In this paper, the high-level waste (HLW) disposal concept in drifts in clay formation with backfilled bentonite buffer is represented numerically using the CODE_BRIGHT developed by the Technical University of Catalonia in Barcelona. The parameters of clay and bentonite used in the simulation are determined by laboratory and in situ experiments. The calculation results are presented to show the hydro-mechanical (HM) processes during the operation phase and the THM processes in the after-closure phase. According to the simulation results, the most probable critical processes for the disposal project have been represented and analyzed. The work also provides an input for additional development regarding the design, assessment and validation of the HLW disposal concept.     

Acid-activated organoclays: preparation, characterisation and catalytic activity of polycation-treated bentonites

Samples of SWy-2 and SAz-1 loaded with increasing amounts of the polycation magnafloc 206, [(Me₂NCH₂CHOHCH₂)_n]ⁿ⁺Cl_n, were acid-treated using 6 M HCl at 95°C for 30, 90 and 180 min. The activity of these acid-activated polycation-exchanged clays for the conversion of α-pinene to camphene and limonene was determined and compared with that from clay samples (without polycation) acid-treated in the same manner. Acid treatment of polycation-exchanged bentonites produced hybrid catalysts which enhanced the activity of the clays for the isomerisation of α-pinene to camphene and limonene. The presence of the polycation had a more marked influence on the activity of samples derived from SAz-1 increasing the yield from 25% for acid-activated SAz-1 with no added polycation to 50% camphene for acid-activated polycation-exchanged SAz-1. The increase in yield for corresponding samples derived from SWy-2 was only from 42 to 52%. This enhancement in yield for samples derived from SAz-1 was attributed to the increased hydrophobicity of the polycation loaded clay whilst the comparable yields for SWy-2 in the absence and presence of polycation may suggest that SWy-2 disperses well in the non-polar α-pinene. The total yields (based on α-pinene) for the most active catalysts was between 80 and 90%. These yields are directly comparable with those obtained by others using zeolites and pillared clays although the acid-activated polycation-treated clays were marginally less selective towards camphene.     

Case History of Damage to a School Building Caused by Differentially Heaving Bedrock

This case study considers the question of whether settlement or heave is the principal cause of damage to a school building near Denver. The building, which was underlain by engineered fill in the center and shallow claystone bedrock beneath the outer wings, experienced progressive deformation and significant damage during a 15-year period. With several millions of dollars of rebuilding costs at risk, the most likely cause of failure needed to be ascertained to arrive at an optimum mitigation solution. The investigation described herein considers the regional geology and its known effect on various types of engineered structures in terms of characteristic damage patterns. The focus progressively narrows to concentrate on the geology and damage patterns of the local area and the site. The findings indicate that the major cause of damage to the building is associated with differential heaving of steeply dipping, expansive bedrock layers. This conclusion was adopted as a basis for subsequent remedial planning and design.     

Predicting Solute Flux through a Clay Membrane Barrier

Measured solute flux breakthrough curves (FBCs) from column tests performed on a semipermeable clay membrane subjected to KCl solutions are compared with predicted FBCs using independently measured flow and transport properties. The predicted FBCs are based on three scenarios: (1) Advective–dispersive transport that neglects membrane behavior; (2) advective–dispersive transport that accounts for the concentration dependency of the effective salt-diffusion coefficient (Ds?) resulting from membrane behavior, referred to as partially coupled transport; and (3) fully coupled transport that includes both the explicit coupling terms (e.g., hyperfiltration, chemico-osmosis) associated with clay membrane behavior and the concentration dependency of Ds?. The FBCs predicted by fully coupled transport agree best with the measured FBCs. However, for the diffusion-controlled conditions of the column tests, the steady-state solute fluxes predicted by partially coupled transport are only 23–69% higher than the measured steady-state fluxes. The results imply that the advective–dispersive transport theory can be used to provide reasonably accurate, albeit somewhat conservative, estimates of steady-state solute flux through clays that behave as semipermeable membranes, provided diffusion is a significant, if not dominant, solute transport process and the concentration dependency of Ds? are taken into account.     

蒙脱土颗粒表面带电性质的研究

研究了常用无机盐(NaCl、KCl、CaCl_2)、pH值以及CMC对蒙脱土颗粒表面电性质的影响。用501型激光电泳电动仪测定蒙脱土颗粒的电泳速度,并用Smoluchowski方程式计算出ζ电位。实验结果表明,无论是否有无机盐存在时,蒙脱土颗粒的ζ电位都不受pH值和离子活度变化的影响,均显负电性。阴离子聚合物CMC加入后,显示的ζ电位是蒙脱土颗粒与CMC负电性的综合效果或CMC的负电性。由此可以肯定就蒙脱土自身来说永远显负电性。     

Influence of temperature on the hydro-mechanical behaviour of a compacted bentonite

This paper reports the results on the influence of temperature (between 20 and 80 °C) on some hydro-mechanical properties of a compacted bentonite. The water retention capacity at higher temperature, both in confined and unconfined conditions, is lower, especially when suction is low. At high temperatures, the swelling capacity of clay decreases, although the influence of temperature is less evident when the applied stress is high. Furthermore, a decrease in swelling pressure as a function of temperature was observed. On the other hand, the measured increase in permeability with temperature is lower than expected on the basis of thermal change in water kinematic viscosity. The transfer induced by temperature between intra-aggregate adsorbed water and inter-aggregate free water may explain most of the features observed, taking into account that the physical characteristics (density, viscosity) of water in each one of these two states are different.     

蒙脱石纳米复合材料基质制备研究

简要介绍了湖南某地钙基膨润土矿的矿石物质组成及性质 ,通过试验研究 ,提出了湿法分级提纯工艺流程 ,获得了蒙脱石含量 >90 %的膨润土精矿 ,为制备无机纳米复合材料提供了高性能的基质材料。     

膨润土对Pb~(2+)的吸附及铝的影响研究

研究膨润土对水溶液中铅的吸附特性以及铝对铅吸附的影响。通过各组吸附实验,建立膨润土对水溶液中铅离子的吸附最佳条件,天然膨润土对铅的吸附平衡时间约为60 min,其吸附符合一级动力学方程;铅吸附最适p H=9;天然膨润土对水溶液中铅离子的吸附规律符合Freundlich等温方程和Langmuir等温方程,呈显著相关性;加入少量铝离子时,吸附除铅能力增强,但继续增加铝浓度,去除能力降低,该现象主要通过铝盐水解所致的p H变化起调节作用,电中和作用不明显。     

Migration behavior of landfill leachate contaminants through alternative composite liners

Four identical pilot-scale landfill reactors with different alternative composite liners were simultaneously operated for a period of about 540 days to investigate and to simulate the migration behaviors of phenolic compounds (phenol, 2-CP, 2-MP, 3-MP, 4-MP, 2-NP, 4-NP, 2,4-DNP, 2,4-DCP, 2,6-DCP, 2,4,5-TCP, 2,4,6-TCP, 2,3,4,6-TeCP, PCP) and heavy metals (Pb, Cu, Zn, Cr, Cd, Ni) from landfill leachate to the groundwater. Alternative landfill liners of four reactors consist of R1: Compacted clay liner (10 cm + 10 cm, k = 10⁻⁸ m/sn), R2: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm + 10 cm, k = 10⁻⁸ m/sn), R3: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn) + bentonite liner (2 cm) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn), and R4: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn) + zeolite liner (2 cm) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn). Wastes representing Istanbul municipal solid wastes were disposed in the reactors. To represent bioreactor landfills, reactors were operated by leachate recirculation. To monitor and control anaerobic degradation in the reactors, variations of conventional parameters (pH, alkalinity, chloride, conductivity, COD, TOC, TKN, ammonia and alcaly metals) were also investigated in landfill leachate samples. The results of this study showed that about 35-50% of migration of organic contaminants (phenolic compounds) and 55-100% of migration of inorganic contaminants (heavy metals) to the model groundwater could be effectively reduced with the use of bentonite and zeolite materials in landfill liner systems. Although leachate contaminants can reach to the groundwater in trace concentrations, findings of this study concluded that the release of these compounds from landfill leachate to the groundwater may potentially be of an important environmental concern based on the experimental findings.     

低品位钙基膨润土活化改性的可行性试验

本文探讨了以河北某地低品位钙基膨润土为原料，制备活性土的机制，阐述了酸处理对试样化学组成和物理性质的影响以及制备的活化土用于实际生产的可行性。