氨氮在土工合成黏土衬垫中的扩散行为研究

氨氮是垃圾渗滤液中最具代表性的污染物之一,但其在土工合成黏土衬垫(GCL)中的扩散行为至今尚未得到重视。开展批式吸附试验和扩散试样浸提试验测定氨氮在GCL中的吸附分配系数;进行扩散试验测定氨氮在GCL中的扩散系数;基于试验得到的吸附分配系数和扩散系数,使用数值软件POLLUTE v7.0对氨氮在GCL中的运移行为进行模拟。试验结果表明,氨氮在膨润土上的吸附分配系数为0.017L/g,在GCL中的扩散系数约为9.0×10-11m2/s。POLLUTE v7.0的模拟结果显示,当考虑扩散存在时,氨氮将提前30 a击穿GCL。     

污染物离子在粘土介质中扩散系数和分配系数的测定(英文)

介绍了利用一种自制的特殊装置,测定污染物离子在粘土介质中迁移的扩散参数D和分配系数Kd的方法。通过一系列污染物在上海粘土中的纯扩散迁移试验,系统中污染物的质量不变,源浓度随试验的进行是下降的,运用一个简单的理论模型,通过拉普拉撕(Laplace)变换方法,对一个单独的试验,可同时推断出扩散系数和分配系数。通过拉普拉撕转换程序求出了阴离子(Cl-)和阳离子(K+,Ca2+,Zn2+,Cu2+)的扩散系数D和分配系数Kd。试验结果发现:阴离子在粘性土壤中的显扩散系数比阳离子的大;一价阳离子K+的显扩散系数比二价阳离子的大。     

基于分子动力学模拟的再生剂-老化沥青扩散机理

采用Materials Studio(MS)分子动力学模拟软件对再生剂-老化沥青扩散体系进行研究.以沥青四组分试验为基础,选取12种分子模型构建再生剂分子组、复合水老化沥青分子组和复合紫外老化沥青分子组.针对在不同模拟时间、模拟温度和沥青成分条件下的老化沥青扩散体系进行模拟,得到扩散体系的扩散系数.结果 表明:随着模拟时间的延长,再生剂在老化沥青扩散体系中的扩散系数变小,同时在复合紫外老化沥青扩散体系中的扩散系数小于复合水老化沥青扩散体系;随着扩散温度的增加,扩散系数增速逐渐变缓;再生剂中油性成分(芳香分和饱和分)的扩散系数大于极性成分(胶质和沥青质),芳香分由于多为链状且相对分子质量较小,其扩散速率在4种组分中最快.     

高密度聚乙烯(HDPE)土工膜之抗有机溶剂浸透测试研究(英文)

本研究利用ASTM F739标准浸透测试方法及浸入试验,探讨三种厚度高密度聚乙烯(HDPE)土工膜,对于三氯乙烯、三氯甲烷、1,2–二氯乙烷及二氯甲烷有机溶剂之抗化学浸透性。研究发现:有机溶剂浸入HDPE为non-Fickian扩散模式,经由浸入试验之吸附数据,可得到有机溶剂在HDPE中的扩散系数及溶解度系数,ANOVA统计分析结果显示:扩散系数及溶解度系数在不同厚度HDPE中有显着差异(p<0.01)。同时,本研究利用浸入试验数据计算HDPE之浸透性,结果发现ASTM F739浸透方法与浸入实验所得到之稳定浸透速率有显着相关(r2=0.947,p<0.001)。因此,简单且快速之浸入试验可应用于评估有机溶剂在HDPE的稳定浸透速率。     

沥青再生剂扩散程度评价与影响因素研究

设计了模拟再生剂在老化沥青中扩散过程的试验方案,并基于软化点试验结果进行回归分析,得到了反映再生剂在老化沥青中扩散程度的相对指标——扩散系数p;分析了再生剂品种、沥青老化程度和环境温度对扩散系数p的影响;基于劈裂强度试验,分析了再生剂扩散程度对再生沥青混合料性能的影响.结果表明:再生剂黏度越大或沥青老化程度越深,再生剂在老化沥青中的扩散程度越低;环境温度和扩散时间的增加能显著提高再生剂的扩散程度;再生剂在老化沥青中的充分扩散有利于再生沥青混合料强度的提高.     

动载-环境耦合作用下氯离子在混凝土中的扩散性能研究

为了研究动荷载与环境因素(温度、氯盐)耦合作用下氯离子在混凝土中的传输行为,设计出一套试验机制,以研究此工况下混凝土的饱水性能、不同应力水平下氯离子的传输行为及动载与温度耦合作用下氯离子的传输行为。试验结果显示,此工况下混凝土的饱水度均在99%以上,可认为氯离子在混凝土中的传输以扩散为主;氯离子的扩散系数随应力水平和温度的提高而加快;并得到此条件下氯离子扩散的活化能为19.9 kJ/mol;通过寿命预测模型得到常温下钢筋混凝土大桥的寿命为89.1a。     

水分在沥青膜中的扩散特征

为研究水分在沥青膜中的扩散特性以及水分扩散行为参数与沥青组分间的关系,用重量法测定了沥青膜在不同浸水时间下的吸湿曲线,并分别基于Fick、Langmuir扩散模型对其吸湿曲线进行拟合,分析了水分扩散行为参数与沥青组分间的相关性.结果表明:水分在沥青膜中存在自由态和结合态2种形态,其扩散行为符合Langmuir扩散模型;浸水初期沥青膜中的水分扩散以吸收自由态水分为主,随着浸水时间的延长,沥青膜中结合态水分逐渐增加而后趋于饱和;沥青膜饱和吸水率、水分吸附系数与沥青质含量呈正相关关系,吸附系数与解吸附系数之比与沥青膜饱和吸水率呈较强的线性关系.     

非饱和土中氯离子扩散规律的试验研究

土中污染物迁移涉及对流和扩散,低流速情况下扩散起主导作用,当前对非饱和土中渗流的研究较为成熟,但对非饱和土中污染物扩散规律的认识还不够深入,其中饱和度控制是非饱和扩散系数测试的技术瓶颈。自制非饱和对流-扩散试验装置,控制入渗过程中土的含水率恒定,以氯离子为示踪剂进行对流–扩散土柱试验,通过切片法测得氯离子浓度剖面,使用非饱和对流–扩散解析解拟合得到氯离子水动力弥散系数,进而求得非饱和有效扩散系数,通过不同含水率下的试验得出有效扩散系数随含水率的变化规律;依据3层土渗流模型计算得到非饱和渗透系数随含水率的变化规律。试验结果表明,试验过程中渗透吸力对含水率的影响可以忽略,本文试验装置含水率控制精确可靠,测得0～100 kPa基质吸力下土中氯离子的有效扩散系数在1.59×10~(-6)～5.22×10~(-6) cm~2/s之间,氯离子的非饱和有效扩散系数随无量纲含水率的减小而线性减小;溶质迁移的弥散度随含水率减小而增大;对数的非饱和渗透系数随含水率线性减小。     

挥发性气体通过填埋场复合覆盖层的一维扩散解析解

为了评价填埋场覆盖层对挥发性气体的防渗性能,建立了挥发性气体在复合覆盖层中的扩散运移模型并采用分离变量法获得了模型解析解。解析解的计算结果与数值解结果吻合得较好。分析结果表明,对于土工膜/土工复合膨润土垫（GM/GCL）与土工膜/压实黏土（GM/CCL）组成的覆盖层,覆盖层顶部气体扩散达到稳态的时间比较接近,约为1.6 a;对于压实黏土（CCL）系统达到稳定状态的时间为0.5 a;稳态时通量依次为6.0×10⁵,1.0×10⁶和7.4×10⁵ mg/ha/a。在这3个覆盖层系统中,GM/CCL对气体扩散的控制性能最差。对于GM/GCL,GCL含水饱和度从0.85增加到1时,覆盖层顶部通量减小了82.5%。饱和时GM/GCL系统顶部气体达到稳态的时间是非饱和情况下的约100倍。对于GM/CCL,CCL含水饱和度从0.1增加到0.85时,覆盖层顶部通量减小了近1个数量级。含水饱和度的变化可导致覆盖层顶部挥发性气体稳态时通量发生数量级的变化。     

GCL对铜离子吸附和隔离性能试验研究

采用蒸馏水和0.01 mol/L铜离子溶液分别水化钠基膨润土防水毯(以下简称GCL)进行渗透试验,并用0.01 mol/L铜离子溶液代替蒸馏水测试GCL渗透系数和渗滤液中铜离子浓度;分析了不同水化处理对GCL吸附铜离子和防渗性能的影响。结果表明:不同水化方式预水化的GCL对铜离子都具有优异过滤效果,两种水化方法对铜离子过滤能力都达到99%以上;相比于0.01 mol/L铜离子溶液直接水化,蒸馏水预水化后GCL吸附性能较好,但防渗性能随着时间的增加而变差。     

Experimental investigation on methane advection and diffusion in geosynthetic clay liners

Geosynthetic clay liners (GCLs) are widely used in landfill and heap-leach facility cover system for mitigating rainfall infiltration and gas migration into atmosphere. Laboratory tests were conducted to investigate methane diffusion and advection through GCLs. Gas permeability coefficient of GCL for the case with moisture content = 47.5% is one and two orders of magnitude greater than the cases with moisture content = 68.5% and 80.9%, respectively, when 20 kPa vertical stress was applied. The batch adsorption tests indicated that adsorption of methane onto bentonite is negligible. The concentration variation for the adsorption of methane onto bentonite can be neglected. However, methane concentration decreased by 14.2% for the test of methane adsorption onto GCL during the first 2–3 days. This is because methane was adsorbed by the geotextiles rather than by the bentonite in GCL. The large porosity and surface area of geotextiles provide lots of micropores for methane adsorption. Analytical model was then developed to analyze the performance of GCL-based liners system with respect to methane transport. The results indicate that methane emission fluxes for the case with SL + GCL are 7.8 and 5.1 times less than the cases with SL + CCL when the moisture contents were 25.9% and 35.1%, respectively. The methane emission fluxes for both of the SL + GCL and SL + CCL can be neglected when they are fully saturated. GCL is recommended to be used in arid and semi-arid regions rather than CCL. GCL is recommended to be used in arid and semi-arid areas rather than CCL. Advection plays a more important role in methane migration through SL + GCL and SL + CCL than that of diffusion. With moisture contents = 25.9% and 32%, methane emission flux attributed to advection accounts for more than 90% of the total emission flux for both cases of SL + GCL and SL + CCL. With the increase of moisture content of SL, the effectiveness of SL in reducing methane emission increases. The saved space for using GCL + SL composite cover compared with using a single SL cover is 0.7 m when the moisture content equals 25.9%, which is 0.5 m greater than the case when moisture content equals 32%. GMB plays a dominant role in inhibiting methane migration and reducing methane emission flux. When moisture content equals 25.9%, the methane emission fluxes for SL + GMB + GCL and SL + GMB + CCL are 343 times and 2643 times less than the cases with SL + GCL and SL + CCL, respectively.     

氢氧根离子在膨润土中的弥散规律及其溶蚀作用

高放废物地质处置库中可能出现的碱性孔隙水,会对膨润土的缓冲封闭性能产生不良影响,尤其是碱性孔隙水中的OH^-离子。本文用NaOH溶液模拟碱性孔隙水,用蒸馏水模拟处置库现场的地下水,对初始干密度为1.70 g/cm³的高庙子(GMZ)膨润土试样开展弥散试验,研究OH^-离子在高压实GMZ膨润土中的弥散规律;用pH值为13和13.8的NaOH溶液模拟孔隙水侵蚀GMZ膨润土试样,研究碱性孔隙水侵蚀,GMZ膨润土的溶解规律。结果表明,非稳态条件下,OH^-离子在GMZ膨润土中的弥散系数为1.49×10^-11~1.89×10^-10 m²/s,且弥散系数随着试样两侧溶液浓度差的减小而降低;高pH值碱性孔隙水侵蚀,首先会造成膨润土中含Si和Al矿物的迅速溶解,溶解速率与时间呈近似线性增长关系,且溶液的pH值越高,溶解速率越快。     

低固结压力下土–膨润土防渗墙填料渗透和扩散系数测试

渗透和扩散是污染物在防渗屏障中迁移的重要方式,当前对低固结压力下土–膨润土防渗墙渗透系数和扩散系数测试是否必须采用柔性壁渗透仪、是否必须对试样进行固结尚无统一看法。按土–膨润土防渗墙施工工艺制备填料,使用柔性壁渗透仪测试了30,50和100 k Pa有效固结压力下填料渗透系数,进行刚性壁土柱渗透–扩散试验测试了10 k Pa固结压力下填料渗透系数和扩散系数,基于加速沥出试验原理提出快速测定高塌落度填料有效扩散系数的透析试验方法。柔性壁渗透试验结果表明,填料流入和流出渗透系数均随水力梯度增大而增大,存在起始水力梯度,柔性壁渗透试验的起始水力梯度在6.82~8,随固结压力由30 k Pa增至100 k Pa,渗透系数由5.21×10~(-8)降至3.78×10~(-8) cm/s。10 k Pa固结压力下,刚性壁渗透–扩散试验测得起始水力梯度为5.67,渗透系数为7.14×10~(-8) cm/s,试验不存在侧壁渗漏,填料中Cl~-有效扩散系数为3.12×10~(-6) cm~2/s。透析试验填料未经固结,测得有效扩散系数为4.45×10~(-6) cm~2/s。掺入6.02%膨润土后,粉土渗透系数降低约4个数量级,有效扩散系数仅降低约一半,扩散将是膨润土系防渗墙中污染物迁移的主要方式。     

酸雨作用下含磷固化剂处理铅锌镉复合污染土的半动态浸出试验研究

酸雨pH可显著影响固化重金属污染土的浸出量。定量评价固化污染土在暴露条件下(例如酸雨)对周边水土体环境的影响,需要明确固化污染土的有效扩散系数和阻滞因子这两个关键参数。现有研究多集中在固化污染土的浸出特性和表观扩散系数,有关有效扩散系数和阻滞因子的研究很少。本次研究旨在研究改进的KMP固化剂固化重金属Pb、Zn、Cd复合污染土在酸雨作用下的有效扩散系数和阻滞因子。解吸附试验表明,随着污染土中重金属Pb、Zn、Cd浓度增加,固化污染土的解吸附量增大,且解吸附曲线满足Freundlich平衡吸附/解吸附方程。半动态浸出试验结果表明,污染土中重金属Pb、Zn、Cd浸出机制主要由扩散控制,且拟合曲线斜率分别为0.60,0.56和0.61,表观扩散系数Dobs为1.05×10~(-16),7.84×10~(-13)和2.11×10~(-12) m~2/s。结合解吸附试验和半动态浸出试验结果可知,Pb、Zn、Cd的阻滞因子Rd分别为17165.6,254.6和109.3,有效扩散系数De分别为1.82×10~(-12),1.96×10~(-10),2.34×10~(-10) m~2/s。与其他学者结果相比,固化污染土中Pb的有效扩散系数低于其他学者的两个数量级,而Zn和Cd的求算结果与其他学者一致。     

膨润土防水毯搭接方式渗流特性试验研究

为了从渗流量和渗透稳定角度深入研究膨润土防水毯搭接处的防渗问题,开发了由压力控制系统和模型试验系统两部分组成的具有施加法向应力作用的接触面渗流试验装置,建立了真实模拟设计提出的防水毯铺设工序的渗流搭接物理试验方法,并通过不同工况下的膨润土防水毯搭接渗流试验,初步探讨了搭接处膨润土发挥防渗作用的最佳状态。结果表明:防水毯的搭接宽度宜大于30 cm;搭接处的膨润土添加量最好在4000~5000 g/m2之间选取;取防水毯规格型号为5000 g/m2能满足防渗体的要求;围压大小和加载路径对搭接处的渗透性影响均较大,若围压先增大然后再减小,搭接处仍能保持较为密实,其渗透性变化不大。     

赤泥渗滤液对改性GCL防渗性能的影响

旨在评价商用土工合成材料黏土衬垫(GCL)用于阻隔赤泥渗滤液的有效性。赤泥渗滤液作用下GCL的防渗特性是评价其防污性能的关键因素。以商用改性GCL中膨润土为研究对象,通过自由膨胀试验,研究了4种赤泥渗滤液中膨润土的自由膨胀指数。以商用改性GCL为研究对象,通过改进滤失试验,研究了4种赤泥渗滤液作为渗透液作用下GCL渗透系数的变化规律,评价了预水化作用对渗透系数的影响。研究还采用清洁自来水作为GCL的渗透液作为对照。结果表明,随着离子强度的增加,改性GCL中的膨润土自由膨胀指数随之减小。预水化处理改性GCL的渗透系数相较于未预水化处理试样降低了5倍左右。在实际工程应用中,建议采用自来水预水化处理GCL,以此充分发挥其防渗性能。随着改进滤失试验中施加气压的增大,不同赤泥渗滤液作用下的改性GCL渗透系数均下降。随着离子强度和一价二价离子摩尔数比的增加,改性GCL的渗透系数随之增大。随着膨润土自由膨胀指数的增加,改性GCL的渗透系数随之减小。与自来水渗透情况相比,赤泥渗滤液渗透作用下,改性GCL渗透系数增大4.35~12.0倍。     

土壤—膨润土对金属离子的阻滞性能及机理研究

以K⁺、Ca²⁺和Fe³⁺为研究对象,考察屏障材料Soil-Bentonite (SB)对不同价态金属离子的阻截性能,并对其吸附机理、运移规律和穿透行为进行探讨,为污染场地封存材料设计提供理论依据。研究结果表明:屏障材料SB对不同价态的金属离子的吸附过程快速,且离子价态越高吸附量越大;吸附过程的拟合符合二级吸附动力学和Langmuir-Freundlich方程。K⁺、Ca²⁺和Fe³⁺在SB中渗透时,渗透系数存在极值,离子价态越高则出现极值的时间越短;各种离子在屏障材料中穿透时,离子价态越高,完全穿透屏障墙体所需时间就越短。因此,在污染场地阻截封存时,高价态金属离子的存在会严重影响屏障材料对污染物的阻截性能。     

Investigating factors influencing polymer elution and the mechanism controlling the chemical compatibility of GCLs containing linear polymers

A study was conducted to investigate (1) physicochemical factors that influence polymer elution from GCLs containing a blend of bentonite and linear (water-soluble) polymer (LPB GCLs) and (2) the mechanism that controls the chemical compatibility of LPB GCLs when polymer elutes. A series of hydraulic conductivity (k), free swell and viscosity tests were performed on a commercial LPB GCL using DI water, varying concentrations of NaCl and CaCl?. Comparable tests were also performed on a conventional bentonite (CB) GCL containing the same untreated bentonite and the same physical properties as the LPB GCL. The LPB GCL showed improved swelling and hydraulic performance compared to the CB GCL when permeated with salt solutions. Total organic carbon analysis of the effluents showed that polymer eluted from the LPB GCL regardless of the permeant solution. However, the rate at which polymer eluted increased as the concentration and valence of the dominant cation increased. The rate at which polymer eluted also increased with hydraulic gradient. The mass of polymer retained inside the GCL matrix did not correlate with the k of the LPB GCL. Free swell tests coupled with chemical analysis suggest that, the improved chemical compatibility of the LPB GCL was due to the ability of the polymer to scavenge cations from the solution which allows the bentonite to undergo adequate swelling during the initial hydration period. Analogous to water-prehydrated CB GCLs, the dispersed structure of the bentonite fabric and increased adsorbed water molecules attained during initial swelling controls the k of the LPB GCL when polymer elutes.     

Analytical model for coupled consolidation and diffusion of organic contaminant transport in triple landfill liners

A triple-layer composite liner consisting of a geomembrane liner (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom liner system to isolate the contaminated leachates. In this paper, one-dimensional quasi-steady-state small deformation model (SDSS) was developed to investigate the behavior of organic chemicals transport in landfill composite liner system considering coupled effect of consolidation, diffusion and degradation. The first and second type bottom boundary conditions are used to derive the analytical solutions. The generalized integral transform technique (GITT) is adopted to derive the analytical solutions. The effect of consolidation on the performance of GMB/GCL/CCL with intact or leaking GMB is investigated. The triple liner under double drainage boundary condition (DDBC) has better performance compared to the case under single drainage boundary condition (SDBC). This is because the velocity induced by consolidation under DDBC is lower than that under SDBC. The effect of GCL consolidation shows an opposite trend compared to CCL consolidation. Considering GCL consolidation can increase the breakthrough time. The effective diffusion coefficient of GCL can be two magnitude orders smaller after consolidation, which provides a better diffusion barrier for the chemical transport. The effects of adsorption and degradation have been analyzed as well. Increasing the adsorption capacity of a deforming composite liner can increase the steady-state bottom flux, which shows the opposite tendency compared to the case without considering consolidation. This is due to the fact that for the case of a deforming composite liner, the advection induced by consolidation includes a new term due to the solid velocity. This velocity will result in the increase the mass of chemical migration through the composite liner.