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1.
为探讨可溶性有机质存在条件下黏土矿物胶体对铀(VI)在饱和多孔介质中迁移的影响,选取2种石英砂(细砂和粗砂)分别构建均质构型的石英砂柱,研究了饱和水流条件下腐殖酸存在时高岭石胶体对铀在2种不同粒径石英砂中迁移的影响。结果表明,示踪溶质在2种均质石英砂柱中的穿透曲线相似且分布对称。当在石英砂柱中只通入铀(VI)溶液时,铀(VI)在2种粒径石英砂柱中的穿透量均较小(<25%),此时大量的铀(VI)通过络合作用吸附在石英砂表面上。当通入溶液中存在腐殖酸和高岭石胶体时,铀(VI)在2种石英砂柱中的穿透量增加,且在600~850 μm石英砂中(58.36%)比250~425 μm石英砂中(42.68%)穿透量更多。这充分表明腐殖酸—高岭石胶体和石英砂粒径是影响铀(VI)在地下环境中迁移的重要因素。  相似文献   

2.
在室内条件下采用垂直土柱易混置换法,研究土壤团聚体大小对非反应性溶质(Cl-)迁移的影响,并以相同直径的细砂柱作为对照,揭示土壤团聚状况对溶质迁移的影响规律。结果表明:在相同实验条件下,随着土壤团聚体直径的减小,孔隙水流速、溶液流速均减慢,在介质颗粒粒径为0.25~0.5mm时发现优势流的存在;通过分析比较土柱与砂柱的穿透曲线、运移参数,发现穿透曲线与土壤孔隙分布状况密切相关;随着土壤团聚体直径的减小,Cl-在土柱中的溶质出流推后,淋洗结束提前,水动力弥散系数(Dsh)逐渐减小,说明介质的孔隙构造是影响溶质运移的一个重要因素。  相似文献   

3.
为探讨可溶性有机质存在条件下黏土矿物胶体对铀(Ⅵ)在饱和多孔介质中迁移的影响,选取2种石英砂(细砂和粗砂)分别构建均质构型的石英砂柱,研究了饱和水流条件下腐殖酸存在时高岭石胶体对铀在2种不同粒径石英砂中迁移的影响。结果表明,示踪溶质在2种均质石英砂柱中的穿透曲线相似且分布对称。当在石英砂柱中只通入铀(Ⅵ)溶液时,铀(Ⅵ)在2种粒径石英砂柱中的穿透量均较小(25%),此时大量的铀(Ⅵ)通过络合作用吸附在石英砂表面上。当通入溶液中存在腐殖酸和高岭石胶体时,铀(Ⅵ)在2种石英砂柱中的穿透量增加,且在600~850μm石英砂中(58.36%)比250~425μm石英砂中(42.68%)穿透量更多。这充分表明腐殖酸—高岭石胶体和石英砂粒径是影响铀(Ⅵ)在地下环境中迁移的重要因素。  相似文献   

4.
近年来,很多学者对溶质在多孔介质中的运移机理做了详细研究.溶质在多孔介质中的运移是由孔隙中的对流以及溶质本身的热动力扩散引起的.水动力弥散是指溶质在多孔介质中的运移由两种作用引起,一是由于平均孔隙流速的宏观作用,二是由于各孔隙通道中流速分布相对于平均孔隙流速的不均匀性和溶质在运动过程中的热动力作用.  相似文献   

5.
孔隙水流速对胶体在饱和多孔介质中运移的影响   总被引:2,自引:0,他引:2  
采用室内石英砂柱出流实验和数学模型,研究了流速对自然土壤胶体、蒙脱石胶体和腐殖酸钠胶体在饱和多孔介质中运移的影响。结果表明:孔隙水流速影响着胶体在多孔介质中的运移过程,流速的提高可加速土壤胶体的出流过程,减小蒙脱石胶体和腐殖酸钠胶体的沉积率。胶体的运移过程除受孔隙水流速的影响外,胶体特性的不同亦决定着胶体运移过程的差异,由于胶体表面性质不同,与介质之间的作用力不同,决定了胶体运移过程中的沉积和释放。  相似文献   

6.
孔隙空间对聚苯乙烯胶体滞留与释放的影响   总被引:1,自引:0,他引:1  
为加深孔隙空间对胶体运移影响的认识,在不同pH与离子强度下,研究了胶体在经酸洗或水洗后的玻璃珠或石英砂中的迁移行为。结果表明:粒径相同的玻璃珠与石英砂(0.45~0.60mm)相比,形状一致的玻璃珠形成的孔隙空间(孔隙率0.38)小于石英砂(0.45)。酸洗与水洗后的玻璃珠表面成分变化不大(0~0.6%),经酸洗的介质后能提供更多有利吸附位点。在高pH(10)环境下,石英砂经酸洗或水洗后,胶体滞留量增大(72.1%和69.2%)。提高溶液pH到10后出现的胶体吸附增加,是颗粒接触点、非流动区或低流速区和涡流区滞留等孔隙空间滞留机制引起的,用DLVO理论无法解释。在离子强度为0.001mol/L或0.05mol/L环境下,酸洗石英砂中胶体滞留量比酸洗玻璃珠的分别高16.3%和28.0%,表明介质孔隙空间增大可加强颗粒接触点、非流动区或低流速区和涡流区滞留,然而优先流能够削弱孔隙空间滞留机制对胶体的滞留。此外,超纯水解吸时仅使少量胶体(3.9%)从玻璃珠与石英砂介质的孔隙涡流区中解吸出来,表明涡流区对胶体的保留不是胶体滞留在介质中的主要机制。  相似文献   

7.
紫色土坡耕地土壤大孔隙流的定量评价   总被引:4,自引:0,他引:4  
为阐明大孔隙丰富且孔径呈两极分化的紫色土坡耕地土壤大孔隙流的运移规律,通过室内土柱试验获取耕作层0~20 cm、非耕作层20~40 cm原状土柱和填装土柱的穿透曲线,分析饱和条件下土壤大孔隙流发生规律,并采用解析法CXTFIT软件拟合了水分优先运移参数,PFSP指标(大孔隙流引起的穿透曲线延展量与水动力弥散作用及两区作用引起的延展量的比值)定量评价土壤大孔隙流的贡献率。研究结果表明:1)以填装土柱水流为平衡基质流计算,耕作层0~20 cm原状土柱中大孔隙流的导水贡献率为66.2%~68.5%,而Br-累积淋出量占总淋出量的62.3%~66.1%。对于非耕作层20~40 cm,土壤大孔隙流导水贡献率为0.2%~1.7%,而Br-随大孔隙流运移的比例却达14.5%~20.5%。说明耕作层土壤中大孔隙流现象远比在非耕作层土壤中更为显著;2)PFSP值结果表明大孔隙流作用对穿透曲线延展量的贡献率最大,两区交换运移作用次之,水动力弥散作用的最小。即PFSP值越大,大孔隙流对总水流通量的贡献率越大。  相似文献   

8.
柑橘地土壤溶质优先运移研究   总被引:2,自引:0,他引:2  
通过室内原状土柱与重塑土柱对比实验,应用溶质穿透曲线研究柑橘地土壤优先流及溶质优先运移的特征。结果表明:柑橘地原状土柱土壤穿透曲线表现出了上升阶段的拐点现象,是优先流与基质流共同作用的结果。原状土柱土体穿透曲线下降初期较陡,并表现出了较长的拖尾特征,重塑土柱下降趋势相对稳定。存在优先路径的土体出流速率稳定性较差,变异系数较大,其平均出流速率是重塑土柱出流速率的3.5倍。优先流作用使溶质相对浓度到达峰值的时间缩短了37.7%,此时造成的溶质运移量却是平衡基质流所造成的溶质运移量的2.5倍,因此优先流能够导致土壤溶质的快速大量迁移。  相似文献   

9.
胶体颗粒对不同粒径饱和多孔介质渗透性的影响   总被引:1,自引:0,他引:1  
探讨胶体颗粒在多孔介质中迁移所发生的物理、化学及生物作用过程,在许多学科中具有重要的科学意义。采用室内石英砂柱实验,开展了定水头条件下不同浓度和粒径的胶体颗粒在饱和多孔介质中的运移行为研究。共使用了3种胶体粒径、3种浓度的胶体溶液和3种粒径范围的石英砂。实验表明:多孔介质的相对渗透系数K/K0(K为各时刻计算所得的渗透系数,K0为初始渗透系数)减小程度与颗粒浓度成正比;胶体颗粒越大,越易在表层沉积,而小颗粒易向下部迁移,但总体来看粒径效应没有浓度效应明显;当胶体颗粒在不同粒径的饱和多孔介质中迁移时,粒径大的多孔介质各段K/K0均有明显降低,而粒径小的只在表层变化明显。不同条件下总体相对渗透系数与时间之间呈二次方相关关系,但当多孔介质粒径较小时,相关性不显著。介质渗流流速及砂柱不同位置胶体颗粒浓度变化与介质渗透性变化相对应。用扫描电镜(Scanning Electron Microscope,SEM)进行定性表征,进一步说明胶体颗粒会堵塞多孔介质孔隙影响其渗透性。实验中发现当输入浓度C0小于0.5 g·L–1且dp/Dp>0.018(dp为胶体颗粒粒径,Dp为石英砂算数平均粒径)时,会出现多孔介质局部K/K0增大的现象。  相似文献   

10.
采用饱和与非饱和填充土柱纵向淋溶研究方法,结合对流弥散模型方程(CDE)对穿透曲线的拟合计算,全面考察了土壤介质水饱和度、土壤水pH/离子强度、土壤孔隙水流速和土壤胶体颗粒大小对天然土壤胶体在实际土壤介质中释放、沉积迁移行为的影响。分别获取胶体扩散系数和阻滞因子值,定量说明实验中水化学、水动力学等条件的作用影响力。结果显示,介质不饱和条件不利于胶体的释放和淋溶;高pH和低离子强度条件对土壤胶体释放与迁移有利;淋溶过程的间断干扰,可以促使土壤胶体的增量淋溶释放;淋溶强度及胶体颗粒粒径大小,能够影响胶体穿透时间和穿透浓度峰值大小。  相似文献   

11.
The relative mobility of pyrithiobac [sodium 2-chloro-6-(4, 6-dimethoxypyrimidin-2-ylthio)benzoate], a new herbicide used for postemergence control of broadleaf weeds in cotton (Gossypium hirsutum), was evaluated and compared against that of bromide (Br(-)) tracer on four soils representative of cotton-growing regions using intact soil columns under saturated flow conditions. Pyrithiobac breakthrough curves were asymmetrical in shape with significant tailing and displaced to the left of 1 pore volume in the Houston Black clay (fine, montmorillonitic, thermic Udic Pellustert), Orelia fine sandy clay loam (fine-loamy, mixed, hyperthermic Typic Ochraqualfs), and Ships silty clay (very-fine, mixed, thermic Udic Chromustert) soils. Breakthrough of pyrithiobac in the Hidalgo sandy loam soil (fine-loamy, mixed, hyperthermic Typic Calciustoll) was delayed and more symmetrical, with peak pyrithiobac concentration reached after 1.2 pore volumes. The immobile pore water (IPW) fractions estimated from the Br(-) breakthrough curves ranged from 20 to 87% of total pore water. The IPW values demonstrated that soils with the greatest amount of IPW (Ships with IPW = 87.3%) exhibited the most rapid movement of pyrithiobac (peak concentration after 0.04 pore volume). The experimentally determined pyrithiobac breakthrough curves confirmed the high mobility of this herbicide in these alkaline and predominantly smectitic soils. These results indicate that pyrithiobac mobility was influenced by soil type and preferential flow processes when leached through intact soil columns.  相似文献   

12.
The mobility of fluorescein and bromide used as tracers in packed soil columns was investigated. Five different soils were used in two application methods: soil surface application and soil incorporation, both of which simulate accepted methods of soil application of termiticides to prevent structural infestation. The breakthrough of bromide and fluorescein in column eluates were measured. The absorbance of fluorescein at 492 nm was pH dependent, and proper adjustments were made after measuring the eluate pH. Although high recoveries of bromide from the soil columns were observed, the breakthrough was different among the soil types, indicating that bromide behaves differently in different soils. Recovery of fluorescein, a weak acid, varied depending upon the pH of the soil used, and was only observed in the eluates of two of the five soils tested. Soil treated with bromide and fluorescein followed by soaking extraction showed high recovery of bromide but low recovery of fluorescein, except for in the most alkaline of the soils tested. If fluorescein is used as a conservative tracer in pesticide soil mobility studies, mobility can be underestimated in acidic soils because the active ingredient might travel more quickly than does the fluorescein.  相似文献   

13.
土壤胶体理化性质对其稳定性和可移动性的影响研究   总被引:3,自引:1,他引:2  
商书波  王丰雨  李绪谦 《土壤》2010,42(6):1015-1019
采用长春市具有代表性的阶地农田的黏壤土、河漫滩的细砂土和黄土台地的粉壤土为基质,以提取的土壤胶体为对象,采用实验室模拟方法研究了土壤胶体理化性质对其稳定性和可移动性的影响。研究结果表明3种土壤胶体的临界絮凝浓度(CFC),与伊利石/蒙脱石矿物含量成反比并随着矿物含量的增大而降低,可能是因为伊利石/蒙脱石矿物是易絮凝矿物,水化驱动力及水化后的不稳定性较大;去除游离氧化铁后的农土去铁胶体提高了稳定性,而黄土去铁胶体和河土去铁胶体降低了稳定性,主要是由不同的土壤胶体去除游离氧化铁后性质改变程度不一样引起的;去除有机质后的农土去有机质胶体、黄土去有机质胶体和河土去有机质胶体降低了CFC,并且降低程度是与土壤胶体的有机质含量成反比。  相似文献   

14.
A transfer‐function method is proposed to determine transport parameters from solute breakthrough data. The method is based on the assumptions that a linear process governs the transport of solute through soil and that the soil is homogeneous. It needs breakthrough data at two different vertical locations from a pulse input of solute to the soil. The method predicts the response by convoluting the input with the transfer function in the time domain. Solute breakthrough data were measured in unsaturated soil columns by time‐domain reflectometry (TDR). An experimental soil column was placed over a supporting column filled with sandy soil. A constant hanging water table, maintained in the lower column, created suction in the upper column and maintained unsaturated conditions. A solution of calcium chloride (CaCl2) was spread over the soil in the upper column during steady flow of water in the column. Resident concentrations of solute in terms of electrical conductivity were measured at two depths by TDR sensors. We analysed breakthrough curves of CaCl2 in 81 experiments to determine the transport parameters in coarse sand, sandy loam soil and clay loam soil by the transfer‐function method. The transport parameters obtained were compared with those determined by the widely used deterministic equilibrium model of the CXTFIT program. The transfer‐function method provided a better fit between the measured and estimated breakthrough curves in almost all cases and resulted in stable values of the parameters. The method is robust against small errors in measurements. It is a mathematically sound and efficient method for analysing breakthrough data.  相似文献   

15.
采用室内砂柱模拟试验方法研究了红壤和黑土两种土壤胶体对草萘胺在砂质土柱中迁移的影响。结果表明,整个淋滤过程中红壤和黑土胶体的回收率比较高,分别达到66.76%和74.75%;胶体促进了草萘胺在砂质土柱中的迁移,与对照相比(无胶体),加入红壤和黑土胶体后草萘胺的回收率分别提高了9.82%和10.63%。但是吸附在胶体上迁移的草萘胺数量比较少,只占到迁移总量的1.15%(红壤)和1.68%(黑土),物理非平衡机制可能在迁移过程中起支配作用。  相似文献   

16.
Adsorption and desorption of salmon sperm DNA on four different colloidal fractions from Brown Soil and clay minerals were studied. The adsorption isotherms of DNA on the examined soil colloids and minerals conformed to the Langmuir equation. The amount of DNA adsorbed followed the order: montmorillonite?fine inorganic clay>fine organic clay>kaolinite>coarse inorganic clay>coarse organic clay. A marked decrease in the adsorption of DNA on organic clays and montmorillonite was observed with the increase of pH from 2.0 to 5.0. Negligible DNA was adsorbed by organic clays above pH 5.0. As for inorganic clays and kaolinite, a slow decrease in DNA adsorption was found with increasing pH from 2.0 to 9.0. The results implied that electrostatic interactions played a more important role in DNA adsorption on organic clays and montmorillonite. Magnesium ion was more efficient than sodium ion in promoting DNA adsorption on soil colloids and minerals. DNA molecules on soil colloids and minerals were desorbed by sequential washing with 10 mM Tris, 100 mM NaCl and 100 mM phosphate at pH 7.0. A percentage of 53.7-64.4% of adsorbed DNA on organic clays and montmorillonite was released, while only 10.7-15.2% of DNA on inorganic clays and kaolinite was desorbed by Tris and NaCl. The percent desorption of DNA from inorganic clays, organic clays, montmorillonite and kaolinite by phosphate was 39.7-42.2, 23.6-28.8, 29.7 and 11.4%, respectively. Data from this work indicated that fine clays dominate the amount of DNA adsorption and coarse clays play a more important role in the binding affinity of DNA in soil. Organic matter may not favor DNA adsorption in permanent-charge soil. The information obtained is of fundamental significance for the understanding of the ultimate fate of extracellular DNA in soil.  相似文献   

17.
Chloride transport was investigated in four columns packed with glass spheres, spheres of a cation exchange resin, a loamy sand and a sandy loam, respectively. Using step input, vertical downward flow and relatively high flow-rates, 0.01 m KCl displaced water in the column packed with glass spheres, otherwise 3.33 × 10?4m CaCl2 displaced or was displaced by 3.33 × 10?3m CaCl2. The breakthrough curves of chloride were analysed to give dispersion coefficients and mobile volumes. It was found that (i) chloride exchanged between mobile and immobile region in the sandy loam, (ii) the dispersion coefficient (K) was linearly related to pore flow velocity (U) for the individual columns, and that (iii) the ratio of dispersivity (dK/dU) to median grain diameter increased with increasing standard deviation of the logarithmicnormal grain size distribution.  相似文献   

18.
The migration of colloids in soils can enhance the leaching of strongly sorbing contaminants. We present a model for the simulation of colloid leaching from unsaturated, aggregated soil media under stationary flow. Transport in the intra-aggregate pores is simulated by convection–dispersion, and transport in the interaggregate pores, and a stagnant layer of water surrounding the aggregates, is simulated by diffusion. The model describes the release of colloids from soil aggregates, sorption and desorption processes at the air–water interfaces, and flocculation and subsequent straining from the flowing water. All three processes were simulated as functions of ionic strength. Transport of ions in intra-aggregate pores was simulated by Fickian diffusion. The model was calibrated against experimental results of colloid leaching from columns packed with natural soil aggregates. The aggregates were of two soils differing in organic matter content. On each soil a single calibrated parameter set could describe the experiments with the three ionic strengths. The parameters for release of colloids from the aggregate surface and the sorption properties of the air–water interface were different for the two soils. The key parameters for leaching were the thickness of the stagnant layer of water surrounding the aggregates, the mechanical dispersion, the maximum concentration of colloids at the surface of the aggregates, the sorption capacity and rate coefficient of the colloids at the air–water interface, and the colloid diffusion coefficient. Simulations were also done with two additional irrigation intensities at one ionic strength. Simulated leaching was greater than measured leaching at both irrigation intensities, but the diffusion-controlled release of colloids from the aggregates was simulated correctly.  相似文献   

19.
This study evaluated the stability of water-suspended biosolid colloids fractionated from municipal and agricultural wastes and their transportability through undisturbed soil monoliths. The aim of the study was to assess potential risks posed by dispersed biosolid colloid particles as carriers of contaminants associated with organic waste amendments applied to soils. All biosolid colloids showed remarkable stability over a wide range of pH conditions, with 50–90% remaining in suspension after 24 h. Lime-stabilized biosolid colloids (LSB) were more stable than poultry manure (PMB) and aerobically digested (ADB) biosolid colloids, with pH and organic matter (OM) content being the dominant factors influencing colloid stability. However, increased colloid stability did not always result in greater transportability. In spite of their higher overall stability, LSB colloids showed low transportability potential through undisturbed soil monoliths averaging < 0.1C/C0, probably due to carbonate dissolution and increased ionic interaction with the soil matrix. The ADB and PMB colloids, with the highest OM content, exhibited increased mobility, particularly through soils with significant macroporosity. Breakthrough curves were mostly irregular, suggesting considerable macropore flow and increased interaction with the soil matrix. Eluent pH and EC fluctuations appeared to mainly affect LSB colloid transport, while the mobility of the remaining biosolid colloids was maintained over a wide range of ionic conditions. The findings of this study suggest that some biosolid colloids derived from soil-applied agricultural or municipal wastes may exhibit considerable mobility through soil macropores with potential to migrate to great distances in subsoil environments. Considering the high surface charge and electronegativity of these colloids, they may be a significant vector for hydrophobic contaminant transport and pollution of groundwater resources.  相似文献   

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