离子强度及pH对不同类型土壤中胶体释放的影响

采用实验室土柱纵向淋溶法,研究了离子强度及pH变化对常熟乌栅土原状、扰动土柱以及东北黑土、江西红壤扰动土柱土壤胶体释放的影响。结果表明离子强度变化对我国不同类型土壤胶体释放影响不同：淋洗液电解质为NaCl时,对于常熟乌栅土以及东北黑土,离子强度减小促进胶体的释放,反之抑制胶体的释放;对于江西红壤,离子强度变化对土壤胶体释放则不产生影响。淋洗液电解质为CaCl2条件下,土壤胶体的释放量低于淋洗液为NaCl,且离子强度变化对三种土壤胶体的释放均不产生明显影响。相同条件下,常熟乌栅土及东北黑土胶体释放量远远大于江西红壤,pH变化则对上述类型土壤胶体释放的影响不明显。研究结果有助于进一步阐明水化学条件的变化对我国不同类型土壤胶体释放的影响规律。     

三峡水库消落带土壤胶体释放与迁移特征

三峡水库消落带是库区陆源污染物进入水库的最后屏障。高强度、周期性的干湿交替对消落带土壤理化性质、结构和可蚀性产生潜在影响,进而影响胶体颗粒的释放和迁移特征。探究消落带土壤胶体的释放与迁移行为是衡量胶体促进污染物迁移入库的重要前提。该研究对比消落带与非消落带土壤,通过原状土柱淋洗试验,研究饱和流中土壤胶体释放及迁移特征。结果表明,消落带原状土柱饱和淋洗液中胶体颗粒浓度先总体快速降低(184.58～28.04 mg/L)再缓慢增加(21.18～97.58 mg/L),存在较大的时间变化(变异系数为0.46)。胶体颗粒累计释放量为714.43 mg,比非消落带土柱高34.4%,而淋洗液的峰值粒径(13.25～19.90μm)和中值粒径(14.98～22.90μm)均远远小于非消落带土柱的相应值,表明反复淹水-排干作用导致消落带土壤中胶体及细颗粒的释放和迁移潜力增大。溶解性有机碳(DOC,Dissolved Organic Carbon)是影响消落带饱和土壤中胶体释放的关键因子,对胶体浓度动态变化的解释率高达42.3%,而水化学因素(EC、Ca~(2+)及Mg~(2+))对非消落带土壤中胶体颗粒的释放影响相对更大。在消落带管理中,应注意减控DOC的流失,以减少消落带土壤胶体颗粒的释放,同时建议加强消落带土壤DOC来源及其与胶体偶合并促进污染物如农化物质迁移进入库区水体的研究。     

水铁矿对磷的吸附及胶体态磷迁移能力预测

土壤中流失的磷进入水体容易引起富营养化污染。目前对于铁矿物胶体结合态磷在土壤孔隙介质中的稳定性和迁移能力的认识还存在不足。本研究采用吸附试验,考察水铁矿对磷的吸附特征以及pH、离子强度和胡敏酸对磷在液相、水铁矿胶体和水铁矿固体上分布的影响;通过DLVO理论,预测水铁矿胶体结合态磷的稳定性和迁移能力。结果表明,假二级动力学模型(R~2=0.964)更适合用于描述磷在水铁矿上的吸附过程,磷在水铁矿上的吸附受液膜扩散、内部扩散和化学吸附等过程控制。Freundlich模型(R2=0.970)对等温吸附的拟合效果好,说明水铁矿对磷的吸附为多层吸附过程。从Langmuir模型参数可知,水铁矿对磷的最大理论吸附量为22.55mg·g~(-1)。水铁矿对磷的吸附能力随pH的升高而降低,随离子强度的升高而升高。然而,低离子强度和高pH有利于反应体系中水铁矿胶体的释放。无论胡敏酸是否存在,在碱性且离子强度不高(1～10mmol·L~(-1))的条件下,有约5%～20%的磷会与水铁矿胶体结合,且这些磷-水铁矿胶体之间的静电斥力较大。根据DLVO理论计算可知,这些带负电荷的胶体之间稳定性较好,在土壤中有一定迁移能力。在实际农业活动中,磷肥的过量施用可能会使大量的磷酸根离子吸附在铁矿物上,促进土壤孔隙水中形成稳定的、带负电的铁矿物胶体,这种磷-铁矿物复合胶体的迁移很可能成为磷迁移的另一种形式。本研究结果可为胶体促进下磷淋失风险评估提供理论和数据支撑。     

原子力显微镜在土壤胶体研究中的应用进展

胶体颗粒是土壤团聚体及土壤结构形成的基础物质,其表面性质及颗粒间相互作用对土壤性质及其肥力作用有着深刻的影响。原子力显微镜（AFM）具有纳米级的分辨率且能够测量物质颗粒间相互作用力的大小,将其应用于土壤胶体研究,可以更加直观、深入地阐明土壤胶体特性、探索土壤胶体作用机理。本文在概要介绍 AFM 的工作原理和特性的基础上,深入探讨了AFM 在测定土壤胶体表面形貌、测定土壤胶体相互作用力方面的研究进展,并对该领域未来的发展进行展望,可为深入揭示土壤胶体颗粒的表面特征及颗粒间相互作用方式、强度和机制,阐明土壤肥力演变过程、污染物在土壤中的迁移机理提供理论参考。     

降雨对土壤胶体释放与迁移的影响研究

降雨作为影响水土流失的主要因子,对表层土壤垂直侵蚀的影响没有得到应有的重视,选取长春地区具有代表性的阶地农田的粘壤土、河漫滩的细砂土和黄土台地的粉壤土为研究对象,用实验室土柱淋滤模拟实验定量研究了降雨对表层土壤中胶体释放与迁移的影响能力,并首次从土壤胶体的释放与迁移的角度解释了土壤的垂直侵蚀作用,从而为长春市水土流失和水土污染防治提供了参考依据.结果表明,土壤环境中降雨对土壤胶体的释放与迁移的影响即对表层土壤垂直侵蚀的影响是不容忽视的,其释放与迁移随降雨周期均具有"脉冲"的规律,在淋滤初期胶体具有比较明显的释放,后来胶体就降到一个较低恒定的水平.降雨通过引起土壤水动力条件和土壤溶液化学两方面变化影响土壤胶体的释放和迁移,初始降雨对土壤表面的侵蚀作用比持续的降雨具有更明显的作用.由于土壤矿物和机械组成不同,降雨对3种土壤的垂直侵蚀程度不同,释放量(垂直侵蚀损失量)为农土土柱>河土土柱>黄土土柱,且介于30-120mg/m~3之间.     

土壤胶体磷环境效应及其影响因素

胶体是磷素在环境中迁移转化的重要载体,土壤胶体磷对磷素生物地球化学循环具有重要作用,其活化迁移对土壤、水环境具有十分重要的影响。本文介绍了国内外土壤胶体磷的分类、分离和分析技术。重点阐述了土壤胶体磷活化、土壤基础理化性质（矿物组成、其他胶体元素、土壤孔隙结构、pH、氧化还原电位）、肥料及土壤改良剂应用对土壤胶体磷环境效应的影响。并针对目前土壤胶体磷流失存在的问题,提出相关对策及展望,以期为后续胶体磷研究和胶体磷污染的治理提供参考。     

恒电荷土壤胶体对Cu2+ 、Pb2+ 的静电吸附与专性吸附特征

供试土壤胶体对Cu2 、Pb2 的吸附强度用pH50 值表示 ,其大小次序为 :土 >黄绵土、黑垆土 >黄褐土。离子强度实验和表面络合反应机制证明恒电荷土壤胶体对Cu2 、Pb2 的吸附含有专性吸附 ,n值可作为判断专性吸附与静电吸附比例的特征值 ,低pH值时 ,以水解 -络合吸附为主 ;高pH值时 ,以水解 -络合与沉淀吸附为主。静电吸附和专性吸附的比例与pH有关 ,各土壤胶体专性吸附百分数大小为 :黄褐土 >土 >黑垆土 >黄绵土。不同土壤胶体在同一介质中对Cu2 、Pb2 的固有络合常数logKintM 值及固有络合ΔG m 负值大小次序与吸附强度大小一致。在定pH定浓条件下 ,考虑离子之间的相互作用时 ,土壤胶体对重金属离子的吸附过程可用BDM等温式描述。供试土壤胶体对Cu2 、Pb2 专性吸附ΔG m 的大小与固有络合ΔG m 接近且大小次序也一致。     

几种物理因素对四氧化三铁纳米颗粒在有机质存在条件下的饱和多孔介质中迁移持留行为的影响

近些年来,环境研究者对纳米颗粒的迁移性进行了部分研究,但是对环境稳定性低、反应活性高的金属氧化物工程纳米颗粒在多孔介质中的运移沉积行为的系统探讨还很不足,尤其是对其在有机质（NOM）存在条件下迁移行为的了解非常有限。本研究选用四氧化三铁磁纳米颗粒（MENPs）作为研究对象,采用填充柱淋溶实验法,对其在饱和多孔介质中的迁移持留行为展开探讨,其目的是考察几种主要介质环境物理因素对其在天然有机质存在条件下的纵向淋溶过程及其在介质中持留量的影响作用。结果显示,不利吸附条件下的MENPs集聚体在多孔介质中的吸附持留及迁移性能取决于多种合力的作用效果。其中,孔隙水流速增大时,MENPs在多孔介质中的迁移性增强,持留性减弱,持留MENPs在介质中的逐层分布随孔隙水流速改变而变化;而且,MENPs在多孔介质中的迁移持留性与介质颗粒的表面物理性质也有关,天然有机质的存在一定程度上可以改善石英砂表面的异质性。另外,介质颗粒粒径大小也是影响MENP-介质间持留机制的重要因子。当多孔介质颗粒粒径大小改变时,MENPs穿透曲线及持留分布曲线随之变化明显,MENPs的吸附沉积机制也相应有所不同。     

土壤团聚状况对Cl~-运移规律的影响

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。     

孔隙水流速对胶体在饱和多孔介质中运移的影响

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。     

Modelling of colloid leaching from unsaturated, aggregated soil

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.     

土壤胶体对砂质土柱中草萘胺迁移的影响

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。     

Transport and re-entrainment of soil colloids in saturated packed column: effects of pH and ionic strength

Purpose

Colloid migration in subsurface environments has attracted considerable attention in recent years because of its suspected role in facilitating transport of strongly adsorbed contaminants to groundwater. The influence of bulk solution pH or ionic strength on model colloid (i.e., latex microsphere, amorphous silica colloids) transport is well established, while little attention has been paid to water-dispersible soil colloids. In this study, saturated packed columns were conducted to explore the mechanism of transport and fate of water-dispersible soil colloids and facilitating transport of Cu during transients in solution chemistry.

Materials and methods

Water-dispersible soil colloids were fractionated from a Cu-contaminated soil sample. Transport of soil colloidal suspensions was conducted with varying pH and ionic strengths, and then, re-entrainment of those retained colloids after completion the transport experiments was conducted by changing pore water solution transient ionic strength and pH conditions. Meanwhile, transport and fate of the Cu strongly adsorbed on the soil colloids were determined under different ionic strength conditions.

Results and discussion

The transport behavior of soil colloids in porous media was found to depend on the pH and ionic strengths of bulk solution. An increase in solution ionic strength and decrease in solution pH resulted in greater deposition which was revealed by the collision efficiency (??). It increased from 0.15 to 1.0 when solution composition changed from 0 to 50?mM NaNO₃ and decreased dramatically from 1.0 to 0.035 as the solution pH converted from 2.97 to 8.94. The results were in agreement with Derjaguin?CLandau?CVerwey?COverbeek theory. Upon stepwise reduction in ionic strength of eluting fluid or enhancement in its pH, a sharp release of colloids retained in the column occurred in each step. Meanwhile, the value of FRE _NaOH that reveals the effect of NaOH solution at pH?11 on the mobilization of retained colloids deposited in the primary minimum increased from 38.6% to 64.6% when the ionic strength of bulk solution changed from 0 to 50?mM NaNO₃ and decreased from 86.7% to 35.8% as the solution pH from 2.97 to 8.94. In addition, the transport and fate of the Cu strongly adsorbed on soil colloids were highly consistent with the results of soil colloids.

Conclusions

The colloid collision efficiency (??) decreased as the pH of bulk solution increased and increased as the ionic strength of bulk solution increased in saturated columns packed with pure quartz sand, and NaOH solution at pH?11 poses a predominant role on mobilization of the retained colloids deposited in the primary minimum. Meanwhile, the strongly adsorbed Cu on soil colloids almost cannot be detached from its carrier under the competition of coexisted cations in the bulk solution and cotransport with its carrier under different ionic strengths.     

胶体态磷和溶解态磷在不同土壤磷饱和度稻田土壤中形态分布

Soil dissolved phosphorus (P) and colloidal P mobilization could be closely related to the degree of phosphorus saturation (DPS). Effects of a wide range of DPS on the distributions of dissolved P and colloidal P in a paddy soil profile were investigated in this study. Dissolved P and colloidal P in water-dispersible soil colloid suspension increased obviously with increasing DPS. The change point of DPS was at 0.12 by using a split-line model. Above the value, dissolved P (3.1 mg P kg-1 ) in soil profile would increase sharply and then transfer downward. Compared with dissolved P, colloidal P was the dominant fraction (78%-91%) of P in soil colloid suspension, and positively related to DPS without a significant change point. The high release of colloids in subsoils with low DPS was attributed to the low ionic strength and high pH value in subsoils. The DPS also had a significant and positive correlation with electrical conductivity (EC), but it showed a negative correlation with pH value. However, the concentration of colloidal P was not greatly correlated to the pH value, EC and optical density of the soil colloid suspension. The results indicated that DPS was an important factor that may affect the accumulation and mobilization of water-extractable colloidal P and dissolved P.     

Stability and transportability of biosolid colloids through undisturbed soil monoliths

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.     

硫酸铝对苏打盐碱土中氟迁移规律的影响

采用土柱淋洗法,研究不同铝氟摩尔比下苏打盐碱土中氟的迁移过程及pH值变化情况。结果表明,苏打盐碱土施铝后,能够明显降低淋洗液的pH值,与空白相比,差异均达极显著水平。并且随着淋洗次数和铝相对含量的增加,pH值呈现逐渐降低的趋势。不同铝氟摩尔比作用下,氟在碱土中的迁移动态及总淋失率存在较大的差别。随着淋洗次数的增加,1∶1处理的每次淋失率变化较缓,(1∶2)～(1∶4)处理呈先增加后降低的趋势,而(1∶5)～(1∶7)处理明显下降。与对照相比,苏打盐碱土上施用硫酸铝可以降低氟在土壤中的总淋失量,进而可以减少土体中的氟向地下水中的迁移,降低人畜通过饮用地下水而带来的摄氟量。但是氟总淋失率的降低程度与铝的相对含量有关,其中1∶4铝氟处理的总淋失率相对较高,而1∶1处理的淋失率相对较低。这可能与添加硫酸铝后苏打盐碱土的pH值变化、铝氧化物和氢氧化物数量变化、土壤胶体带电性变化及土壤自身铝的释放有关。     

Comparability of and Alternatives to Leaching Tests for the Assessment of the Emission of Inorganic Soil Contamination (11 pp)

Goal, Scope and Background

The suitability of leaching tests for the assessment of soil water concentrations is a controversial issue. The aim of this paper is to review and critically discuss the applicability and comparability of leaching tests in the scope of groundwater risk assessment of inorganic contamination and to discuss soil water sampling methods as alternative.

Main Features

First, the theoretical background of leaching tests and the main leaching controlling parameters (pH, redox, ionic strength, reaction kinetics, surface, and speciation) are discussed. Experience with common batch leaching tests (the German DEV S4 test (S4), saturation soil extraction (SSE), ammonia nitrate extraction (ANE), and pHstatic tests) are compiled and an emphasis is set on the comparability of the results of batch leaching tests. Additionally, the comparability between batch tests and column tests is discussed and comparison studies are reviewed. As a feasible alternative, soil water sampling strategies (the suction cup method and centrifugation) are outlined.

Results and Conclusions

For an expedient application of leaching tests, it is crucial to identify the main release controlling parameters, which can be both site and contaminant specific. Possible controlling parameters are, for example, pH, redox conditions, specific surface area of the investigated material, liquid to solid-ratio, ionic strength, cation exchange capacity, DOC, speciation, temperature and contact time. It depends on the release process of the contaminant in the investigated material, which parameters are influencing the release predominantly. The following questions have to be answered: Is the release process availability controlled or solubility controlled and are there kinetic limitations? Suction cups are particularly useful for long-term monitoring. In contrast, centrifugation is a fast and simple method to sample soil water also at larger and heterogeneous sites. SSE or similar batch tests for coarse material are suitable if the soil water cannot be investigated directly. Contaminant concentrations of the SSE fit best to contaminant concentrations in soil water compared to other leaching tests. Concentrations measured with S4 tests are usually significantly lower than in real soil water due to the unrealistically high liquid to solid-ratio. The ANE is used for the evaluation of plant uptake. It does not represent realistic soil water concentrations. Cationic contaminants are usually significantly higher concentrated in ANE eluates. pHstatic tests provide an evaluation of the pH dependency of contaminant release and buffer capacity of the investigated material. It provides indications to release processes and often explains deviations in the results of different leaching tests. Previous practical experience and fundamental research studies show that a conversion of leaching test results, as is proposed by the (already withdrawn) DIN V 19735, is impossible. Correlations of results from different methods, regarding different kinds of materials and different sites, are not significant. This is due to different leaching processes.

Recommendation

. For short-term risk assessment, soil water should be sampled and investigated directly by suction cups (for monitoring purposes) or centrifugation (for inventory purposes). If this is not possible, the SSE or analogous batch tests for coarse material with a narrow L/S ratio should be applied. A suggestion could be a modified saturation soil extraction where a soil column is saturated and the eluate is removed by suction at the bottom of the column. With this method, an unsaturated column test could follow in the same vessel. In order to assess the long-term leaching behavior, total contents of the investigated material have to be taken into account additionally. Furthermore, it is essential to understand the dominant physical and chemical release processes and to figure out the main leaching controlling parameters. Therefore, the following methods are recommended: pHstatic tests at different pH values provide an insight to leaching processes and possible future leaching scenarios. Batch tests similar to the S4 procedure with different L/S ratios are useful to find out whether the release process is solubility or availability controlled. Additionally, this method allows the determination of maximum solubility and maximum availability, respectively. Furthermore, unsaturated column tests provide an insight into leaching processes and releasable amounts even though they require great experimental effort. Other leaching tests like S4 or ANE are not suitable for the estimation of soil water concentrations.     

土霉素在土壤中的垂直迁移及其影响因素研究

采用土柱淋溶法,研究了土霉素在土壤中的垂直迁移特性,探讨了不同土壤类型、淋溶体积、淋溶液pH值、施药量等因素对土霉素在土壤中淋溶迁移的影响。结果表明,在红壤、黑钙土、赤红壤3种不同类型的土样中,土霉素的迁移深度为：赤红壤〉红壤〉黑钙土;土霉素主要富集在土壤表层,其含量随土壤深度增加而明显降低;同一深度的土壤中土霉素含量随着淋溶液体积的增加而增大,随pH值增大而减小;土霉素在土层中的含量分布、淋溶深度与其施药量均呈正相关;当淋溶液中含有一定量的土霉素溶液时,土霉素在土壤中的迁移深度明显增加。