Sorption capacity on lead,copper and zinc by clay soils from South Wales,United Kingdom

The sorption capacity of five clay soils from South Wales in the United Kingdom was investigated using two main tests; physico-chemical and batch equilibrium (BET). The physico-chemical property results show that soil weathered mudrocks (MR1), glacial till (GT1), and estuarine alluviums (NEA4, PEA3 and CEA3) are capable of being used as landfill liners and are chosen for further sorption tests. The batch tests (i.e. sorption tests) on soil suspension produce adsorption-pH curves, showing increasing adsorption at higher pH levels. The sorption data are also presented using adsorption isotherm curves and are best fitted using the Langmuir adsorption equation that yields the maximum adsorption capacity of the soils. The sorption capacity of soils are ranked as estuarine alluvium soils>glacial till>weathered mudrocks. Estuarine alluvium soils show a good buffering capacity and high sorption capability compared to glacial till and weathered mudrocks. The study also discovers that the maximum sorption capacities are highly influenced by the chemical properties of the soils.     

A surface complexation and ion exchange model of Pb and Cd competitive sorption on natural soils

The bioavailability and fate of heavy metals in the environment are often controlled by sorption reactions on the reactive surfaces of soil minerals. We have developed a non-electrostatic equilibrium model (NEM) with both surface complexation and ion exchange reactions to describe the sorption of Pb and Cd in single- and binary-metal systems over a range of pH and metal concentration. Mineralogical and exchange properties of three different acidic soils were used to constrain surface reactions in the model and to estimate surface densities for sorption sites, rather than treating them as adjustable parameters. Soil heterogeneity was modeled with >FeOH and >SOH functional groups, representing Fe- and Al-oxyhydroxide minerals and phyllosilicate clay mineral edge sites, and two ion exchange sites (X⁻ and Y⁻), representing clay mineral exchange. An optimization process was carried out using the entire experimental sorption data set to determine the binding constants for Pb and Cd surface complexation and ion exchange reactions.Modeling results showed that the adsorption of Pb and Cd was distributed between ion exchange sites at low pH values and specific adsorption sites at higher pH values, mainly associated with >FeOH sites. Modeling results confirmed the greater tendency of Cd to be retained on exchange sites compared to Pb, which had a higher affinity than Cd for specific adsorption on >FeOH sites. Lead retention on >FeOH occurred at lower pH than for Cd, suggesting that Pb sorbs to surface hydroxyl groups at pH values at which Cd interacts only with exchange sites. The results from the binary system (both Pb and Cd present) showed that Cd retained in >FeOH sites decreased significantly in the presence of Pb, while the occupancy of Pb in these sites did not change in the presence of Cd. As a consequence of this competition, Cd was shifted to ion exchange sites, where it competes with Pb and possibly Ca (from the background electrolyte). Sorption on >SOH functional groups increased with increasing pH but was small compared to >FeOH sites, with little difference between single- and binary-metal systems. Model reactions and conditional sorption constants for Pb and Cd sorption were tested on a fourth soil that was not used for model optimization. The same reactions and constants were used successfully without adjustment by estimating surface site concentrations from soil mineralogy. The model formulation developed in this study is applicable to acidic mineral soils with low organic matter content. Extension of the model to soils of different composition may require selection of surface reactions that account for differences in clay and oxide mineral composition and organic matter content.     

Interaction of fluoride with hydroxyaluminum-montmorillonite complexes and implications for fluoride-contaminated acidic soils

In acidic soils and aquatic environments, polymeric hydroxyaluminum (HyAl) cations with various OH/Al ratios are ubiquitous. Hydroxyaluminum-montmorillonite (HyAl-Mt) complexes are widely distributed in acidic to slightly acidic soils and aquatic environments. The fixation of HyAl cations on Mt can significantly modify the mineralogical and electrochemical properties of the host clay, thereby substantially influencing adsorption/desorption and transport of many nutrients and pollutants. In the present study, HyAl-Mt complexes were synthesized through adsorption of polymeric HyAl cations with OH/Al ratio of 1.6 on Na-saturated Mt (Na-Mt). Interaction of F⁻ with HyAl-Mt was investigated in acidic conditions and the environmental implications for F⁻-contaminated soils were also addressed. Results indicated that the effects of pH on F⁻ sorption by HyAl-Mt were slight in the pH range of 5.0–9.0, whereas sorption increased rapidly with decreasing pH when pH was below 4.5. At initial pH >4.0, ligand exchange was the main mechanism for F⁻ sorption. At initial pH 3.02 and high initial F⁻ concentrations, several synergic mechanisms, such as coprecipitation, scavenging and surface adsorption were involved in F⁻ removal from solution, which resulted in an abrupt and discontinuous increase in sorption capacity of HyAl-Mt for F⁻ with increasing initial F⁻ concentration, and a slight dependency of F⁻ sorption on HyAl-Mt dosage. Compared with Na-Mt, sorption capacities of HyAl-Mt for F⁻ were significantly enhanced by interlayering and coating with polymeric HyAl cations. HyAl-Mt would be important natural scavengers for F⁻. The presence of HyAl-Mt in acidic soils could greatly retard F⁻ transport and bioavailability in soil environments. Interaction of F⁻ with HyAl-Mt may mitigate acidification of F⁻-contaminated acidic soils. Application of synthetic HyAl-Mt may be one alternative for remediation of acidic F⁻-contaminated soils.     

Sorption of Th(IV) on Na-rectorite: Effect of HA, ionic strength, foreign ions and temperature

The sorption of Th(IV) on Na-rectorite as a function of pH, ionic strength, temperature, soil humic acid (HA) and foreign ions was studied by using a batch technique under ambient conditions. The results indicated that the sorption of Th(IV) on Na-rectorite is strongly depended on pH, ionic strength and temperature. The presence of HA enhanced Th(IV) sorption at low pH and had no obvious effect on Th(IV) sorption at high pH. The sorption of Th(IV) decreased with increasing temperature, indicating that the sorption process of Th(IV) on rectorite was exothermic. Sodium-rectorite and HA were characterized by acid–base titration to obtain the pK_a, and the constant capacitance model (CCM) modeled the sorption data very well with the aid of FITEQL 3.2. HA/Th(IV) addition sequences affected Th(IV) sorption in the ternary systems. The sorption of Th(IV) on Na-rectorite may be dominated by surface complexation, while cation exchange also contributes partly to the sorption.     

岩溶区典型土壤对Cd2+的吸附特性

文章采用有序批试验,就岩溶区两种典型石灰土（棕色、黑色石灰土）对Cd2+的吸附行为进行研究。试验结果表明:石灰土对重金属Cd2+具有较强的吸附能力（平均吸附率范围89.84~98.84）,黑色石灰土的吸附能力高于棕色石灰土,吸附量随平衡浓度的增加而增大;Langmuir和Freundlich方程均能很好地描述两种石灰土对Cd2+的等温吸附过程,Freundlich方程拟合最优;两种石灰土吸附镉的动力学特征相似,吸附过程可分为快速反应、慢速反应和吸附平衡3个阶段,棕色石灰土对Cd2+吸附动力学的最优模型为Elovich方程和双常数方程（R>0.9）,黑色石灰土仅在Cd2+初始浓度为100 mg/L条件下,Elovich方程、双常数方程和W-M方程的模拟达到较显著水平（R>0.8）;有机质、碳酸钙含量及CEC值是影响石灰土对Cd2+吸附能力的主控因素,铁、铝、硅氧化物含量对Cd2+吸附影响不大;综合热力学、动力学及影响因素分析认为石灰土对Cd2+吸附机理包括土壤颗粒表面官能团的专性吸附及不均匀粒内扩散、静电作用等非专性吸附过程。      

The development of a multi-surface soil speciation model for Cd (II) and Pb (II): Comparison of two approaches for metal adsorption to clay fractions

The mobility of toxic metals in soils or sediments is of great concern to scientists and environmentalists since it directly affects the bioavailability of metals and their movement to surface and ground waters. In this study, a multi-surface soil speciation model for Cd (II) and Pb (II) was developed to predict the partition of metals on various soil solid components (e.g. soil organic matter (SOM), oxide mineral, and clay mineral). In previous study, the sorption of metal cations on SOM and oxide minerals has been evaluated by thermodynamically based surface complexation model. However, metal binding to soil clay fractions was normally treated in a simplistic manner: only cation exchange reactions were considered and exchange coefficient was assumed unity. In this study, the binding of metals onto clays was described by a two-site surface sorption model (a basal surface site and an edge site). The model was checked by predicting the adsorption behavior of Cd (II) and Pb (II) onto three selected Chinese soils as a function of pH and ionic strengths. Results showed that the proposed model more accurately predicted the metal adsorption on soils under studied condition, especially in low ionic strength condition, suggesting that adsorption of metals to soil clay fractions need to be considered more carefully when modeling the partition of trace elements in soils. The developed soil speciation model will be useful when evaluating the movement and bioavailability of toxic metals in soil environment.     

Effects of organic matter heterogeneity on sorption and desorption of organic contaminants by soils and sediments

This review highlights the major progress over the last decade on characterization of geochemically heterogeneous soil/sediment organic matter (SOM) and the impacts of SOM heterogeneity on sorption and desorption of hydrophobic organic contaminants (HOCs) under equilibrium and rate limiting conditions. Sorption and desorption by soils and sediments are fundamental processes controlling fate and transport of less polar and nonpolar organic pollutants in surface aquatic and groundwater systems. Recent studies have shown that soils and sediments exhibit an array of HOC sorption phenomena that are inconsistent with an early partition model based on an assumption of homogeneous gel-like SOM. Increasing data have revealed that isotherm nonlinearity, varied sorption capacity, sorption–desorption hysteresis, and slow rates of sorption and desorption are characteristics for HOC sorption by soils and sediments. These phenomena have been shown to result from different types of condensed SOM that exhibit capacity limiting sorption processes. Recent findings of glass transition phenomena and the nonlinear HOC sorption by humic acids provide a scientific foundation for drawing an analogy between humic acids and synthetic organic polymers that supports a dual mode model for sorption by soils and sediments. Humic acid is glassy or rigid at temperatures lower than its glass transition temperature and exhibits relatively nonlinear sorption isotherms for HOCs. Fractionation and quantification of SOM indicate that soils and sediments contain significant amounts of black carbon and kerogen of different origins. These particulate organic materials have rigid 3-dimensional structures and are often less polar compared to humic substances. Limited studies show that black carbon and kerogen exhibit nonlinear sorption for HOCs and may dominate the overall nonlinear sorption by soils and sediments.     

Sorption behavior of heavy metal pollutants onto shales and correlation with shale geochemistry

The sorption of lead (II) and cadmium (II) on seven shales belonging to the Proterozoic Vindhyan basin, central India, and a black cotton soil, Mumbai, India, was studied and compared with sorbent geochemistry. The sorption equilibrium studies were conducted under completely mixed conditions in batch reactors (pH=5.0 and ionic strength= 0.01 M) at room temperature. The Freundlich model provided better fits to the experimental data compared to Langmuir model. High cadmium and lead sorption was observed for the calcareous shales with greater than 5% CaCO₃. The Freundlich isotherm parameter relating to sorption capacity, i.e., K_F, yielded a strong correlation with the calcium carbonate and calcium oxide content across the various geosorbents studied. The observed sorption pattern may be attributed to complex formation of CaCO₃ with Pb²⁺ and Cd²⁺ leading to surface precipitation. Moreover, the Ca²⁺ present in the sorbents may also involve in ion exchange reaction with lead and cadmium.     

Sorption kinetics of naphthalene and phenanthrene in loess soils

A laboratory study was executed to investigate the effect of surfactants to enhance sorption of polycyclic aromatic hydrocarbon (PAH) contaminants in loess soil. Phenanthrene and naphthalene were chosen as organic contaminant indicators in loess soil modified by the cation surfactant hexadecyltrimethylammonium (HDTMA) bromide. The kinetic behavior of sorption during transport in natural and modified loess soil was studied. The results indicated that sorption rate in the cation surfactant modified loess soils was at least 3 times faster than that of the natural soil. A first-order kinetics model fitted the sorption data well for both soils. The sorption rates of the two organic compounds were related to their primary residual quantity on the soils. The experiments showed that sorption amounts approached constant values approximately within 30 and 90 min for naphthalene and phenanthrene at 298–318 K, respectively. The rate constants, however, displayed negative correlation with increasing temperature. With changing temperature, the activation energy was calculated at –6.196–1.172 kJ/mol for naphthalene and –28.86–15.70 kJ/mol for phenanthrene at 298–318 K. The results can be used to predict the sorption kinetics of phenanthrene and naphthalene in loess soils, and in a wider perspective, be used to better understand the transport of petroleum contaminants in the soil environment.     

Distribution of branched tetraether lipids in geothermally heated soils: Implications for the MBT/CBT temperature proxy

Branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids occur in soils and peat bogs and are assumed to be produced by anaerobic bacteria. Two indices based on the distribution of these lipids in soils, the Cyclisation of Branched Tetraethers (CBT) and the Methylation of Branched Tetraethers (MBT) index have been shown to linearly relate to pH, and to mean annual air temperature (MAT) and pH, respectively. To directly evaluate the impact of changes in soil temperature on the MBT/CBT proxy, we determined these indices in soils sampled from a transect away from two hot springs in California, which provided a set of soils similar in composition but with different temperatures (12–41 °C). The CBT values of these geothermally heated soils show a good relation with pH (R² 0.76), similar to that of a global MBT/CBT calibration set. Also, the relationship between MBT, soil pH and temperature for the geothermally heated soils is similar to that of a global soil calibration set, although the intercept for the geothermally heated soils is significantly lower, likely because our data set is based on in situ soil temperatures rather than MAT. The results confirm the dependence of the MBT index on soil temperature and pH and support the applicability of the MBT/CBT indices as a proxy for continental palaeotemperatures and past soil pH.     

Sorptive stabilization of organic matter in soils by hydrous iron oxides

Strong correlations between iron oxides (FeOx) and organic matter (OM) in soils have implied the importance of the former in stabilizing the latter. One mechanism thought to be important in this stabilization is sorption. We tested this possibility by reductively dissolving FeOx in a wide variety of soils and measuring the organic carbon (OC) that was solubilized. The OC dissolved from non-FeOx phases via anion exchange was corrected for by parallel control extractions. The resultant pool, reductively soluble OC, made up a minor amount of total soil OC in all but one of these soils, indicating that simple sorption reactions do not stabilize the bulk of soil OC in most mineral soils. OC:Fe ratios in the extracts from 2/3 of these soils were less than 0.22 (wt/wt), consistent with a sorbed state for this OC and showing that OC sorption by FeOx in these soils is limited by the amount of FeOx. The remaining soils had low pH and high OM concentrations; their higher OC:Fe ratios indicate inclusion of precipitated organo-Fe complexes in the extracts, which are likely only partially extracted by our method. The high volumetric ratios of OM to FeOx found in correlations between them from the literature are inconsistent with a dominant sorption control and point instead to stabilization to other mechanisms such as organo-Fe complexes or ternary associations among FeOx, OM and other minerals.     

Sorption and distribution of adsorbed metals in three soils of India

The mobility and bioavailability of heavy metals depends on the metal retention capacity of soil and also on the geochemical phases with which metals are associated. Laboratory batch experiments were carried out to study the sorption and distribution of Cd, Ni and Pb in 3 soils differing in their physicochemical properties from India: Oxyaquic Haplustalf (SL1), Typic Haplustalf (SL2) and Typic Haplustert (SL3). The heavy metal adsorption was studied by isotherms and the distribution coefficient (K_D) for each metal was obtained from the linear regressions of the concentration of metal remaining in equilibrium solution and the amount adsorbed. In general, the sorption capacity for all the metals decreased in the order: SL3>SL2>SL1. Among metals, the sorption capacity in all the soils decreased in the order: Pb>>Ni>Cd. Distribution of sorbed metals at various equilibrating concentrations was studied by sequential extraction. Results showed significant differences in the distribution of metals in these soils. At higher additions (such as 200 μM l⁻¹) most of the metals were extracted in their more mobile fractions, exchangeable and/or inorganic in contrast to their original partitioning in soils, where they were preferentially associated with the less mobile residual fraction. Largest percentages of metals extracted in the exchangeable fraction corresponded to those soil–metal systems with smaller K_D values, e.g. Cd, Ni and Pb in SL1 and Cd and Ni in SL2. In neutral and alkaline soils (SL2, pH=7.1, and SL3, pH=8.6) Pb was predominantly extracted from the inorganic fractions and this corresponded to higher K_D values for Pb in these soils. The predominance of metals associated with the exchangeable fraction together with low K_D values indicates higher mobility of metals retained in the acidic soil (SL1, pH=5.2) compared with the others.     

Phosphorus transport in shallow groundwater in peri-urban Kampala, Uganda: results from field and laboratory measurements

To understand Phosphorus (P) sources and transport processes in the subsurface in Bwaise III Parish, Kampala, P attenuation and adsorption capacities of soils were studied in situ and from laboratory measurements. Relationships between sorption parameters and soil matrix properties, rates and mechanism of the adsorption process and soil P fractions were also investigated. P was generally higher in the wet than the dry season, but for both seasons, the maximum was 5 mgP/l. P transport mechanisms appeared to be a combination of adsorption, precipitation, leaching from the soil media and by colloids with the latter two playing an important role in the wet season. The sorption process comprised two phases with the first stage rate constants being about fourfold those of the second stage. The Langmuir isotherm described the sorption data well (R ² ≥ 0.95) with the second soil layer exhibiting the highest sorption maximum (C _max) (average value 0.6 ± 0.17 mgP/gDW). The best prediction of C _max had organic carbon, Ca, available P and soil pH. Residual P consisting mostly of organics was the main fraction in all the layers followed by inorganic HCl-P and NaOH-P in the top and middle layers, respectively. Loosely bound P (NH₄Cl-P) was the least fraction (<0.4% of total P) in all layers indicating the high binding capacity of P by the soils. The study results suggest that P dynamics is related to Ca, Fe and organic carbon content of the soils.     

Contribution of lipids to the nonlinear sorption of polycyclic aromatic hydrocarbons to soil organic matter

The sorption isotherms of benzene, naphthalene, fluorene and phenanthrene for a suite of whole and lipid-extracted soils are presented. The sorption of benzene to two different peats displays linear characteristics which are consistent with the partitioning model of sorption. The sorption of the PAHs to three different mineral soils show marked nonlinear character. The nonlinear sorptive character of the soil organic matter can be described by site specific sorption occurring within the soil organic matrix. Removal of the lipids via Soxhlet extraction increases the nonlinear character of the sorption isotherms as well as doubles the sorptive capacity of the mineral soils for the PAHs studied. This indicates that the lipids naturally present in the soil strongly compete for hydrophobic sorption sites present in the soil organic matter matrix.     

Inorganic arsenic sorption by drinking-water treatment residual-amended sandy soil: effect of soil solution chemistry

Previous studies in our laboratory have demonstrated that drinking-water treatment residuals are effective sorbents of arsenic V. However, the effect of soil solution chemistry on arsenic V sorption by drinking-water treatment residuals-amended soils remains to be explored. The current study uses a batch incubation experimental set up to evaluate the effect of soil solution pH, competing ligands, and complexing metal on arsenic V sorption by a sandy soil (Immokalee series) amended with two rates (25 and 50 g kg^?1) of aluminum and iron-based drinking-water treatment residuals. Experiments were conducted at three initial arsenic loads (125, 1,875, 3,750 mg kg^?1) and a constant solid: solution ratio of 200 g L^?1. An optimum equilibration time of 8 days, obtained from kinetic studies, was utilized for sorption experiments with both aluminum and iron drinking-water treatment residual-amended soil. Presence of phosphate decreased arsenic V sorption by both aluminum and iron drinking-water treatment residual amended soils, with a strong dependence on pH, drinking-water treatment residual types, drinking-water treatment residual application rates, and phosphate concentrations. Addition of sulfate had no effect on arsenic V sorption by aluminum or iron drinking-water treatment residual-amended soil. A complementing effect of calcium on arsenic V sorption was observed at higher pH. Results elucidating the effect of soil solution chemistry on the arsenic V sorption will be helpful in calibrating drinking-water treatment residual as a sorbent for remediation of arsenic-contaminated soils.     

有机组分土-水分配系数的确定(英文)

有机组分的土水分配系数(Kd)是描述有机组分在地下系统中吸附特征的重要参数。同时,它也是物质运移模拟和环境评价中的主要参数之一。影响Kd的因素可概括为三个方面:土壤性质、有机组分本身特征及水相的物理化学性质。一般而言,对于非极性和弱极性有机组分,土壤中的有机质含量(foc )是影响Kd的最主要因素。但是,对于极性有机组分(POCs), 特别是在土壤有机质含量较低的情况下,土壤中矿物的种类和含量、水化学组分特征(pH、离子力等)经常在吸附过程中起重要作用。实验室内测定Kd的方法包括批实验和柱实验方法。批实验法适用于研究Kd较高情况下的吸附。在Kd较低的情况下,如低有机质土壤对极性有机污染物的吸附,土柱色谱法(SCC)是更适宜的选择。另外,可用土柱色谱法快速了解各种因素对吸附过程的影响,并获取详细的吸附和解吸信息。应用土柱色谱法时应当注意非平衡吸附和可能的柱堵塞问题。很多文献中提到结合柱实验和已有的吸附数据来预测土壤有机碳标准化的分配系数Koc(=Kd/foc)。但是,如果没有考虑吸附中特定的作用过程(如矿物吸附),对极性有机组分Koc的预测将会产生很大的误差。在环境评价中,将从一种土壤测定的Koc 应用到不同性质的土壤中,可能会导致错误的认识。在进行室内实验时,应把标准土(如Eurosoi     

Effects of soil type and fertilizer on As speciation in rice paddy contaminated with As-containing pesticide

Inorganic arsenic (As) pesticides have been widely used for decades in many countries. However, insufficient data are available on the chemical speciation of inorganic arsenicals in tropical paddy soils. Inorganic As-containing pesticides were used in tropical countries, a few decades ago, however, their fate have not been studied. Hence, the objective of this study was to determine fractionation of inorganic arsenicals and to assess As lability with/without fertilizer application using a static incubation experiment. Eight soils from wet and dry regions of Sri Lanka were amended with 1,000 mg/kg arsenate for this purpose. The FT-IR and XRF results suggested that soils in the wet region were rich in Fe/Al-oxides. Paddy soils in the dry zone showed high As lability. These low-humic gley soils have low Fe/Al oxyhydroxide and alkaline pH. In contrast, the wet zone had soils with higher As retention capacity, high amounts of Fe/Al oxyhydroxide, and acidic pH. Arsenic lability increased considerably 30 days after fertilizer application. Overall, As lability was mainly influenced by soil mineralogical and chemical properties, i.e., Fe/Al oxyhydroxide, pH, organic matter, and fertilizer application.     

Adsorption Behavior of Hexavalent Chromium in Vadose Zone

Adsorption behavior of Cr (VI) in vadose zone, which is silty clay and clayey soil, was studied through kinetics experiments, isothermal adsorption experiments under various conditions, including different ph, temperature and organic contents. The results from kinetics experiments showed that the sorption progress of Cr (VI) has clear features in different stages, and adsorption equilibrium showed at 30 min, the adsorption rate of silty clay and clayey soil were 60%. The isothermal adsorption curve of Cr (VI) fitted closely with Freundlich equation model. When pH is 3-5 a plateau were seen, thereafter with increase in pH the adsorption rate of Cr (VI) dropped sharply and the minimum achieved at pH 10, the adsorption rate were only 35%. Adsorption rate of Cr (VI) increased gradually with the increase of temperature, the temperature of vadose zone is 14.7 ℃, according to the experimental results, the adsorption rate of Cr (VI) is about 40%. The use of organics represents an important contribution to the sorption of Cr (VI), sorption rate up to 100% when 30% of organic content. These studies will provide basis for manager to minimize the impacts, and provide basic data for pollution prevention and remediation of vadose zone.     

Using different amendments to reduce heavy metals movement in soils

With long-term use of sewage waste, heavy metals can accumulate to phytotoxic levels and resulted in reduced plant growth and/or enhanced metal concentrations in plants, as a result food chain. If these metals penetrate too rapidly in a particular soil, especially with high water table, they can pollute ground water supplies. The aim of this research is prevention of movement of waste water-borne heavy metals in soils of southern parts of Tehran. These waste waters are used for irrigation of agricultural lands at southern regions since many years ago. For this purpose, 6 soil samples from southern parts of Tehran city and 2 ones from Zanjan city without lime and organic matter were selected. In laboratory, sorption capacities of the soils for Ni, Cd and Pb were compared with those of calcite, Nabentonite, zeolite, illite and hematite amendments. The method was carried out by equilibration of known quantities of these adsorbents and soils with solutions containing these elements. The results showed that among the 5 amendments, calcite and Na-bentonite had the greatest sorption percentages of the 3 elements and illite had the least one. The retention capacity of calcite and Na-bentonite for Cd was highest in all 8 soils. However, retention capacities of these 2 minerals for Pb and Ni were higher than those of loamy soils without lime and organic matter and also sandy soils. Because of abundance and low price of calcite, this amendment is preferred to Na-bentonite. Therefore, calcite is recommended for adding to soils with low sorption capacity of Ni, Cd and Pb.     

黏性土渗透性温度效应实验研究

由于全球气候变暖、城市热岛效应加剧和核废料地质处置等原因,温度对黏性土工程性质的影响日益受到关注。本文在实验的基础上,采用直接测量法,对南京下蜀土、淤泥质土以及混合土3种试样,进行了5°～45°温度下的变水头渗透实验,分析了温度对黏性土渗透性的影响。实验结果表明:温度对3种试样的渗透性均有较大影响。温度越高,渗透性越大;试样的密度越大,渗透系数随温度变化率越低;在3种试样中,混合土的渗透系数高于淤泥质土和下蜀土的对应值,而淤泥质土的渗透系数又略大于下蜀土。最后对黏性土渗透性的温度效应机理进行了分析,认为水的动力黏滞性,黏粒的双电层厚度以及土的微结构三方面因素的共同作用引起了黏性土渗透性的温度效应。