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1.
A two-parameter mathematical model based on some physical assumptions was developed for the adsorption of water vapor by soils: W = W mh[(p/p 0) − (p/p 0)3 + (p/p 0)6] + W res. It was shown that one of the model’s parameters is close to a conventional soil-hydrological constant, namely, the maximum hygroscopic moisture, or maximum hygroscopicity W mh. The second parameter reflects the residual water content W res as the content of immobilized water, which is bound to the most active part of the adsorbing surface, is adsorbed at the initial stage of adsorption (0 ≤ p/p 0 ≤ 0.05), and later does not participate in the adsorption processes. Methods were proposed for the differential calculation of singular points and parameters of the model corresponding to the characteristic physical phenomena of water vapor adsorption in soils. The model was tested for the quantitative assessment of the interaction between the soil solid phase and the water vapor in different soils (a soddy-strongly podzolic soil, an ordinary chernozem, a chestnut soil, and a medium-columnar solonetz). A method was proposed for calculating the integral adsorption energy E max of the soil solid phase-water vapor interaction. It was shown that the E max values are determined by the physicochemical properties of the soils and characterize the capacity of the separate soil horizons for adsorbing water vapor. The relationship of the integral adsorption energy of the soils with the relative pressure of the water vapor and the water content was studied.  相似文献   

2.
This study investigated the effect of different farming practices over long time periods on the sorption‐desorption behavior of Cu, Cd, and Zn in soils. Various amendments in a long‐term field experiment over 44 y altered the chemical and physical properties of the soil. Adsorption isotherms obtained from batch sorption experiments with Cu, Cd, and Zn were well described by Freundlich equations for adsorption and desorption. The data showed that Cu was adsorbed in high amounts, followed by Zn and Cd. In most treatments, Cd ions were more weakly sorbed than Cu or Zn. Generally, adsorption coefficients KF increased among the investigated farming practices in the following order: sewage sludge ≤ fallow < inorganic fertilizer without N ≈ green manure < peat < Ca(NO3)2 < animal manure ≤ grassland/extensive pasture. The impact of different soil management on the sorption properties of agricultural soils for trace metals was quantified. Results demonstrated that the soil pH was the main factor controlling the behavior of heavy metals in soil altered through management. Furthermore, the constants KF and n of isotherms obtained from the experiments significantly correlated with the amount of solid and water‐soluble organic carbon (WSOC) in the soils. Higher soil pH and higher contents of soil organic carbon led to higher adsorption. Carboxyl and carbonyl groups as well as WSOC significantly influenced the sorption behavior of heavy metals in soils with similar mineral soil constituents.  相似文献   

3.
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4.
Amounts of inorganic phosphate (P) sorbed by two unfertilized soils, during times less than required to reach equilibrium, were affected by the ionic strength and cation species of the matrix solution. For non-equilibrium conditions the amounts of P sorbed increased with increasing ionic strength and were greater with Ca2+ than Na+. For higher P additions, resulting in equilibrium solution P concentrations greater than 30 to 40μrnole 1?1, the effects of the matrix solution on P sorption were maintained at equilibrium, whereas at lower P additions the dependence of sorption on matrix solution composition was eliminated at equilibrium. Equilibrium sorption isotherms for each soil and matrix solution were described by three Langmuir equations, which corresponded to distinct concentration ranges or regions (I, II, and III) on the overall isotherm. The free energies of sorption (ΔG) for each region, were essentially independent of the soil matrix solution. The sorption maxima for regions I and II of the isotherm for a particular soil were also virtually independent of the matrix solution used. The sorption maximum for region III, however, was markedly dependent on the matrix solution, implying a potential-determining (p.d.) sorption mechanism.  相似文献   

5.
Abstract

Phosphate sorption isotherms were determined for 16 representative major soils developed from different parent materials on Okinawa. Phosphate sorption characteristics were satisfactorily described by the Langmuir equation, which was used to determine phosphorus (P) sorption maxima of the soils. Phosphate sorption maxima ranged from 630 to 2208 mg P kg‐1 soil (mean 1,362 mg P kg‐1). The standard P requirement (i.e., the amount of P required to attain 0.2 mg P L‐1 equilibrium solution) followed the same trend as sorption maximum (r =0.94***), with values ranging from 132 to 1,020 mg P kg‐1 soil (mean 615 mg P kg‐1). This mean value corresponds to fertilizer addition of 923 kg P ha‐1 indicating that the soils have high P fertilizer requirements. Results of simple linear regression analysis indicated that sorption maximum was significantly correlated with clay content, organic matter, oxalate iron (Fe), pyrophosphate Fe, DCB aluminum (Al), oxalate Al, and pyrophosphate Al, but not with DCB Fe, pH, or available P content. The best regression model for predicting sorption maximum was the combination of clay, organic matter, pyrophosphate Fe, and DCB Al which altogether explained 79% of the variance in sorption maximum. The equation obtained could offer a rapid estimation of P sorption in Okinawan soils.  相似文献   

6.
Abstract

Phosphate (P) sorption isotherms have been widely used to characterize the P status and to establish fertilizer requirements of soils. Recently, mechanistic models have successfully described the nutrient uptake by plants under changing soil and plant parameters. Phosphorus sorption characteristics of eleven representative soils of the Appalachian Region of the United States were evaluated, and experimental P adsorption data were fitted to Temkin, Freundlich, and Langmuir equations to determine the relative importance of the soil parameters in P retention and supply to plant roots. The Barber and Cushman model was used to predict the effect of P fertilization on P uptake by plant. The soils of Appalachia differ considerably with respect to the retention of added P. All three isotherm equations gave good fit with the experimental data and were reliable to describe the P quantity/ intensity relationships of these soils. The following sequence of P adsorption capacity in various soils was established: Tate (BA)? Hayesville (Bt) > Westmoreland (Bt2) ～ Upshur (Btl) ～ Gilpin (A) > Lily (A) ～ Dandridge (E) ～ Watauga (Ap) > Ashe (A) ～ Berks (A) ～ Dekalb (A). In spite of the great differences among soil properties related to surface area and degree of weathering of these soils, the content of free iron (Fe) oxides was the only soil property that correlated with the constants of the isotherm equations. Amounts of P required to give 0.20 μg P/mL varied with soils and were closely related to the constants of the isotherm equations. Soil P parameters from the P adsorption isotherms were used to determine a measure of Cli, b, and De instead of those used conventionally in the Barber and Cushman (1981) model to predict P uptake by corn. Predicted P uptake by corn varied with soils, even at the same P concentration in equilibrium solution (0.20 μg P/mL) or when an equal amount (90 μg P/mL) of P was added to all soils. Predictions of P uptake, however, were not correlated with the amount of P required to give 0.20 μg P/mL in 0.01M CaCl2 solution or with the constants of the isotherm equations used. Diffusion coefficient and equilibrium P concentration in solution, and two intensity factors, were more important than buffer power in predicting P supplied to roots. These findings may help to explain the lack of significant correlations between the constants of the P isotherm equations and P uptake.  相似文献   

7.
New analytical solutions are proposed for the problem of the convective-dispersion transfer of salts in a soil layer of finite and semifinite thickness at the boundary conditions of the first and third kinds on the soil’s surface under the alternating (pulsating) impact of washing water. Numerical studies (computer experiments) of the salt transfer equation were performed for the equilibrium sorption and linear sorption isotherms in soils with deep and shallow groundwater tables and for nonequilibrium irreversible sorption (characterized by biological transformation in the soil solution following the first-order kinetics) to examine the effect of the upper and lower boundary conditions on the transfer of salts in a soil. The analysis revealed relationships between the parameters of the convective diffusion equation (for which simpler equations were proposed for calculating the irrigation rates from the average salt content in the soil layer before and after washing), which included the filtration rate, the physicochemical features of the soil and salts, and the degree and depth of the preset desalination. The use of the initial and permissible salt concentrations averaged for the studied layer was substantiated for the first time. After wide experimental validation, the obtained equations can be used in soil-reclamation practice.  相似文献   

8.
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9.
Abstract

The adsorption of selenium (Se) in the selenate form and its desorption by phosphate in four soils with different physiochemical properties were studied in the laboratory. To determine adsorption isotherms for selenate 25 mL of solutions containing 1 to 100 ppm of Se were added to 2.5 g of soil. Desorption isotherms were determined by resuspending the samples in phosphate solution. The selenate sorption process was adequately described by the Freundlich equation. In pine forest and woodland soils, characterized by the highest organic matter content and cation exchange capacity (CEC) values, the isotherms were classified as L type, since the amount of Se sorbed appeared to move towards saturation. The organic matter content played the most important part in the adsorption of Se, while pH appeared to have a small effect on the ability of the soil to adsorb Se. The high CaCO3 content of the pine forest soil may have contributed in increasing the Se adsorption notwithstanding the high pH value. The cultivated and arable soils showed a reduced sorption capacity. The sorption could be described by an S type curve. At low concentrations of Se the affinity of the solid phase was less than that of the liquid phase. By increasing the concentration of Se in solution, the affinity of the solid phase increased and the sorption was favored. Selenate desorption by water was negligible, whereas the amount of Se desorbed by phosphate varied among the different soils. The desorption experiments indicated that a significant portion of the sorbed Se was irreversibly retained. This suggests the existence of linkages which allow the release of Se in the soil solution only after physico‐chemical variation such as exchange with phosphate ions.  相似文献   

10.

Purpose

Sorption of antimony on soils is the primary factor that influences its immobilization and migration in the environment. In the present study, the sorption of Sb(V) onto seven Chinese soils with different physicochemical properties was investigated for exploring the relationship between the sorption capacity of Sb(V) and the physicochemical properties of the soils.

Materials and methods

Sorption isotherms and kinetics experiments were performed to ascertain the sorption capacity and the kinetic rate, respectively. The relationship between the sorption capacity of Sb(V) and the physicochemical properties of the soils was analyzed by multiple linear regressions.

Results and discussion

The results showed that the sorption isotherms fitted with both the Langmuir and Freundlich equations very well (R 2?=?0.936–0.997), and the sorption kinetic of Sb(V) onto the seven Chinese soils followed a pseudo-second-order reaction. The maximum sorption capacity of Sb(V) on the soils ranged from 134 to 1,333 mg?kg?1. Nearly 94 % of the variability in maximum sorption of Sb(V) modeled by Freundlich equation could be described by FeDCB (dithionite–citrate–bicarbonicum extractable), and nearly 98 % of the variability could be described by FeDCB and AlDCB.

Conclusions

Multiple linear regressions can be successfully applied to analyzing the relationship between sorption capacity and soil properties. FeDCB and AlDCB played important roles in Sb(V) sorption onto soils. It would be useful to understand the environmental behaviors of Sb and for the implementation of risk assessment management and remediation strategies of Sb.  相似文献   

11.
本试验测定了浙江省几种代表性土壤对磷的等温吸持特性。实测值与Frundlich、Langmuir、两项式Langmuir和Temkin方程都很符合,相关系数变化范围在0.919-0.999之间,都达到极显著水平。其中以简单Langmuir等温式与本实验资料最为吻合。从Langmuir方程得到的土壤吸持特性值(k×qm)被认为与土壤供磷特性有关。几种供试样品的(k×qm)值是:针铁矿21100>黄筋泥4218>黄筋泥田991>青紫泥798>粉泥田660>高岭石485>老黄筋泥田423>泥质田298。根据土壤吸持特性值以田菁进行盆栽试验来估算作物磷肥需要量,结果表明,供磷强度0.3ppm P基本能满足田菁早期生长的需要。为使不同土壤达到相同的供磷强度,(k×qm)值大的土壤要求更高的有效磷值。供试土壤的几种磷素指标:E值、Bray1-P值和(NaOH-Na2C2O4)法值对(k×qm)值的变化比较敏感,而EDTA-P和Olsen-P指标对(k×qm)值的变化较为迟钝。  相似文献   

12.
土壤垂向分层和均匀处理下水分差异的数值探讨   总被引：2，自引：0，他引：2  
在现有众多的陆面过程模型中,对土壤水分的定量描述一般是假设垂向分布均匀,取表层土壤质地来表示整个垂向土壤质地。垂向分层和均匀处理下的土壤水分是存在差异的,这种差异有多大目前少有研究。设置3组不同饱和导水率组合的层状土壤代表不同区域的非均匀土壤,取3组层状土壤的上层土壤代表整个均匀土壤,通过建立一维土壤水分运动模型分析这种差异,同时分析饱和导水率、饱和含水量、残余含水率、孔隙大小分布参数和形状参数对层状土壤和均匀土壤的渗透量和储水量差异的敏感性,探讨垂向层状和均匀处理下土壤水分运动的差异。研究结果表明:1)建立的一维土壤水分运动模型模拟的土壤水分剖面与Yeh解析解和室内五水转化试验的土壤水分剖面一致,表明模型无论是考虑还是不考虑根系吸水都具有可靠性。2)采用垂向均匀方式处理,上下层饱和导水率相差越大的层状土壤,各水文变量的差异越大。当层状土壤上下层饱和导水率相差1.5倍时,层状土壤和均匀土壤的水分分布差别小于0.05 cm~3×cm~(-3);而当层状土壤上下层饱和导水率相差达3.3倍时,层状土壤和均匀土壤的水分分布差别达0.15 cm~3×cm~(-3),渗漏量相差20 cm以上,储水量相差5 cm左右。3)相对于层状土壤下层,均匀土壤下层的持水能力更差,水流速度更快,导致下层水分分布减小,渗漏量增加,储水量减小。4)形状参数n对渗透量的敏感性最强,土壤孔隙大小分布参数对储水量的敏感性最强,形状参数n其次。在实际应用中,如果一个区域的土壤上下层饱和导水率相差较大,那么垂向均匀处理可能会导致很大的误差,和实际土壤的水分分布相差很大,这会严重影响土壤水分的准确估计,在实际处理中需要认真考虑。  相似文献   

13.
Abstract

Sorption of trace quantities of Cd in four soils of different chemical and mineralogical properties, was studied. Initial Cd concentrations were between 15 to 150 μg. 1?1. The sorption isotherms were linear and had a positive intercept in three of the soils, indicating a constant partition‐high affinity sorption isotherm (Giles et. al6). The data also followed the Freundlich sorption isotherm, and the Freundlich K parameter was taken as a measure of the relative affinity of the different soils for the Cd metal sorbed. Cadmium sorbed was extracted by IN‐NH4C1 followed by 0.1N HC1, and the fraction remaining in the soils was considered specifically sorbed Cd. This fraction also followed a linear sorption isotherm, and was around 30% for the four soils studied. The sorption order for the amount of specifically sorbed Cd showed that the Boomer soil (kaolinite‐iron oxides) had the lowest affinity for specific sorption of this metal. This was taken as evidence that kaolinite and iron oxides have a lower capacity for retaining cadmium through specific sorption mechanism(s) than the materials present on the other soils (2:1 layer silicates and humic substances). The existence of specific mecha‐nism(s) responsible by the sorption of trace quantities of Cd in soil solutions has important implications on soil‐plant relationships, Cd mobility in soil profiles and control of Cd activity in soil solutions.  相似文献   

14.
Sorption of phosphorus (P) in complete soil profiles in northern Europe is not adequately documented. I measured the sorption in genetic horizons of four cultivated soils (Inceptisols, Spodosol) in Finland using both field‐moist and air‐dried soil samples, fitted modified Freundlich equations (Q = a × Ib ? q) to the data, and presented the results in quantity/intensity (Q/I) graphs. Least‐squares‐estimates for the parameters of the modified Freundlich equation (a, b, q) were found to be imprecise measures of sorption. Values derived from the fitted equations (the amount of P sorbed at the P concentration of 2 mg litre?1 and P buffering capacity at the same concentration) were more precise. Both were correlated with concentrations of oxalate‐extractable iron and aluminium. In all soils, there was a distinct difference in sorption between the fertilized Ap horizons and the subsurface horizons, which retained P strongly. Most of the sorption capacity was located in the B horizons at depths between 0.3 and 0.7 m. The results demonstrate the effects of soil‐forming processes and human impact on the sorption of P in the soils. Drying the samples prior to the sorption experiments altered the shape of the Q/I graphs. It increased dissolution of P at small P concentrations, sorption at large P concentrations, and the estimates for P buffering capacity. The effects of drying soil samples on the results and the imprecision of the parameters estimated with the modified Freundlich equation should be taken into account when interpreting results of Q/I experiments.  相似文献   

15.
Soil particle size distribution (PSD), particularly the active clay fraction, mediates soil engineering, agronomic and environmental functions. The tedious and costly nature of traditional methods of determining PSD prompted the development of water sorption‐based models for determining the clay fraction. The applicability of such models to semi‐arid soils with significant amounts of calcium carbonate and/or gypsum is unknown. The objective of this study was to validate three water sorption‐based clay prediction models for 30 calcareous soils from Iran and identify the effect of CaCO3 on prediction accuracy. The soils had clay content ranging from 9 to 61% and CaCO3 from 24 to 97%. The three water sorption models considered showed a reasonably fair prediction of the clay content from water sorption at 28% relative humidity (RMSE and ME values ranging from 10.6 to 12.1 and −8.1 to −4.2, respectively). The model that considers hysteresis had better prediction accuracy than the other two that do not. Moreover, the prediction errors of all three models arose from under‐prediction of the clay content. The amount of hygroscopic water scaled by clay content decreased with increasing CaCO3 content. The low organic carbon content of the soils and the low fraction of low‐activity clay minerals like kaolinite suggested that the clay content under‐predictions were due to large CaCO3 contents. Thus, for such water‐sorption based models to work accurately for calcareous soils, a correction factor that considers the reduction of water content due to large CaCO3 content should be included.  相似文献   

16.
 The spatial in situ variability of soil N2O emissions (measured by micro-chambers, radius 0.033 m), N2O content, water content, NO3 –, NH4 +, inorganic carbon and organic carbon concentrations was investigated on a silt loam by means of geostatistical methods and nonparametric statistics. The sampling grid consisted of different spacings between sampling points which ranged from 0.1 m to 50 m. There were no significant correlations between N2O emissions and soil parameters (P>0.1) when all the sampling points were considered. In the centre of the grid a "hot area" was localized with significantly higher N2O emissions, and NO3 – and NH4 + concentrations (P≤0.05). Within this hot area the N2O soil content significantly correlated with N2O emissions (P≤0.05). When semiovariograms were computed without data of the hot area samples, N2O emissions showed a weak spatial correlation (range: 4.3 m). The calculations including all data led to pure nugget effects for all parameters except for soil water content (range >40 m) and N2O soil content (range 16.4 m). Received: 19 December 1997  相似文献   

17.
This study compared the degradation of [carboxyl-14C] 2,4-dichlorophenoxyacetic acid (2,4-D) (C2,4-D) and [ring-U-14C] 2,4-D (R2,4-D) in 114 agricultural soils (0–15 cm) as affected by 2,4-D sorption and soil properties (organic carbon content, pH, clay content, carbonate content, cation exchange capacity, total microbial activity). The sample area was confined to Alberta, Canada, located 49–60° north longitude and 110–120° west latitude and soils were grouped by soil organic carbon content (SOC) (0–0.99%, 1–1.99%, 2–2.99%, 3–3.99% and >4% SOC). Degradation rates of C2,4-D and R2,4-D followed first-order kinetics in all soils. Although total microbial activity increased with increasing SOC, degradation rates and total degradation of C2,4-D and R2,4-D decreased with increasing SOC because of increased sorption of 2,4-D by soil and reduced bioavailability of 2,4-D and its metabolites. Rates of R2,4-D degradation were more limited by sorption than rates of C2,4-D degradation, possibly because of greater sorption and formation of bound residues of 2,4-D metabolites relative to the 2,4-D parent molecule. Based on the sorption and degradation parameters quantified, there were two distinct groups of soils, those with less than 1% SOC and those with greater than 1% SOC. Specifically, soils with less than 1% SOC had, on average, 2.4 times smaller soil organic carbon sorption coefficients and 1.4 times smaller 2,4-D half-lives than soils with more than 1% SOC. In regional scale model simulations of pesticide leaching to groundwater, covering many soils, input parameters for each pesticide include a single soil organic carbon sorption coefficient and single half-life value. Our results imply, however, that the approach to these regional scale assessments could be improved by adjusting the values of these two input parameters according to SOC. Specifically, this study indicates that for 2,4-D and Alberta soils containing less than 1% SOC, the 2,4-D pesticide parameters obtained from generic databases should be divided by 2.5 (soil organic carbon sorption coefficient) and 1.5 (half-life value).  相似文献   

18.
Zinc sorption–desorption by sand, silt and clay fractions of six representative calcareous soils of Iran were measured. Sand, silt and clay particles were fractionated after dispersion of soils with an ultrasonic probe. Zinc sorption analysis was performed by adding eight rates of Zn from 6 to 120 μmol g?1. For the desorption experiment, samples retained after the measurement of Zn sorption were resuspended sequentially in 0.01 M NaNO3 solution and shaken for 24 h. Results indicated that Zn sorption by soil fractions increased in the order clay > silt > sand, and correlated negatively with CaCO3 content and positively with cation exchange capacity (CEC) and smectite content. Results indicated that for all fractions, the Langmuir equation described the sorption rates fairly well. In contrast to sorption, Zn desorption from soil fractions increased in the order sand > silt > clay, and correlated positively with CaCO3 content, CEC and smectite content. Results showed that parabolic diffusion and two constant equations adequately described the reaction rates of Zn desorption. In general, for all soils studied, the coarser the particle size, the less Zn sorption and more Zn desorption, and this reflects much higher risk of Zn leaching into groundwater or plant uptake in contaminated soils.  相似文献   

19.
Usage of alkaline and saline groundwater with elevated concentrations of fluoride (F−) for irrigation of pastures requires an assessment of the mobility of F− within the plant-water-soil continuum. Factors influencing F− sorption and desorption in 95 Australian soils were examined. Pronounced differences in F− sorption were observed across the soils, but these differences could not be explained by differences in soil pH, electrical conductivity or organic carbon. Rather, sorption was correlated with the content of Fe/Al hydrous oxides and kaolinite in soil. Sorption of F− onto soils increased the solution pH and the ratio of (F− adsorbed) to (OH− desorbed) was consistently below 1, thereby indicating that adsorption of F− results in the release of water and hydroxyl groups from, or co-adsorption of protons to, the sorbent surface. Maximum sorption occurred at pH values of approximately 5–6, whilst sulphate slightly increased (<5%) F− sorption. Desorption was slightly decreased (~3%–7%) in presence of sulphate anions. Hence, it is unlikely that irrigation of soil with alkaline and saline groundwater, in combination with soil applications of gypsum and sulphur to limit pH fluctuations, would increase mobility of F− in soil. Finally, the irrigation of soil columns with 1200–1500 mm of alkaline and saline groundwater containing 0.18 mM F−, as would commonly occur in irrigation systems using coal seam gas associated water in Australia, resulted in a F− concentration of 0.05 mM at 10 cm depth and the measured values were in excellent agreement with modelled F− movement based on sorption parameters. Thus, sorption parameters can be used to identify soils which minimize movement of F− because of their strong F− sorption. Based on these results, safe limits for irrigation of soil can be established which avoid F− toxicity risks to plants, animals and contamination of water resources.  相似文献   

20.
Sorption of volatile organic contaminants by soils (a review)   总被引：1，自引：0，他引：1  
The sorption of volatile organic compounds (VOCs)—the most common, mobile, but relatively poorly studied contaminants—by soils is considered. Typical VOCs of different classes, the major processes determining their retention by soils, the main rules and mechanisms of VOC sorption, and the experimental methods of its measurement are characterized. The common approximation models and geometrical shapes of VOC sorption isotherms are discussed. Provisional analytical ranges of experimental VOC sorption values in the aqueous and the vapor phases at low and high relative concentrations are reported.  相似文献   

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