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1.
The adsorption-desorption equilibrium of atrazine (2-chloro, 4-ethylamino, 6-isopropyl amino-1, 3, 5 triazine) was studied by the batch equilibration method at 27 ± 1 °C on four soils of Hyderabad. Adsorption isotherms conformed to the Freundlich equation (A = KC1/n ). K increased in the same order as the organic C content of the soils. Desorption studies were conducted by repeated replacement of 5 mL of the supernatant equilibrium solutions after adsorption, with 0.01 M CaCl2. Desorption isotherms showed considerable hysteresis which was more prominent when the desorption was carried out with higher adsorbed concentration of atrazine. Desorption from the lowest level of adsorbed atrazine (3 to 5 μg g?1 soil) was close to the adsorption isotherm. The cumulative desorption after four desorption steps covering five days was significantly different at the 1% level, for different initial adsorbed concentrations of atrazine. Desorption was significantly higher at the lowest adsorbed level of atrazine. The soils differed significantly at 6% level for desorption and the amount desorbed decreased in the inverse order of organic C. Desorption isotherms also conformed to Freundlich equation but K andn values were both higher than that for adsorption and increased with increase in initially adsorbed concentration of atrazine. Desorption thus confirmed the irreversible nature of the adsorption of atrazine on these soils. The quantitative factors and reasons for desorption are discussed.  相似文献   

2.
Chang  T. W.  Wang  M. K.  Lin  C. 《Water, air, and soil pollution》2002,138(1-4):199-209
While sorbate/sorbent, sorbate/water, and sorbent/water (S/W)ratios in a batch system are known to affect the adsorption ofsorbate, the effect of different S/W ratios on the adsorptionof inorganic sorbates has seldom been addressed. This studyinvestigates the adsorption phenomena of Cu2+ in differentsorbate/sorbent/water ratios in a batch system. Batch experimentsare performed to examine the adsorption, and the linear (K D), Langmuir (K L), and Freundlich (K F) adsorption coefficients of Cu2+ in lateritic soil. These experiments are conducted using solutions with initial concentrations of 0.5 to 50 mg Cu2+ L-1 equilibratedwith an appropriate amount of soil to give S/W ratios of 0.1 to 2 g mL-1. Although the variations in the sorbed amountand adsorption coefficients apparently originate from a changein the sorbate/sorbent/water ratio, only the equilibrium concentration significantly affects adsorption. On the otherhand, the linear and Langmuir isotherm cannot adequately describethe adsorption data. In this study, the Freundlich equation gavean excellent fit to the adsorption data with a goodness-of-fit(R2) > 0.984. However, adsorption isotherms should be regarded as only a curve-fitting model or a mathematical tool and cannot be employed to interpret any particular adsorptionmechanism. Meanwhile, the solids effect reveals that K F andmaximum adsorption (b) of the Langmuir equation increase when S/W ratio decreases. The sorbate in the stagnant phase must beconsidered as part of the equilibrium concentration in the solidphase to avoid underestimating the sorbed amount at a lower S/Wratio and/or a higher sorbate concentration level.  相似文献   

3.
The increasing frequency of chemically contaminated groundwater, occurring as a result of improperly managed waste disposal or accidental spills, presents a need for research on the fate of chemical mixtures in the soil. The batch equilibration technique was used to measure adsorption of 14C ring-labeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) for a Palouse silt loam (Pachic Ultic Haploxeroll) and a Pembroke silty clay loam (Typic Paleudalf). The solution phase consisted of mixtures of methanol-water and hexane-water containing up to 33.3 % organic solvent by volume. Aqueous solubility limited atrazine concentrations to 100 μmol L?1 except for an additional isotherm determined in 33.3 methanol-water at up to 1542 μmol L?1 The Freundlich adsorption coefficient indicated that the Palouse adsorbed more atrazine than the Pembroke with K values of 4.95 and 0.54, respectively. Both soils showed a significant decrease in K as the percentage methanol increased. Adsorption isotherms from a 33. 3 methanol-water system were of the Freundlich type for atrazine concentrations of 0.25 to 1542 μmol L?1. In the hexane-water systems, K decreased as the fraction of hexane increased and the Pembroke soil adsorbed less atrazine than the Palouse soil. These results suggest that the introduction of nonaqueous solvents such as methanol and hexane decreased adsorption and increased the potential for atrazine mobility.  相似文献   

4.
Residues of antibiotic pharmaceutical compounds (APCs) found in the environment are suspected to be translocated into the food chain and to provoke the formation of resistant microorganisms. However, the behavior of APCs in soils is largely unknown. In the present study batch experiments were carried out with sulfapyridine (SPY) and p‐aminobenzoic acid (ABA) amended to two loess Chernozem samples. Due to different fertilization in the course of a long‐term field experiment samples differed substantially in the concentration of organic carbon (Corg 1.6 and 2.4%) and composition of soil organic matter (SOM). APCs in soil extracts were analyzed by high performance liquid chromatography. The KF values of the Freundlich isotherm for SPY were 2.2 (1.6% Corg) and 5.5 (2.4% Corg). The Koc values were 101 and 308. The different Koc values indicated that not only the quantity but also the composition of SOM affected the SPY adsorption. Adsorption of SPY was substantially higher in moist than in air‐dry soil. ABA, consisting of a carboxyl group instead of the sulfonamide group substituted with a N‐heterocycle, was much less adsorbed than SPY (KF 0.2). From this it was concluded that the N‐heterocycle significantly contributed to the adsorption of SPY.  相似文献   

5.
Desorption experiments were conducted on 21 soils at 3 atrazine concentrations. The Freundlich isotherm was used to estimate atrazine desorption. For the relationship between Freundlich isotherm coefficients, log K F and 1 / n, 1 / n was also represented by a linear regression of log K F as in the case of atrazine adsorption. All the linear regression lines of desorption exhibited larger slopes and intercepts than those of adsorption. When the atrazine concentration was high, the slope and intercept values were smaller than those for the desorption regression lines. The results showed that the larger the capacity of a soil to adsorb atrazine, the lesser the amount of atrazine desorbed. For the cultivated soils except for Andisols, the percentages of atrazine taken from solutions using the sequential exchange method after the first adsorption experiments, were the same as those desorbed from soils in relation to the initial amount adsorbed. Thus, reversible adsorption occurred in the soils due to weak physical adsorption.  相似文献   

6.
The adsorption kinetics and adsorption parameters of metolachlor, atrazine, deethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (HA) were investigated in a soil profile in a maize field formed from recent alluvial deposits in a river basin in Greece. We used the batch equilibrium method modified to simulate field conditions as closely as possible for the use and practices related to soil applied pre‐emergence herbicides. Pseudo‐equilibrium times, determined by kinetic studies, were achieved after 16, 16, 24, 24 and 48 hours for metolachlor, DIA, DEA, HA and atrazine, respectively. At pseudo‐equilibrium the percentage of the adsorbed amount increased in the order of DEA (10%) < DIA (14%) < atrazine (27%) < metolachlor (43%) ≪ HA (94%) which indicates that more than 57% of all compounds except for HA are in solution and available for transport to deeper soil layers when conditions similar to those simulated in the laboratory exist in the field. Adsorption isotherms of all compounds and in most of the cases correlated well with the Freundlich model and adsorption coefficients (Kf) decreased with increased soil depth. Principal component and multiple regression analyses confirmed the importance of the soil organic carbon content on the adsorption capacity of soils for all compounds except HA in the plough layers (0–40 cm). In the subsurface soils (40–110 cm) variables such as clay content and pH were more important. For HA, the Kf values determined for the plough and subsurface soil layers were better correlated with clay content and pH. Also in the subsurface soils, the variation in organic carbon content was not correlated with the variation of Kf values. Thus calculated Koc‐f‐values misrepresent the adsorptive capacity of these soils towards the compounds studied.  相似文献   

7.
采用批量平衡实验,研究了纳米粘土矿物与原粘土矿物对除草剂阿特拉津的吸附解吸特陛。结果表明,粘土矿物对阿特拉津的吸附-解吸均能用Freundlich方程很好地拟合。随着溶液中阿特拉津浓度的增加,粘土矿物对阿特拉津的吸附量增加;粘土矿物粒径越小,吸附量越大,纳米粘土矿物的吸附量显著大于原粘土矿物。粘土矿物对阿特拉津吸附量大小顺序为：纳米SiO2）纳米蒙脱石〉凹凸棒石〉蒙脱石〉SiO2。粘土矿物对阿特拉津的解吸表现出一定的滞后效应,即粘土矿物吸附的阿特拉津越多,解吸的越少。粘土矿物对阿特拉津的解吸率大小顺序为：SiO2〉凹凸棒石〉纳米蒙脱石〉纳米SiO2〉蒙脱石。  相似文献   

8.
Five peat soils and a mineral soil were artificially contaminated with 137Cs. Soil solution activity and radio–lability of 137Cs were monitored over 709 days to quantify progressive 137Cs fixation. The peat soils fixed large amounts of 137Cs, but less than the mineral soil did. Distribution coefficients (Kd, cm3 g?1) ranged from 30 to 5000 at the end of equilibration. A labile 137Cs distribution coefficient, Kdt, was estimated by a method involving solid ? solution equilibration in dilute solution. In a separate study several concentrations of KCl were added to soils in increasing concentration both before and after the addition of 137Cs. Differences in apparent adsorption strength of radiocaesium indicated that K+ induced the collapse of expanded mineral interlayers, thereby trapping ions. It seemed that I37Cs adsorbs at sites in the small micaceous clay fraction of the peat soils. The different rates of 137Cs adsorption and fixation in the peat and mineral soils, in which the rate of access of 137Cs to fixation sites in peat soils is less, seems to have been caused partly by lack of K, and partly by the scarcity of fixation sites.  相似文献   

9.
Abstract

The “Four-plane model” is one of the surface complexation models developed for analyzing the electrostatic charge of synthetic oxides. This model which was applied to the B horizon of Andisols, was equilibrated with an electrolyte solution containing KCl, KNO3, K2SO4 in the concentration range of 0.0033, 0.01, 0.033, 0.1 M, and pH range of 2 to 11. The amounts of NO3 -, Cl-, SO4 2-, and K+ adsorbed were determined from the products remaining in the liquid phase. The increase in the pH value results in the increase of K+ adsorption, and decrease of anion adsorption. The increase in the equilibrium concentration increased both K+ and anion adsorption. The parameters of the model were determined by measurements and the iterative method. The model have a good agreement between calculated and measured values of cation and anion adsorption. Among the anion species, the amount of adsorbed anions was in the order of SO4 2-?Cl->NO3 -. The differences in the degree of adsorption were mainly associated with the differences in the equilibrium constants of surface complexation. The surface complexation of the anions produced a negative charge and increased cation adsorption. The degree of surface complexation was most significant in the K2SO4 solution, and the phenomenon was considered to be important not only for anion adsorption but also for cation adsorption on Andisols.  相似文献   

10.
Adsorption and desorption of the herbicides glyphosate [N-phosphonomethyl-aminoaceticacid], simazine [6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine] and atrazine [6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine] were studied in four sandy soils from Western Australia. Distribution coefficients (Kds) were calculated from breakthrough curves (BTCs) resulting from leaching step changes in concentrations through small saturated columns of soil at flow rates ranging from 0.3 to 30 m day–1. A comparison was made with Kds obtained after batch equilibrating solutions of the herbicides with the same soils. The Kds of herbicides in soils decreased with increasing flow rate and most strongly for glyphosate in soils rich in clay content. Resulting increases in mobility of about 40–50% were estimated for simazine and atrazine and > 50% for glyphosate at flow rates of 3 m day–1. Adsorption and desorption rates were estimated by fitting numerically simulated BTCs to experimental BTCs. Best fits were obtained with a time-dependent Freundlich adsorption equation. The resulting coefficient for time dependency in the equation suggests that the rates of adsorption and desorption are controlled mainly by diffusion in an adsorbing layer on or in soil particles.  相似文献   

11.
吸附反应时间对潮土中除草剂阿特拉津吸附行为的影响   总被引：2，自引：0，他引：2  
A batch experiment was performed to investigate nonequilibrium adsorption behavior of atrazine （2-chloro-4-ethylamino-6-isopropylamlno-1,3,5-triazlne） on a fluvo-aquic soil. The amount of atrazine sorbed increased with increasing adsorption contact periods. For a range of initial atrazlne concentrations, the percentage of atrazine sorbed within 24 h ranged from 24% to 77% of the observed total amount sorbed for the longest contact period; when adsorption contact periods were more than 72 h, the deviations in curves fitted using a nonlinear Freundllch equation gradually became less. The opposite trend was observed for the atrazine concentrations in solution. The effect of adsorption contact periods on atrazine adsorption behavior was evaluated by interpreting the temporal variations in linear and nonlinear Freundlich equation parameters obtained from the phase-distribution relationships. As the adsorption contact period increased, the nonlinear Freundlich capacity coefficient kf showed a significant linear increase （r^2 = 0.9063, P 〈 0.001）. However, a significant negative linear correlation was observed for the nonlinear coefficient n, a dimensionless parameter （r^2 = 0.5666, P 〈 0.05）. Furthermore, the linear distribution coefficient kd ranged from 0.38 to 1.44 and exhibited a significant linear correlation to the adsorption contact period （r^2 = 0.72, P 〈 0.01）. The parameters kf and n obtained from a time-dependent isotherm rather than the distribution coefficient kd estimated using the linear Freundlich equation were more appropriate to predict the herbicide residue in the field and thus more meaningful for environmental assessment.  相似文献   

12.
Atrazine and metolachlor are extensively used pesticides in agricultural activities in northwest Ohio. Adsorption coefficients are often used to model pesticide fate and transport. Many physical-chemical parameters, such as organic matter, clay content, pH, and ionic strength, affect pesticide adsorption. Adsorption kinetics and adsorption isotherms were studied by batch experiment. Effects of humic acid, solution pH, and ionic strength on atrazine and metolachlor adsorption were also approached. After 24 h, both atrazine and metolachlor reached adsorption equilibrium in three local soils. Adsorption isotherms were described by Freundlich equations. The Freundlich coefficient (Kf) ranged from 0.14 to 4.47 (L kg–1) for atrazine, and 0.04 to 5.30 (L kg–1) for metolachlor. Adsorption capacity decreased in the order Sloan loam > Del Rey loam > Ottokee fine sand. Koc values varied considerably for both pesticides: metolachlor > in Sloan loam, atrazine metolachlor in Del Rey loam, and atrazine > metolachlor in Ottokee fine sand. In addition to organic matter content, clay played a key role in adsorption in the Del Rey loam and Ottokee fine sand. Higher adsorption was observed at pH 5 for both pesticides. As pH decreased to 3 and increased to 11, adsorption decreased. Adsorption increased as ionic strength increased.  相似文献   

13.
The adsorption of a radioisotope of caesium, 137Cs, has been interpretation and ratio and solution measured on four soils with differing clay mineralogies. All measurements have been made using unwashed soils in suspensions shaken for 2 h at 20°C. The effects of concentration in potassium and caesium, the nature of the background electrolyte and the soil:solution ratio have been investigated. The results are expressed either as the distribution coefficient, KD or as Freundlich isotherms. The distribution coefficient of each of the soils decreases markedly as the concentration of caesium increases. The adsorption properties of the soils are not determined by the dominant clay mineralogy alone. Adsorption is always lower in 0.01 m CaCl2 solution than in water. The addition of potassium has relatively little effect on adsorption of trace amounts of caesium; however, KD decreases with increasing concentrations of stable caesium. The major reason for the dependence of KD on the soil: solution ratio is found to be the non-linear adsorption isotherm; the influence of the varying compositions of the solution and exchange complex is minor. The validity of the use of a single KD value as an indicator of adsorption capacity and the meaning of the relative values of the Freundlich parameters are considered. The implications of these findings for the use of radiotracers and the usefulness of KD as an indicator of bioavailability are discussed.  相似文献   

14.
The adsorption of herbicides on soil colloids is a major factor determining their mobility, persistence, and activity in soils. Solvent extraction could be a viable option for removing sorbed contaminants in soils. This study evaluated the extractability of three herbicides: 2,4 dichlorophenoxy-acetic acid (2,4-D), 4-chloro-2-methylphenoxypropanoic acid (mecoprop acid or MCPP), and 3,6-dichloro-2-methoxybenzoic acid (dicamba). Three solvents (water, methanol, and iso-propanol) and three methods of extraction (column, batch, and soxhlet) were compared for their efficiencies in removing the herbicides from three soils (loamy sand, silt loam, and silty clay). Both linear and non-linear Freundlich isotherms were used to predict sorption intensity of herbicides on soils subjected to various extraction methods and conditions. High Kdand Kfr, and low N values were obtained for all herbicides in silty clay soil by batch extraction. Methanol was the best solvent removing approximately 97% of all added herbicides from the loamy sand either by column or soxhlet extraction method. Isopropanol ranked second by removing over 90% of all herbicides by soxhelet extraction from all three soils. However, water was ineffective in removing herbicides from any of the soils using any of the three extracting procedures used in this study. In general, the extent of herbicide removal depended on soil type, herbicide concentration, extraction procedure, solvent type and amount, and extraction time.  相似文献   

15.
A new sampling system has been developed for the measurement of time-averaged concentrations (TWA) and diffusion coefficients of organic micropollutants in aquatic environments. The system is based on the diffusion of targeted organic compounds through a rate-limiting membrane and the subsequent accumulation of these species in a bound, hydrophobic solid-phase material. Two separate prototype systems are described. One is suitable for the sampling of carbamates such as carbaryl, carbofuran, 3-hydroxycarbofuran, baygon, propham, clorpropham, and the other one for s-triazines such as atrazine, prometryn, propazine, simazine, terbuthylazine, terbutryn, metribuzin, cyanazine, and metamitron pesticides. The systems use solid-phase material (47-mm?C18 Empore disk) as the receiving phase but are fitted with rate-limiting membranes of either polysulfone or polycarbonate. For the two designs investigated, the cumulative uptake of all target analytes was considered over exposure periods of 7?days. The determined sampling rates ranged from 0.1323 to 0.0465?L?day?1 with both membranes. The best system was the one with the polysulfone membrane allowing a better cumulative uptake.  相似文献   

16.
Adsorption–desorption of added phosphorus (P) was studied in a batch experiment using anion-exchange resin. Total P sorbed by adding 400 mg P kg?1 by Nigerian soil ranged from 10.8 mg kg?1 in the Idofian Basement complex to 35.5 mg kg?1 in Alkaleri Sandstone, representing 3 and 9% of applied P. Phosphorus release kinetics was apparently described by the first-order, second-order, Elovich, parabolic diffusion and fractional power equations, but not in soils derived from sandstone. The mechanism underlying the release pattern was concluded to be dissolution followed by diffusion of sorbed P from the good fit to the Elovich and parabolic diffusion equations. The inability to clearly relate the P sorbed by the soil to OH- and SO4 2- released into the soil solution during the adsorption process further corroborated the above conclusion, thereby overruling the possibility of ligand exchange as a dominant mechanism in the sorption/desorption of P in these soils.  相似文献   

17.
On the relation of herbicide adsorption and soil organic fraction Freundlich adsorption isotherms were measured for four herbicides (atrazine, terbuthylazine, chlorotoluron, isoproturon) and 24 soil horizons, which are typical of Schleswig-Holstein, northern Germany. The relationship between the adsorption constant (KFr) of a chemical and the fraction of organic carbon (fOC) of the soil horizons was evaluated. Chemical specific K'OC-values, that are independent of soil organic carbon fraction varied considerably for each herbicide (CV about 50%); therefore these values as well as KOC-values, that are determined by linear regression of KFr and fOC should be evaluated critically before application. K'OC- and KOC-values derived from experiments showed decreasing affinity of the herbicides to soil horizons in the order terbuthylazine > chlorotoluron > atrazine ? isoproturon. Calculation of KOC from KOW or water solubility of each herbicide, however, led to changes in the above mentioned ranking. Hence, especially KOW or water solubility based KOC-values may lead to false conclusions concerning chemical mobility. For atrazine, terbuthylazine and isoproturon Freundlich adsorption constants increased overproportionally with increasing organic carbon content of soils. The relationships between KFr and fOC therefore were described better by a non-linear equation (second order polynom) than by a linear approach. Contrary, for chlorotoluron a linear relation between KFr and fOC holds at least for the range of fOC investigated in this study.  相似文献   

18.
Understanding the role of organic acids on phosphorus (P) sorption capacity of soils is very important for its economic and friendly management. Combining P application with low-molecular weight organic acids could result in its higher plant availability for prolonged time. Therefore, citric and oxalic acid (at the rate of 1.0 mM kg?1 soil) were evaluated for their effect on P sorption capacity and its plant availability in two different textured calcareous soils. Organic acids decreased P sorption capacity and organic carbon partition coefficient (Koc) whereas increased Gibbs free energy (ΔG) of P. Organic-acid-treated soils required lesser quantity of P fertilizer to produce soil solution P concentration optimum for plant growth (external P requirement [EPR0.2]), that is, 0.2 mg L?1. Citric acid was efficient than oxalic acid in the above effects. P sorption parameters of Freundlich model were negatively correlated with lime potential and ΔG whereas had positive correlation (P < 0.05) with EPR0.2 and Koc. Incubation with oxalic acid increased available P in loamy sand and loam soil by 20% and 30%, respectively. Thus, organic acids could help reduce application rate of P fertilizer through lowering its adsorption in highly P-fixing soils without compromise on yield.  相似文献   

19.
A method for the measurement of Pb and Cd in equilibrium soil solutions involving soil equilibration with a dilute Ca electrolyte, centrifugation and filtration to <0.2 μm was evaluated. The procedure was subsequently used for the analysis of 100 Pb- and 30 Cd-contaminated soils. Solutions were analysed for Pb- and Cd using graphite-furnace AAS and the concentrations of Pb2+ and Cd2+ were estimated using standard speciation calculations. The concentrations of Pb and Cd found in the soil solutions were in the range 3.5–3600 μg dmp ?3 and 2.7–1278 μg dm ?3 respectively; both ranges represented less than 0.1% of the total metal concentration in the soils. Depending on solution pH, Pb +2 accounted for between 42–78% of Pb in solution while about 65% of Cd in solution was present as Cd+2. The concentrations of Pb2+ and Cd2+ in solution suggested that the soil solutions were undersaturated with respect to the solid phases PbC03 and CdC03 but supersaturated with respect to Pb5(P04)3Cl and, for some samples, Cd3(P04)2 respectively. However, for both metals, a good empirical relationship was obtained between the total metal concentration in soil (mol kg?1), free metal concentration in solution (mol dm?3) and solution pH. The relationships took the general form of a pH-dependent Freundlich adsorption equation: For both lead and cadmium relationships, the values ofn and K1 were close to unity, so that the distribution coefficient could be estimated from pH and a single metal-dependent constant, K2. The algorithms appeared to be valid over a metal concentration range of four logarithmic units and pH range of 3.5–7.5.  相似文献   

20.
The effects of sorbed phosphate on the kinetics of Cu^2 secondary adsorption on three major types of soils in southern and Central China were studied using the batch method and flow (or miscible displacement) techniques.Both of the methods showed that diffusions were the ratedetermining steps in the Cu^2 adsorption by the soils.By the flow method,the course of Cu^2 adsorption kinetics consisted of two steps-sn initial rapid process and a later slow process of Cu^2 adsorption;while by the batch method,the 90% of Cu^2 adsorption reaction was found to finish within first 1 minute.The results obtained using the flow method also indicated that for red soil and yellow-brown soil ,Cu^2 adsorptions during the initial reaction periods were restrained when the soils sorbed phosphate,whereas the adsorption reactions were stimulated at the final time,For grey Chao soil,sorbed phosphate retarded the Cu^2 adsorption in the whole reaction period.The results obtained using the batch method and low techniques all implied that the different effects of sorbed phosphate would be attributed to its effects on Cu^2 ion diffusion in soil solution.  相似文献   

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