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1.
Recently, application of sewage sludge or effluents resulted in raising the concentrations of some heavy metals in some agricultural soils of Iran. Experiments were conducted to evaluate the competitive adsorption of lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) on six calcareous soils. Adsorption characteristics were evaluated by equilibration of 1 g of each soil sample with 20 ml of 0, 10, 20, 30, 40, 50, 100, or 200 mg L?1 of their nitrate solutions and 0.01 M NaNO3 as background electrolyte. Furthermore, solid/liquid distribution coefficients (Kd) of studied metals, as an index of soil capacity to resist a change of the soil solution concentration, were calculated. Results indicated that amounts of adsorbed Pb, Cu, Zn, and Cd increased with increase in their concentrations in the contact solutions, but this trend was more pronounced for Pb and Cu than the others. For all studied soils and metals, Langmuir equation described the adsorption behavior fairly well. Furthermore, Langmuir and Freundlich equation parameters were positively correlated to cation exchange capacity (CEC) and smectite contents; whereas, they were negatively correlated to sand content. Considering Kd values, the selectivity sequence of the metal adsorption was Pb > Cu > Zn > Cd. Therefore, the risk of leaching and also plant uptake of Zn and Cd will be higher as compared to those of the other elements.  相似文献   

2.
The prediction of the mobility of arsenic (As) is crucial for predicting risks in soils contaminated with As. The objective of this study is to predict the distribution of As between solid and solution in soils based on soil properties and the fraction of As in soil that is reversibly adsorbed. We studied adsorption of As(V) in suspensions at radiotrace concentrations for 30 uncontaminated soils (pH 4.4–6.6). The solid–liquid distribution coefficient of As (Kd) varied from 14 to 4430 l kg?1. The logarithm of the concentration of oxalate‐extractable Fe explained 63% of the variation in log Kd; by introducing the logarithm of the concentration of oxalate‐extractable P in the regression model, 85% of the variation in log Kd is explained. Double labelling experiments with 73As(V) and 32P(V) showed that the As to P adsorption selectivity coefficient decreased from 3.1 to 0.2 with increasing degree of P saturation of the amorphous oxides. The addition of As(V) (0–6 mmol kg?1) reduced the Kd of 73As up to 17‐fold, whereas corresponding additions of P(V) had smaller effects. These studies suggest that As(V) is adsorbed to amorphous oxides in soils and that sites of adsorption vary in their selectivity in respect of As and P. The concentration of isotopically exchangeable As in 27 contaminated soils (total As 13–1080 mg kg?1) was between 1.2 and 19% (mean 8.2%) of its total concentration, illustrating that a major fraction of As is fixed. We propose a two‐site model of competitive As(V)–P(V) sorption in which amorphous Fe and Al oxides represent the site capacity and the isotopically exchangeable As represents the adsorbed phase. This model is fitted to 73As adsorption data of uncontaminated soils and explains 69% of the variation of log Kd in these soils. The log Kd in contaminated soils predicted using this two‐site model correlated well with the observed log Kd (r = 0.75). We conclude that solubility of As is related to the available binding sites on amorphous oxides and to the fraction of As that is fixed.  相似文献   

3.
THE HIGH- AND LOW-ENERGY PHOSPHATE ADSORBING SURFACES IN CALCAREOUS SOILS   总被引：2，自引：0，他引：2  
The two-surface Langmuir equation was used to study P adsorption by 24 calcareous soils (pH 7.2-7.6; 0.8-24.2 per cent CaCO3) from the Sherborne soil series, which are derived from Jurassic limestone. High-energy P adsorption capacities (x″m) ranged from 140–345 μg P/g and were most closely correlated with dithionite-soluble Fe. Hydrous oxides therefore appear to provide the principal sites, even in calcareous soils, on which P is strongly adsorbed (x″m 6–51 ml/μg P). The low-energy adsorption capacities (x″m) ranged from 400–663 μg P/g and were correlated with organic matter contents and the total surface areas of CaCO3 but not with per cent CaCO3, pH, or dithionite-soluble Fe. Total surface areas of CaCO3 in the soils ranged from 4.0 to 8.5 m2/g soil. Low-energy P adsorption capacities agree reasonably with values (100 pg P/m2) for the sorption of phosphate on Jurassic limestones but phosphate was bonded much less strongly by soil carbonates (k″= 0.08–0.45 ml/μg P) than by limestones (k～10.0 ml/μg P). Low-energy P adsorption in these soils is tentatively ascribed to adsorption on sites already occupied by organic anions (and probably also by bicarbonate and silicate ions) which lessen the bonding energy of co-adsorbed P.  相似文献   

4.
Sulfate (SO4 2–) movement and transport in soils has received considerable attention in recent years. In most soils, SO4 2– coexists with a variety of natural organic compounds, especially organic acids. Studies were conducted to assess the effect of low-molecular-weight organic acids (eight aliphatic and five aromatic acids) on SO4 2– adsorption by variable charge soils from Chile and Costa Rica. The effects of type of organic acid, pH, type of soil, and organic acid concentration were investigated. In one experiment, a 1.0 g soil sample was equilibrated with 25 ml 0, 0.5, 1.0, 2.0, 4.0, or 6.0 mM K2SO4 in 1 mM NaCl in the presence or absence of 5 mM citric acid. In the second set of experiments, the adsorption of 2 mM SO4 2– in soils at pH 4 or pH 5 in the presence or absence of one of 13 organic acids at a concentration of 2 mM or 5 mM was studied. Results showed that citric acid significantly decreased SO4 2– adsorption by the two soils. Sulfate adsorption decreased with increasing pH of the equilibrium solution. Aliphatic acids, with the exception of cis-aconitic acid, decreased the amount of SO4 2– adsorbed by the two soils, with oxalic, tartaric, and citric acid showing the greatest effect. The differences in pH values of the equilibrium solutions in the presence and absence of organic acids were significantly, but negatively, correlated with the amount of SO4 2– adsorbed, suggesting chemisorption of SO4 2– and the release of hydroxide ions. The ionization fraction values of the organic acids at the equilibrium pH were correlated with the amounts of SO4 2– adsorbed, suggesting that the protonation of surface hydroxyl groups of the mineral phase increased as the strength of the ionization of the acid increased, thus creating more positively charged surfaces. Received: 12 February 1997  相似文献   

5.
Risk assessment of heavy metals in soil requires an estimate of the concentrations in the soil solution. In spite of the numerous studies on the distribution of Cd and Zn in soil, few measurements of the distribution coefficient in situ, Kd, have been reported. We determined the Kd of soils contaminated with Cd and Zn by measuring metal concentrations in the soil and in the soil solution and attempted to predict them from other soil variables by regression. Soil pH explained most of the variation in logKd (R2 = 0.55 for Cd and 0.70 for Zn). Introducing organic carbon content or cation exchange capacity (CEC) as second explanatory variable improved the prediction (R2 = 0.67 for Cd and 0.72 for Zn), but these regression models, however, left more than a factor of 10 of uncertainty in the predicted Kd. This large degree of uncertainty may partly be due to the variable degree of metal fixation in contaminated soils. The labile metal content was measured by isotopic dilution (E value). The E value ranged from 18 to 92% of the total metal content for Cd and from 5 to 68% for Zn. The prediction of Kd improved when metals in solution were assumed to be in equilibrium with the labile metal pool instead of the total metal pool. It seems necessary therefore to discriminate between ‘labile’ and ‘fixed’ pools to predict Kd for Cd and Zn in field contaminated soils accurately. Dilute salt extracts (e.g. 0.01 m CaCl2) can mimic soil solution and are unlikely to extract metals from the fixed pool. Concentrations of Cd and Zn in the soil solution were predicted from the concentrations of Cd and Zn in a 0.01 m CaCl2 extract. These predictions were better correlated with the observations for field contaminated soils than the predictions based on the regression equations relating logKd to soil properties (pH, CEC and organic C).  相似文献   

6.
土壤对镉的吸附与解吸——Ⅱ.吸附势与解吸势   总被引：7，自引：0，他引：7       下载免费PDF全文
陈怀满 《土壤学报》1988,25(3):227-235
本文提出了吸附势(logKa)和解吸势(logKd或相对解吸势logKdr)两个有关吸附和解吸的强度概念,并进行了理论推导和实验验证。logKa和logKd或logKdr是影响土壤或胶体吸附和解吸因素的综合反应。实验证实logKa可用于表征土壤胶体对Cd的相对选择性,并且对胶体吸附Cd有着良好的预测性;logKdr可用于表征土壤胶体对Cd的相对固定能力,并可用于估测Cd的污染程度。盆栽试验表明,随着土壤胶体logKa的增加,或logKdr的降低,稻草或糙米中Cd的含量下降。可以预期,吸附势和解吸势不但在土壤物理化学,土壤环境化学研究中,而且在植物营养化学、水化学、以及界面化学等方面有可能获得实际应用。  相似文献   

7.
Organotin compounds (OTC) are deposited from the atmosphere into terrestrial ecosystems and can accumulate in soils. We studied the adsorption and desorption of methyltin and butyltin compounds in organic and mineral soils in batch experiments. The adsorption and desorption isotherms for all species and soils were linear over the concentration range of 10–100 ng Sn ml?1. The strength of OTC adsorption correlated well with the carbon content and cation exchange capacity of the soil and was in the order mono‐ > di‐ > tri‐substituted OTCs and butyltin > methyltin compounds. The OTC adsorption coefficients were much larger in organic soils (Kd > 104) than in mineral soils. The adsorption and desorption showed a pronounced hysteresis. Trimethyltin adsorption was partly reversible in all soils (desorption 2–12% of the adsorbed amounts). Dimethyltin, tributyltin and dibutyltin exhibited reversible adsorption only in mineral soils (desorption 4–33% of the adsorbed amounts). Mono‐substituted OTCs adsorbed almost irreversibly in all soils (desorption < 1% of adsorbed amounts). Trimethyltin was more mobile and more bioavailable in soils than other OTCs. It might therefore be leached from soils and accumulate in aquatic ecosystems. The other OTCs are scarcely mobile and are strongly retained in soils.  相似文献   

8.
Irrigation with low-quality water may change soil hydraulic properties due to excessive electrical conductivity (ECw) and sodium adsorption ratio (SARw). Field experiments were conducted to determine the effects of water quality (ECw of 0.5–20 dS m?1 and SARw of 0.5–40 mol0.5 l?0.5) on the hydraulic properties of a sandy clay loam soil (containing ～421 g gravel kg?1 soil) at applied tensions of 0–0.2 m. The mean unsaturated hydraulic conductivity [K(ψ)], sorptive number (α) and sorptivity coefficient (S) varied with change in ECw and SARw as quadratic or power equations, whereas macroscopic capillary length, λ, varied as quadratic or logarithmic equations. The maximum value of K(ψ) was obtained with a ECw/SARw of 10 dS m?1/20 mol0.5 l?0.5 at tensions of 0.2 and 0.15 m, and with 10 dS m?1/10 mol0.5 l?0.5 at other tensions. Changes in K(ψ) due to the application of ECw and SARw decreased as applied tension increased. Analysis indicated that 13.7 and 86.3% of water flow corresponded to soil pore diameters <1.5 and >1.5 μm, respectively, confirming that macropores are dominant in the studied soil. The findings indicated that use of saline waters with an EC of <10 dS m?1 can improve soil hydraulic properties in such soils. Irrigation waters with SARw < 20 mol0.5 l?0.5 may not adversely affect hydraulic attributes at early time; although higher SARw may negatively affect them.  相似文献   

9.
A method is described for the rapid and simple assay of soil β-glucosidase activity. It involves colorimetric estimation of ρ-nitrophenol released by β-glucosidase activity when soil is incubated in McIlvaine buffer (pH 4.8) with ρnitrophenyl βd-glucoside and toluene at 30°C for 1 hr. The method has been applied to three different soils. The range of β-glucosidase activity in cultivated soils was from 10.1 to 15.2 mµ mole per min per gram of dried soil. Km value for ρ-nitrophenyl β-d-glucoside was 3.3 × 10-4 M. Optimum pH was 4.8.  相似文献   

10.
Quantity–intensity relations of potassium (K) were worked out for guava orchard soils. Equilibrium activity ratio of potassium (ARe k) ranged from 0.46?×?10?3 to 21.30?×?10?3 (mol L?1)0.5. The majority of the samples had less than 1?×?10?3 (mol L?1)0.5, indicating K depletion in these soils due to continuous K mining. ARe k was significantly and positively correlated with available forms of K, K saturation percentage, labile K (KL), and specific-site K (KX) and negatively correlated with free energy of exchange (–ΔG). The potential buffering capacity (PBC0 K) of K varied from 8.8 to 286.2 cmol kg?1/(mol L?1)0.5. PBC0 K was positively and significantly correlated with clay content. Sixty percent of the soils had ΔK0 values of less than 0.1 cmol kg?1. High KG (Gapon selectivity coefficent) indicated high affinity for K in these soils. Leaf K was positively and significantly correlated with ΔK0, KL, and KX and negatively correlated with –ΔG.  相似文献   

11.
Cadmium distribution coefficients, K d were determined at low Cd concentrations (solute: 0.2 to 3.0 μg Cd dm?3, soil: 0.044 to 1.1 mg Cd kg?1) for 63 Danish agricultural soils. The K d values ranged from 15 to 2450 L kg?1. About 40% of the soils had K d values below 200 L kg?1. The observed K d values correlated very well with soil pH (r 2 = 0.72). Introducing soil organic matter content as a second parameter improved the correlation some (r 2 = 0.79). No further improvements were obtained by introducing traditional soil parameters as clay, silt, fine sand, coarse sand and CEC or ‘reactive’ parameters as oxyhydroxides of Mn, Fe and Al. The identified regression equation for predicting K d values indicates that K d approximately doubles for each 0.5 unit increase in pH or 2% increase (weight basis) in organic matter content.  相似文献   

12.
Abstract

Heavy‐metal inhibition of nitrification in soils treated with reformulated nitrapyrin was investigated. Clarion and Okoboji soils were treated with ammonium sulfate [(NH4)2SO4] and a nitrification inhibitor. Copper(II) (Cu), Zinc(II) (Zn), Cadmium(II) (Cd), or Lead(II) (Pb) were added to each soil. A first‐order equation was used to calculate the maximum nitrification rate (K max), duration of lag period (t′), period of maximum nitrification (Δt), and the termination period of nitrification (t s). In the Clarion soil, the K max decreased from 12 mg kg?1 d?1 without the nitrification inhibitor to 4, 0.25, 0.86, and 0.27 mg kg?1 d?1, respectively, when the inhibitor and Cu, Zn, Pb, or Cd were applied. In the Okoboji soil, K max decreased from 22 mg kg?1 d?1 with no inhibitor to 6, 3, 4, and 2 mg kg?1 d?1, respectively, when an inhibitor and Cu, Zn, Pb, or Cd were added. The t′ varied from 8 to 25 d in the Clarion soil and from 5 to 25 d in the Okoboji soil, due to addition of Cu, Zn, Pb, or Cd and the inhibitor.  相似文献   

13.
Heats of adsorption and adsorption isotherms of ammonia gas were measured at 300 K (27 °C) on outgassed soil saturated with Na+, K+, NH4+, Ca2+, or Mg2+ ions. The Ca and Mg soils adsorbed apparently one more NH2 molecule per exchangeable ion than the Na and K soils, mostly in the relative pressure range o to 0.005, but not much more than the NH4 soil. The initial heat of adsorption was c. 75 kJ mol-1 on the Ca and Mg soils and c. 60 kJ mol-1 on the other soils. The results suggest that most NH, is sorbed on these soils through reactions not involving exchangeable cations.  相似文献   

14.
The effects of zeolite application (0, 4, 8 and16 g kg?1) and saline water (0.5, 1.5, 3.0 and 5.0 dS m?1) on saturated hydraulic conductivity (K s) and sorptivity (S) in different soils were evaluated under laboratory conditions. Results showed that K s was increased at salinity levels of 0.5‐1.5 dS m?1 in clay loam and loam with 8 and 4 g zeolite kg?1 soil, respectively, and at salinity levels of 3.0–5.0 dS m?1 with 16 g zeolite kg?1 soil. K s was decreased by using low and high salinity levels in sandy loam with application of 8 and 16 g zeolite kg?1, respectively. In clay loam, salinity levels of 0.5–3.0 dS m?1 with application of 16 g kg?1 zeolite and 5.0 dS m?1 with application of 8 g zeolite kg?1 soil resulted in the lowest values of S. In loam, all salinity levels with application of 16 g zeolite kg?1 soil increased S compared with other zeolite application rates. In sandy loam, only a salinity level of 0.5 dS m?1 with application of 4 g zeolite kg?1 soil increased S. Other zeolite applications decreased S, whereas increasing the zeolite application to 16 g kg?1 soil resulted in the lowest value of S.  相似文献   

15.
Studies on selenium adsorption were conducted on seleniferous and non‐seleniferous soils of north‐west India. Soils were equilibrated with graded levels of Se ranging from 1 to 100 μg ml—1 tagged with 75Se in the presence of sulphate, nitrate and phosphate ions, generally being applied to soils as inorganic fertilizers. The adsorption of Se on different soils, both in the presence and absence of competing anions, increased with increase in the level of Se added. Adsorption of Se conformed to Langmuir equation. In the absence of any competing anions, adsorption maxima of Se for different soils ranged from 270 to 461 μg g—1. The corresponding values decreased appreciably in the presence of competing anions; per cent decrease ranged from 3 to 21 at 10 μg SO4‐S ml—1, from 8 to 40 at 60 μg NO3‐N ml—1 and 32 to 56 at 15 μg H2PO4‐P ml—1. The bonding energy of Se in different soils decreased by 33 to 66 per cent in the presence of only phosphate ions. The changes in bonding energy were inconsistent in the case of nitrate and sulphate ions. At equal concentration of added P and Se, the amount of P adsorbed was 2 to 3 times the amount of Se adsorbed. With increasing concentration of Se, greater amounts of S were released in the equilibrium solution. The distribution coefficients (Kd) decreased significantly in the presence of different anions; the effect was conspicuous in the case of phosphate ions.  相似文献   

16.
For forty-one soils (pH > 5.0) from southern England and eastern Australia, the Langmuir equation was an excellent model for describing P adsorption from solutions < 10-3M P, if it was assumed that adsorption occurs on two types of surface of contrasting bonding energies. For most of these soils, which were relatively undersaturated with P, this equation may be written as: where x = adsorption, k = adsorption/desorption equilibrium constant, xm= monolayer adsorption capacity, and c = equilibrium solution concentration. The relative magnitude of the parameters for each surface were approximately: xm= 0.3 x″m=0.3 and k′= 100 k. More than 90 per cent of the native adsorbed P occurs on the high-energy surface in most soils.  相似文献   

17.
SOLUBILITY AND SORPTION OF CADMIUM IN SOILS AMENDED WITH SEWAGE SLUDGE   总被引：1，自引：0，他引：1  
The mechanisms governing the retention and release of Cd in two soils, a loam and a loamy sand, pretreated with anaerobically digested sewage sludges or with chemical fertilizers, were studied using batch equilibration in 0.05 m Ca(NO3)2 solution containing up to 6 μg Cd/ml. Adsorption rather than precipitation as Cd3(PO4)2 limited solution Cd2+ concentration. With the addition of 50 μg Cd/g, however, precipitation as CdCO3 was likely at pH 7.6. Cadmium adsorption increased with increasing soil pH. The differences in Cd adsorption between different soil treatments were attributed mainly to the soil pH (6.9 to 7.9) induced by sludge application. About 82 to 92 per cent of adsorbed Cd was retained by cation exchange and complexing sites. Soils treated with sludge increased the amount of exchangeable Cd but reduced the amount of complexed Cd compared with the fertilized soil. Cadmium retention by cation exchange became more dominant as the amount of Cd in the soil was increased.  相似文献   

18.
Assessing metal contamination of sediments requires knowledge of the geochemical partitioning of trace metals at the sediment-water interface. Under controlled laboratory conditions, sequential extraction was conducted to determine the associations of metals (Cd, Cr, and Zn) and radiotracers (109Cd, 51Cr, and 65Zn) with various geochemical phases and the different partitioning and mobility of metals for two types of surface sediments collected from the Huanghe and Changjiang Rivers in Eastern China. The residual phase was the major phase for stable metal binding, indicating that these sediments had little subjection to recent anthropogenic influences. Fe–Mn oxides were the next important binding phases for metals. The partitioning of metals in various geochemical phases as a function of the duration of the radiolabeling was also examined. Trace metals transferred among the different geochemical phases over the 30 days radiolabeling period, particularly between the carbonate and Fe–Mn oxides phases. The freshwater-sediment distribution coefficients (K d) of three metals were investigated in batch experiments using the radiotracer technique. The decreasing K d with increasing metal concentration(from 0.5 to 200 μg L-1) may be explained by competitive adsorption. The metal K d in sediments from the Changjiang River was greater than those from the Huanghe River, presumably because of the higher Fe/Mn and organic carbon contents in Changjiang River sediment. The K d decreased with increasing total suspended solid load from 3 to 500 mg L-1, and was Cr > Zn > Cd. For Cd and Zn, increasing the pH from 5 to 8 resulted in an increase in K d due to the reduced H+ competition and increasing sorptionpotential. However, the K d for Cr in the sediments from both rivers showed no relationship with pH, presumably becauseof the complexity of the Cr species and environmental behavior.  相似文献   

19.
Two Oxisols (Mena and Malanda), a Xeralf and a Xerert from Australia and an Andept (Patua) and a Fragiaqualf (Tokomaru) from New Zealand were used to examine the effect of pH and ionic strength on the surface charge of soil and sorption of cadmium. Adsorption of Cd was measured using water, 0.01 mol dmp?3 Ca(NO3)2, and various concentrations of NaNO3 (0.01–1.5 mol dm?3) as background solutions at a range of pH values (3–8). In all soils, the net surface charge decreased with an increase in pH. The pH at which the net surface charge was zero (point of net zero charge, PZC) differed between the soils. The PZC was higher for soils dominated by variable-charge components (Oxisols and Andept) than soils dominated by permanent charge (Xeralf, Xerert and Fragiaqualf). For all soils, the adsorption of Cd increased with an increase in pH and most of the variation in adsorption with pH was explained by the variation in negative surface charge. The effect of ionic strength on Cd adsorption varied between the soils and with the pH. In Oxisols, which are dominated by variable-charge components, there was a characteristic pH below which increasing ionic strength of NaNO3 increased Cd adsorption and above which the reverse occurred. In all the soils in the normal pH range (i.e. pH>PZC), the adsorption of Cd always decreased with an increase in ionic strength irrespective of pH. If increasing ionic strength decreases cation adsorption, then the potential in the plane of adsorption is negative. Also, if increasing ionic strength increases adsorption below the PZC, then the potential in the plane of adsorption must be positive. These observations suggest that, depending upon the pH and PZC, Cd is adsorbed when potential in the plane of adsorption is either positive or negative providing evidence for both specific and non-specific adsorption of Cd. Adsorption of Cd was approximately doubled when Na rather than Ca was used as the index cation.  相似文献   

20.
We studied the dynamics of Cd uptake and depuration in epilithic periphyton and in the grazing amphipod Hyalella azteca. Both stable Cd, sufficient to achieve an aqueous concentration of 90 ng L?1, and its radiotracer 109Cd, were added during 1987 to the epilimnion of oligotrophic Lake 382 of the Experimental Lakes Area in northwestern Ontario. Cadmium dynamics within both periphyton and Hyalella were rapid, with equilibrium being approached within two weeks. For periphyton, the Cd uptake rate constant (K uw ) was 3.8×104 d?1 with a depuration rate of 0.29 d?1. For Hyalella the depuration rate was 0.36 d?1, 10% due to growth dilution and 90% to excretion or desorption. The total Cd uptake rate (k ut ) by Hyalella was 6.1×104 d?1, with more of the uptake (58%) derived from food (periphyton) than from water. Hyalella assimilated 80% of ingested Cd. Steady-state bioconcentration factors (BCF) were at least 10-fold higher than previously published values for Amphipoda. In periphyton and Hyalella the BCF were 1.2×105 and 3.2×105, respectively.  相似文献   

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