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1.
The objective of this study was to examine the effect of soil pH on zinc (Zn) sorption and desorption for four surface soils from the Canterbury Plains region of New Zealand. Zinc sorption by the soils, adjusted to different pH values, was measured from various initial solution Zn concentrations in the presence of 0.01 M calcium nitrate [Ca(NO3)2]. Zinc desorption isotherms were derived from the cumulative Zn desorbed (µg g?1 soil) after each of 10 desorption periods by sequentially suspending the same soil samples in fresh Zn‐free 0.01 M Ca(NO3)2. Zinc sorption and desorption varied widely with soil pH. Desorption of both native and added Zn decreased continuously with rising pH and became very low at pH values greater than 6.5. The proportion of sorbed Zn that could be desorbed back into solution decreased substantially as pH increased to more than 5.5. However, there were differences between soils regarding the extent of the hysteresis effect.  相似文献   

2.
Solution cadmium (Cd) concentrations and sorption and desorption of native and added Cd were studied in a range of New Zealand soils. The concentration of Cd in solution and the concentrations and patterns of native soil Cd desorbed and added Cd sorbed and desorbed varied greatly between the 29 soils studied. Correlation analysis revealed that pH was the most dominant soil variable affecting solution Cd concentration and sorption and desorption of native and added Cd in these soils. However, organic matter, cation exchange capacity (CEC) and total soil Cd were also found to be important. Multiple regression analysis showed that the log concentration of Cd in solution was strongly related to soil pH, organic matter and total Cd, which in combination explained 76% of the variation between soils. When data from the present study were combined into a single multiple regression with soil data from a previously published study, the equation generated could explain 81% of the variation in log Cd solution concentration. This reinforces the importance of pH, organic matter and total Cd in controlling solution Cd concentrations. Simple linear regression analysis could at best explain 53% of the total variation in Cd sorption or desorption for the soils studied. Multiple regression analysis showed that native Cd desorption was related to pH, organic matter and total Cd, which in combination explained 85% of the variation between soils. For sorption of Cd (from 2 μg Cd g–1 soil added), pH and organic matter in combination explained 75% of the variation between soils. However, for added Cd desorption (%), pH and CEC explained 77%. It is clear that the combined effects of a range of soil properties control the concentration of Cd in solution, and of sorption and desorption of Cd in soils. The fraction of potentially desorbable added Cd in soils could also be predicted from a soil’s Kd value. This could have value for assessing both the mobility of Cd in soil and its likely availability to plants.  相似文献   

3.
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   

4.
Sorption of added inorganic phosphate (P) was irreversible in four contrasting soils and hydrous ferric oxide gel during 16 h desorption after 40 h sorption at the same (iso)pH. Irreversibility increased with increasing time of desorption above 30 h. When the amount of P which was chemisorbed during the sorption step was subtracted from the amount desorbed, the latter fell on the isotherm describing the more-physical, potential-determining sorption. No pH change occurred during desorption and net negative charge decreased by 1 equivalent per mole P desorbed. These results suggested that only more-physically sorbed P was desorbed at the iso-pH. The more-physically sorbed P was also reversible with respect to changes in the ionic strength and cation species of the desorbing solution. The isotopic exchangeability of the more-physically sorbed P was at least ten times greater than that of chemisorbed P. With increasing sorption time, both the ease of desorption and exchangeability of sorbed P decreased. Subsequent to desorption, the exchangeability of the remaining sorbed P also decreased. These observations are interpreted in terms of the concurrent changes in the amounts of chemisorbed and more-physically sorbed P.  相似文献   

5.
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   

6.
High phosphate (Pi) sorption in soils is a serious limiting factor for plant productivity and Pi fertilization efficiency, particularly in highly weathered and volcanic ash soils. In these soils, the sorbed Pi is so strongly held on the surfaces of reactive minerals that it is not available for plant root uptake. The use of phosphate-solubilizing microorganisms (PSM) capable of Pi desorption seems to be a complementary alternative in the management of these soils. The aim of this study was to evaluate the effectiveness of the soil fungus Mortierella sp., a known PSM, to desorb Pi from four soil minerals differing in their Pi sorption capacity. The fungus was effective in desorbing Pi from all tested minerals except from allophane, and its desorption depended on the production of oxalic acid. The effectiveness of the fungus to desorb Pi was ranked as montmorillonite > kaolinite > goethite > allophane. The quantity of desorbed Pi increased by increasing the amount of sorbed Pi. The Pi sorption capacity expressed as P0.2 value (amount of P required to increase a solution P concentration up to 0.2 mg L?1) was a good indicator of the effectiveness of Mortierella sp. to desorb Pi from soil minerals.  相似文献   

7.
On the reversibility of phosphate sorption by soils   总被引：4，自引：0，他引：4  
Sorption of phosphate was induced by incubating phosphate with samples of two soils. Both desorption and further sorption of phosphate were then measured on separate subsamples of the incubated soils. The effects of varying the amount of phosphate incubated with the soil and of period of desorption, or of further sorption, were measured on one soil; the effect of period of incubation was measured on the other. Plots of desorbed phosphate versus concentration were continuous with plots of newly sorbed phosphate versus concentration. Neither of these coincided with the plots of the original additions of phosphate. These results were compatible with a model for the reaction between soil and phosphate in which phosphate is initially adsorbed and subsequently diffuses beneath the adsorbing surfaces. Sorption is reversible in the sense that a continuous curve of sorbed and desorbed phosphate is obtained when these are measured in opposite directions by increasing, or decreasing, the solution concentration of phosphate. However, because dynamic processes are involved, an earlier position of a plot of sorbed phosphate against concentration is not retraced when the concentration is changed.  相似文献   

8.
Cadmium sorption was measured in 10 agricultural soils with pH ranging from 4.5 to 7.9, and total Cd content from 0.27 to 1.04 μg g?1 dry soil. With initial Cd concentrations of 0.5 to 100.0 μM, sorption from 0.002 M CaCl2 was described by the Freundlich adsorption equation but the gradients of the isotherms increased when the initial concentrations were below 0.5 μm. This indicates that there are specific sites of differing sorption energy; differences between soils in the gradients of the isotherms at low initial concentration could largely be accounted for by their contents of ‘free’ Fe2O3. When initial concentrations were below 0.5 μm there was a linear relationship between the quantity of Cd sorbed and the final concentration in solution. This relationship held with all soils except that of lowest pH from which there was a net loss of Cd to the solutions. Desorption was measured from three soils with contrasting pH. With the soil of lowest pH, over 80 per cent of sorbed Cd was desorbed to 0.002 m CaCl2 and up to 30 per cent to 100 or 500 μm solutions of heavy metal chlorides. In contrast, only very small proportions (<1.25 per cent) were desorbed from the other soils with pH 6.7 and 7.8. The results indicate that Cd is strongly sorbed by soils of pH of above 6.0 when added in amounts comparable to additions in sewage sludges or phosphatic fertilizers, and illustrate the importance of liming as a means of reducing the mobility of this metal in soils.  相似文献   

9.
Sorption and desorption of cobalt by soils and soil components   总被引：2，自引：0，他引：2  
The sorption of Co by individual soil components was studied at solution Co concentrations that were within the range found in natural soil solutions. Soil-derived oxide materials sorbed by far the greatest amounts of Co although substantial amounts were also sorbed by organic materials (humic and fulvic acids). Clay minerals and non-pedogenic iron and manganese oxides sorbed relatively little Co. It is considered that clay minerals are unlikely to have a significant influence on the sorption of Co by whole soils. Cobalt sorbed by soil oxide material was not readily desorbed back into solution and, in addition, rapidly became non-isotopically exchangeable with solution Co. In contrast, Co was relatively easily desorbed from humic acid and a large proportion of the Co sorbed by humic acid remained isotopically exchangeable. Cobalt sorbed by montmorillonite was more easily desorbed than that sorbed by soil oxide but less easily than that sorbed by humic acid. Cobalt sorption isotherms for whole soils at low site coverage were essentially linear and the gradients of isotherms increased with pH. A comparison of isotherm gradients for whole soils and individual soil components supported the suggestion that Co sorption in whole soils is largely controlled by soil oxide materials.  相似文献   

10.
An experiment was conducted to observe the phosphate sorption potential of some soils of Bangladesh. Three soil series of calcareous origin, namely Sara (Aquic Eutrochrept), Gopalpur (Aquic Eutrochrept) and Ishurdi (Aeric Haplaquept), and two soil series of non-calcareous origin, namely Tejgaon (Rhodic Paleustult) and Ghatail (Aeric Haplaquept), were selected. The soils were equilibrated with dilute solution of calcium chloride containing graded concentrations of phosphate (0, 1, 2, 5, 10, 25 and 50?μg?P?mL?1), and the amount of phosphate sorbed or desorbed was determined. Although all the soils showed potential for sorbing phosphate from applied phosphorus, their ability to sorb phosphorus differed. Increasing rates of phosphate application increased the amount of P sorption but reduced phosphate sorption percentage in all soils except Tejgaon. Phosphate was sorbed by the soils in the order: Tejgaon > Ghatail > Ishurdi > Gopalpur > Sara at 50?μg?P?mL?1 application. Soils possessing higher amounts of free iron oxide and clay sorbed more phosphate from applied phosphorus.  相似文献   

11.
Abstract

Laboratory experiments were carried out to evaluate lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) sorption‐desorption by three soils of contrasting characteristics. Talamanca (silt loam, montmorillonite, Calcic Haploxeralfs), Mazowe (clay, kaolinite, Rhodic Kandiustalf), and Realejos (sandy silt loam, allophane, Typic Hapludands). A second objective was to study the effect of nitriloacetic acid (NTA) on the sorption process. The Talamanca soil, which had a native pH of 6.4 and presented the highest effective cation exchange capacity (ECEC), sorbed more of each of the metal tested than did the other two soils. When the other two soils were compared metal sorption was also related to pH and ECEC. The very low sorption capacity showed by Realejos may be attributed to the low net surface negative charge density of this soil, arising from its allophanic nature. A common feature of the three soils was the relative strong sorption of both Pb and Cu relative to Cd and Zn with Pb showing the highest sorption levels. The selectivity sequences of metals retention were Pb>Cu>Zn>Cd for Talamanca soil, Pb>Cu>Zn≈Cd for Mazowe, and Pb>Cu>Cd>Zn for Realejos. Metal desorption values were low. The order of metal desorption (Cd≈Zn>Cu>Pb) was the same for the three soils studied. Quantitative differences observed in the extractability of the sorbed metals between the soils (Realejos>Mazowe>Talamanca) indicated that soil properties which enhanced metal sorption contributed at the same time to slow down the backward reaction. The addition of NTA to the soil suspension significantly depressed metal sorption by the three soils investigated. Compared with the free ligand system Pb, Cu, Zn, and Cd sorption in the presence of NTA decreased roughly 50%.  相似文献   

12.
Abstract

In this study the influence of zeolite application and soil liming on cadmium (Cd) sorption by soils in Greece was investigated. The zeolite was natural and consisted mainly of clinoptilolite. The soil samples were strongly acid surface horizons of an Alfisol limed from a pH of 4.0 to 8.5, and a neutral Bt horizon. The result showed that liming and zeolite application substantially increased sorption of Cd in the soils. Cadmium sorption was described adequately by the Freundlich equation whereas the Langmuir model failed to describe Cd sorption in the soils. The Freundlich constant K increased in value by zeolite application as well as by soil liming. A strong relationship was observed between this parameter and soil pH. A high percentage of cadmium sorbed was released in the desorption procedure. The amount of Cd released was reduced by zeolite application as well as by soil liming. It is concluded that zeolite application as well as soil liming increased Cd sorption by the soils.  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.
采用批平衡实验方法,研究了四环素（TC）在褐土和红壤中的吸附和解吸,以及Cd2＋对四环素在两种土壤上吸附和解吸的影响。结果表明,四环素在褐土和红壤中的吸附可以用Freundlich等温吸附方程拟合,所得lgKf分别为3.039和3.169,这表明四环素在红壤中的吸附能力较强。此外,四环素在两种土壤上的解吸过程都存在滞后现象,所得lgKf,des分别为3.292和3.877,这将可能威胁到土壤环境和人体健康。常见重金属Cd2＋的存在会促进四环素在两种土壤上的吸附,在红壤中表现显著（P〈0.05）;同时红壤中四环素的lgKf,des有所增加,而在褐土中的变化不大。  相似文献   

15.
Cadmium sorption and desorption behaviour of hydroxy-Alinterlayered montmorillonite (pillared) was compared with unpillared montmorillonite. Characteristic properties of themontmorillonite, whose interlayer cations were replaced byhydroxy-Al polymers, are its thermal stability up to ～500 °C and increased surface area of about 300 × 103 m2 kg-1. The cation exchange capacity was reduced by ～30% after interlayering withpositively charged hydroxy-Al polymers.Cadmium sorption data for the two montmorillonites fitted verywell (R2 = 0.98 to 0.99) to the Freundlich equation. Inthe concentration range (0.89–17.79 μM Cd L-1) used for the experiment, the unpillared montmorillonite sorbed moreCd than the pillared montmorillonite. Cadmium is possibly retained by electrostatic and chemisorption mechanisms by thepillared montmorillonite whereas electrostatic attraction ismainly responsible for Cd sorption by unpillared montmorillonite. After 5 extractions with 0.01 M NaNO3the amount of Cd desorbed varied between 30–47 and 34–59% for unpillared and pillared montmorillonites, respectively. At lower concentrations of initially sorbed Cd, the amount ofCd desorbed was nearly equal for the two samples.  相似文献   

16.
The leaching of phosphorus (P) within soils can be a limiting consideration for the sustainable operation of intensive livestock enterprises. Sorption curves are widely used to assist estimation of P retention, though the effect of effluent constituents on their accuracy is not well understood. We conducted a series of P‐sorption–desorption batch experiments with an Oxic Haplustalf (soil 1), Haplusterts (soils 2 and 3), and a Natrustalf (soil 4). Phosphorus sources included effluent, orthophosphate‐P in a matrix replicating the effluent's salt constituents (the reference solution), and an orthophosphate‐P solution. Treated soils were incubated for up to 193 days before sequential desorption extraction. Effluent constituents, probably the organic or particulate components, temporarily increased the vulnerability of sorbed‐P to desorption. The increase in vulnerability was removed by 2–113 days of incubation (25°C). Despite vigorous extraction for 20 consecutive days, some P sorbed as part of the treatments of soils 1 and 2 was not desorbed. The increased vulnerability due to effluent constituents lasted a maximum of about one cropping season and, for all other treatments, adsorption curves overestimated vulnerability to desorption. Therefore, adsorption curves provide a conservative estimate of vulnerability to desorption where effluent is used in continued crop production in these soils.  相似文献   

17.
The sorption of cadmium(Cd) is one of the most important chemical processes in soil, affecting its fate and mobility in both soil and water and ultimately controlling its bioavailability. In order to fundamentally understand the sorption/desorption of Cd in soil systems, X-ray absorption fine structure spectroscopy(XAFS) has been applied in numerous studies to provide molecular-level information that can be used to characterize the surface adsorption and precipitation reactions that Cd can undergo. This information greatly improves our current knowledge of the possible chemical reactions of Cd in soil. This paper critically reviews the mechanisms of Cd sorption/desorption at the mineral-water interface based on XAFS studies performed over the past twenty years. An introduction to the basic concepts of sorption processes is provided, followed by a detailed interpretation of XAFS theory and experimental data collection and processing,ending finally with a discussion of the atomic/molecular-scale Cd sorption mechanisms that occur at the soil mineral-water interface. Particular emphasis is placed on literature that discusses Cd adsorption and speciation when associated with iron, manganese, and aluminum oxides and aluminosilicate minerals.Multiple sorption mechanisms by which Cd is sorbed by these minerals have been found, spanning from outer-sphere to inner-sphere to surface precipitation,depending on mineral type, surface loading, and pH. In addition, the application of complementary techniques(e.g.,113 Cd nuclear magnetic resonance(NMR) and molecular dynamics simulation) for probing Cd sorption mechanisms is discussed. This review can help to develop appropriate strategies for the environmental remediation of Cd-contaminated soils.  相似文献   

18.
Abstract

Copper (Cu) is bound strongly to organic matter, oxides of iron (Fe) and manganese (Mn), and clay minerals in soils. To investigate the relative contribution of different soil components in the sorption of Cu, sorption was measured after the removal of various other soil components; organic matter and aluminum (Al) and Fe oxides are important in Cu adsorption. Both adsorption and desorption of Cu at various pH values were also measured by using diverse pasture soils. The differences in the sorption of Cu between the soils are attributed to the differences in the chemical characteristics of the soils. Copper sorption, as measured by the Freundlich equation sorption constants [potassium (K) and nitrogen (N)], was strongly correlated with soil properties, such as silt content, organic carbon, and soil pH. The relative importance of organic matter and oxides on Cu adsorption decreased and increased, respectively, with increasing solution Cu concentrations. In all soils, Cu sorption increased with increasing pH, but the solution Cu concentration decreased with increasing soil pH. The cumulative amounts of native and added soil Cu desorbed from two contrasting soils (Manawatu and Ngamoka) during desorption periods showed that the differences in the desorbability of Cu were a result of differences in the physico‐chemical properties of the soil matrix. This finding suggests that soil organic matter complexes of Cu added through fertilizer, resulted in decreased desorption. The proportions of added Cu desorbed during 10 desorption periods were low, ranging from 2.5% in the 24‐h to 6% in the 2‐h desorption periods. The desorption of Cu decreased with increasing soil pH. The irreversible retention of Cu might be the result of complex formation with Cu at high pH.  相似文献   

19.
Cadmium sorption experiments were performed using four soil separates of different chemical and mineralogical composition, adding Cd solutions with initial concentrations ranging from 15 to 150 μg l?1. At the soils pHs, the sorption isotherms were a mixture of a constant partition isotherm with a high affinity one. Also, more than 90% of the initially added Cd was sorbed by all four soils. These results indicate a high affinity of these soils for trace amounts of Cd. The effect of pH was, in general, to decrease the amount of sorbed Cd as the pH decreased. The sorption isotherms were linear at all pH's. Also, the data fitted the Freundlich's sorption isotherm in all cases, but not Langmuir's. Freundlich's k values were found to be a good index of the relative Cd sorption affinities of the four soils at all the pH's used. It was found that the structural and chemical nature of the soils sorbent complex was a more important parameter than the CEC when studying the sorption of these trace amounts of Cd by soils.  相似文献   

20.
The potential for surface and groundwater contamination of soil applied herbicides is partly dependent on soil properties. Sorption and desorption of diuron and norflurazon were studied in seven soils representative of the southern citrus-belt of Florida using the batch-equilibrium technique. Sorption of herbicides was influenced by soil properties. Sorption coefficients (K d) ranged from 0.84 to 3.26 mL g?1 for diuron and 0.63 to 2.20 mL g?1 for norflurazon indicating weak to moderate binding of herbicides to soil. For norflurazon, K dwas significantly related to organic C content, soil pH, and cation exchange capacity. For diuron, absence of a significant relationship between K dand selected soil properties suggests that the soil properties other than those studied may play a role in determining sorption on these soils. Desorption studies showed that higher amounts of diuron and norflurazon was desorbed by water than by 0.5 M CaCl2. An inverse relationship was apparent between herbicides sorbed and that which was desorbed among the soils studied. The soil which exhibited higher sorption had lower desorption and the soil which exhibited lower sorption had higher desorption.  相似文献   

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