土壤中铁氧化物对铅吸附-解吸的影响

选择上海地区广泛分布的水稻土,通过静态吸附平衡试验,比较土壤去除非晶质氧化铁和去除游离氧化铁后对Pb2+的吸附-解吸行为,采用数学模型拟合,探讨3种土壤的最佳拟合方程、最大吸附的理论值和亲和能力,进而研究非晶质氧化铁和游离氧化铁对Pb2+吸附-解吸的影响。结果表明,去除氧化铁后吸附能力和亲和能力均减弱,原土的最大吸附量为29.21 g/kg,非晶质氧化铁的贡献值为3.52 g/kg,游离氧化铁的贡献值为8.32 g/kg。     

Competitive Retention of Lead and Cadmium on an Agricultural Soil

Lead and cadmium contamination of an agricultural soil has been studied using batch and column experiments. Thermodynamics of theretention phenomena may be represented by a Langmuir isotherm foran aqueous metal concentration up to 100 mg L^-1. First order kinetics with respect to the solid phase yield good predictabilityfor both batch and column experiments. Kinetics and thermodynamics of lead retention predominate over those ofcadmium. As a consequence, lead is preferentially retainedand can even displace sorbed cadmium. In the event of anspill involving both metals, cadmium would move further inthe soil and its aqueous concentration downstream could beeven higher than that of the influent solution, increasingpotential risks. A two-region model has been used to fit all the experimental results. Satisfactory predictions for column experiments are obtained with parameters which are consistent with those obtained for the batch experiments, for which sorption is described by a Langmuir isotherm including competitive retention.     

Adsorption–desorption of metolachlor and atrazine in Indian soils: effect of fly ash amendment

The effect of two fly ashes as soil amendment on the adsorption–desorption of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylphenyl)] and atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) was studied in alluvial and laterite soils. The adsorption data for both the herbicides fitted well the Freundlich equation, and Freundlich adsorption coefficient (K _f) increased with an increase of fly ash amount. Both the fly ashes differed in their extent to increase herbicide sorption, and the effect was different in different soils. Atrazine was sorbed more in the soils/soils?+?fly ash mixtures than the metolachlor. The K _f values showed significant correlation with the amount of fly ash amendment (correlation coefficient, R?>?0.982). The desorption isotherms also fitted the Freundlich equation, and desorption showed hysteresis which increased with an increase in the content of fly ash amendment. The free energy change (ΔG) indicated that the sorption process is exothermic, spontaneous, and physical in nature. The study has shown that fly ash as soil amendment significantly increased the sorption of metolachlor and atrazine, but the effect is soil- and fly ash-specific.     

Sorption and desorption of salinomycin sodium in clay, loamy sand, and sandy soils

Salinomycin sodium (BIO-COX) is polyether ionophore, commonly used in the poultry industries for the prevention of coccidial infections and promotion of growth. Salinomycin sodium (SAL-Na) is very toxic, and may be fatal, if swallowed, inhaled, or absorbed through the skin than many other antibiotics, thus evaluating their fate in the soil environment is of importance. Sorption of SAL-Na was measured in clay, loamy sand, and sandy soil at different pH 4, 7, and 9, and desorption with phosphate buffer (pH 7) using batch equilibration technique. SAL-Na was sorbed by all the soils studied, the sorption of SAL-Na by the sandy soil increased as the pH decreased, while the sorption of salinomycin in clay and loamy sand soil increased as the pH increased. Desorption of salinomycin from the soil with phosphate buffer (pH 7) over the 24 h period was 80-95% of the amount added. The similar trend was observed in desorption with pH 4, 7 and at different concentrations and slight less desorption was observed in pH 9. When compared to clay and loamy sand soil, sandy soil was recorded maximum (95%) desorption.     

Effect of temperature on single and competitive adsorptions of Cu(II) and Zn(II) onto natural clays

This study conducted a combined adsorption-sequential extractionanalysis (CASA), by which five phases (i.e., exchangeable, carbonate, Mn-Oxide, organic, and Fe-Oxide phases) of adsorbed heavy metals were analyzed, to investigate temperature effects on single and competitive adsorptions of Zn(II) and Cu(II) ontonatural clays. In the case of single adsorption of Zn, the exchangeable phase adsorption decreased from 65 to 40%, but thecarbonate phase adsorption increased from 30 to 40%, with an increase in temperature from 15 to 55 °C. However, in itscompetitive adsorption with Cu, Zn was mostly present in the exchangeable phase (over 90%), and with an increase in temperature, the exchangeable phase adsorption decreased only 10%. In the case of Cu, over 50% among the total amount of adsorption was present in the carbonate phase in both cases ofsingle and competitive adsorptions. The carbonate phaseadsorption of Cu increased from 56 to 61% and from 60 to 66% in single and competitive adsorptions, respectively, with atemperature increase. These results show that in the case of Zn,the major mechanism of retention in natural clay soils might beexchangeable phase adsorption, especially in the case of competitive adsorption with Cu. However, in the case of Cu, the major mechanism might be carbonate phase adsorption, which is known to be a more immobile phase than exchangeable phase adsorption. It seems that the adsorption of Zn and Cu onto natural clays is an endothermic reaction, which represents thatthe adsorption equilibrium constants and capacities increase with a temperature increase, with the exception of exchangeablephase adsorption.     

Adsorption of antimony(V) by floodplain soils, amorphous iron(III) hydroxide and humic acid

Antimony (Sb) emissions to the environment are increasing, and there is a dearth of knowledge regarding Sb fate and behaviour in natural systems. In particular, there is a lack of understanding of sorption of the oxidised Sb(V) species onto soils and soil phases. In this study sorption of Sb(V) by two organic rich soils with high levels of oxalate extractable Fe was examined over the pH range of 2.5-7. Furthermore, the sorption behaviour of Sb(V) was examined in two phases mimicking those dominant in the experimental soils, namely a solid humic acid and an amorphous Fe(OH)3, across the same pH range. Sorption of Sb by the soils and the humic acid fitted a Freundlich type isotherm, with the equation parameters reflecting changes in bonding affinity corresponding to pH changes. The soils sorbed >75% of the added Sb in all trials, and 80-100% at pH values less than approximately 6.5. The Fe(OH)3 retained >95% of the added Sb in all experiments. The humic acid sorbed up to 60% of the added Sb at acidic pH values, but sorption decreased to zero at higher pH values. Further adsorption studies are recommended, such as examining the effects of ion competition and changes in ionic strength.     

Rate-Limited Desorption of Volatile Organic Compounds from Soils and Implications for the Remediation of a Louisiana Superfund Site

The rates of desorption of trichloroethylene (TCE) and 1,3-dichlorobenzene (DCB) from a silty soil at a Superfund site and a silty-clayey soil from an uncontaminated bottomland hardwoodswamp in Baton Rouge, Louisiana were studied in laboratory batchsystems. The effect of the age of soil contamination was studiedusing a laboratory-spiked soil incubated for 3 days, 3 months and5 months. An empirical non-linear model was used to describe thebi-phasic nature of desorption with one fraction (labile) beingreleased in relatively short periods of time (typically 24–100 hr) and a second fraction (non-labile or irreversible) beingresistant to desorption. The non-linear model parameters, viz.,the fraction of the chemical released rapidly (F), and the firstorder desorption rate coefficients, k ₁ and k ₂respectively for the labile and slowly released fractions weredetermined by fitting the experimental data to the model. Thedata fit the model well as indicated by the high r ² values.The estimate of k ₁ was good. However, the values of k ₂are known with less precision due to the limited duration of theexperiment and number of samples taken at long times. In addition, desorption kinetics of 3 and 5-month old contaminatedsoils showed that progressively less amount of contaminant was available for facile desorption (lower F) compared to freshly contaminated soil. The labile fraction had desorption rate constants of the order of 10^-1 h^-1, whereas the slowlyreleased fraction had rate constants of the order of 10^-4 h^-1 in accord with literature reported values for a varietyof other compounds and soils. Possible mechanisms describing these rates and implications for the site clean up are discussed.     

Soil-Water Partitioning and Desorption Hysteresis of Volatile Organic Compounds from a Louisiana Superfund Site Soil

The adsorption and desorption of three volatile organic compounds (1,2- dichloroethane, 1,1,2- trichloroethane and 1,1,2,2-tetrachloroethane) from a previously uncontaminated clayey soil sample from a Superfund site in North Baton Rouge,Louisiana was studied. In the linear range of the adsorption isotherm, the partition constants were not affected by the presence of the co-solutes. The adsorption isotherms over a wide concentration range on the soil followed the nonlinearFreundlich isotherm. The desorption of the compounds showedsignificant hysteresis at all concentrations studied. Approximately 20 to 70% of the adsorbed mass of organic compounds resisted the desorption even after five months ofsuccessive desorption steps. The desorption of four compounds(1,2-dichloroethane, 1,1,2-trichloroethane, 1,4-dichlorobenzeneand hexachlorobutadiene) from a contaminated soil sample fromthe same site was also studied. The aqueous concentration declined as the successive desorption steps progressed. For hexachlorobutediene the desorption can be visualized as occurring in two stages. The first stage involved a loosely bound or reversible fraction and the second stage involveda tightly bound or resistant fraction.     

Effects of pH and low molecular weight organic acids on competitive adsorption and desorption of cadmium and lead in paddy soils

The bioavailability and ultimate fate of heavy metals in the environment are controlled by adsorption-desorption process. Batch equilibrium experiments were performed to assess the effects of pH and low molecular weight organic acids (LMWOAs) on competitive adsorption and desorption of cadmium and lead in paddy soils from China. The results indicated that both soils exhibited greater sorption capacity for lead (Pb) (1.37-1.61-fold) than cadmium (Cd) as estimated by the maximum sorption parameter (Q) from the Langmuir equation. The Langmuir bonding energy coefficient (b) and distribution coefficient (K (d)) were greater for Pb than for Cd, furthermore, b (binary) and K (d) (single) were greater than b (single) and K (d binary), indicating that competition for sorption sites promote the retention of both metals on more specific sorption sites. Both Cd and Pb desorption as a function of solution pH was characteristic of "S" pattern. The presence of LMWOAs inhibited Cd or Pb desorption at the low concentrations (≤0.1 mmol L(-1)) but promoted Cd and Pb desorption at higher concentrations (≥0.5 mmol L(-1) for citric acid and ≥1 mmol L(-1) for malic and oxalic acid). The two paddy soils had a greater d (Cd) than d (Pb) in the presence of LMWOAs, indicating that Cd desorption was more affected by the presence of LMWOAs in binary metal system.     

Phosphorus sorption–desorption behaviour of river bed sediments in the Abshineh river, Hamedan, Iran, related to their composition

Phosphorus (P) sorption by sediments may play a vital role in buffering P concentration in the overlying water column. To characterize P sorption–desorption in the river bed sediments, 17 bed sediment samples collected from Abshineh river, in a semi arid region, Hamedan, western Iran were studied through a batch experiment and related to sediment composition. The sorbed fraction ranged from 4.4% to 5.4% and from 38.5% to 86.0% of sorption maxima when 20 and 1,500 mg P kg^?1, respectively, was added to the sediment samples. Phosphorus sorption curves were well fitted to the Langmuir model. Zero equilibrium P concentration ranged from 0.10 to 0.51 mg P l^?1 and varied with sediment characteristics. Phosphorus desorption differed strongly among the studied bed sediments and ranged from 10.8% to 80.2% when 1,500 mg P kg^?1 was added. The results of the geochemical modelling indicated that even under low P addition (2 mg l^?1), the solutions are mainly saturated with respect to hydroxyapatite and ß-tricalcium phosphate minerals and undersaturated with respect to other Ca and Mg minerals, whereas under higher P addition (150 mg l^?1), most Ca–P solid phases, except the most soluble mineral (brushite), will likely precipitate. A Langmuir sorption maximum was positively correlated with carbonate calcium. Estimated P retention capacity of the bed sediments are generally lower and zero equilibrium P concentration values higher in upstream sites than at the downstream sites, suggesting that sediments in upstream and downstream may act as source and sink of P, respectively.     

Visualising the equilibrium distribution and mobility of organic contaminants in soil using the chemical partitioning space

Assessing the behaviour of organic chemicals in soil is a complex task as it is governed by the physical chemical properties of the chemicals, the characteristics of the soil as well as the ambient conditions of the environment. The chemical partitioning space, defined by the air-water partition coefficient (K(AW)) and the soil organic carbon-water partition coefficient (K(OC)), was employed to visualize the equilibrium distribution of organic contaminants between the air-filled pores, the pore water and the solid phases of the bulk soil and the relative importance of the three transport processes removing contaminants from soil (evaporation, leaching and particle erosion). The partitioning properties of twenty neutral organic chemicals (i.e. herbicides, pharmaceuticals, polychlorinated biphenyls and volatile chemicals) were estimated using poly-parameter linear free energy relationships and superimposed onto these maps. This allows instantaneous estimation of the equilibrium phase distribution and mobility of neutral organic chemicals in soil. Although there is a link between the major phase and the dominant transport process, such that chemicals found in air-filled pore space are subject to evaporation, those in water-filled pore space undergo leaching and those in the sorbed phase are associated with particle erosion, the partitioning coefficient thresholds for distribution and mobility can often deviate by many orders of magnitude. In particular, even a small fraction of chemical in pore water or pore air allows for evaporation and leaching to dominate over solid phase transport. Multiple maps that represent soils that differ in the amount and type of soil organic matter, water saturation, temperature, depth of surface soil horizon, and mineral matters were evaluated.     

Models for the adsorption of organic compounds at gas-water interfaces

The solvation parameter model is used to characterize interactions responsible for adsorption at the gas-water interface for bulk water at 15 and 25 degrees C, snow at -6.8 degrees C, mineral-supported water films (alumina, calcium carbonate and quartz) at 15 degrees C, and dry soil at 15 degrees C. The mineral-supported water films and dry soil adsorption data are modeled at different relative humidities in the range 40-99%. The models produce satisfactory results with standard errors of the estimate of 0.12 to 0.17 for regression of the model predicted adsorption equilibrium constants against the experimental values (range for equilibrium constants -2 to -7 log units). The water surface is polar with a significant capacity for dipole-type and hydrogen-bonding interactions. In addition, it is strongly electron lone pair repulsive. Dispersion interactions favor adsorption at the water surface. Mineral-supported water films at relative humidities greater than 40% demonstrate adsorption properties similar to bulk water. The adsorption characteristics, however, depend on the relative humidity and the nature of the support. In the case of dry soil the adsorption properties at different relative humidities cannot simply be explained by adsorption of a water film covering the soil surface and the changes in adsorption characteristics with relative humidity are more complex than the mineral-supported water films.     

Recovery of sulfate saturated soils in the Plynlimon catchments, mid-Wales following reductions in atmospheric S inputs from the 1980s to 2011

Sulfate adsorption capacity of B-horizons of base-poor, predominantly stagnopodzol, soils from the Plynlimon catchments, mid-Wales was determined by combination of laboratory adsorption and desorption isotherms. Results show that sulfate adsorption capacity of a range of stagnopodzol (Histic-stagno-podzol (Leptic), WRB), brown podzolic soil (Histic-umbrisol (Leptic), WRB) and stagnohumic gley (Histic-stagno-gleysol, WRB) B-horizons was positively related to the amounts of extractable (pyrophosphate and oxalate) Fe + Al, with the stagnopodzol and brown podzolic soil Bs horizon having the largest adsorption capacity and stagnohumic gley Bg horizon the smallest adsorption capacity. Results show that dissolved organic carbon (DOC) has a negative but limited effect on sulfate adsorption in these soils. Results obtained from a set of historical soil samples revealed that the grassland brown podzolic soil Bs horizon and afforested stagnopodzol Bs horizon were highly saturated with sulfate in the 1980s, at 63% and 89% respectively, whereas data from some recently sampled soil from two sites revisited in 2010-11 indicates that percentage sulfate adsorption saturation has since fallen substantially, to 41% and 50% respectively. Between 1984 and 2009 the annual rainfall-weighted mean excess SO(4)-S concentration in bulk precipitation declined linearly from 0.37 mg S l(-1) to 0.17 mg S l(-1). Over the same period, flow weighted annual mean stream water SO(4)-S concentrations decreased approximately linearly from 1.47 mg S l(-1) to 0.97 mg S l(-1) in the plantation afforested Hafren catchment compared to a drop from 1.25 to 0.69 mg S l(-1) in the adjacent moorland catchment of the Afon Gwy. In flux terms, the mean decrease in annual stream water SO(4)-S flux has been approximately 0.4 kg S ha(-1) yr(-1), whilst the recovery in stream water quality in the Afon Cyff grassland catchment has been partly offset by loss of SO(4)-S by desorption from the soil sulfur pool of approximately 0.2 kg S ha(-1) yr(-1).     

氟氯烃检测中的富集采样研究

本文用自制的吸附采样管和解吸装置完成了大气中痕量氟氯烃的采样测定,其吸附效率达８５％以上,解吸效率达８７％,富集倍数达１１４４倍。研究了温度对吸附和解吸效率的影响。     

A Computational Fluid Dynamic Model for Prediction of Organic Dyes Adsorption from Aqueous Solutions

Modelling of the removal of synthetic dyes from aqueous solutions by adsorbents is important to develop an appropriate treatment plan using adsorption process. This paper presents a computational fluid dynamic model incorporating the Langmuir isotherm scheme and second-order kinetic expression to describe the adsorption process. The governing equation of the model was numerically solved using PHOENICS software to simulate synthetic dyes adsorption from the aqueous system. The experimental results presented in this study and taken from the literature for the removal of synthetic dyes were compared with those results predicted by the numerical model. The predicted outputs of the model match the experimental measurements satisfactory. A sensitivity analysis of the major parameters that influence the percent of dye removal from solution phase has been carried out. Three of the main parameters taken into account were the kinetic rate constant, amount of dye adsorbed at equilibrium and the Langmuir isotherm constant. It was found that the model is most sensitive to the amount of dye adsorbed at equilibrium. This effect is most obvious at the early stages of the adsorption process when the rate of dye removal is very fast. Quantification of the reaction mechanism allows developing an appropriate remediation strategy based on the adsorption process.     

Uptake of arsenic by alkaline soils near alkaline coal fly ash disposal facilities

The attenuation of arsenic in groundwater near alkaline coal fly ash disposal facilities was evaluated by determining the uptake of arsenic from ash leachates by surrounding alkaline soils. Ten different alkaline soils near a retired coal fly ash impoundment were used in this study with pH ranging from 7.6 to 9.0, while representative coal fly ash samples from two different locations in the coal fly ash impoundment were used to produce two alkaline ash leachates with pH 7.4 and 8.2. The arsenic found in the ash leachates was present as arsenate [As(V)]. Adsorption isotherm experiments were carried out to determine the adsorption parameters required for predicting the uptake of arsenic from the ash leachates. For all soils and leachates, the adsorption of arsenic followed the Langmuir and Freundlich equations, indicative of the favorable adsorption of arsenic from leachates onto all soils. The uptake of arsenic was evaluated as a function of ash leachate characteristics and the soil components. The uptake of arsenic from alkaline ash leachates, which occurred mainly as calcium hydrogen arsenate, increased with increasing clay fraction of soil and with increasing soil organic matter of the alkaline soils. Appreciable uptake of arsenic from alkaline ash leachates with different pH and arsenic concentration was observed for the alkaline soils, thus attenuating the contamination of groundwater downstream of the retired coal fly ash impoundment.     

Treatment of wastewater containing arsenic using Rhazya stricta as a new adsorbent

The effective removal of heavy metals from aqueous wastes is among the most important issues for many industrialized countries. Removal of arsenic (As) from aqueous solutions was studied using Rhazia stricta biomass. The batch experiments are carried out to investigate the effect of the significant process parameters such as pH, contact time, solute concentration and adsorbent dose. The optimum pH required for maximum adsorption was found to be 5. The equilibrium data for the adsorption of As(V) on R. stricta are tested with various adsorption isotherm models such as Langmuir, Freundlich, Tempkin and Generalized equation. Results indicate the following order to fit the isotherm: Langmuir (1 and 2)?>?Tempkin?>?Generalized form?>?Freundlich. A comparison of two kinetic models showed that our data fitted well to the Elovich model.     

复配修饰黏土对四环素的吸附及其应用探究

分别采用十二烷基三甲基溴化铵(DTAB)和十二烷基磺酸钠(SDS)对十二烷基二甲基甜菜碱(BS-12)修饰高岭土(K)进行复配修饰,以批处理法探究其对紫色土(PS)吸附四环素(TC)的影响.结果表明:TC吸附是自发、吸热和熵增的反应,各供试材料对TC的吸附均符合Langmuir模型,且相同条件下60％复配修饰效果更佳....     

Partition Constants and Adsorption/Desorption Hysteresis for Volatile Organic Compounds on Soil from a Louisiana Superfund Site

The adsorption of four volatile organic compounds (1,4-dichloro-benzene, 1,2-dichloroethane, 1,2,2-trichloroethane and 1,1,2,2,-tetrachloroethane) on three soil types from a Superfund site (Petroprocessors Inc) in Baton Rouge, LA was studied with the purpose of obtaining an overall correlation for inclusion in a groundwater transport model being developed for site remediation. The soil-water partition constant, K_d was determined using a standard ASTM procedure (E–1195–87). Using the data for different soil types (fraction organic carbon between 0.11% and 1.13%) and different mineral surface areas (7 to 45 m²/g), the organic carbon contribution (K_oc) and the mineral matter contribution (K_min) to the partition constant were determined. The soils obtained were either from the Pleistocene period or recent shallow deposits at the site. Both log K_oc and log K_min were linearly correlated to log K_ow, the octanol-water partition constant. This data provided the basis for obtaining a general correlation for K_d on different soil types at the site. The predicted values were in agreement with that for a composite soil from the same site. The desorption of compounds from the high clay soil after the 24 hour adsorption period was observed to show a biphasic behavior, namely, an easily desorbed fraction and a desorption resistant fraction. The easily desorbed fraction was found to be satisfactorily predicted using the conventional K_d as obtained from the adsorption experiment. The slowly desorbing fraction had a time constant of several weeks. The concentration in the desorption resistant compartment was found to be dependant on the initial amount of contaminant available for adsorption. The aqueous phase concentration in equilibrium with the desorption resistant fraction was found to be 8 g/L for dichlorobenzene and 12 g/L for dichloroethane.     

The fate and persistence of polychlorinated biphenyls in soil

The fate and persistence of PCBs 28, 52, 101, 138, and 180 artificially introduced into three soils was studied under a variety of field conditions for up to 415 d following initial contamination. A relationship was detected between ln Koa (octanol/air partition coefficient) and the experimentally observed first-order loss rate constant that was statistically significant at at least the 90% level in all but one instance. In nearly all experiments, PCB persistence was greater in soils of higher organic carbon content. Soil temperature and moisture content were also indicated as important influences on persistence. Significantly longer half-lives were observed in a soil in which initial PCB contamination had occurred ca. 1 year previously. A mass balance showed the most likely mechanism of loss to be volatilisation. Losses attributable to aerobic biodegradation could not be ruled out, but those due to leaching, uptake by biota, and soil erosion were demonstrated to be negligible. First-order rate constants (Kv) were determined for volatilisation of the same congeners from soil under a variety of controlled laboratory scenarios. Multiple linear regression analysis (MLRA) showed the most important influences on kv to be ln Koa (adjusted for soil temperature) and soil organic carbon content. Limited evidence was observed for a relationship between kv and soil moisture content, but not water flux. When tested against field measurements, the MLRA-derived relationship between kv and independent variables predicted to within a factor of 2.5, the persistence of PCBs 28, 52, and 101, However, it did not account for the influence of the age of contaminant association with the soil, soil moisture content or water flux, and failed to function for soils of high organic content, or where ln Koa exceeds ca. 23.