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1.
Distribution coefficients of Cd, Co, Ni, and Zn in soils 总被引：17，自引：0，他引：17
Batch adsorption experiments were conducted with a mixture of solutes at low equilibrium concentrations of Cd (0.7-12.6 μg1−1 ), Co (18-118μg1−1 , Ni (22-330 μg 1−1 ), and Zn (40-1480 μg1−1 ) in 38 different soils. Statistical correlations indicated that metal sorption onto the soils was influenced by the presence of clays and hydrous oxides of Fe and Mn. Based on calculated distribution coefficients for these metals, Co will generally exhibit the highest mobility in soils, but the mobility of Zn will increase faster with decreasing pH. Two types of empirical relationships are developed from these data to estimate values for the distribution coefficients. 相似文献
2.
3.
Caesium and strontium diffusion through sodium montmorillonite at elevated temperature 总被引：1，自引：0，他引：1
Counter ionic migration rates of dilute Cs+ and Sr2+ against sodium in a Na-montmorillonite gel are measured using a radially perfused diffusion cell. Enhanced or surface diffusion for caesium is observed both at ambient and elevated temperature. To quantify these surface diffusivities the ion-exchange properties of the diffusing species are required. Thus, exchange isotherms for caesium against sodium on montmorillonite at 22 and 90°C are given for 10−1 , 10−2 , and 10−3 M background NaCl concentrations. Caesium counterion surface diffusivities at 22 and 90°C are 2.2*10−6 and 8.0 * 10−6 cm2 s−1 , respectively. These values are found to be essentially independent of background ionic strength over the range 10−3 to 10−1 m NaCl. Experimental evidence of enhanced transport through Na-montmorillonite for the divalent cation Sr2+ is also confirmed with a surface diffusivity of 2 * 10−6 cm2 s−1 at 22°C and in 10−1 m NaCl. 相似文献
4.
The reactions of cadmium with calcium carbonate surfaces 总被引：1，自引：0，他引：1
The reaction of cadmium with calcite was studied with 10−6 –10−2 M Cd2+ using 4g CaCO3 and 50 ml solution. The calcite-water suspension was equilibrated for 2 d before adding Cd(NO3 )2 . The CaCO3 surface has a high affinity for Cd and at < 1 μmol g−1 a linear adsorption isotherm (C-type) describes the reaction, whereas precipitation of CdCO3 on calcite predominates at higher Cd additions. In the latter case pH decreased and solutions were undersaturated with respect to CaCO3 indicating that CdCO3 prevented the CaCO3 surface from reacting with the acidity generated from CdCO3 precipitation. The data for low Cd additions suggests that an ideal surface solid solution is formed between CdCO3 and CaCO3 and the Thorstenson and Plummer equation expressing the pIAP values of surface solid solutions is valid. Equilibrium was attained for low Cd additions in several minutes, whereas precipitation was a slow process; at the changeover point distinction between the two processes is difficult. The reacting surface area calculated from the maximum adsorption of Cd is 0.5-1.0 times that measured by the BET method.
The Cd-reacting surface areas of four natural calcareous minerals were much less than those found by the BET method which includes the surfaces of other minerals present. The Thorstenson and Plummer equation may be a useful way to relate solution composition and carbonate-adsorbed Cd in contaminated soils. 相似文献
The Cd-reacting surface areas of four natural calcareous minerals were much less than those found by the BET method which includes the surfaces of other minerals present. The Thorstenson and Plummer equation may be a useful way to relate solution composition and carbonate-adsorbed Cd in contaminated soils. 相似文献
5.
Synthetic goethite used to study the effects of reaction time and temperature on the pH-dependent sorption of Ni, Zn and Cd was associated with amorphous silica. Ni interacted with dissolved Si and formed a Ni/Si precipitate on the goethite surface. Individual metals added at a concentration of 0.5 μmol g?1 and sorbed during a reaction period of 504 hours (21 days) at 35°C were extracted by 0.7 M HNO3 for 14 days. At the end of this period 11,28 and 40 percent of Ni, Cd and Zn, respectively, were not extracted whereas 20 percent of the total Fe content of the goethite and 39 percent of the associated Si were dissolved. During the sorption process metals became immobilized in the goethite particles. This effect can be related to a diffusion of metal ions into micropores. A total mobilization of sorbed metals can only be achieved by a complete dissolution of the goethite. The strong fixation of Ni, Zn and Cd by goethite suggests that additions of this Fe oxide could be used to ameliorate highly contaminated sludges or soils. 相似文献
6.
Long-term reactions of Ni, Zn and Cd with iron oxyhydroxides depend on crystallinity and structure and on metal concentrations 总被引：1，自引：0，他引：1
Iron oxyhydroxides are long-term sinks for toxic trace metals and are suggested as factors to explain long-term metal immobilization in soil. It is unknown how crystallinity and crystal structure of iron (Fe) oxyhydroxides affect the long-term kinetics of trace metal adsorption. Adsorption kinetics of nickel (Ni), zinc (Zn) and cadmium (Cd) on to four synthetic Fe oxyhydroxides (hydrous ferric oxide (HFO), ferrihydrite (FH), goethite (GT), haematite (HT)) were characterized in suspensions during 70 days at different initial metal concentrations and various pH values (3.8–7.0) maintained within 0.2 units. The slow reactions, defined as those occurring beyond day 1 were most pronounced in GT and least in HT. The extent of the slow reaction was surprisingly unrelated to crystallinity or microporosity as determined by N2 adsorption. Freundlich adsorption isotherms fitted to the data show that ageing between 1 and 70 days decreases metal concentrations in solution by factors of 2–30 (Ni), 1–20 (Zn) and 1–4 (Cd) depending on the type of oxyhydroxide. These factors become significantly larger at smaller concentrations for Ni and Zn in some oxyhydroxides and this concentration dependency suggests that slow reactions are not only related to diffusion. The short-term adsorption strength of carrier-free metal radio-isotopes was similar at 1 or 70 days after reaction with these iron oxyhydroxides and excludes the possibility that long-term reactions are related to solid-phase transformations or changes in solution properties. The extent of slow reactions in GT decreased with decreasing pH and was less than a factor 2 within 70 days at pH 3.7. The results confirm that slow reactions in Fe oxyhydroxides can explain lessened metal availability by ageing in pH neutral soils. The uncertainty of their actual structure and crystallinity in soils does not allow quantitative predictions based on the behaviour of synthetic oxyhydroxides. 相似文献
7.
We compared rates of desorption of heavy metals from goethite, an important soil constituent, in order to understand the mechanisms of sorption and desorption better. Samples of goethite were reacted with salt solutions of heavy metals for 2 hours or for 8 weeks. The metals were Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb. Desorption was then induced by successive treatments with 0.7 m HNO3 for up to 360 hours followed by complete dissolution of the goethite particles. After brief sorption (2 hours), a large proportion of the sorbed metals was desorbed by brief treatment (15 minutes) with HNO3. This suggests that the metals were mainly sorbed on, or close to, external goethite surfaces. After longer sorption (8 weeks), even 360 hours of extraction with 0.7 m HNO3 did not recover all of the sorbed metals. Complete dissolution of the goethite particles was necessary. This suggests that the eight heavy metals had penetrated the goethite particles deeply. When desorption was summarized using a pragmatic equation, it was only for brief sorption followed by brief desorption that indices of the rate of desorption were well correlated with measures of the rate of sorption as obtained in an earlier work. When desorption was described with a mechanistic model, observed desorption was often faster than predicted and the discrepancy was greatest with the shorter periods of desorption. The discrepancy was marked for Ni, Cr and Co. We think this was because large portions of these metals were incorporated into the goethite structure by lattice diffusion and were therefore held close to the surface. When the acid dissolved some of the goethite these metals were released. For long‐term desorption and for most metals, the ratio of observed to predicted desorption decreased with increasing ionic radius. We think that this reflects a changing balance between lattice and pore diffusion, with lattice diffusion more important for metals with radii near that of Fe (Cr, Co, Ni), and pore diffusion more important for the larger cations of Cd and Pb. Manganese was an exception. Desorption was at first faster than predicted but then declined to be close to predicted values. This suggests that Mn mostly penetrated more deeply by pore diffusion. 相似文献
8.
A sample of goethite was mixed for periods which ranged from 2 hours to 8 weeks with solutions of dilute nitrate salts of Pb, Hg, Cd, Zn, Cu, Ni, Co, Mn, Cr and Al. The amount of sorption after each period was measured for an appropriate pH range for each metal. The sorption behaviour was characterized both by using characteristics of the sorption curves such as the pH at which half of the added metal was sorbed (pH50) and by fitting a model in which sorption was mainly characterized by an affinity constant and by a diffusion constant. Initial sorption, whether characterized by the pH50 or by the affinity constant, was closely correlated with the appropriate dissociation constants of the metals. The greater the affinity of the metals for hydroxide ions, the greater their affinity for the goethite surface. The metals differed in the rate at which they continued to react with the goethite. Lead had the slowest continuing reaction, cobalt the fastest. The continuing reaction was due to diffusion into the particles. It was characterized by the fitted diffusion constant and by the change with time in the pH50. For seven of the eight divalent metals, these were correlated with the ionic radius of the metals: the larger the radius, the slower the reaction. For Al and Cr, rates were slower than would be expected from the ionic radii and we suggest this shows that these ions react as the larger M(OH)2+ ions. The behaviour of Ni was consistent with oxidation of the surface species and diffusion of Ni(OH)2+ ions. The continuing reaction was similar to that observed when metal ions react with soils and suggests that their reaction with iron oxides is important in soils. The results also show that studies in which sorption is measured at only one period of reaction are incomplete and the application of equilibrium models to such results is misleading. 相似文献
9.
P. Villaverde D. Gondar J. Antelo R. López S. Fiol & F. Arce 《European Journal of Soil Science》2009,60(3):377-385
The effect of pH on the adsorption of copper (Cu), lead (Pb) and cadmium (Cd) by a peat soil was studied, and the results compared with those corresponding to cation binding by a dissolved peat humic acid (HA), and interpreted with a NICA–Donnan model. A potentiometric titration technique was used to determine the adsorption isotherms for H+ , at different ionic strengths, and for Cu2+ , Pb2+ and Cd2+ at different pH values, in a peat soil. The effect of the ionic strength on proton binding was similar for the soil (solid) organic matter and for dissolved HA. The adsorption isotherms for cation–peat and the binding curves cation–dissolved HA are almost parallel, although more cation was adsorbed per kg of C in the dissolved HA. The effect of pH on cation binding is similar for dissolved organic matter and for the organic soil. At low metal concentration the amount of adsorbed metal followed the order Cu2+ > Pb2+ > Cd2+ . The cation-binding parameters obtained with the NICA–Donnan model allow excellent simulation of the effect of pH on the adsorption of Cu, Pb and Cd ions in the studied peat soil. The binding constants for the peat suspension were greater than the corresponding generic parameters for dissolved HA. Speciation calculations showed that for Cu and Pb, the most abundant fraction was the metal adsorbed on peat, whereas for Cd the most abundant fraction was dissolved metal. 相似文献
10.
Abstract. Different types of contaminants such as polycyclic aromatic hydrocarbons (PAHs) and metals coexist in different chemical forms in soil. Although bioremediation of organics has been widely studied, little attention has been paid to changes in metal behaviour during the bioremediation process. In this study, the diffusion gradient in thin-film (DGT) technique was used to assess changes in potentially bioavailable Cd and Cr fluxes in soil during the bioremediation of phenanthrene. Fluxes of Cd were low (< 0.2pgcm−2 s−1 ) and increased to 0.4–0.9 pg cm−2 s−1 , while Cr(III) fluxes showed an approximately tenfold increase. Results showed that there was increased mobilization of metals associated with the fungal reduction of phenanthrene concentrations by Penicillium frequentans. 相似文献
11.
Abstract. Use of high biomass crops such as the willow Salix viminalis to extract metals for soil remediation has been proposed as an alternative to the low biomass-producing hyperaccumulating plants. High yields compensate for the moderate heavy-metal concentrations in the shoots of such species. We report the first long-term trials using Salix viminalis to extract heavy metals from two contaminated soils, one calcareous (5 years) and one acidic (2 years). Total metals extracted by the plants were 170 g Cd ha−1 and 13.4 kg Zn ha−1 from the calcareous soil after 5 years, and 47 g Cd ha−1 and 14.5 kg Zn ha−1 from the acidic soil after 2 years; in the first year outputs were negligible. After 2 years, Salix had performed better on the acidic soil because of larger biomass production and higher metal concentrations in shoots. Addition of elemental sulphur to the soil did not yield any additional benefit in the long term, but application of an Fe chelate improved the biomass production. Cd and Zn concentrations were significantly higher in leaves than stems, highlighting the necessity to collect leaves as well as shoots. On both soils, concentration in shoots decreased with time, indicating a decrease in extraction efficiency. 相似文献
12.
Abstract. Phytoextraction is the remediation of heavy metal contaminated soils using plants that take up metals. Hyperaccumulating plants such as Thlaspi caerulescens are often studied for their possible use for decontamination of Cd and Zn rich soils, but few field trials have been reported, although they are necessary to validate the results of hydroponic and pot studies. This article reports field data for T . caerulescens grown on a calcareous and an acidic soil, both contaminated 20 years ago by either atmospheric depositions or septic-tank wastes. Accelerated cropping using transplants grown three times in eight months was compared to Thlaspi sown twice during the same period. Both were followed by one crop of sown Thlaspi . High Cd and Zn concentrations in the plant shoots compensated for the low biomass production. Annual metal exports with transplanted Thlaspi were 130 g Cd ha−1 and 3.7 kg Zn ha−1 on the calcareous soil and 540 g Cd ha−1 and 20 kg Zn ha−1 on the acidic soil. We concluded that within the framework of the Swiss legislation, remediation of Cd-contaminated soils could be achieved within less than 10 years with one crop of Thlaspi per year, but differences in soil properties could affect the rate of phytoextraction significantly. Total Zn content in both soils was too high to be remediated by T . caerulescens in a realistic time span. Thlaspi did not decrease the NaNO3 -extractable fraction of Cd or Zn in either of the soils. 相似文献
13.
Release of potassium from some benchmark soils of India 总被引：1，自引：0，他引：1
Release of potassium from 15 surface samples of benchmark Alluvial, Red and Black soils of India to 0.01 M solutions of BaCl2 , CaCl2 , NH4 Cl and NaCl was studied in soils either untreated or pretreated with 5 × 10−3 M KCl. In the untreated soils, the efficacy of the extractants declined in the sequence: BaCl2 > NH4 Cl > CaCl2 > NaCl. Cumulative K-release was greatest from Black soils, followed by Red and Alluvial soils. From soils pretreated with 5 * 10−3 M KCl, more K was released than retained, and more 'native' K was released than that from untreated soils. Increase in the release of 'native' K decreased in the sequence: Red > Alluvial > Black soils. The amounts of surface and internal K, desorption rate constants and parabolic diffusion constants were calculated from K release to the various electrolytes. 相似文献
14.
Characterizing heavy-metal adsorption on oxides and oxyhydroxides 总被引：10，自引：0，他引：10
Adsorption of Cu(II), Zn(II), Co(II) and Cd(II) on three different substrates: goethite, alumina and silica, was investigated over the pH range from 3.5 to 10. The consistent variation in the pH at which 50% of the metal is adsorbed (pH50) indicates that the identity of the adsorbing ion is the principal factor determining the pH range over which adsorption occurs. However, the nature of the substrate does play a lesser role. The proton coefficient, χ, ranged from about 0.5 to 1.8, and was correlated with the difference between pH50 and the pH for 50% precipitation. It is suggested that for most metal-substrate systems, for which χ is about 1, MOH+ plays a dominant role in adsorption. Increasing the substrate concentration decreased pH50 for adsorption of metals on goethite, but there was little change in χ. The change in pH50 was inversely related to χ. While the effect of the nature and concentration of the background electrolyte on Cu(II), Zn(II) and Co(II) adsorption depended on the substrate, increased ionic strength was found to decrease Cd(II) adsorption on all substrates. 相似文献
15.
Cadmium, Ni and Zn ions in aqueous solution were allowed to react with clay fractions (< 2 μm) separated from soils with a wide range of mineralogical composition and properties. Sorbed metals were separated into two components, termed specifically and non-specifically bound, by a controlled washing procedure using 10?2M Ca(NO3)2.Sorption reactions were characterized by Δ pH50 values, by shapes of adsorption curves, and by measuring separation factors and distribution coefficients under prescribed conditions. Three reaction types were identified, viz., (i) those associated with soil adsorbing surfaces dominated by iron oxides; these appear to be controlled by mechanisms which involve metal-ion hydrolysis and result accordingly in relative sorption affinities of Zn > Ni > Cd; (ii) those associated with organic surfaces for which metal-ion hydrolysis was of little significance and little difference in metal-ion affinity was evident; at lower pH-values, Cd and Ni were somewhat preferred over Zn, with the converse at higher pH-values; (iii) those associated with 2:1 layer lattice silicates which exhibit greater preference for Zn, i.e., Zn >> Ni, Cd and higher affinities for each metal at lower pH-values (< 5) than is shown by clays dominated by iron oxides. There was also evidence of greater relative affinity for Ni shown by clay fractions dominated by fine kaolinites when compared with other clays.This investigation has shown that a range of sorption processes are involved in reactions of heavy metals with soils. We caution against undue emphasis on any particular sorption process in developing theoretical sorption models as a basis of understanding and solving problems connected with pollution and plant nutrition; we also stress the need for studies with colloids separated from soils in conjunction with those using synthetic adsorbents as models for soil constituents. 相似文献
16.
The adsorption characteristics of heavy metals: cadmium(II), chromium(III), copper(II), nickel(II), lead(II), and zinc(II) ions by kaolin (kaolinite) and ballclay (illite) from Thailand were studied. This research was focussed on the pH, adsorption isotherms of single-metal solutions at 30–60 °C by batch experiments, and on ion selectivityin mixed and binary combination solutions. It was found that, except Ni, metal adsorption increased with increased pH of the solutions and their adsorption followed both Langmuir and Freundlich isotherms. Adsorption of metals in the mixture solutions by kaolin was: Cr > Zn > Cu ≈ Cd ≈ Ni > Pb, and for ballclay was: Cr > Zn > Cu > Cd ≈ Pb > Ni. The adsorption of metals was endothermic, with the exception of Cd, Pb and Zn for kaolin, Cu and Zn for ballclay. Kaolin and ballclay exhibited relatively hard Lewis base adsorption site. The presence of other metals may reduce or promote the adsorption of heavy metals. The presence of Cr3+ induced the greatest reduction of metal adsorptiononto kaolin, as did the presence of Cu2+ for ballclay. 相似文献
17.
The proportion of metals in soils in equilibrium with soil solution can be determined using isotopic dilution. For this purpose, an isotope dilution mass spectrometric (IDMS) technique has been applied for the elements Cd, Cr, Cu, Mo, Ni, Pb, Tl and Zn. Conventionally, sorbed amounts of heavy metals in soils are analysed by ethylenediamine tetra-acetic acid (EDTA) extraction. The IDMS technique and EDTA extraction were both applied to 115 soil samples and compared. For Cd, Cu, Ni, Pb and Zn, the results of the IDMS technique correlated well with the results of EDTA extractions ( r s (Cd) = 0.965, r s (Cu) = 0.916, r s (Ni) = 0.878, r s (Pb) = 0.922, r s (Zn) = 0.962; all at P < 0.001). For Cd and Zn, no significant differences between the results of both methods could be observed, which suggests that EDTA and IDMS determined the same pool. EDTA extracted more Cu, Ni and Pb than was determined by IDMS (7, 26 and 13%, respectively). The correlation between EDTA extraction and IDMS for Cr was significant but weak ( r s (Cr) = 0.361). For Tl and Mo, EDTA extraction and IDMS did not correlate, and IDMS yielded larger concentrations than EDTA. This can be explained by the fact that Tl and Mo do not form stable EDTA complexes, which are essential for the EDTA technique. Recovery experiments demonstrated that added Cd, Cu, Mo, Ni, Pb, Tl and Zn could be recovered successfully by IDMS analysis (mean recovery = 103 ± 9%). Adsorption isotherms for soil samples were determined for Tl, thereby demonstrating that IDMS gave a better estimation of the native content of sorbed Tl in soils than EDTA extraction. 相似文献
18.
Toxic effect of cadmium and nickel on soil enzymes and the influence of adding sewage sludge 总被引：4，自引：0，他引：4
Sewage sludge is increasingly used as an organic amendment to soil, especially to soil containing little organic matter. However, little is known about the utility of this organic amendment in the reclamation of soil polluted with heavy metals. We studied the effects of adding sewage sludge on enzymatic activities of a semi-arid soil contaminated with Cd or Ni in the laboratory. The activities of urease, phosphatase, β-glucosidase and protease-BAA were measured in soil containing concentrations of Cd or Ni in the range 0–8000 mg kg−1 soil, and their inhibition was compared with those of the enzymatic activities in the same soil amended with sewage sludge and containing similar concentrations of the heavy metals. The inhibition was tested for three different incubation times to determine changes in the effect of the heavy metals on hydrolase activity with the time elapsed after contamination. Ecological dose (ED) values of Cd and Ni were calculated from three mathematical models which described the inhibition of the enzymatic activities with increasing concentrations of heavy metal in the soil. For urease and phosphatase activities, the ED values for Cd and Ni increased after application of sewage sludge to soil, indicating a decrease in Cd and Ni toxicity. The other two enzymes (β-glucosidase and protease-BAA) were less sensitive to Cd or Ni contamination, and it was more difficult to determine whether addition of sewage sludge had affected the inhibition of these enzymes by the heavy metals. 相似文献
19.
Fate of nitrogen in cattle slurry following surface application or injection to grassland 总被引：6，自引：0，他引：6
Two field experiments commencing in winter (December) and spring (April) were conducted to determine the fate of nitrogen (N) in cattle slurry following application to grassland. In each experiment three methods of application were used: surface application, and injection ± the nitrification inhibitor, nitrapyrin. Slurry was applied at 80t ha−1 , (≡248 kg total N ha−1 in the winter experiment, and 262 kg N ha−1 in the spring experiment). From slurry applied to the surface, total losses of N through NH3 volatilization, measured using a system of wind tunnels, were 77 and 53 kg N ha−1 3 volatilization loss to ∼2 kg N ha −1 . Following surface application, loss by denitrification, measured using an adaptation of the acetylene-inhibition technique, was 30 and 5 kg N ha−1 for the two experiments. Larger denitrification losses were observed for the injected treatments; in the winter experiment the loss from the injected slurry without nitrapyrin was 53 kgN ha −1 , and with nitrapyrin 23 kgN ha−1 . Total denitrification losses for the corresponding injected treatments in the spring experiment were 18 and 14 kg N ha −1 . Apparent recoveries of N in grass herbage in both experiments broadly reflected the differences between treatments in total gaseous loss. 相似文献
20.
Lateritic soils developed from dolerite contained larger amounts of goethite and haematite than those developed from granite. The goethite/(goethite + haematite) ratio in granitic soils ranged from 0.55 to 1 and from 0.29 to 0.83 in doleritic soils. Maghemite ranged in abundance from 0 to 10% and it only occurred in duricrust. Mole % Al substitution ranged from 16 to 33% in goethite and from 2.5 to 10% in haematite and was similar for both granitic and doleritic soils. Al substitution in maghemite was <5%. A significant, positive correlation (P<0.01) occurred between Al substitution in goethite and the amount of gibbsite in the soil. The dehydroxylation temperature of goethite ranged from 292 to 334°C and was positively correlated with the mole % Al substitution. Goethite crystals varied in size from 16 to 26 nm and haematite crystals from 18 to 59 nm. Goethite and haematite crystals occurred as aggregates of subrounded platy crystals.
Iron oxides obtained by NaOH treatment contained much of the minor element contents of the soils; mean concentrations (μg g−1 ) were: Zn 19.9, Cu 31, Mn 68, Ni 140, Co 32, Cr 394 and V 696. These minor elements were most abundant in iron oxides derived from dolerite, but were not preferentially associated with goethite or haematite. 相似文献
Iron oxides obtained by NaOH treatment contained much of the minor element contents of the soils; mean concentrations (μg g