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1.
In northern Spain and elsewhere in the world, many vineyards are located on steep slopes and are susceptible to accelerated soil erosion. Contaminants, notably Cu, originating from repeated application of copper‐based fungicides to the vines to prevent mildew, are transported and stored in the sediments deposited close to valley bottoms. In this study, the contents and distribution of Cu in 17 soil samples and 21 sediment samples collected from vineyard stands were determined. In addition, the effect of pH on Cu release from vineyard soils and sediments was quantified. The total Cu content (CuT) in the soils varied between 96 and 583 mg kg?1, and was between 1.2 and 5.6 times greater in sediment samples. The mean concentration of potentially bioavailable Cu (CuEDTA) in the sediments was 199 mg kg?1 (46% of CuT), and was 80 mg kg?1 (36% of CuT) in the soils. Copper bound to soil organic matter (CuOM) was the dominant fraction in the soils (on average, 53% of the CuT), while in sediment samples CuOM values varied between 37 and 712 mg kg?1 and were significantly greater (P < 0.01) than in the soils. Copper associated with non‐crystalline inorganic components (CuIA) was the second most important fraction in the sediments, in which it was 3.4 times greater than in the soils. Release of Cu due to changes in the pH followed a U‐shaped pattern in soils and sediments. The release of Cu increased when the pH decreased below 5.5 due to the increased solubility of the metal at this pH. When the pH increased above 7.5, Cu and organic matter were released simultaneously.  相似文献   

2.
The effect of Cu(II) sulfate on N20 reduction was studied in anaerobically incubated freshwater sediment at 15 °C. At Cu concentrations from 100 to 5000 μg g?1, a concentration-dependent decrease in sediment pH was observed in conjunction with a decrease in N20 reduction in Cu2+ treated sediment in flask-microcosms analyzed immediately after metal addition. However, if flask-microcosms were amended with Cu2+ and then pre-incubated to allow the sediment pH to naturally return to its original pH (7.1), an inhibitory effect was only produced at 5000 μg Cu g?1 sediment. Copper retention studies showed that up to 96.4% of the added Cu2+ (2500 μgg?1) was retained by sediment.  相似文献   

3.
Abstract

The importance of various soil components on copper (Cu) retention by Spodosois was investigated. Copper sorption and extraction were conducted on samples from the B horizon from six Danish Spodosois. The investigation was conducted on untreated samples, on hydrogen peroxide‐treated samples (to remove organic matter), on oxalate‐treated samples [to remove amorphous to poorly crystalline aluminum (Al) and iron (Fe) oxides], on hydroxylamine‐treated samples [to remove manganese (Mn) oxides]. Subfractions treated with hydrogen peroxide (H2O2) were further treated with oxalate and citrate‐bicarbonate‐dithionite (CBD). Sorption of Cu from an initial 10‐6 M solution after 48 hours was determined in the pH range 3 to 7 using 0.1M sodium nitrate (NaNO3) as the background electrolyte. The pH‐dependent sorption curve (sorption edge) was shifted to a higher pH with decreasing Al oxide content in the soils, and for the treated sample after removal of organic matter and Al and Fe oxides. A negligible effect was seen after removal of the Mn oxides because of their low abundance. Extraction of sorbed Cu at pH 4 to 6 with 0.1M nitric acid (HNO3) for 24 hours confirmed the sorption results, in inasmuch as removal of the Al (and Fe) oxides increased Cu extractability. Therefore, it was concluded that in the soils investigated, Cu retention is mainly determined by the oxalate‐extractable Al fraction with a minor contribution due to crystalline Fe oxides.  相似文献   

4.
The aim of this work is to assess the effect of planting patterns on the spatial distribution of total copper and other Cu fractions in vineyard soils. Both classical and geostatistical tools were used for the study. The soil of the plot had a loam texture and was strongly acid. The mean total Cu concentration (CuT) was 368 mg kg−1. The mean value of potential available fractions was 188 mg kg−1 for CuEDTA and 122 mg kg−1 for CuDPTA, whereas the mean exchangeable Cu (CuEX) was 5·2 mg kg−1. All Cu measurements exhibited a wide variation. These values are very high compared with those found in non‐polluted soils, and they can affect the soil, plants and microorganisms. The best correlation for CuEX was with soil pH, whereas for CuEDTA, CuDPTA, and CuT, the best correlation was with soil organic carbon. Directional semivariograms were fitted with a spherical model (parallel to plant rows) and a periodic model (perpendicular) showing a dependence on orientation and distance. All Cu measurements were higher along plant rows than among them, finding a periodic pattern in the variance for the normal direction from plant rows. However, in site‐specific management, it is crucial not only to describe the pattern of variation but also to estimate the Cu content in the soil. Copper concentration maps were estimated by kriging interpolation. These maps show a higher Cu accumulation along the cultivated rows than the uncultivated rows. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

5.
We studied short‐scale variation in the total concentration of copper and its fractions in a soil vineyard. Soil samples were collected at a depth of 0–20 cm between plant rows (1), between individual plants (2) and at their base (3) in a vine‐grown plot in NW Spain. The mean total content in Cu (Cut) in the soil was found to be 97 mg kg−1 and that of potentially available Cu (CuEDTA) 34 mg kg−1. Copper bound to organic matter (CuOM) and to non‐crystalline inorganic soil components (CuIA) were the dominant fractions and accounted for 34% of total copper each. The contents in exchangeable (Cue), pyrophosphate‐extractable (Cup), oxalic/oxalate‐extractable (Cuo) and total copper (Cut) exhibited statistically significant correlations with pH, sum of base cations (S), cation‐exchange capacity (CEC) and exchangeable calcium (Cae). Both total and fractional copper contents were higher in plant rows than between them, particularly in the centre of the plot. Also, CuOM and CuIA were higher in planting rows than between rows. These copper results may have been influenced by the vine‐growing practices of the area and also by the distribution of plants and their pruning. This variability pattern for Cu distribution is crucial with a view to minimising potential adverse effects of fungicides and optimising any reclamation treatments needed. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

6.
Concentrated solutions of copper (Cu2+), dichromate (Cr2O2? 7) and aresenate (AsO4 3?) ions (CCA solutions) are used extensively in the New Zealand timber preservation industry. These ions are therefore, potential soil pollutants at timber treatment sites. Sorption of these three ions was examined by the surface and sub-surface horizons of two free-draining New Zealand soils over a range of soil solution pH values. Copper sorption by both soils increased substantially with increasing pH and was greater in the surface compared with the sub-surface horizons. Less dichromate was sorbed than the other two ions and wa similar in both surface and sub-surface horizons for each soil. Dichromate sorption increased with decreasing pH. Arsenate sorption from solutions containing all three ions was not greatly different to influenced by changes in soil solution pH. Arsenate sorption was generally greater in the sub-surface horizons of both soils. Sorption from solutions containing all three ions was not greatly different to sorption from solutions containing the single metal ions. Sorption behaviour for each ion is related to its chemistry and the soil chemical properties of each horizon. Results suggest that in the event of soil contamination by CCA solution, the immediate leaching potential of the initial ions species present would increase in the following order: Cu2+ < HAsI 4 ? ? Cr2O 7 2? .  相似文献   

7.
This study characterizes the effects of water–soil flooding volume ratio and flooding time on copper (Cu) desorption and toxicity following multiple floodings of field-collected soils from agricultural sites acquired under the Comprehensive Everglades Restoration Plan (CERP) in south Florida. Soils from four field sites were flooded with three water–soil ratios (2, 4, and 6 [water] to 1 [soil]) and held for 14 days to characterize the effects of volume ratio and flooding duration on Cu desorption (volume ratio and flooding duration study). Desorption of Cu was also characterized by flooding soils four times from seven field sites with a volume ratio of 2 (water) to 1 (soil) (multiple flooding study). Acute toxicity tests were also conducted using overlying waters from the first flooding event to characterize the effects of Cu on the survival of fathead minnows (Pimephales promelas), cladocerans (Daphnia magna), amphipods (Hyalella azteca), midges (Chironomus tentans), duckweed (Lemna minor), and Florida apple snails (Pomacea paludosa). Acute tests were also conducted with D. magna exposed to overlying water from the second and third flooding events. Results indicate that dissolved Cu concentrations in overlying water increased with flooding duration and decreased with volume ratio. In the multiple flooding study, initial Cu concentrations in soils ranged from 5 to 223 mg/kg (dw) and were similar to Cu concentration after four flooding events, indicating retention of Cu in soils. Copper desorption was dependent on soil Cu content and soil characteristics. Total Cu concentration in overlying water (Cuw) was a function of dissolved organic carbon (DOC), alkalinity, and soil Cu concentration (Cus): log(Cuw)?=?1.2909?+?0.0279 (DOC)?+?0.0026 (Cus)???0.0038 (alkalinity). The model was validated and highly predictive. Most of the desorbed Cu in the water column complexed with organic matter in the soils and accounted for 99% of the total dissolved Cu. Although total dissolved Cu concentrations in overlying water did not significantly decrease with number of flooding events, concentrations of free Cu2+ increased with the number of flooding events, due to a decrease in DOC concentrations. The fraction of bioavailable Cu species (Cu2+, CuOH+, CuCO3) was also less than 1% of the total Cu. Overlying water from the first flooding event was only acutely toxic to the Florida apple snail from one site. However, overlying water from the third flooding of six out of seven soils was acutely toxic to D. magna. The decrease in DOC concentrations and increase in bioavailable Cu2+ species may explain the changes in acute toxicity to D. magna. Results of this study reveal potential for high Cu bioavailability (Cu2+) and toxicity to aquatic biota overtime in inundated agricultural lands acquired under the CERP.  相似文献   

8.
Copper adsorption and desorption under acid conditions by soil clay fractions separated from Vertisol, Planosol and Gleyic Acrisol has been studied in 0.01 M Ca(NO3)2. A Freundlich equation was appropriate to describe Cu adsorption. Within the range of 150 to 2600 mg of copper per kg of soil clay fraction the proportions of Cu not displaced during 5 successive 48-hour desorptions with 0.01 M Ca(NO3)2 decreased with increasing adsorption density and at the lower pHs. The proportions ranged from as high as 0.98 in th case of the Vertisol clay (pH 5.3) to as low as 0.12 (88% desorption) in the Planosol clay (pH 4.5). Measurement of separation factors (ga Cu/Ca) showed that the preference of the clay surface for Cu over Ca decreased in the order: Gleyic Acrisol > Planosol > Vertisol. A considerable amount of sorbed copper could be solubilized by decreasing pH values to 4 when in the Planosol clay 39% was desorbed and 45% was desorbed in the Gleyic Acrisol clay.  相似文献   

9.
The effects of Cu(II) sulfate on sediment respiration were investigated in a 3-phase aquatic microcosm, containing a calcareous, southern Ontario stream sediment. In Cu2+ treated flask-microcosms, with the pH restored to 7.1, both aerobic and anaerobic CO2 evolution were unaffected by 5000 jig Cu g?1 sediment over a 40-day period at 15 °C. Oxygen consumption in sediment was initially unaffected by 5000 μg Cu g?1. However, after 35 to 40 days, a significant reduction of 28% was observed. The added Cu?2+ was removed from the water column and the sediment solution. In microcosms containing 5000 μg g?1 of total Cu, only 1.00 ± 0.76 μg g?1 was water soluble Cu, and the free cupric cation (Cu2+) concentration was below the detection limit of the specific ion electrode (less than 0.01 μg g?1). Maximum Cu retention (98.6%) was observed at 2800 μg Cu g?1, above which fractional retention decreased. In a calcareous, organic rich, sediment of pH 7.1, Cu+ was essentially unvailable to exert a toxic effect on respiration.  相似文献   

10.
Phosphate-induced zinc retention in a tropical semi-arid soil   总被引：14，自引：0，他引：14  
Zinc (Zn) deficiency symptoms and sporadic responses to applied Zn are being observed frequently in the Nigerian savanna, and one cause is thought to be the growing use of phosphorus (P) fertilizers. This study was designed to test the hypothesis of P-induced Zn retention in the soils. Soil mixed eith P was incubated at field capacity for 3 weeks at 30 ± 2°C. P levels added to the soil were 0, 500, 1000 and 2000 mg per kg soil. After 3 weeks of incubation, water-soluble Zn in soil decreased by 92% and exchangeable Zn by 78% with 2000 mg kg?1 of applied P. Zn levels ranging from 0 to 200 mg kg?1 were added to the P-incubated soil to determine the Zn sorption isotherm and retention capacity. The P-treated soil retained 93 ± 2% of added Zn compared with 52 ± 2% of the control soil. P treatment changed the Zn sorption isotherm from an L-curve isotherm to an H-curve isotherm, indicating strong affinity of P-treated soil for Zn, probably as a result of the formation of Zn-phosphate complexes on the soil surface and precipitation at sufficiently large concentrations of P and Zn. At 2000 mg P kg?1, up to 90% of Zn retained by the soil was bound in solid form as ZnHPO4. Varying the soil pH from 3.5 to 9.0, Zn retention by the soil was related to Zn hydrolysis with maximum adsorption occurring at pH 7.3 ± 0.2. The dependence of sorbed Zn on Zn(OH)2° at pH 3.5–7.4 of P-treated soil indicated that significant van der Waals forces might be involved in Zn retention. The implication of the results of this study for the region is that fertilizer-P placement around a growing crop plant, commonly practised to maximize fertilizer-P efficiency, can potentially limit Zn solubility and availability.  相似文献   

11.
Abstract

To investigate the activity of free cadmium (Cd2+), copper (Cu2+), lead (Pb2+), and zinc (Zn2+) ions and analyze their dependence on pH and other soil properties, ten contaminated soils were sampled and analyzed for total contents of Cd, Cu, Pb, and Zn (CdT, CuT, PbT, and ZnT, respectively), 0.43 MHNO3‐extractable Cd, Cu, Pb, and Zn (CdN, CuN, PbN, and ZnN, respectively), pH, dissolved organic matter (DOC), cation exchange capacity (CEC), ammonium oxalate extractable aluminum (Al) and iron (Fe), and dissolved calcium [Ca2+]. The activity of free Pb2+, Cd2+, Cu2+, and Zn2+ ions in soil solutions was determined using Donnan equilibrium/graphite furnace atomic absorption (DE/GFAA). The solubility of Cd in soils varied from 0.16 to 0.94 μg L‐1, Cu from 3.43 to 7.42 μg L‐1, Pb from 1.23 to 5.8 μg L‐1, and Zn from 24.5 to 34.3 μg L‐. In saturation soil extracts, the activity of free Cd2+ ions constituted 42 to 82% of the dissolved fraction, for Cu2+the range was 0.1 to 7.8%, for Pb2+ 0.1 to 5.1% and for Zn2+2 to 72%. The principal species of Cd, Cu, Pb, and Zn in the soil solution is free metal ions and hydrolyzed ions. Soil pH displayed a pronounced effect on the activity of free Cd2+, Cu2t, Pb2+, and Zn2+ ions.  相似文献   

12.
Abstract

The environmental impact of copper sulfate (CuSO4#lb5H2O) must be evaluated before the chemical can be registered as a pesticide to control the apple snail (Pomacea canaliculata) in Hawaii's wetlands. To help achieve this goal, we investigated the sorption‐desorption reactions of CuSO4#lb5H2O with six wetland‐taro soils (Tropaquepts) of Hawaii. Our results indicated that: (i) copper (Cu) was sorbed rapidly: 98.0–99.9% of the added Cu was removed from solution within one hour when the loading rate was less than or equal to 300 mg Cu kg‐1 [initial Cu concentration = 30.0 mg Cu L‐1 or 12 kg (ha‐cm)‐1 as CuSO4#lb5H2O which is 10 times the maximum recommended rate of pesticide applications, (ii) Cu sorption increased as soil pH increased from 5.0 to 8.0, and (iii) sorption capacity varied from 210 mg Cu kg‐1 in a Tropaquept from Kauai Island to 500 mg Cu kg‐1 in another Tropaquept from Maui Island, after seven days of incubation at soil‐solution pH 6.0 and total solution Cu concentration of 0.10 mg Cu L‐1, a Cu level deemed toxic to some living organisms. It appears that more Cu was sorbed (less Cu remained in solution) if the soil contained high organic carbon (C) and low indigenous Cu. Also, there was an inverse relationship between Cu sorption and desorption by the soils tested: the more Cu a soil can sorb, the tighter it holds Cu, and the less Cu it releases. Since soil pH increases by 1 to 1.5 units upon flooding and Cu sorption increases with increasing pH, the recommended practice of flooding the soil for at least 48 hours between CuSO4#lb5H2O application and crop planting should be followed.  相似文献   

13.
The amount of sorbed metal ion released from CaC03 by 16 different extractants was found to vary with the chemical nature of the solution and the metal ion involved. In general, acid solutions dissolved a high proportion of both substrate and Cu, Ph, Cd coatings; complexing agents dissolved the same coatings but left most of the calcite; and competing cations (e.g. NH4 +, Ca2+) displaced primarily chemisorbed Cd and Cu. In Zn studies, little metal ion was retrieved by any extractant due to the limited solubility of the coatings formed at pH < 7.7. The diverse behavior observed in the sorption studies has been interpreted in terms of solubility and absorption equilibria. The pH of the CaC03 suspensions was high enough to precipitate all added Pb as hydroxy species, and excess Cu tended to precipitate at pH > 6.4 if one increased the soluble carbonate level (e.g. by adding acid). Unlike Cd and Cu, Zn was not chemisorbed; it formed sparingly soluble compounds such as ZnC03.2Zn(OH)2, with excess coming out as Zn(OH)2 at pH > 7.7. The significance of the results in respect to the mobility of metal ions in calcareous soils, and the evaluation of available levels, has been considered.  相似文献   

14.
The dependency of the retention of dissolved organic carbon (DOC) on mineral phase properties in soils remains uncertain especially at neutral pH. To specifically elucidate the role of mineral surfaces and pedogenic oxides for DOC retention at pH 7, we sorbed DOC to bulk soil (illitic surface soils of a toposequence) and corresponding clay fraction (< 2 μm) samples after the removal of organic matter and after removal of organic matter and pedogenic oxides. The DOC retention was related to the content of dithionite‐extractable iron, specific surface area (SSA, BET‐N2 method) and cation exchange capacity (pH 7). The reversibility of DOC sorption was determined by a desorption experiment. All samples sorbed 20–40 % of the DOC added. The DOC sorption of the clay fractions explained the total sorption of the bulk soils. None of the mineral phase properties investigated was able to solely explain the DOC retention. A sorption of 9 to 24 μg DOC m–2 indicated that DOC interacted only with a fraction of the mineral surface, since loadings above 500 μg m–2 would be expected for a carbon monolayer. Under the experimental conditions used, the surface of the silicate clay minerals seemed to be more important for the DOC sorption than the surface of the iron oxides. The desorption experiment removed 11 to 31 % of the DOC sorbed. Most of the DOC was strongly sorbed.  相似文献   

15.
Influence of carbonate on the reaction of heavy metals in soils   总被引：3，自引：0，他引：3  
The reaction of Cu, Zn and Cd with soils with carbonate contents ranging from 0 to 75 mg g−1 was studied before and after removal of soil carbonates with acetate buffer at pH 5. Treatment with acetate buffer caused a strong decrease in metal retention by those soils containing carbonates, although if no carbonate was originally present, the treatment caused little effect or even an increase in the amounts sorbed. Before the treatment, adsorption of increasing amounts of Cu and Zn was accompanied by a continuous increase in Ca + Mg released, and those soils containing carbonate released Ca + Mg in excess of their exchangeable amounts, due to dissolution of carbonates and/or penetration of the heavy metal into the carbonate structure. It is suggested that Cu was preferentially retained by the treated soils through precipitation of Cu oxide, and by adsorption on the soil carbonates in the case of the original samples. Zn was removed from the solution by the original carbonate soils through formation of ZnCO3. Treated soils were likely to retain Zn by cation exchange and/or adsorption. Adsorption was probably the main process involved in retention of Cd. In all cases pH was the master variable in controlling the extent and probably the nature of the reaction.  相似文献   

16.
Abstract

The study aims at determining the cobalt retention properties of various soil components. Therefore, cobalt (Co) sorptions and extractions were carried out using an Oxisol sample before (untreated) and after successive removal of organic matter and active manganese (Mn) oxides (H2O2‐treated) and iron (Fe) oxides (H2O2+CBD‐treated). A synthetic goethite was included for comparison. Sorption of the four sorbents was determined over a range of Co concentrations (initially 10‐8 M to 10‐4 M), pH values (3 to 8) and reaction times (2 hours to 504 hours). The Co species sorbed was Co(ll), since oxygen exclusion during sorption had no effect on the amount sorbed. The pH‐dependent sorption curve (sorption edge) was shifted to lower pH at decreasing initial Co concentration and increasing reaction time. The displacements, in particular of the sorption edges corresponding to the lowest initial Co concentrations, to successively higher pH following removal of Mn oxides, organic matter and Fe oxides could be attributed to sorption onto sites of decreasing Co affinity [Mn oxides (and organic matter) > Fe oxides > kaolinite]. Extractions of sorbed Co at pH 5.5–7.5 with 2 M HCI showed that the extractability decreased with increasing sorption time and decreasing initial Co concentration. The untreated and H2O2‐treated soil samples retained sorbed Co at least as firmly as the synthetic goethite, whereas the H2O2+CBD‐treated sample (kaolinite) was clearly less effective. The results emphasized the importance of the soil Mn and Fe oxides for Co retention in soils but also the necessity of taken interior sorption sites into consideration.  相似文献   

17.
Batch and upflow column leaching experiments were used to evaluate the nature and extent of Cu and Zn solubilization from contaminated soil by nitrilotriacetic acid (NTA) in 0.025 M NaClO4. In batch soil suspensions, NTA levels of 10?5 to 10?3 M substantially promoted Cu and Zn release from the metal-enriched soil. The ability of NTA to enhance Cu and Zn solubility decreased with increasing solution acidity probably due to competitive binding of NTA by protons and Fe released by hydrous oxide dissolution. However, in the pH range typically encountered in northeastern U.S. soils, soluble metal levels were nearly constant for a given NTA concentration. Leaching soil columns with NTA solutions enhanced Cu release more than Zn, as the enrichment ratio (cumulative metal leached by NTA compared to the 0.025 M NaClO4 control leachate) after 85 pore volumes displacements was 23.6 and 4.3 for Cu and Zn, respectively. While Cu release by 0.01 M CaCl2 differed little from the control, 0.01 M CaCl2 was substantially more effective than 10?5 M NTA in displacing bound Zn. The data reflect different retention mechanisms for Cu and Zn in this soil.  相似文献   

18.
Our study is one of the first attempts to document the copper (Cu) speciation in the rhizosphere of forest soils and to determine the importance and the influence of the microbial community on Cu speciation. In order to do this, bulk and rhizosphere samples were collected from field sites located close to industrial facilities. The rhizosphere materials were sampled under trembling aspen (Populus tremuloides Michx.) and separated from the bulk soils in the field. A characterization of the microbial populations was made by measuring microbial biomass C and N, urease and dehydrogenase activities. In soil water extracts, chemical properties were also measured, as well as total water-soluble Cu concentration (CuWS) and free-ion Cu activity (Cu2+). The residual Cu speciation was obtained by modelling, using MINEQL+ 4.5. In all cases, the Cu speciation was dominated by organic forms of Cu, the proportion of which increases with increasing pH. The reverse pH effect was observed for Cu2+. Moreover, almost systematically higher concentrations for all Cu variables were reported in the rhizosphere as compared to the bulk soils. The results also showed that microbial variables explained 22% of the distribution of CuWS and Cu2+ in bulk samples, a proportion that reached 61.5% in rhizospheric samples. In the rhizosphere, relationships between pH, microbial biomass N and Cu2+ indicated that microorganisms influenced Cu by modifying the pH of the solution through nitrogen assimilation. Furthermore, links found between urease activity, biomass variables, solid- and liquid-phase organic carbon and CuWS suggested that microbial mineralization could partly supply Cu to the solution fraction of the rhizosphere through root decay. This study reveals that microorganisms have a strong influence on Cu speciation in the rhizosphere of forest soils and suggests that a realistic understanding and representation of Cu dynamic in the rhizosphere must take microbial activity into account. Further investigations are needed to identify and establish precisely how microbial processes impact on Cu speciation.  相似文献   

19.
Thin film A.S.V. was used to study the specific sorption of Cd, Pb and Cu by hydrous oxides (Mn, Fe, and Al) or clay mineral suspensions from acetate buffer solutions containing 10 to 100 μg L?1 of each metal ion. The amount sorbed varied with system pH (range 3 to 9), substrate crystal form, the ratio of adsorbent to absorbate present, and the metal ion involved. Uptake by hydrous Mn(IV) oxide was near total over the whole pH range. With other particulates the pH required for onset of sorption varied with solid phase composition, with uptake subsequently increasing steadily with increasing pH. In general, affinity and relative uptake values followed the sequences Pb > Cu > Cd and Mn(IV) oxides > Fe(III) oxides > A1(OH)3 > clays > iron ores. The solid phases loaded with sorbed metal were equilibrated with a range of extractant solutions used in soil/sediment studies, and the results confirmed that chemi-sorption was the main retention process. Significant release was achieved using extractants that attacked the substrate or formed stable complexes with the metal ion.  相似文献   

20.
The amount of metal ion sorbed by the solids increased with increasing pH over the range 3 to 6, and with mixtures of clay-cellulose or illite-humic acid the uptake corresponded to the direct addition of individual substrate adsorption values. When the humic acid samples were admixed with Na+-form kaolinite or montmorillonite, there was some reduction in adsorption, attributable to component interactions, and this effect was most marked in the presence of Cu and Zn ions. In alkaline media there was competition between the ability of the organic material to form soluble metal humates and the tendency of the clays to strongly retain the sparingly soluble metal hydroxy species formed at pH > 6. In most systems studied retention by the solid phase predominated. In the presence of tannic acid there were distinct pH regions in which the four metal ions formed compounds of limited solubility, with the pH for maximum precipitation ranging from 4.5 (Cu) to 7 (Cd). The introduction of clay suspensions increased the amount precipitated/sorbed in these pH regions. The amount of Cu, Pb, Zn or Cd retained by mixed suspensions varied markedly with pH, nature of the clay and the chemical nature of organic components.  相似文献   

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