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1.
Effect of cell contact and iron(III)-oxide form on bacterial iron reduction By means of a semipermeable membrane the influence of the separation of cells from Fe(III)-oxides (125–63 μm) was studied in model experiments using iron-reducing bacteria (Clostridium butyricum S 22 a and Bacillus polymyxa S 55) which lower the Eh considerably. Synthetic sieved (125–63 μm) hematite (Merck) was included in dialytic bags (pores < 20 Å), incorporated in a glucose-mineral salt broth (pH 7–7.2) and inoculated (anaerobically, 30°C). Fe(II) production (in solution), pH and Eh were measured (and the rH calculated) at regular intervals. In the second experiment, the preferential reduction of lepidocrocite, hematite and goethite was investigated, by mixing 59Fe-labelled oxide forms with other crystalline oxides or with x-ray amorphous Go-soil material (all sieved at 125–63 μm).  相似文献   

2.
No‐tillage management can increase soil surface layer organic C (OC) levels compared with conventional tillage. The mechanisms underlying this increase in highly weathered tropical soils, such as Ferralsols, are not well established. The objective of this study was therefore to evaluate the influence of mineralogy on aggregation and the apportionment of OC across aggregate size fractions in a Brazilian Ferralsol under native vegetation (NV) and no‐tillage management for 10 (NT10) or 20 (NT20) yrs. Under native vegetation, soil OC generally increased with increasing aggregate size while, in response to changing management, soil OC increased in the order NT10 (8.8 g/kg) < NT20 (12.7 g/kg) < NV (19.1 g/kg). There were no significant differences in the mineralogy of the clay size fractions among the three treatments, with the notable exception of the CBD‐extractable Fe oxide fraction (FeCBD). The FeCBD fraction comprises various pedogenic Fe(hydr)oxides and increased from NT10 (33.9 g/kg) to NT20 (64.2 g/kg). The OC/FeCBD mass ratio within aggregates increased in the order NT10 <  NT20 <  NV while R2 values for OC and FeCBD occurrence follow this same trend, with the NT10 soil showing a weaker correlation (R2 = 0.178) compared with the NV soil (R2 = 0.533). We propose that formation of organo‐Fe(III) oxide associations is promoted with implementation of NT management and the consequent reduction in macroaggregate turnover. The development of the OC‐Fe(III) oxide associations and their evolution over time within aggregates to more thermodynamically stable entities will strongly influence the long‐term preservation of soil OC.  相似文献   

3.
The regime of observations revealed that the Eh dynamics in soddy-podzolic and alluvial soils in the Middle Cis-Urals region depends not only on the rate of iron (hydr)oxides reduction but also on the rate of opposite reactions in the gleyed horizons. Both processes depend on the temperature. The Eh value decreases on heating in automorphic soils, when the reduction of Fe(III)-(hydr)oxide particles accelerates. On the contrary, in gley soils, the Eh decreases on cooling, probably, because of the reactions opposing the reduction of Fe(III)-(hydr)oxide particles, including Fe(II) fixation on the surface of mineral particles. Fe(III)-(hydr)oxides are, for the most part, preserved in gleyed soils of the Cis-Urals; the content of (Fe2O3)dit reaches 3.3% with iron minerals being usually represented by goethite. The increase in moistening influences the soil parameters (i.e., the redoxpotential rH and the content of conventional red pigment Hemconv) in an intricate manner. Both direct and reverse branches on the curve of the Hemconv-rH dependence point to the equilibrium and nonequilibrium conditions in the soil. The reverse branch probably stands for the initial phase of gleying in strongly humified soils, where, despite extra electrons in the solution, the brown pigment in the form of Fe(III)-(hydr)oxides is preserved.  相似文献   

4.
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   

5.
Abstract

The extractant Mehlich‐1 is routinely used in Brazil for determination of soil nutrients, whereas Mehlich‐3 has been suggested as a promising extractor for soil fertility evaluation. Both were used for extraction of molybdenum (Mo) in Brazilian soils with Mo dosage by the KI+H2O2 method. The Langmuir and Freundlich isotherms were used to study soil Mo adsorption. Mehlich‐1 extracted more Mo than Mehlich‐3 in soils with high contents of organic matter, clay, and iron (Fe) oxides. Mehlich‐3 and Mehlich‐1 extractions correlated positively and significantly with amorphous Fe oxides, crystalline Fe oxides, and organic matter. Molybdenum recovering rates correlated to crystalline Fe oxides and clay contents but not to organic matter, pH, and Mo adsorption capacity. Amorphous and crystalline Fe oxides, clay, and organic matter were responsible for most of the Mo adsorption. The Langmuir isotherm described better the Mo adsorption to soil amorphous Fe oxides and organic matter than the Freundlich isotherm.  相似文献   

6.
Abstract

It has been showed that Chao’s method [extraction with 0.1 mol L?1 hydroxylamine hydrochloride (NH2OH-HCl) at pH 2.0 for 30 min], which is commonly used to extract manganese (Mn) oxides and occluded heavy metals from soil samples, is not suitable for Andisols because of low solubility, and thus low extractability, of Mn oxides in such soils. Therefore, a new method is evaluated here, for extracting Mn oxides and occluded heavy metals from Andisols, Entisols and Inceptisols. The method has three steps: (1) reduction of Mn oxides with 0.01 mol L?1 NH2OH-HCl (pH 5.0) for 16 h, (2) recovery of re-adsorbed metals by short-time extraction with 0.5 mol L?1 ammonium chloride in 0.02 mol L?1 hydrochloric acid, and (3) washing with ultrapure water. This method achieves a higher rate of extraction of Mn oxides than does Chao’s method, especially from Andisol samples. Standard addition experiments showed that both the new method and Chao’s method can successfully extract released cadmium (Cd), cobalt (Co), nickel (Ni) and zinc (Zn) from Mn oxides with little re-adsorption. The selectivity of Mn oxide extraction by the new method, indicated by the rate of extraction of iron (Fe) oxides and the aluminum (Al)/Mn and silicon (Si)/Mn extraction ratios, is comparable to that of Chao’s method. Thus, the new method should be useful for extracting Mn oxides and occluded Cd, Co, Ni, and Zn from soil samples. Moreover, because the new method achieved nearly complete extraction of NH2OH-HCl reactive Mn oxides even from Andisol samples, the method is more applicable to Andisol samples than Chao’s method.  相似文献   

7.
Arsenic(As) contamination in soil and water poses a serious threat to the ecosystem health and human beings, and is of widespread concern. The main As species found in soil and water are arsenite As(Ⅲ) and arsenate As(Ⅴ). Because As(Ⅲ) is more toxic and often more mobile than As(Ⅴ), many remediation strategies aim to oxidize As(Ⅲ) to As(Ⅴ). In the environment, the reduction of As(Ⅴ) under anaerobic conditions is mainly mediated by microorganisms, but the oxidation of As(Ⅲ) under aerobic conditio...  相似文献   

8.
Greenhouse experiment was conducted to assess the iron (Fe) and zinc (Zn) fractionation patterns in soils of arbuscular mycorrhizal (AM) fungus-inoculated and uninoculated maize plants fertilized with varying levels of Fe and Zn. Soil samples were collected for Fe and Zn fractions and available Fe, Zn and phosphorus (P) contents besides organic and biomass carbon (BMC), soil enzymes and glomalin. Major portion of Fe and Zn fractionations was found to occur in the residual form. Mycorrhizal symbiosis increased the organically bound forms of Fe and Zn while reducing the crystalline oxide, residual Fe and Zn fractions, indicating the transformation of unavailable forms into available forms. Soil enzymes, viz. dehydrogenase and acid phosphatase activities in M+ soils, were significantly higher than M? soil consistently. Overall, the data suggest that mycorrhizal symbiosis enhanced the availability of Fe and Zn as a result of preferential fractionation and biochemical changes that may alleviate micronutrient deficiencies in calcareous soil.

Abbreviations: AM: arbuscular mycorrhiza; Fe: Iron; Zn: Zinc; P: Phosphorous; Amox-Zn: amorphous oxide bound zinc; Cryox-Zn: crystalline oxide bound zinc; DAS: days after sowing; DTPA: diethylene Triamine Penta Acetic Acid; MnO2-Zn: manganese oxide bound zinc; OC-Zn: organically bound zinc; WSEX: water soluble plus exchangeable zinc; MnO2 Fe: manganese oxide bound iron; OC-Fe: Organically bound iron; WSEX Fe: water soluble plus exchangeable iron.  相似文献   

9.
We investigated the extractability of manganese (Mn) and iron (Fe) oxides from typical Japanese soils (Entisols, Inceptisols, and Andisols) by 0.5?mol?L?1 hydroxylamine hydrochloride (NH2OH-HCl) extraction (pH 1.5; 16?h shaking at 25°C; soil:solution ratio 1:40), referred as to HHmBCR, which is Step 2 (used for the reducible fraction) of the modified BCR (Community Bureau of Reference) sequential extraction procedure. The HHmBCR procedure extracted almost all Mn oxides from the non-Andisol samples, but failed to extract a part of the Mn oxides from some Andisol samples. The procedure extracted most short-range ordered Fe oxides from non-Andisol samples, but it extracted only 7.5% and 13% of the short-range ordered Fe oxides from allophanic and non-allophanic Andisol samples, respectively. This remarkably low extractability of Fe oxides suggests that the HHmBCR method is not suitable for extracting oxide-occluded heavy metals from Andisols. Since the extraction rate of short-range ordered Fe oxides from various soils with the extractant was negatively correlated with the amounts of oxalate- and pyrophosphate-extractable Al even when the variability of the extraction pH was reduced by increasing the soil:solution ratio from 1:40 to 1:500, the extractability of Fe oxides would be negatively affected by the presence of active Al, including allophane/imogolite, amorphous Al, and Al-humus complexes. Because these Al constituents are abundant in Andisols, they would be at least partially responsible for the lower extractability of Fe oxides by HHmBCR from Andisols.  相似文献   

10.
An investigation was conducted using Typic Haplustept, sandy loam soil, to investigate the interactive effects of phosphorus (P) and manganese (Mn) fertilization on native iron (Fe) pools in soil and their availability to wheat (cv. PBW-343) crop. Phosphorus fertilization moved Fe from residual mineral fraction of Fe to manganese oxides (MnOX), organic matter (OM), amorphous (AMPOX), and crystalline (CRYOX) Fe and Al oxide fractions. However, Mn application decreased specifically adsorbed (SAD)–Fe and CRYOX–Fe but increased OM–Fe and mineral fraction of Fe. Available Fe in soil decreased as Olsen P and P:Mn ratio increased in the soil. Higher Olsen P (>60 mg P kg?1soil) reduced mean Fe uptake by shoot. P content and P:Mn ratio in soil as well as in root and shoot were inversely related to Fe concentration in both the plant parts. The role of soil Fe associated with oxides and organic matter was found most notable in Fe nutrition of wheat.  相似文献   

11.
The mobility of soil P is greatly influenced by the redox potential (Eh), which depends on the reducing activity of soil microorganisms. Standard extraction methods for the determination of the mobile soil P disregard the P mobilization caused by the influence of microorganisms on Eh, while P test methods that include soil microbial activities are lacking. Thus, the Fe(III)‐reduction test was investigated for its suitability to determine the P fraction that is mobilized in soil under reducing conditions (PRed). In this test, the soil‐microbial reducing activity is measured from the microbial Fe(III) reduction combining a bioassay with 7 d incubation and a chemical extraction using 1M KCl. After the incubation, Eh in 26 different soil samples ranged from –282 to –123 mV. The concentration of PRed in the soil samples ranged from concentrations below the limit of detection to 84.9 mg kg–1 and was on average of all soil samples by a factor of 2.4 to 18 smaller than the P fractions determined by standard soil P–extraction methods. As standard agronomic and environmental P extractants, respectively, water (PH2O), dithionite citrate bicarbonate (PDith), ammonium oxalate (POx), ammonium lactate (PAL), double lactate (PDL), and sodium bicarbonate (POlsen) were selected. The PRed fraction was not correlated with PAL, PDL, Polsen, and the degree of P saturation, but with PH2O (r = 0.43*), PDith (r = 0.60***), and POx (r = 0.61***). Furthermore, PRed depended on the concentration of amorphous Fe oxides (FeOx, r = 0.53**) and was closely correlated with the concentration of microbially reduced Fe (FeRed, r = 0.94***). This indicated the influence of the Fe(III)‐reducing activity of soil microorganisms on P mobilization. In subsoils, low in Fe(III)‐reducing activity, no P was released by the Fe(III)‐reduction test, which was in contrast to the results from the other chemical extraction methods. Additional alterations of the microbial activity by inhibiting and activating amendments, respectively, clearly affected the microbial Fe(III)‐reducing activity and the associated release of PRed. Thus, PRed, determined by the Fe(III)‐reduction test, might be termed as the fraction that is potentially released from soil by microbial reduction.  相似文献   

12.
Theoretical Considerations of the reductive dissolution of iron(III) oxides At the case of equilibrium, the extent of reductive dissolution of iron(III) oxides can be obtained by the Nernst equation. At a given pH, the maximum Fe2+ concentration depends on the standard potential Eo of the system, which decreases with increasing stability of the oxide. Crystal imperfections as well as increasing surface area lead to an increase of the equilibrium Fe2+ concentration, whereas the influence of ionic replacement cannot be determined in general. The formation of stable Fe2+ complexes or of solid Fe2+ compounds results in a higher extent of reduction. From theoretical calculations it is concluded, that, for the bacterial reduction of iron oxides, the electron transfer between donor and Fe(III) precedes the protolytic dissolution of the oxide.  相似文献   

13.
The influence of some complexing agents of (poly)aminopolycarboxylic acids (diethylenetriaminopentaacetic acid (DTPA), ethylenediaminotetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and iminodiacetic acid (IDA)) on the sorption of Cu2+ by crystal and amorphous (hydr)oxides of Fe(III), Al(III), and Mn(IV) that are widespread mineral components of soils was studied. The obtained results are considered in terms of complex-formation in the solution and on the sorbent’s surface. The effect of the complexing agents on the metal sorption (mobilization/immobilization) is determined by (1) the stability, structure, and sorption capability of compexonates formed in the solution; (2) the acidity, and (3) the nature of the sorbent. The desorption effect on Cu2+ cations was found to change in the following sequence of complexing agents: EDTA > DTPA ? NTA > IDA. The high-dentate complexing agents (EDTA, DTPA) had the greatest impact on ?u2+ cations bound with crystalline (hydr)oxides of Fe, Al, and Mn. The low denticity of the complexing agents (IDA, NTA) and binding of ?u2+ with amorphous sorbents leads to the weakening of desorption. The decrease in acidity promoted the mobilization of the metal under the influence of complexing agents; the increase in acidity caused its immobilization. The growth in the mobility of heavy metals bound with soil (hydr)oxides of Fe, Al, and Mn due to the complexing agents entering the surface and ground water is considered a factor of ecological risk.  相似文献   

14.
Abstract

We evaluated the validity of Tessier’s method as applied to the extraction of manganese (Mn) and iron (Fe) oxides in Japanese Andisols and other soil types in Japan. Using the original Tessier’s extractant mixture, 0.04 mol L?1 hydroxylamine hydrochloride in 25% acetic acid (0.04 mol L–1 NH2OH-HCl in 25% HOAc), we found that substantial amounts of short-range-ordered Fe oxides were not extracted from allophanic Andisol samples and that considerable amounts of total Fe oxides were not extracted from all soil types. Relatively high extraction pH and large amounts of short-range-ordered Fe oxides in the Andisol samples might be responsible for incomplete extraction. Stoichiometric calculation indicated that the concentration of NH2OH-HCl might be insufficient for complete extraction of Fe oxides. The extracted amounts of Mn and Fe increased with increasing concentration of NH2OH-HCl in the extractant, and most of the Mn and Fe oxides in the soil samples, including samples with as much as 5.6% Fe, were extracted with 0.6 mol L–1 NH2OH–HCl in 25% HOAc. As judged from the simultaneous dissolution of aluminum (Al) and silicon (Si) minerals, extraction selectivity of Fe oxides with 0.6 mol L–1 NH2OH-HCl in 25% HOAc was comparable to that of the original Tessier’s method and better than that of a modified Community Bureau of Reference (BCR) sequential extraction procedure or a method using an extractant consisting of a mixture of oxalate and ascorbate, especially for Andisol samples.  相似文献   

15.
消落带土壤铁的形态变化及其对有效磷的影响   总被引：4，自引：0，他引：4  
Fe3+还原为Fe2+的过程中会增加磷酸铁的溶解,影响磷的化学行为及有效性。本文采用室内模拟试验研究了三峡库区消落带土壤铁的形态变化及其对有效磷的影响。消落带旱地和水田土壤经淹水和落水处理后,活性铁、水溶性铁增加,其他各形态铁变化较小。旱地土壤在不同的有机质和淹水落水处理下,其活化铁、游离铁、络合铁、水溶性亚铁、和交换性亚铁均为淹水处理高于落水处理,其中活性铁在各处理间呈现出显著性差异,其他则各处理间差异均未达到显著性水平;水田下层活性铁高于上层,且落水处理间呈显著差异。氧化铁及亚铁之间总处于不断的相互转化中,活性铁、络合铁和有机质正相关。旱地土壤中的有效磷各处理间差异显著,水田有效磷淹水处理高于落水处理。  相似文献   

16.
Abstract

The changes in availability and uptake of boron (B) by M.26 apple rootstocks as affected by applications of different forms and rates of nitrogen (N) were examined. The study was carried out in a greenhouse using soil with low contents of organic matter, clay, calcium carbonate, NH4‐oxalate soluble aluminum (Al) and iron (Fe), NH2OH·HCl extractable manganese (Mn), poor cation exchange capacity and low pH. Soil N application was in the form of urea, calcium nitrate, ammonium sulphate, or ammonium nitrate at rates of 0, 17, 34, and 51 mg N kg?1. After 1, 3, and 5 days of N application, soil B fractions were determined: B in soil solution, B specifically and non‐specifically adsorbed on soil surfaces, B occluded in Mn oxyhydroxides, and B occluded in crystalline Al and Fe oxides. The results showed that N as calcium nitrate and ammonium nitrate increased B both in soil solution and non‐specifically adsorbed on soil surface and decreased B concentration on Al and Fe oxides. This indicates that N‐NO3 inhibited B sorption on Fe and Al oxides. Maximum B desorption from Fe and Al oxides was obtained within one day after N‐NO3 was supplied. Nitrogen application as calcium nitrate and ammonium nitrate increased availability and uptake of B by plant roots. Thus, it was concluded that apple trees planted on coarse‐textured soils where risk of B deficiency is high, calcium nitrate or ammonium nitrates would be appropriately to apply to keep B more available.  相似文献   

17.
The availability of various boron (B) fractions in soil to M.26 apple (Malus spp.) rootstock was examined. The study was carried out in a greenhouse on soils with diverse chemical and physical properties. The following B fractions were determined: (i) B in soil solution, (ii) B non‐specifically adsorbed on soil surface, (iii) B specifically adsorbed on soil colloid surfaces, (iv) B occluded in Mn oxyhydroxides, (v) B occluded in noncrystalline aluminum (Al) and iron (Fe) oxides, (vi) B occluded in crystalline Al and Fe oxides, (vii) B fixed with soil silicates, and (viii) total soil B. In the studied soils there were: 0.07–0.17 mg kg‐1 B in soil solution, 0.01–0.03 mg kg‐1 B non‐specifically adsorbed on soil surface, 0.04–0.08 mg kg‐1 B specifically adsorbed on soil colloid surfaces, 0.28–0.67 mg kg‐1 B occluded in manganese (Mn) oxides, 4.03–17.22 mg kg‐1 B occluded in noncrystalline Al and Fe oxides, 8.93–50.62 mg kg‐1 B occluded in crystalline Al and Fe oxides, 12.2–42.5 mg kg‐1 B fixed with soil silicate, and 52.9–82.2 mg kg‐1 total B. Simple correlation analysis showed positive correlation between B contents in M.26 apple rootstocks and amounts of B in soil solution (r=0.77), B non‐specifically adsorbed on soil colloid surfaces (r=0.65), B specifically adsorbed on soil surface (r=0.76) and B occluded in Mn oxyhydroxides (r=0.77). No relation was found between plant B contents and amounts of B occluded in non‐crystalline and crystalline Al and Fe oxides, B fixed with soil silicates and total B. The results indicated that extraction of B by 0.1 M NH2OH HCl solution adequately represented amounts of B in soil solution, B non‐specifically and specifically adsorbed on soil compound surfaces and B occluded in Mn oxyhydroxides to assess availability of B to apple trees.  相似文献   

18.
Zhu  Meng  Hu  Xuefeng  Tu  Chen  Luo  Yongming  Yang  Ruyi  Zhou  Shoubiao  Cheng  Nannan  Rylott  Elizabeth L. 《Journal of Soils and Sediments》2020,20(2):763-774
Purpose

The mobility of arsenic (As) in soils is fundamentally affected by the clay mineral fraction and its composition. Diphenylarsinic acid (DPAA) is an organoarsenic contaminant derived from chemical warfare agents. Understanding how DPAA interacts with soil clay mineral fractions will enhance understanding of the mobility and transformation of DPAA in the soil-water environment. The objective of this study was to investigate the speciation and sorption structure of DPAA in the clay mineral fractions.

Materials and methods

Twelve soils were collected from nine Chinese cities which known as chemical weapons burial sites and artificially contaminated with DPAA. A sequential extraction procedure (SEP) was employed to elucidate the speciation of DPAA in the clay mineral fractions of soils. Pearson’s correlation analysis was used to derive the relationship between DPAA sorption and the selected physicochemical properties of the clay mineral fractions. Extended X-ray absorption fine structure (EXAFS) LIII-edge As was measured using the beamline BL14W1 at Shanghai Synchrotron Radiation Facility (SSRF) to identify the coordination environment of DPAA in clay mineral fractions.

Results and discussion

The SEP results showed that DPAA predominantly existed as specifically fraction (18.3–52.8%). A considerable amount of DPAA was also released from non-specifically fraction (8.2–46.7%) and the dissolution of amorphous, poorly crystalline, and well-crystallized Fe/Al (hydr)oxides (20.1–46.2%). A combination of Pearson’s correlation analysis and SEP study demonstrated that amorphous and poorly crystalline Fe (hydr)oxides contributed most to DPAA sorption in the clay mineral fractions of soils. The EXAFS results further demonstrated that DPAA formed inner-sphere complexes on Fe (hydr)oxides, with As-Fe distances of 3.18–3.25 Å. It is likely that the steric hindrance caused by phenyl substitution and hence the instability of DPAA/Fe complexes explain why a substantial amount of DPAA presented as weakly bound forms.

Conclusions

DPAA in clay mineral fractions predominantly existed as specifically, amorphous, poorly crystalline, and crystallized Fe/Al (hydr)oxides associated fractions. Amorphous/poorly crystalline Fe rather than total Fe contributed more to DPAA sorption and DPAA formed inner-sphere complexes on Fe (hydr)oxides.

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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.

Purpose

Soil temperature is a fundamental parameter affecting not only microbial activity but also manganese (MnIII,IV) and iron (FeIII) oxide reduction rates. The relationship between MnIII,IV oxide removal from oxide-coated redox bars is missing at present. This study investigated the effect of variable soil temperatures on oxide removal by MnIII,IV and FeIII oxide-coated redox bars in water-saturated soil columns in the laboratory.

Materials and methods

The Mn coatings contained the mineral birnessite, whereas the Fe coatings contained a mixture of ferrihydrite and goethite. Additionally, platinum (Pt) electrodes designed to measure the redox potential (EH) were installed in the soil columns, which were filled with either a humic topsoil with an organic carbon (Corg) content of 85 g kg?1 (pH 5.8) or a subsoil containing 2 g Corg kg?1 (pH 7.5). Experiments were performed at 5, 15, and 25 °C.

Results and discussion

Although elevated soil temperatures accelerated the decrease in EH after water saturation in the topsoil, no EH decreases regardless of soil temperature occurred in the subsoil. Besides soil temperature, the importance of soil organic matter as an electron donor is highlighted in this case. Complete removal of the MnIII,IV oxide coating was observed after 28, 14, and 7 days in the soil columns filled with topsoil at 5, 15, and 25 °C, respectively. Along the Fe redox bars, FeIII reducing conditions first appeared at 15 °C and oxide removal was enhanced at 25 °C because of lower EH, with the preferential dissolution of ferrihydrite over goethite as revealed by visual differences in the FeIII oxide coating. Oxide removal along redox bars followed the thermodynamics of the applied minerals in the order birnessite > ferrihydrite > goethite.

Conclusions

In line with Van’t Hoff’s rule, turnover rates of MnIII,IV and FeIII oxide reduction increased as a result of increased soil temperatures. Taking into account the stability lines of the designated minerals, EH-pH conditions were in accordance with oxide removal. Soil temperature must therefore be considered a master variable when evaluating the oxide removal of redox bars employed for the monitoring of soil redox status.
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