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1.
PurposeThe production of technosols to remediate polluted or sealed urban soils to sustain new green areas is mainly empirical. For this, our research aims to contribute with the scientific knowledge base for purpose designing of technosols. Since iron minerals play an important role for many different functions of soils, we simplified a technique to incorporate and stabilize iron minerals in a substrate: a sand coated with an amorphous iron (hydr)oxide, a 2-line ferrihydrite (2L-FH).Materials and methodsThe 2L-FH was precipitated by neutralization of a concentrated FeCl3 solution. The suspension was homogeneously mixed with the sand and the mixture was dried at 35 °C. The mechanical stability of the 21 2L-FH-coated sand was determined by shaking the aggregates in water for 0, 1, 10, 100, and 1 000 min. The degree of coating detachment and the properties of the coating after shaking were characterized through (a) Fe content, (b) zeta-potential and particle size of the detached particles, (c) the specific surface area (SSA) of the coated sand, and (d) its surface structure using scanning electron microscopy (SEM). A phosphate adsorption isotherm was performed to measure the P-sorption capacity of the shaken samples and to test the 2L-FH-quartz attachment stability against the surface charge reduction of the 2L-FH associated with P adsorption.Results and discussionA reduced Fe loss (30 %) and smaller sizes of the coating detached particles in the sample shaken for 1 000 min indicate that a fractioning and reattachment of these aggregates occurred during the agitation process, resulting in a smoother surface (SEM), and a larger SSA and P-sorption capacity. The coated shaken samples showed P-adsorption capacities (5.3–6.34 μmol P g?1) comparable to high loadings of phosphate in soils, and low detachment of Fe (7–14 %) in spite of negativity surface charge increase.ConclusionsThe practical novel coating process along with the 1 000-min shaking produced a mechanical resistant and P-adsorptive effective coated sand that could sustain the needs of plants in further experiments. 相似文献
2.
PurposeThe 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 methodsTwelve 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 discussionThe 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. ConclusionsDPAA 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. 相似文献
3.
PurposeArsenite and arsenate leaching from iron (hydr)oxides is one major parameter affecting the mobility of arsenic in the natural environment. In the process of arsenic transfer to groundwater, the retention capacity of arsenic by different iron (hydr)oxides needs to be investigated. The aim of this study is to determine the retention capacity of arsenite or arsenate from the ferrihydrite, lepidocrocite, or magnetite-coated sand column in the leaching process as well as the influence factors on leaching.Materials and methodsThe leaching of arsenite and arsenate from columns loaded with ferrihydrite, magnetite, or lepidocrocite-coated quartz sand was examined, and the influence factors such as pH, phosphate, and humic acid (HA) contents on leaching and retention were also investigated.Results and discussionThe retention performance of As(III) and As(V) depended on the type of iron (hydr)oxides: ferrihydrite?>?magnetite?>?lepidocrocite. The retention capacities of As(III) and As(V) by amorphous ferrihydrite versus magnetite and lepidocrocite are 3.25, 5.63 (As(III)) and 1.75, 3.65 (As(V)) times higher. The retention capacity of arsenic is largely affected by the pH of leaching solutions. The retention of As(III) by ferrihydrite is efficient in near-neutral or slightly acidic environments. The addition of phosphate or HA significantly affected the leaching and retention. The addition of phosphate severely inhibited the leaching and retention of As(III) and As(V) by ferrihydrite, and the inhibitory effect was more obvious along with the increase of phosphate concentration. The retention of As(III) and As(V) by ferrihydrite was significantly enhanced by the addition of low-dose HA but was inhibited by the addition of excessive HA.ConclusionsRetention performance of As(III) and As(V) from a ferrihydrite-coated sand column is greater than a magnetite- or a lepidocrocite-coated sand column, and the influence factors such as pH, phosphate, and HA affect the leaching and retention of As(III) and As(V). The results theoretically underlie the application of iron (hydr)oxide in arsenic pollution control. 相似文献
4.
Abstract A number of iron oxides (hematite, goethite, lepidocrocite, maghemite, and magnetite) or short‐range ordered precipitates (ferrihydrite) may be found in soil environments, but in the rhizosphere the presence of organic ligands released by plants (exudates) or microorganisms promote the formation of ferrihydrite. Iron ions are liberated into soil solution by acidic weathering of minerals and then precipitated either locally or after translocation in soil environments. Humic and fulvic acids as well as organic substances produced by plants and microorganisms are involved in the weathering of primary minerals. Organic compounds play a very important role in the hydrolytic reactions of iron and on the formation, nature, surface properties, reactivity, and transformation of Fe oxides. Organic substances present in the rhizosphere interact with Fe promoting the formation of ferrihydrite and organo‐mineral complexes. The solubility of Fe precipitation products is usually low. However, the formation of soluble complexes of Fe(II) or Fe(III) with organic ligands, usually present in the rhizosphere increases the solubility of Fe‐oxides. Mobilization of Fe from Fe oxides by siderophores is of great importance in natural systems. They can form stable Fe(III) complexes (pK up to 32) and thus mobilize Fe from Fe(III) compounds. These higher Fe concentrations are important for the supply of Fe to plant roots which excrete organic acids at the soil–root interface. Iron oxides adsorb a wide variety of organic and inorganic anions and cations, which include natural organics, nutrients, and xenobiotics. There is competition between anions and cations for the surfaces of Fe‐oxides. Root exudates suppress phosphate or sulfate adsorption on Fe‐oxides. This is a mechanism by which plant roots mobilize adsorbed phosphate and improve their phosphate supply. Anions adsorption on iron oxides modify their dispersion/flocculation behavior and thus their mobility in the soil system. That can increase or decrease the possibility of contact between Fe‐oxides and organics or organisms able to dissolve them. 相似文献
5.
Abstract Manganese (Mn) in soils occurs mainly as hydrous oxides in the form of nodules, concretions or coatings on the surface of soil particles playing an important role in the retention of nutrients or heavy metals. Boron (B) is one of these elements found to be fixed by Mn‐oxides in a relatively available form. This research was conducted to study B sorption by Mn‐oxides prepared in the laboratory in relation to soil pH. Two Mn‐oxides were prepared as coatings on the surface of quartz sand, pyrolusite and birnessite. Boron sorption experiments carried out with uncoated sand (US), pyrolusite‐coated sand (PS), and birnessite‐coating sand (BS) showed that B sorption was increased in PS and BS in comparison to US. Total B sorption was greater on BS than PS and BS sorbed more unrecoverable B by dilute hydrochloric acid method. In US and PS, B sorption was linearly increased with pH. In BS, maximum B sorption occurred at pH 8.5. The operating mechanisms seems to be H bonds between boric acid and OH groups in pyrolusite and lingand exchange between borate and surface hydroxyls in birnessite. 相似文献
6.
Dissimilatory iron-reducing bacteria play a fundamental role in catalysing the redox transformations that ultimately control the mobility of As in anoxic environments, a process also controlled by the presence of competing anions. In this study, we investigated the decoupling of As from loaded Al and Fe (hydr)oxides by competing anions in the presence of iron-reducing bacteria. Hematite, goethite, ferrihydrite, gibbsite and three aluminium-substituted goethites (AlGts) were synthesised and loaded with arsenate, followed by anaerobic incubation with different phosphate or carbonate-containing media in the presence of catalytic iron-reducing bacteria. Soluble Al, As, Fe and P contents were measured in aliquots by inductively coupled plasma optical emission spectrometry following periodical sampling. Shewanella putrefaciens cells were able to utilise both non-crystalline and crystalline Fe (hydr)oxides as electron acceptors, releasing Fe and As into solution. Phosphate and carbonate affected the Fe bioreduction, probably due to the precipitation of metastable mineral phases and also to phosphate-induced stabilisation on the hydroxide surfaces. Phosphate precipitation acted as a sink for As, thus limiting its mobilisation. The highest fraction of desorbed As by phosphate was observed for gibbsite, followed by AlGts. Similarly, gibbsite showed significant amounts of arsenate displaced by carbonate. In spite of its low crystallinity, ferrihydrite was the most efficient compound in retaining arsenate, possibly due to As co-precipitation. This study provides new insight into the management of As-contaminated soils and sediments containing Al-goethites and gibbsite, where the Fe activity may be too low to co-precipitate As-bearing vivianite. Thus, the dynamics of As(V) in flooded soils are significant in agriculture and environmental management. 相似文献
7.
PurposeThe main objective of this study was to investigate the effects of abiogenic and biogenic factors, and their interaction, on aggregate stability determined at different particle sizes. Materials and methodsSoil samples with the same land use pattern were collected and fractioned into five aggregate sizes: 10–15 mm, 5–10 mm, 2–5 mm, 0.25–2 mm, and <?0.25 mm. Contents of iron/aluminum (Fe/Al) oxides, soil organic carbon (SOC), clay, and mean weight diameter (MWD) values for aggregates at different sizes were determined. The respective contributions of these factors were further estimated using path analysis. Results and discussionThe results showed that SOC contents in A horizon declined with the increase of aggregate size. Highest amorphous iron oxide (Feo) contents were observed in 0.25–2 and 2–5 mm aggregates, but highest amorphous aluminum oxide (Alo) contents were found in 5–10 mm aggregates. Abiotic factors (Fe/Al oxides, clay) played a more important role in determining the formation of <?0.25 mm aggregates, whereas both abiotic and biotic factors play an effective role in stabilizing larger aggregates (0.25–2, 2–5, 5–10, and 10–15 mm). The organo-mineral complexes played a certain role in the stability of soil aggregates, especially the larger aggregates. ConclusionsWe conclude that abiotic and biotic factors play variable roles in soil aggregates at different sizes, and more studies are needed to better assess their respective roles to improve our understanding of soil aggregation. 相似文献
8.
Ferrihydrite occurs in soils undergoing rapid weathering, and in soils containing soluble silicate or organic anions which inhibit the formation of more crystalline iron oxides. Because of its very high specific surface area and adsorptive capacity (analogous to allophane), ferrihydrite can profoundly influence soil properties, even if present in only low concentrations. Ferrihydrite was recognised as a mineral by the International Mineralogical Association in 1975. Its structure and chemical formula, however, are not yet clearly understood. Most evidence to date indicates hexagonal-close-packed layers of O 2′, OH, and H 2O with Fe(III) occupying octahedral positions and giving a trigonal unit cell (a=0.508 nm; c=0.94 nm). Some samples appear to have only a partially ordered structure and uncertainty exists as to how to name such material. Natural ferrihydrites commonly contain up to about 9% Si and the role and location of silicate are subjects of active research. At concentrations greater than 5-10%, ferrihydrite in soils can usually be identified by X-ray diffraction. At lower concentrations, a combination of methods can be indicative. Acid-oxalate-extractable iron is a convenient and often useful indicator of the presence and quantity of ferrihydrite in a soil, though it cannot be regarded as a means of positive identification. 相似文献
9.
Abstract Ferruginous deposits from the outfall and backfill of a newly‐installed drainage scheme in a poorly drained alluvial soil have been characterised using selective chemical dissolution, X‐ray diffraction, and chemical analysis and compared with the iron (Fe) deposits found in various micro‐environments within the soil profile. In the drainage ditch and on the permeable backfill around the drainage pipes, the mineralogy of the ferruginous deposits is dominated by the poorly ordered mineral, ferrihydrite, whereas within the soil environment the hydrous iron oxides display a wider range of structural order. It is probable that the initial precipitation product is poorly‐ordered material but that within the soil transformation to a more well ordered mineral, goethite, can occur. 相似文献
10.
Iron hydroxides are subdivided into thermodynamically unstable (ferrihydrite, feroxyhyte, and lepidocrocite) and stable (goethite)
minerals. Hydroxides are formed either from Fe 3+ (as ferrihydrite) or Fe 2+ (as feroxyhyte and lepidocrocite). The high amount of feroxyhyte in ferromanganic concretions is proved, which points to
the leading role of variable redox conditions in the synthesis of hydroxides. The structure of iron hydroxides is stabilized
by inorganic elements, i.e., ferrihydrite, by silicon; feroxyhyte, by manganese; lepidocrocite, by phosphorus; and goethite,
by aluminum. Ferrihydrite and feroxyhyte are formed with the participation of biota, whereas the abiotic formation of lepidocrocite
and goethite is possible. The iron hydroxidogenesis is more pronounced in podzolic soils than in chernozems, and it is more
pronounced in iron-manganic nodules than in the fine earth. Upon the dissolution of iron hydroxides, iron isotopes are fractioned
with light-weight 54Fe atoms being dissolved more readily. Unstable hydroxides are transformed into stable (hydr)oxides, i.e., feroxyhyte is spontaneously
converted to goethite, and ferrihydrite, to hematite or goethite. 相似文献
11.
PurposeThe aim of this paper is to enlighten the role of highly reactive iron (Fe) minerals in soil organic carbon (SOC) preservation in soil aggregates. Materials and methodsThe effects of four long-term (37-year) fertilization regimes (NPK, chemical fertilization; NPKM, chemical fertilization + cattle manure; M, cattle manure; CK, non-fertilization control) on organic carbon (OC) stability, soil iron fractions in bulk soil, and soil aggregates were studied to characterize the capacity and mechanism of Fe minerals to preserve SOM in soil. Results and discussionLong-term fertilization significantly altered the Fe fractions in soil and soil aggregates. The two applications with manure (NPKM and M) increased the non-crystalline Fe content, while the chemical fertilizer (NPK) increased the crystalline Fe content. Besides, long-term fertilization with manure greatly increased the content of SOC and soil total nitrogen (STN). The non-crystalline Fe was positively correlated with the SOC content in both soil and soil aggregates. Meanwhile, the long-term fertilization treatments greatly changed the mass distribution and OC content of soil aggregates. ConclusionsLong-term manure fertilization promoted the formation of non-crystalline Fe fractions, which bounds to SOC to form soil macro-aggregates. Thus, the formation of SOC-Fe association in soil and soil aggregates plays a crucial role in SOC preservation. 相似文献
12.
Adsorption of the imidazolinone herbicides imazapyr, imazethapyr, and imazaquin on synthetic ferrihydrites, either freeze-dried or not-freeze-dried, has been studied. The synthetic ferrihydrites were characterized by X-ray diffraction, scanning electron micrographs, and specific area determination. On each ferrihydrite, adsorption was found to be strongly dependent on pH. The highest extent of adsorption took place at pH values close to the pK(a) of the carboxylic group of the herbicides. No adsorption was observed at pH > 8. The freeze-drying process reduced the adsorptive capacity of the ferrihydrite by formation of larger aggregates provoking a decrease of the surface area. The chemical differences between the herbicides did not strongly affect the adsorption process of the herbicides. However, imazaquin was more adsorbed than the other two herbicides, in particular at pH close to its pK(a). 相似文献
13.
As a consequence of intensive mining of the western Erzgebirge since medieval times, floodplain soils of the Mulde river contain large concentrations of arsenic (As) (>50 mg kg −1). Arsenic in soil is often bound to poorly crystalline Fe and Mn (hydr)oxides, which may dissolve under reducing conditions. Part of the As may also exist in primary minerals, predominately sulphides, or in secondary minerals formed upon weathering. In order to better understand the impact of seasonal flooding, we surveyed As‐bearing mineral phases, especially of iron (Fe) (hydr)oxides. Because Fe (hydr)oxides are clay‐sized, soil samples were fractionated into six particle‐size fractions. The fractions were digested with aqua regia for determination of total element concentrations, extracted with hydroxylammonium chloride (NH 3OHCl; selective for Mn (hydr)oxides and NH 4 oxalate), and analysed by X‐ray diffraction and scanning electron microscopy. The largely similar distribution of As and lead (Pb) suggested the potential co‐existence of the two elements in primary or secondary mineral phases. However, neither As–Pb minerals nor any other As mineral were detected. Association with Mn oxides was negligible. The predominant As‐bearing phases were poorly crystalline Fe (hydr)oxides, which also incorporated large amounts of Pb and were affected by redox dynamics. 相似文献
14.
PurposeSoils have the ability to retain potentially toxic elements (PTEs) through different chemical processes that promote low mobility of these elements, such as the precipitation of secondary phases of Fe, which facilitate the adsorption/co-precipitation of PTEs. The main objective of this study was to evaluate the mobility of PTEs present in an acid solution in two soils with different concentrations of calcite, understanding the role of secondary iron phases in the retention of these elements. Materials and methodsTo evaluate this phenomenon, intact soil columns of two different types of soils from the Sonora River in Northwest Mexico were exposed to an acid solution with high concentration of dissolved PTEs (mainly Fe, Al, and Cu). Results and discussionThe Tinajas soil was free of carbonates while the Bacanuchi soil had more carbonate content than the Tinajas soil. Secondary precipitates corresponding to secondary phases of iron (mainly ferrihydrite and jarosite) were identified by X-ray diffraction. Using scanning electron microscopy, the PTEs retained in the soils were identified. The presence of calcite favored the neutral pH values in the collected leachates in the Bacanuchi soil; consequently, the mobility of the PTEs present in the acid solution was nullified. Furthermore, this process facilitated the retention of the toxic elements in the Bacanuchi soil. ConclusionsThe retention of PTEs was 100% in the Bacanuchi soil where the natural acid-neutralizing capacity in this soil was associated with calcite. The formation of secondary phases of Fe, among them ferrihydrite, jarosite, and schwertmannite, mainly in Bacanuchi soil, promoted the retention of Al, As, Cd, Cu, Fe, Mn, and Pb (elements analyzed in this work). Results of this work can provide key insights to improve cleanup and conservation strategies in mining sites. 相似文献
15.
PurposeThis study was conducted in order to examine the effect of colloidal particles on electrochemical properties of charged larger size materials.Materials and methodsA self-made streaming potential apparatus was used to measure the zeta potentials of Fe/Al oxide-coated quartz. The effects of colloidal particles of kaolinite and montmorillonite on the electrochemical properties of Fe/Al oxide-coated quartz were investigated through comparing the difference in zeta potential of the coated quartz in electrolyte and clay suspension.Results and discussionThe change of zeta potentials of the coated quartz, when clay suspensions flowed through, increased with the increasing concentrations of kaolinite and montmorillonite and degree of coating with Fe/Al oxides, and decreased with increased ionic strength of the suspensions. Electrostatic attraction between clay colloids and the coated quartz was the key factor influencing the interaction between the oppositely charged particles. The deposition of colloidal particles of kaolinite and montmorillonite on coated quartz and the overlapping of the diffuse layers of electrical double layers between the oppositely charged particles were responsible for the change in zeta potential of Fe/Al oxide-coated quartz. The relative contribution of the deposition of clay particles to the change in zeta potential was greater than that of the overlapping of diffuse layers.ConclusionsWhen clay suspensions flowed through the saturated sand of Fe/Al oxide-coated quartz, both overlapping of diffuse layers between charged sand and clay particles and deposition of clay particles contributed to change of zeta potential of the coated quartz. 相似文献
16.
Abstract Variations in the plant growth media were achieved by combining kaolinite clay (<l μm esd.), silt (2–50 μm esd.) and sand (100–250 μm esd.) in various ratios. Peds of different sizes were separated from an Okolona clay soil and used as a growth media. A layer (3 cm thickness) of the sand, silt or clay and their combinations were intercalated between sandy loam soil material in a lucite coated cardboard carton. After 21 days the plants were harvested and analyzed for a number of growth parameters and related to the physical and micromorphology of the central control layer. Germination and emergence of sorghum seed were delayed in the finer aggregates. An increase in aggregate size increased the root elongation. An examination of thin sections showed that most of the roots in the finer aggregates were grown in interpedal regions whereas in the larger aggregates roots were found in both the intrapedal as well as interpedal regions. An increase in clay content of the central layer reduced the root growth. Silt also reduced root growth but not to the extent of the clay. Maximum root growth and penetration occurred in the mixture containing about 50 percent sand. Better root growth was observed in a sandy to sandy loam texture than clay to clay loam texture. 相似文献
17.
ABSTRACT Reducing the arsenic (As) concentration in rice grains is of great interest from a human health perspective. Iron (Fe) materials immobilize As in soils, thereby effectively reducing the As concentration in rice grains. We investigated the effect of by-product Fe materials obtained from the casting industry on the As mobility in two soils (soil A and soil B) by a long-term (approximately 100 days) flooded soil incubation experiment. The examined Fe materials were spent steel shot (SSS), fine spent casting sand (SCS) containing steel shot, and two kinds of residual Fe materials (RIMs) from steel shot production. Commercial Fe materials used to immobilize As (zero-valent Fe and ferrihydrite) were tested for comparison. The dissolved As in soil solution of controls for soil A and soil B reached approximately 100 and 800 μg L ?1, respectively. The effect on As immobilization of all the by-product Fe materials increased with time and was comparable to or greater than that of commercial ferrihydrite, except for SCS. The additions of SSS and RIMs decreased by more than 90% of the dissolved As in soil A and decreased by more than 50% in soil B after 100 days incubation. Overall, the effect of the by-product Fe materials on the solubility of silicon and phosphorus was much less than that of the commercial Fe materials. Considering the cost advantage over commercial Fe materials, the Fe materials obtained from the casting industry as by-products are promising amendments for the immobilization of As in paddy soils. 相似文献
18.
Manganese dioxide (birnessite) was coated with two levels of Fe and Al oxides and CaCO 3, and the influence of these coatings on the surface features and the reactivity of MnO 2 with respect to the oxidation and sorption of As(III) (arsenite) was examined. For all untreated and coated MnO 2 samples, the depletion (oxidation plus sorption) of As(III) by the samples follows first-order kinetics. The rate constants are smaller for the samples with the high levels of coating of Fe and Al oxides and CaCO 3 on MnO 2 than they are for the untreated MnO 2 and the MnO 2 with the low levels of coating. The extent of masking of the electron-accepting sites on the MnO 2 for converting the toxic As(III) to the less toxic As(V) significantly varies with the kinds and levels of coatings. Coatings of Fe and A1 oxides and CaCO 3, on MnO 2 distinctively affect the sorption of As. Manganese oxide evidently catalyzes the sorption of As by Al oxide through oxidation of As(III) to As(V). The relative affinities of the oxides of Mn, Fe, and Al and CaCO 3, toward As(III) and As(V) account for the coating effects. 相似文献
19.
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 (Fe 2O 3) 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 Hem conv) in an intricate manner. Both direct and reverse branches on the curve of the Hem conv-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
20.
Abstract To examine sonic dispersion as an extraction procedure for DTPA micronutrient test, soil DTPA solution suspensions were sonicated to extract Fe, Zn, Mn, and Cu. The elements extracted after 15 or 60 seconds sonication were compared with those extracted after 1/2 or 2 hours shaking. The mean differences between Fe, Zn, Mn, or Cu extracted after 15 seconds sonication and those extracted after 1/2 hour shaking were not significant. However, the extractions obtained after 2 hours shaking were significantly higher than those obtained after 15 or 60 seconds sonication. The elements extracted after 15 or 60 seconds sonication correlated significantly with those extracted after 1/2 or 2 hours shaking. Therefore, 15 or 60 seconds sonication can replace 2 hours shaking in the extraction procedure for DTPA micronutrient test. However, 15 seconds sonication is more convenient than 60 seconds and does not require cooling of soil solution suspension during sonication. Therefore 15 seconds sonication ‐ a replacement for 2 hours shaking to extract Fe, Zn, Mn, and Cu ‐ is recommended. 相似文献
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