Heavy metal sorption on soil minerals affected by the siderophore desferrioxamine B: the role of Fe(III) (hydr)oxides and dissolved Fe(III)

Phytoextraction of heavy metals from polluted soils has often been found to be limited by the bioavailability of the pollutants. Inorganic or organic ligands are occasionally used as complexing agents to enhance the mobility of the heavy metals. However, the opposite effect is also possible. We studied the influence of the hydroxamate siderophore desferrioxamine B (DFOB) on the sorption of Cu, Zn and Cd to clay minerals, with the emphasis on the role of dissolved Fe(III) and Fe(III) minerals. Depending on the surface charge of the minerals and on pH, sorption of heavy metals can be either enhanced or diminished. We show here that this effect of DFOB disappears if dissolved Fe(III) is added to suspensions of clay minerals in excess to DFOB. We found that the solid Fe(III) phases ferrihydrite and goethite did not impede the effect of DFOB on the sorption of heavy metal, however. Between pH 4 and 10, DFOB completely prevented Cu sorption on ferrihydrite. A strong mobilizing effect was also observed for Zn, but not for Cd. In presence of goethite, concentrations of dissolved Cu, Zn and Cd were enhanced only above approximately pH 5, 7 and 8, respectively. Below these pH values the binding of these metals to goethite was even stronger with than without DFOB. In the absence of heavy metals, DFOB‐promoted dissolution of ferrihydrite was much faster than that of goethite due to the larger surface area of ferrihydrite. In the alkaline pH range, where sorption of DFOB on the surfaces of the iron oxides was greater, dissolution of both minerals was reduced.     

Extraction of metal ions sorbed on hydrous oxides of iron(III)

Extraction of metal ions presorbed on Fe(III) hydrous oxide suspensions using 20 different chemical reagents has confirmed that bonding to several different sites can be involved. Up to half of the sorbed Cd was moderately weakly bound, and was displaced by Mg, Ca and Na chloride solutions but these reagents released little Cu or Pb, and < 20% of the Zn. Reagents which partially dissolved gel suspensions (e.g. mineral acids, EDTA, reducing agents) released > 80% of the sorbed metal ion, but a small fraction remained as a limited solubility interaction product in each case. Sorption and extraction behavior using samples containing goethite and/or hematite reflected the lower solubility of these solids in the various solutions. ‘Aged’ gels bound metal ions less strongly than freshly precipitated hydrous oxide. The extraction data has been interpreted in terms of displacement reactions, formation of complex ions, and specific adsorption (or coprecipitation). The significance of hydrous oxide formation in metal ion scavenging from natural waters and subsequent release processes has been considered.     

Poorly ordered hydrous Fe oxides, colloidal dispersion and soil aggregation. I. Effect of humic macromolecules on surface and colloidal properties of Fe (III) polycations

Model humic macromolecules, obtained by auto-oxidation of the catechol-glycine system, were adsorbed on poorly ordered hydrous iron oxides, Fe(OH)_2.8. The pH was nearly constant at c. 6 in order to simulate natural soil and river environments. When the amount of organic carbon adsorbed on 1 g of poorly ordered ferrihydrite increased from 0 to 70 mg, the ligand OH exchange was very small, but the zero point of charge of suspensions progressively shifted from 7.3 to 5.6, and net surface charge, which was initially positive, progressively became negative, suggesting an adsorption mechanism with positive charge neutralization. Consequently, colloidal stability changed from rapid to slow flocculation. The ferrihydrite-haematite exothermic reaction partially shifted from 400°C to higher temperatures as a function of adsorbed organic matter, and ferrihydrite solubility progressively increased by formation of soluble iron-organic complexes. These results were explained more satisfactorily by the concept of colloidal organ- mineral association than by organic coatings on surfaces.     

Poorly ordered hydrous Fe oxides, colloidal dispersion and soil aggregation. II. Modification of silty soil aggregation with Fe(III) polycations and model humic macromolecules

Poorly ordered ferrihydrites, more or less associated with synthetic humic macro-molecules, were added to a poorly structured temperate silty soil. Manipulation of the net soil charge through these additions was measured by potentiometric titration and cation exchange capacity. The consequences of anchoring positively charged Fe hydrous oxides on negative permanent clay surface charges were studied. Both cementation and aggregate water-stability increased with increase in adsorbed iron. The aggregation process was studied by using micromorphology and ultramicromorphology, water retention curves, mercury porosimetry and a fractal approach. Aggregate water-stability was studied when the soils were air-dried, with some irreversible aggregation, and oven-dried or wetted from – 1.5 MPa to – 1 kPa thereafter. Soils with added Fe(III) polycation–humic macro-molecule associations were less positively charged, less cemented and less stable than soils amended with Fe(III) polycations alone. The effect of these treatments on slaking is discussed.     

Fe(III)-EDDHA and -EDDHMA sorption on Ca-montmorillonite, ferrihydrite, and peat.

The effectiveness of Fe chelates as Fe sources and carriers in soil can be severely limited by the adsorption of Fe chelates or chelating agents in the solid phase. To study this phenomenon, well-characterized peat, Ca-montmorillonite, and ferrihydrite were used as model compounds, and the adsorption of Fe-EDDHA and Fe-EDDHMA chelates were studied. Sorption isotherms for the meso and racemic isomers of these chelates on the soil materials are described. The variability of sorption with pH in peat and ferrihydrite was also determined because both have variable surface charge at different pH values. In montmorillonite, at low concentrations, the retention of Fe from the Fe-EDDHMA chelate is greater than the one of the Fe-EDDHA chelate. As well as the concentration increased, the inverse situation occurs. The behavior of both meso and racemic isomers of chelates in contact with Ca-montmorillonite is similar. The Fe-meso-EDDHA isomer was highly adsorbed on ferrihydrite, but the racemic isomer is not significantly retained by this oxide. For Fe-EDDHMA isomers, the racemic isomer was more retained by the oxide, but a small sorption of the racemic isomer was also observed. Results suggest that Fe-EDDHA chelates were more retained in peat than Fe-EDDHMA chelates. The most retained isomer of Fe-EDDHA was the meso isomer. For Fe-EDDHMA, the adsorption was very low for both racemic and meso isomers.     

Reductive dissolution of crystalline and amorphous Fe(III) oxides by microorganisms in submerged soil

Summary Reduction of Fe(III) of amorphous and crystalline Fe(III) oxides to Fe(II) in flooded soils was studied using ⁵⁹Fe(OH)₃ and ⁵⁹Fe₂O₃. The results indicated that Fe(III) in the amorphous oxide was readily amenable to microbial reduction in anaerobic soil condition whereas Fe(III) in the crystalline oxide was not. Following soil submergence, the native as well as the applied crystalline Fe(III) oxides were rapidly converted into the amorphous form. The transformation of the crystalline oxides to the amorphous form appears to be a prerequisite for the reduction of Fe(III) of the oxide. This transformation, probably through hydration, is also mediated by microorganisms.     

被锰、铁和铝固定的磷的性质的比较研究

An experiment was conducted to examine the role of Mn in P fixation through comparing with Al and Fe.Hydroxides and oxides of Al,Fe and Mn were prepared in lab under opened and closed conditions to react with phosphate,The newly formed Mn hydroxide showed the strongest P-fixing ability,even several times higher than Fe hydroxide ,but became the lowest rapidly due to ageing when exposed to air,Mn oxide showed the lowest P-fixing ability,Therefore,a sound consideration on P fixation should be based on both quantities and P-fixing abilities of the compounds of Fe,Al and Mn,The importance of Mn on P availability should receive more attention especially under oxidation-reduction dynamic conditions.     

A Study on Al(III) and Fe(II) Ions Sorption by Cattle Manure Vermicompost

Cattle manure vermicompost has been used for the adsorption of Al(III) and Fe(II) from both synthetic solution and kaolin industry wastewater. The optimum conditions for Al(III) and Fe(II) adsorption at pH?2 (natural pH of the wastewater) were particle size of ≤250?µm, 1 g/10 mL adsorbent dose, contact time of 4 h, and temperature of 25°C. Langmuir and Freundlich adsorption isotherms fitted reasonably well in the experimental data, and their constants were evaluated, with R ² values from 0.90 to 0.98. In synthetic solution, the maximum adsorption capacity of the vermicompost for Al(III) was 8.35 mg g^?1 and for Fe(II) was 16.98 mg g^?1 at 25°C when the vermicompost dose was 1 g 10 mL^?1, and the initial adjusted pH was 2. The batch adsorption studies of Al(III) and Fe(II) on vermicompost using kaolin wastewater have shown that the maximum adsorption capacities were 1.10 and 4.30 mg g^?1, respectively, at pH?2. The thermodynamic parameter, the Gibbs free energy, was calculated for each system, and the negative values obtained confirm that the adsorption processes were spontaneous.     

Kinetic Speciation of Ni(II) in Model Solutions and Freshwaters: Competition of Al(III) and Fe(III)

The competing ligand exchange method was used to investigate the competitive binding of Ni(II) by Al(III) and Fe(III) in model aqueous solutions and freshwaters. Graphite furnace atomic absorption spectrometry and adsorptive cathodic stripping voltammetry were used to monitor the rate of uptake of the Ni by Chelex 100 chelating resin and dimethylglyoxime as the competing ligands, respectively. The results have revealed that Ni(II)–humate complexes were more labile in presence of the mixture of Al(III) and Fe(III), compared to the lability of the Ni(II)–humate complexes when only one of the two, Al(III) or Fe(III), was present. The environmental significance of this work is that in model solutions simulating freshwater containing humic substances and the target trace metal Ni(II) and cations, Al(III) and Fe(III), the competitive binding of Ni(II), Al(III) and Fe(III) by humic substances makes Ni(II)–humate complexes labile, releasing free Ni²⁺–aqua complex, which reported to be toxic.     

Lactic acid decreases Fe(II) and Fe(III) retention but increases Fe(III) transepithelial transfer by Caco-2 cells

Lactic acid (LA) has been proposed to be an enhancer for dietary iron absorption, but contradictory results have also been reported. In the present study, fully differentiated Caco-2 cell monolayers were used to evaluate the effects of LA (1-50 mmol/L) on the cellular retention and transepithelial transport of soluble non-heme iron (as ferric nitrilotriacetate). Our data revealed a linear decline in Fe(III) retention with respect to the concentration of LA added. In the presence of 50 mmol/L LA, retention of Fe(III) and Fe(II) decreased 57% and 58%, respectively. In contrast, transfer of Fe(III) across the cell monolayer was doubled, while Fe(II) transfer across the cell monolayer decreased 35%. We conclude that LA reduces cellular retention and transepithelial transport of Fe(II) by Caco-2 cells in a dose-dependent manner. However, while LA also reduces retention of Fe(III) by Caco-2 cells, the transfer of Fe(III) across cell monolayers is enhanced, possibly due to effects on paracellular transport.     

Inorganic anion sorption and interactions with phosphate sorption by hydrous ferric oxide gel

The sorption of inorganic anions by hydrous ferric oxide gel (Fe gel) from 10 ^?1 M NaClO₄ at pH 6.5 decreased in the order: orthophosphate (H₂PO₄)>arsenate (H₂AsO₄) = selenite (HseO3) > silicate (H₄SiO₄) > molybdate (MoO²₄^?) > sulphate (SO²₄^?) > selenate(SeO²₄^?)>chloride (Cl^?) = nitrate (NO^?₃). When each anion was added to Fe gel with an equimolar quantity of H₂PO^?₄, there was no detectable effect of SO²₄^?, SeO²₄^?, Cl^?, and NO^?₃ on the amount of H₂PO^?₄ sorbed. Other anions depressed H₂PO₄ sorption in the order H₂AsO₄ >HseO₃ > H₄SiO₄ > MoO²₄. At the lowest level of anion addition (500 mmol kg ^?1), H₂PO₄ sorption was depressed by no more than 6% of the sorption level in the absence of a competing anion. In contrast, at the highest level of anion addition (1700 mmol kg-¹ of each), H₂AsO₄ decreased H₂PO₄ sorption by 44%. The sorption of SO₄^? was completely eliminated when this anion was added with equimolar amounts of H₂PO₄. The ability of anions to compete with H₂PO₄ for sorption sites could not be explained solely by the results obtained for the sorption of each anion alone. Thus, H₂AsO₄ was more competitive than H₂PO₄ when added together, even though more H₂PO₄ than H₂AsO₄ was sorbed when each anion was added alone. Although H₂PO₄ was sorbed in larger amounts, there is no evidence to suggest that H₂PO₄. H₂AsO₄, and HseO₃ were sorbed on different sites.     

Significance of hydrous iron oxides in enhancing P sorption of soils with the addition of sodium hydrosulfite (Na2S2O4)

Phosphorus sorption (P_sor) of soils is affected by redox conditions. It has been shown that P_sor of lowland soils at a pH value of about 4.3 increases when a small amount of sodium hydrosulfite (Na₂S₂O₄) is added and decreases when an excess amount of (Na₂S₂O₄) is added to the mixture of a soil and P solution. Hydrous Fe-Al oxides, manganese dioxide (MnO₂) exchangeable Ca, models of reactive components with P in soils, were examined to identify the factors responsible for the increase of P_sor in lowland soils when a small amount of Na₂S₂O₄ was added. For clarifying the contribution of the hydrous Fe-Al oxides, goethite and 7 hydrous Fe-Al oxides (Fe/Al atomic ratio: 1/0, 5/1, 2/1, 1/1, 1/2, 1/5, and 0/1) were used. The P_sor of all these materials increased when they were treated with a small amount of Na₂S₂O₄ although the increase was the smallest for the hydrous Al oxide among the 7 oxides. Thus, the hydrous Fe oxides, and Al oxide to a smaller extent, play an important role in the increase in P_sor of the lowland soils treated with a small amount of Na₂S₂O₄ The P_sor of the hydrous Fe oxides was not appreciably affected by the addition of MnO₂. The increase in P_sor of the Ca-saturated Hachirogata soil was almost the same as that of the Nasaturated Hachirogata soil, indicating that exchangeable Ca did not affect appreciably the increase of P_sor in reduced soils at a pH value of about 4.3.     

The influence of aminopolycarboxylates on the sorption of copper (II) cations by (Hydro)oxides of iron,Aluminum, and manganese

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.     

红壤中铝、锰和铁在酸雨作用下的释放特征

酸雨作用下红壤中Al、Mn和Fe的释放大多具有阶段性特征,旦土壤不同,其阶段性特征存在明显的差异。多数情况下同一土壤中Al和Fe的阶段性释放特征较为相似。3种元素累积释放量(Q)随淋溶量(H)的变化符合二次模型:Q=A B1H B2H2。经过9150～10650mm的酸雨淋溶以后,与对照(pH5.6)相比,pH4.5的酸雨使Al累积释放量增加8.16%～87.49%,Mn增加-4.29%～24.75%,Fe增加5.78%～86.03%;pH3.5的酸雨使Al累积释放量增加68.59%～158.60%,Mn增加26.11%～205.53%,Fe增加8.48%～138.88%。3种元素对酸雨的敏感性依次是:Al>Fe>Mn。其累积释放量在不同土壤之间表现出基本一致的特点:Al和Mn的释放量较为接近,且远远大于Fe的释放量。     

Molybdate sorption by oxides of aluminium and iron

The sorption of molybdate by goethite, hematite, bayerite and α-Al₂O₃ was studied as a function of molybdate concentration and pH. The sorption isotherms exhibited double sorption plateaus in which the amount of Mo sorbed in the second plateau was double that in the first. This was attributed to the polymerization of molybdates as the concentration increases. Furthermore Mo sorption was found to be associated with a cosorption of Na cations, probably present to maintain electroneutrality in the surface zone. The sorption showed high sensitivity towards the pH, attaining a maximum at pH 4. For the iron oxides the decrease in sorption was much less pronounced on the acid side of the pH maximum and occured at lower pH values than that of the Al oxides. Molybdate sorption is explained in terms of a ligand exchange reaction between molybdate and surface hydroxyls.     

Behaviour of Co, Fe, Mn and Ni in the Po Estuary (Italy)

The behaviour of Co, Fe, Mn, and Ni was investigated in the mixing area of the Po river in six surveys over the period March 1992 to June 1995 during low-to-medium solid load and flow conditions. The concentrations (nM) of dissolved elements for the riverine and marine end-members respectively were in the ranges 0.09 to 0.93 and 0.24 to 0.98 for Co, 10 to 53 and 5 to 20 for Ni, 12 to 87 and 5 to 33 for Fe, and 10 to 155 and 26 to 105 for Mn. Co and Mn behave non-conservatively in the Po estuary; an addition to the dissolved phase occurred for these elements that was more marked in the summer period. The concentrations of dissolved and particulate Ni decreased almost linearly with increase in salinity, with more marked variations in dissolved Ni concentration in winter than summer. The concentrations of dissolved and particulate Fe also varied conservatively with salinity. This unusual behaviour for dissolved Fe is attributed to the analytical procedure which excluded kinetically inert colloidal species.     

Release Kinetics of Si,Al, Fe,and Mn from Acid Soils in the Presence of EGCG

Plant polyphenols can affect soil processes. In the present study, batch experiments were conducted to study the effects of epigallocatechin gallate on the release kinetics of silicon (Si), aluminum (Al), iron (Fe), and manganese (Mn) from acid Anthrosol and Luvisol. The results indicated that the optimal model describing the release kinetics of these elements was a double constant, simple Elovich, or parabolic diffusion equation, and a first-order equation was not suitable. These elements went through an initial rapid-release phase, followed by a slower-release phase. The order of release amounts and rates for Anthrosol was Si > Al > Fe > Mn, but they were different at different phases. However, the order for Luvisol was always Al > Mn > Si > Fe. Meanwhile, the release amount and rate of every element was in the order Luvisol > Anthrosol. The results of this study could help to resolve Al and Mn toxicity in acid soils.     

Baseline of Ca,Mg, Fe,Mn and Al Concentrations in Catatumbo River Surficial Sediments

Ca, Mg, Fe, Mn and Al were determined in surficial sediment samples from Catatumbo River (including sediments from major tributaries) a binational basin shared by both Venezuela and Colombia in approximately 30% and 70%, respectively. The global mean concentration of the metals was Al > Fe > Mg > Ca > Mn (0.376; 0.304; 0.063; 0.042; 5.9 × 10^-4 mmol g^-1 dry weight). The objectives of this investigation were (1) to establish metal-concentration baselines, and (2) to determine spatial distribution of Ca, Mg, Fe, Mn and Al concentrations, in bed sediment samples from Catatumbo River (including sediments from major tributaries). As Catatumbo River is the main tributary to Lake Maracaibo system (South America's largest inland lake), its impact on the eutrophication process of Lake Maracaibo due to the formation of metal/phosphorus complexes is discussed.     

Metal ion interaction with the hydrous oxides of aluminium

Suspensions of Al(OH)3 gel, gibbsite or alumina were loaded with varying amounts of Cu, Cd, Zn, or Pb ions by varying the system pH. A complex relationship between metal uptake and equilibrium pH was noted (due to substrate buffering) but total loss of metal ion from solution was observed at pH > 6.5. The pre-loaded particles were back-extracted with fifteen different chemical solutions and the percentage of sorbed ion retrieved generally varied along the sequence NaCl, CaCl₂ < MgCl₂, NH₄NO₃ < CH₃OOONH₄, Na citrate, Na₄P₂O₇, EDTA, DTPA ≈ CH₃OOOH, H₂C₂O₄, HCI, HN0₃. The recovery value varied with initial surface loading and an observed minimum around 1 gruel M²⁺ per 20 mg solid is considered to reflect changes in metal species nature (e.g., bonded M²⁺, MOH⁺, precipitated M(OH)₂) and substrate surface charge. In the ‘minima’ region less than 10% of metal ion was displaced by many reagents. With different loadings up to 40% was displaceable by salts (i.e., weakly sorbed) while acids or complex formers at times released over 90 % of the pre-sorbed metal species. It was concluded that the degree of metal ion interaction varied with the initial system pH, with retention being due to a combination of weak adsorption, occlusion in gels, chemi-sorption and precipitation of M(OH)₂.     

Effects of Soil Sample Storage Treatment on the Composition and Fe,Al, and Mn Speciation of Soil Solutions Obtained by Centrifugation

Soil solution chemistry is a powerful tool for studying many aspects of soil science. Among several isolation techniques, centrifugation appears most promising as a method of extracting the soil solution in the laboratory. However, some operational conditions must be defined. The present work reports the influence of sample storage on the observed composition of the soil solution of two Brazilian soils submitted to different managements. Since metal speciation in soil solution significantly influences metal bioavailability, a second experiment was conducted to evaluate the effects of storage on Fe, Al, and Mn speciation by size exclusion chromatography (HPLC-SEC). The results showed that the effects of soil handling prior to solution extraction had a significant effect on soil solution composition, mainly when the sample was dried and rewetted. Only the samples that were kept refrigerated (4 °C) for 15 days led to results comparable to those obtained from fresh soils. However, considering the patterns of the UV detection chromatograms and metal distribution, only field moist samples should be used in studies related to Al, Mn, and Fe speciation in the studied soils.