Evidence of microbial control of Hg0emissions from uncontaminated terrestrial soils     

Johannes Fritsche  Daniel Obrist  Christine Alewell 《植物养料与土壤学杂志》2008,171(2):200-209

It is known that in wetland soils and soils contaminated with mercury (Hg), direct biotic reduction of Hg²⁺ to Hg⁰ leads to Hg⁰ emissions to the atmosphere. In terrestrial soils, numerous factors have been reported that control Hg⁰ emissions, but it is still unclear if biotic processes are also important. In this study, microbiological activity of Cambisol monoliths from a subalpine grassland with Hg concentrations of approx. 100 ng g^–1 were manipulated in laboratory incubation experiments. Elemental Hg emissions were recorded together with CO₂ emission rates as proxy for microbiological respiration. Emissions of Hg⁰ increased from approx. 5 ng m^–2 h^–1 up to 130 ng m^–2 h^–1 with stimulated biological activity (glucose addition, increase in temperature) and decreased with inhibited activity (chloroform fumigation, autoclaving, drying). Similar patterns with evasion rates of >90 ng m^–2 h^–1 were observed after dried soils were remoistened again. Our results indicated that processes leading to Hg⁰ emissions from uncontaminated terrestrial soils are at least partly controlled by biotic processes. However, it is still uncertain if Hg⁰ emission is caused directly by biotic reduction of Hg²⁺ or indirectly by abiotic reduction, induced by products of microbiological degradation, e.g., humic acids.  相似文献   

Soil and sediment properties affecting the accumulation of mercury in a flood control reservoir     

Fred E. Rhoton  Sean J. Bennett 《CATENA》2009,79(1):39-48

Mercury accumulations in some fish species from Grenada Lake in north Mississippi exceed the Food and Drug Administration standards for human consumption. This large flood control reservoir serves as a sink for the Skuna and Yalobusha River watersheds whose highly erodible soils contribute to excessively high sediment yields and impaired water quality. This study was conducted to characterize the distribution of total Hg in watershed soils and determine the relationship between the easily transportable clay, organic C (OC), and Fe oxide fractions and the movement of Hg from upland sources to reservoir sinks. Cores were collected from soils, of different land-use, representative of the three soil orders (Alfisols, Entisols, and Vertisols) found in the watersheds. Sediment cores were collected from the Yalobusha River and Grenada Lake. In the laboratory, soil cores were sampled by horizon while sediment cores were sampled in 10 cm increments. These samples were characterized for total Hg, particle size distribution, OC, Fe oxide contents, and pH. Mercury concentrations ranged from 10 to 112 µg kg^− 1 in the soil profiles, with average regression coefficient (r²) values of 0.104, 0.362, and 0.06 for Hg versus clay, OC, and Fe oxides, respectively. River sediment cores had Hg concentrations ranging from 0 to 38 µg kg^− 1, and significant (1% level) r² values of 0.611, 0.447, and 0.632 versus clay, OC, and Fe oxides, respectively. Mercury concentrations in the lake sediment ranged from 0 to 125 µg kg^− 1. The r² values for Hg versus clay, OC, and Fe oxides in the lake sediment were 0.813, 0.499, and 0.805, respectively, all significant at the 1% level. These results indicate that total Hg is poorly correlated with the clay, OC, and Fe oxide fractions at depth in the soil profiles because maximum Hg concentrations occur in the surface horizons due to atmospheric in-fall. The statistically significant r² values for Hg versus these components in the sediment cores are the result of particulate clay, Fe oxides, and finely divided OC sorption of Hg from solution during the runoff and sediment transport process. The higher correlations for the lake sediment reflect an enrichment of the Hg-laden clay fraction relative to stream sediment through flocculation and sedimentation processes in the slack-water environment of the reservoir.  相似文献   

溶液体系中非生物因素对胡敏酸还原汞的影响   总被引：1，自引：0，他引：1  

JIANG Tao  WEI Shi-Qiang  D. C. FLANAGAN  LI Meng-Jie  LI Xue-Mei  WANG Qiang  LUO Chang 《土壤圈》2014,24(1):125-136

As a global pollutant process,the reduction of mercury(Hg)is especially important.One pathway is through an abiotic reduction with humic acids(HAs),which is controlled by different factors,including initial Hg and HA concentrations,pH,temperature and light.In this study,three humic acids were selected to illustrate the Hg~(2+)abiotic reduction mechanisms by HAs,and to identify the key limiting factors for reduction rates and amounts.In addition,the initial status of the HAs as a solid or in an aqueous solution were also compared,to help explain why HAs show different dominant characteristics(e.g.complexation or reduction)in the reaction process with Hg.Results indicated that HAs were able to reduce Hg abiotically.Higher initial Hg,higher HA concentrations and either high(8.1)or low(3.6)solution pH decreased the HA reduction capacity.In addition,Hg°production rates increased with increasing temperature,and the same trend was observed with light exposure.Humic acids added as an aqueous solution resulted in significantly greater Hg°production than addition as a bulk solid.Finally,the Hg reduction rate and capacity varied significantly(P0.05)with HAs from different sources.These findings helped to explain why HAs showed different dominant characteristics(e.g.complexation or reduction)in the reaction process with Hg,and evidentially demonstrated the existence of a possible pathway of Hg~(2+)reduction,which indicated that humic substances in natural environments,especially in water bodies,could act either as a sink or a source for Hg.  相似文献   

Early detection of the effects of compaction in forested soils: evidence from selective extraction techniques     

Muhammad Farrakh Nawaz  Guilhem Bourrié  Fabienne Trolard  Jacques Ranger  Sadaf Gul  Nabeel Khan Niazi 《Journal of Soils and Sediments》2016,16(9):2223-2233

  相似文献   

Modeling the elemental mercury cycle in Pallette Lake,Wisconsin, USA     

Grace M. Vandal  William F. Fitzgerald  Kristofer R. Rolfhus  Carl H. Lamborg 《Water, air, and soil pollution》1995,80(1-4):529-538

The spatial and temporal distribution of elemental Hg (Hg°) and reactive Hg (Hg_R) has been studied on Pallette Lake, Wisconsin during May – August, 1993 and May, 1994. In general, Hg° concentrations near the lake surface greatly exceeded saturation with respect to atmospheric Hg° indicating a flux out (?) of the lake. Evasional losses were estimated using a thin film model and averaged ?101 pmol m^?2 d^?1 during July and August, 1993. A large portion of atmospherically deposited Hg is re-emitted. Thus, in-lake Hg° production' and evasion to the atmosphere will significantly reduce the amount of Hg which is transported to the sediments, the principal site of methylation. Laboratory experiments were conducted to ascertain the rate of Hg° formation from Hg(II). Reduction was significantly lower in heat sterilized lakewater suggesting Hg° production was biologically mediated. The temporal distribution of epilimnetic Hg°, as measured at the lake center, was influenced by Hg° evasion, Hg° production and advective transport of water parcels of differing Hg content. Spatial gradients in Hg° and Hg_R were identified and a transport model was employed to estimate the advective flux of Hg°. The importance of atmospheric deposition and sediment-water interaction as sources of Hg_R to epilimnetic waters were examined. Porewater concentrations of Hg° and Hg_R were determined on several occasions. During May, 1994, the depletion of lakewater Hg_R following a input pulse due to rain was observed and the estimated removal rate (16–20% d^?1) agrees well with reduction rates obtained in the laboratory (23% d^?1).  相似文献   

Alkalinity generation by Fe(III) reduction versus sulfate reduction in wetlands constructed for acid mine drainage treatment     

Melanie A. Vile  R. Kelman Wieder 《Water, air, and soil pollution》1993,69(3-4):425-441

Despite the widespread use of wetlands for acid mine drainage (AMD) treatment, alkalinity generating mechanisms in wetlands and their abiotic and biotic controls are poorly understood. While both dissimilatory sulfate reduction and Fe(III) reduction are alkalinity-generating mechanisms, only the former has been considered as important in wetlands constructed for AMD treatment. This study was conducted to determine the extent to which Fe(III) reduction occurs and the extent to which sulfate reduction versus Fe(III) reduction contributes to alkalinity generation in 5 wetlands constructed with different organic substrates (Sphagnum peat with limestone and fertilizer, Sphagnum peat, sawdust, straw/ manure, mushroom compost) that had been exposed to the same quality and quantity of AMD for 18–22 months. These substrates had Fe oxyhydroxide concentrations of 250–810 μmol Fe g^?1 dry substrate. Flasks containing 100 g of wet substrate along with either 150 mL of wetland water or 130 mL of wetland water and 20 mL of 37 % formalin were incubated at 4 °C in January and 25 °C in May. On days 0, 2, 4, 8, 12 and 16, the slurry mixtures were analyzed for concentrations of H⁺, Fe²⁺ and SO₄ ^2?. The bulk of the evidence indicates that for all except the mushroom compost wetland, especially at 25 °C, biologically-mediated Fe(II) reduction occurred and generated alkalinity. However, in none of the wetlands, regardless of incubation temperature, was there evidence to support net biological sulfate reduction or its attendant alkalinity generation. Sulfate reduction and concurrent Fe(III) oxyhydroxide accumulation may be important in the initial stages of wetland treatment of AMD, both contributing to effective Fe retention. However, as Fe(III) oxyhydroxides accumulate over time, Fe(III) reduction could lead not only to decreased Fe retention, but also to the potential net release of Fe from the wetland.  相似文献   

Iron compounds and oil biodegradation in overmoistened contaminated soils: A review of publications     

Yu. N. Vodyanitskii 《Eurasian Soil Science》2011,44(11):1250-1259

In Russia, the areas of oil pollution gradually shift toward the north into the zone of increased moistening with widespread hydromorphic soils. In this zone, the role of the rapid aerobic degradation of hydrocarbons decreases, while that of slow anaerobic degradation increases. The biological reduction of Fe(III) only proceeds at the expense of the energy of oxidation of organic substances, including oil hydrocarbons, in the oil-polluted soils. This favors the development of technogenic gleying. In contrast to the uncontaminated background soils, in which gleying is correctly considered a degradation process, the same process in the oil-contaminated mineral soils plays a positive role, because it is accompanied by the oxidation of organic pollutants, which otherwise penetrate into rivers and lakes with water flows. The role of Fe(III) reduction may be significant: at one of the oil-spill sites, one-third of the organic pollutants degraded within twelve years after an accident in the anaerobic zone due to Fe(III) reduction. Both iron hydroxides and clay minerals enriched in Fe(III) participate in the reduction processes. In the anaerobic zone, the destruction of organic pollutants begins several years after the relevant natural microorganisms become active. The reduction of Fe(III) reaches its maximum faster than the process of methanogenesis. Upon the soil’s cooling in the winter, the reduction of Fe(III) is replaced by the spontaneous formation of iron oxides (oxidogenesis). Thus, alternating reduction ↔ oxidation reactions proceed in the soils with a contrasting temperature regime. Iron oxides formed in the winter are reduced to Fe(II) in the summer and, thus, resume the associated oxidation of organic pollutants upon the stagnant moisture regime. Therefore, upon monitoring of hydromorphic oilcontaminated soils, special attention should be paid to the forms of iron compounds.  相似文献   

Mercury speciation adsorption (MESA) method for combustion flue gas: Methodology,artifacts, intercomparison,and atmospheric implications     

Eric M. Prestbo  Nicolas S. Bloom 《Water, air, and soil pollution》1995,80(1-4):145-158

Chemical speciation of mercury (Hg) in a wide variety of combustion flue gas matrices has been determined using the mercury speciation adsorption (MESA) method. The MESA sampling system for gas phase Hg species employs a series of heated, solid phase adsorbent traps. Flue gas oxidized Hg species (Hg(II) and MMHg) are adsorbed by a potassium chloride (KCl) impregnated soda lime sorbent. Elemental Hg (Hg⁰) is collected by an iodated carbon sorbent after passing through the KCl/soda lime sorbent. Total Hg (Hg_t) is determined by summation of species. In the laboratory, cold vapor atomic fluorescence spectroscopy (CVAFS) is used for detection of Hg collected on the solid sorbents, after appropriate sample digestion and preparation. The MESA method has been evaluated for species stability, matrix effects, breakthrough, artifacts and precision. Based on eight duplicate samples a mean precision of 6.8% 11% and 4.5% (relative percent difference) has been calculated for Hg⁰, Hg(II) and Hgt respectively. Intercomparison of the MESA method with other methods shows very good agreement for Hgt. Mass balance calculations at 5 sites range from 75 to 140%, with a mean of 97±25%. Overall mean speciation results from 19 separate determinations suggest that Hg(II) has a 1 sigma range of 40 to 94% in coal combustion flue gas at, the inlet to pollution control devices.  相似文献   

Impact of the state-of-the-art of flue gas cleaning on mercury species emissions from coal-fired steam generators     

J. Fahlke  A. Bursik 《Water, air, and soil pollution》1995,80(1-4):209-215

When balancing the element mercury (Hg) two coal-fired power plant units — one with slag tap boilers (ST, 2 × 220 MW) and one with a dry bottom boiler (DB, 475 MW) were compared. Both systems are provided with electrostatic precipitators (ESP), nitrogen oxides removal (DeNO_x) and flue gas desulfurization (FGD) systems. The Hg in the flue gas is predominantly in gas phase. Only 15 % of the Hg introduced by the coal leaves the unit with the bottom or fly ash. Depending on the operating mode, 30 to 40 % of the Hg is separated in the FGD systems. The overall separation rate for the total system ranges between 45 to 55 %, the residue is emitted in the form of gaseous Hg species. At full load, the Hg concentration in the cleaned gas is less than 6 μg/m³. In the flue gas path of another dry bottom boiler (DB1, 480 MW) the concentrations of the gaseous species of bivalent mercury (Hg²⁺), elemental mercury (Hg⁰), and total mercury content (Σ Hg) were determined. The sum of the concentrations of Hg²⁺ and Hg⁰ is in agreement with the measurement of Σ Hg. Directly downstream of the boiler Hg²⁺ dominates with 77 %, while Hg⁰ amounts to 23 %. In the high-dust DeNO_x system Hg⁰ is oxidized almost completely to Hg²⁺ (96 %). Air heater and electrostatic precipitator do not influence the Hg species concentrations. The FGD system eliminates approximately 80 % of the Hg²⁺. At the same time the quantity of Hg⁰ increases by the factor 10. In the cleaned gas Hg⁰ dominates with 76 % as compared to Hg²⁺ with 24 %. At full load the concentration of Σ Hg in the cleaned gas is also below 6 μg/m³.  相似文献   

Determination of Mercury Content in a Shallow Firn Core from Greenland by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry     

Jacqueline L. Mann  Stephen E. Long  Christopher A. Shuman  W. Robert Kelly 《Water, air, and soil pollution》2005,163(1-4):19-32

The total mercury content was determined in 6 cm sections of a shallow 7 m firn core and in surrounding surface snow from Summit, Greenland (elevation: 3238 m, 72.58^°N, 38.53^°W) collected in May 2001 by isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS). The focus of this research was to evaluate the capability of the ID-CV-ICP-MS technique for measuring trace levels of Hg typical of polar snow and firn. Highly enriched ²⁰¹Hg isotopic spike is added to approximately 10 mL melted core and thoroughly mixed. The Hg²⁺ in the sample is reduced on line with tin(II) chloride (SnCl₂) and the elemental Hg (Hg^°) vapor pre-concentrated onto gold gauze using a commercial amalgam system. The Hg is then thermally desorbed and introduced into a quadrupole ICP-MS. The blank-corrected Hg concentrations determined for all samples ranged from 0.25 to 1.74 ng/L (ppt) (average 0.59 ± 0.28 ng/L (1σ)) and fall within the range of those previously determined by Boutron et al. [Geophys. Res. Lett. 25, 1998, 3315–3318] (≤ 0.05–2.0 ng/L) for the Summit site. The average blank value was 0.19 ± 0.045 ng/L (n = 6, 1σ) and the method detection limit was 0.14 ng/L. The Hg values specifically for the firn core range from 0.25 to 0.87 ng/L (average 0.51 ± 0.13 ng/L (1σ)) and show both values declining with time and larger variability in concentration in the top 1.8 m.  相似文献   

Modification of soil physical properties by manipulating the net surface charge on colloids through addition of Fe(III) polycations     

R. T. SHANMUGANATHAN  J. M. OADES 《European Journal of Soil Science》1982,33(3):451-465

The addition of 0.07 per cent Fe in the form of polycation of molecular weight 10000–50000 flocculated soil suspensions. Higher concentrations of Fe(III) caused redispersion of the clay. Electrophoretic and electron microscopic studies confirmed the flocculation-dispersion phenomena. The soil suspensions with higher concentrations of Fe(III) gave points of zero charge (PZC) between pH values 5.0 and 6.0. The flocculation resulted in microaggregation and created pores 40–100 μm in diameter. This led to an increased water-holding capacity and hydraulic conductivity and lower bulk densities and modulus of rupture. The soils treated with Fe(III) polycations were shown to be more friable than untreated soils.  相似文献   

Abiotic reduction of mercury by humic substances in aquatic system — an important process for the mercury cycle   总被引：1，自引：0，他引：1  

B. Allard  I. Arsenie 《Water, air, and soil pollution》1991,56(1):457-464

The potential ability of humic substances to reduce Hg(II) to Hg(0) in aqueous systems and, consequently, strongly influence Hg speciation and mobility in the environment is known but has not been studied in detail. A demonstration of the redox behavior of Hg in the presence of humic substances is made in the present work. Calculations show that the reduction is thermodynamically possible. The effects of some chemical parameters (pH, aerobic/anaerobic conditions, presence of chloride) on the process were studied experimentally. Hg(0) production was highest in O₂-free systems in the absence of chloride at pH ca 4.5, when ca 25% of initially 2x10^?6 M Hg(II) was reduced to Hg(0) in 50 hr. The presence of a competing ion (10^?4 M Eu) in the system as well as methylation of the carboxyl groups in the humic substance considerably reduced the Hg(0) production. The practical importance of the abiotic reduction of Hg in the environment is pointed out.  相似文献   

An experimental study of two potential methylation agents of mercury in the atmosphere: CH3I and DMS     

B. Hall  N. S. Bloom  J. Munthe 《Water, air, and soil pollution》1995,80(1-4):337-341

Experimental results from a study of the gas and aqueous phase reactions of elemental mercury (Hg⁰) with methyl iodide (CH₃I) and dimethyl sulfide (DMS) are presented. In aqueous phase experiments with CH₃I we found no observable increase in methyl mercury (MeHg). A small formation of MeHg, however, was observed in some (but not all) gas phase experiments in sunlight. A loss of Hg⁰ and a simultaneous formation of oxidized mercury (Hg(II)) was also observed in these experiments. No reaction, neither methylation or oxidation, was found between Hg⁰ and DMS under any conditions investigated. These experiments suggest that a simple homogeneous gas or aqueous phase methylation of Hg⁰ by DMS or CH₃I in the atmosphere cannot account for the significant levels of MeHg observed in precipitation.  相似文献   

The gas phase oxidation of elemental mercury by ozone   总被引：2，自引：0，他引：2  

B. Hall 《Water, air, and soil pollution》1995,80(1-4):301-315

The gas phase reaction between elemental mercury (Hg⁰) and ozone (0₃) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s/v) ratios. At 0₃ concentrations above 20 ppm, a loss of Hg⁰ and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of 3±2×10^?20 cm³ molec.^?1 s^?1 at 20 °C. This corresponds to an atmospheric Hg half-life of about one year at a mean global 0₃ concentration of 30 ppb.  相似文献   

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

Nouri Hassan  John D. Murimboh  Chuni L. Chakrabarti 《Water, air, and soil pollution》2008,193(1-4):131-146

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.  相似文献   

Effects of Several Metals on Both Fe(III)‐ and Cu(II)‐Reduction by Roots of Fe‐Deficient Cucumber Plants     

《Journal of plant nutrition》2013,36(10-11):2069-2079

Abstract

The ferric‐chelate reductase induced by Fe deficiency is also able to reduce other ions such as Cu²⁺. This Cu(II)‐reduction has been less studied and it has been suggested that Cu²⁺ ion rather than Cu²⁺‐chelate serves as the substrate. Ferric‐chelate reductase activity is inhibited by some metals, but the mechanisms implicated are not known. In the present work we use Fe‐deficient cucumber seedlings to study the interactions of Cu²⁺, Ni²⁺, Mn⁴⁺, and Fe³⁺ on both Fe(III)‐reduction and Cu(II)‐reduction activities. The response of Cu(II)‐reduction activity to Cu concentration, in the presence or absence of citrate, was also studied. Results showed that inhibition of the ferric‐chelate reductase activity by Cu²⁺ or Ni²⁺ could be partially reversed by increasing the concentration of Fe‐EDTA. The Cu(II)‐reduction activity was even stimulated by Fe‐EDTA or Ni²⁺; it was inhibited by a high concentration of Cu²⁺ itself; and it was not affected by the absence of citrate. Mn⁴⁺ caused a moderate inhibition of both Fe(III)‐reduction and Cu(II)‐reduction activities. Results agree with the hypothesis that free Cu²⁺ ion is the substrate for Cu(II)‐reduction and suggest that the mechanisms involved in Fe(III)‐reduction and Cu(II)‐reduction could have some differences and be affected by metals in different ways. The mode of action of metals on the reductase activity are discussed, but they are still not well known.  相似文献   

Aluminum and iron(III) species in the soil solution including organic complexes with citrate and humic substances     

Jrg Gerke 《植物养料与土壤学杂志》1997,160(3):427-432

The solubility of Al and Fe in soil is of relevance for their toxicity and availability, respectively, to plant roots. Humic substances as the main part of stable soil organic matter and citrate which is often excreted by P deficient plants are strong complexants of Al and Fe(III). Therefore, equations were developed to calculate the Al and Fe(III) species distribution in the soil solution in the presence of humic substances and citrate as organic ligands. Calculations in the pH range 4.0–7.0 showed that at higher pH humic-Al complexes were the most important species whereas AlOH-citrate^? dominated between pH 4.0 and 5.4. Free monomeric Al and AlSO₄⁺ were of minor relevance. Iron(III) species calculations showed that humic-Fe complexes were the main species in the pH range 4.0–7.0. But if mugineic acid, a Fe complexing phytosiderophore released into the rhizosphere by graminaceous plant species, was present in the soil solution (10^?6 M), Fe-mugineic acid complexes accounted for most of the Fe in solution. Fe-citrate^? was relevant at lower pH but contributed little to Fe(III) species at pH > 6.0. The results demonstrate the strong importance of the considered organic ligands for Fe and Al in the soil solution.  相似文献   

Effect of Cadmium(Ii) and Anion Type on the Ageing of Ferrihydrite and its Subsequent Leaching under Neutral and Alkaline Conditions     

Lin  Xiaomei  Burns  Robert C.  Lawrance  Geoffrey A. 《Water, air, and soil pollution》2003,143(1-4):155-177

The effect of cadmium(II) on the transformation of ferrihydrite[with Cd(II):Fe(III) ratios ranging from 0 to 5 mole %] in neutral and alkaline media (pH 7-11), combined with the effects of electrolyte type (NO₃ ^-, Cl^-, and SO₄ ^-2), was investigated at 20 °C over a period of 1 yr. The presence of Cd(II) strongly retards the conversion of ferrihydrite into hematite and/or goethite at pH 7–10, with decreases in the rate of transformation dependent on the amountof Cd(II). At a Cd(II):Fe(III) mole ratio of 1%, the transformation rate is NO₃ ^- > Cl^- > SO₄ ^-2, which correlates with the relative affinitiesof the anions for the ferrihydrite surface. The presence of Cd(II) promotes hematite formation at pH 9 and 10, whereas atpH 11 goethite is almost the sole product. With increasinginitial Cd(II) concentrations, increasing incorporationof Cd(II) into the products is observed. For 5 mole %Cd(II), ～ 2.5 mole % of Cd(II) is included in thetransformation products, principally hematite, while at pH 11, with 1 mole % Cd(II), all of the Cd(II) incorporates into thegoethite lattice. Transmission electron micrographs show that the presence of Cd(II) leads to a reduction in size and promotesthe twinning of goethite crystals, and can result in ellipsoidal-shaped hematite crystals. Leachability of Cd(II) fromfresh and aged coprecipitated Cd(II)-ferrihyrdite is dependent onthe extent of transformation of the ferrihydrite, with 70–90% of the Cd(II) leachable from ferrihydrite, while goethite is ableto incorporate and remove more Cd(II) than hematite.  相似文献   

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

P. A. Wahid  N. V. Kamalam 《Biology and Fertility of Soils》1993,15(2):144-148

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.  相似文献   

Effect OF pH and iodide on the adsorption of mercury(II) by illite     

W. P. Hamilton  R. R. Turner  M. M. Ghosh 《Water, air, and soil pollution》1995,80(1-4):483-486

The effect of I concentration on the mobility of Hg(II) in clay suspensions was studied over an environmentally-significant pH range. The addition of I decreased the adsorption of Hg(II), except at very low (50μg/L) I concentrations. In suspensions of greater I concentration (1.5 and 50 mg/L), Hg(II) adsorption was independant of pH; allow concentrations, Hg(II) adsorption decreased with increasing pH, presumably due to competition from hydroxycomplexes for surface adsorption sites. I was an effective extradant for Hg, outperforming all other halides in extraction efficiency.  相似文献