Kinetics Of Iron Research Articles

Dissolution Kinetics of Iron‐, Manganese‐, and Copper‐Containing Synthetic Hydroxyapatites

Micronutrient-substituted synthetic hydroxyapatite (SHA) is being evaluated by the National Aeronautics and Space Administration's (NASA) Advanced Life Support (ALS) Program for crop production on long-duration human missions to the International Space Station or for future Lunar or Martian outposts. The stirred-flow technique was utilized to characterize Ca, P, Fe, Mn, and Cu release characteristics from Fe-, Mn-, and Cu-containing SHA in deionized (DI) water, citric acid, and diethylene-triamine-pentaacetic acid (DTPA). Initially, Ca and P release rates decreased rapidly with time and were controlled by a non-SHA calcium phosphate phase(s) with low Ca/P solution molar ratios (0.91-1.51) relative to solid SHA ratios (1.56-1.64). At later times, Ca/P solution molar ratios (1.47-1.79) were near solid SHA ratios and release rates decreased slowly indicating that SHA controlled Ca and P release. Substituted SHA materials had faster dissolution rates relative to unsubstituted SHA. The initial metal release rate order was Mn >> Cu > Fe which followed metal-oxide/phosphate solubility suggesting that poorly crystalline metal-oxides/phosphates were dominating metal release. Similar metal release rates for all substituted SHA (approximately 0.01 cmol kg-1 min-1) at the end of the DTPA experiment indicated that SHA dissolution was supplying the metals into solution and that poorly crystalline metal-oxide/phosphates were not controlling metal release. Results indicate that non-SHA Ca-phosphate phases and poorly crystalline metal-oxide/phosphates will contribute Ca, P, and metals. After these phases have dissolved, substituted SHA will be the source of Ca, P, and metals for plants.

A kinetic model of ferrous iron oxidation by Acidithiobacillus ferrooxidans in a batch culture

The batch oxidation kinetics of ferrous iron by Acidithiobacillus ferrooxidans were examined at different oxygen transfer rates and pH in an aerated stirred tank and a bubble column. The microbial growth, oxygen consumption rate and ferrous and ferric iron were monitored during the biooxidation. A kinetic model was established on the basis of the Michaelis-Menten kinetic equation for bacterial growth and the constants estimated from experimental data (maximum specific growth rate 0.069 h-1, saturation constant 2.9 g/dm3, and biomass yield coefficient based on ferrous iron 0.003 gd.w./gFe). Values calculated from the model agreed well with the experimental ones regardless of the bioreactor type and pH conditions.

Intracellular kinetics of iron in reticulocytes: evidence for endosome involvement in iron targeting to mitochondria

AbstractIn erythroid cells the vast majority of iron (Fe) released from endosomes must cross both the outer and the inner mitochondrial membranes to reach ferrochelatase that inserts Fe into protoporphyrin IX. In the present study, we developed a method whereby a cohort of 59Fe-transferrin (Tf)-laden endosomal vesicles were generated, from which we could evaluate the transfer of 59Fe into mitochondria. Iron chelators, dipyridyl or salicylaldehyde isonicotinoyl hydrazone (SIH), were able to bind the 59Fe when they were present during a 37°C incubation; however, addition of these agents only during lysis at 4°C chelated virtually no 59Fe. Bafilomycin A1 (which prevents endosome acidification) and succinylacetone (an inhibitor of 5-aminolevulinate dehydratase) prevented endosomal 59Fe incorporation into heme. Importantly, both the myosin light chain kinase inhibitor wortmannin and the calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7), caused significant inhibition of 59Fe incorporation from 59Fe-Tf-labeled endosomes into heme, suggesting that myosin is required for Tf-vesicle movement. Our results reaffirm the astonishing efficiency of Tf-derived Fe utilization in hemoglobin (Hb)-producing cells and demonstrate that very little of this Fe is present in a chelatable pool. Collectively, these results are congruent with our hypothesis that a transient endosome-mitochondrion interaction mediates iron transfer between these organelles. (Blood. 2005;105:368-375)

An authigenic iron phosphate phase in estuarine sediments: composition, formation and chemical reactivity

Reductive dissolution experiments and microprobe analyses reveal the existence of a discrete iron–phosphorus phase (Fe–P) in intertidal freshwater sediments from the eutrophic Scheldt estuary (Belgium and The Netherlands). This mineral phase is found at all depths sampled (0–50 cm) and exhibits a remarkably uniform composition and chemical reactivity. It accounts for more than 70% of total phosphorus in the sediments, and is quantitatively extracted by ascorbate at near-neutral pH. High molar P/Fe ratios (0.7–0.8), and identical dissolution kinetics of phosphorus and iron in pH7.5 ascorbate solution, point to a hydrous ferric phosphate mineral. Bulk sediment Fe(III)/Fe(II) ratios measured with Mössbauer spectroscopy are also consistent with a predominantly ferric, rather than ferrous, iron phosphate phase. Mineral precipitates collected in situ on Teflon strips reveal active formation of ferric phosphate phases in the upper oxidized sediment layer at the freshwater sampling site, but also at a downstream brackish site. Oxidative precipitation and subsequent burial of iron phosphate explain the large-scale removal of nutrient phosphorus from the water column in the freshwater portion of the estuary. In the downstream brackish and marine portions of the estuary, this sedimentary phosphorus sink is limited by the increased availability of sulfate, as sulfide produced by sulfate reduction converts the reactive ferric phosphate pool into iron sulfides.

Dissolution kinetics of iron in liquid zinc

In hot dip galvanizing, steel strip is coated by immersion in a bath of molten zinc. The principal reactions that occur at the steel/liquid zinc interface are (1) dissolution of iron and (2) nucleation and growth of intermetallic compounds. In order to improve the management of industrial galvanizing baths, it is essential to evaluate the flux of dissolved iron that diffuses into the bath from the sheet. For this purpose, a rotating disk device has been developed to study the dissolution and diffusion of iron in pure liquid zinc at the temperature usually employed in galvanizing baths (465degreesC). Since the dissolution reaction is controlled by diffusion under these conditions, the diffusion coefficient of iron in liquid zinc has been measured and found to be:

The Effect of Adsorbed Atomic Hydrogen on the Electrochemical Dissolution Kinetics of Iron

A functional dependence of the potentiostatic dissolution rate of iron on the metal surface coverage with hydrogen (θ) is found. An increase in the anodic current with time after the potential jump is related to the decrease in θ. A potential dependence of the dissolution rate of iron at θ = const is obtained. The high Tafel slope of this polarization curve shows that the first one-electron stage of iron ionization is substantially irreversible.

A two-stage decision support tool for restoring tidal flows to flood mitigation drains affected by acid sulfate soil: case study of Broughton Creek floodplain, New South Wales, Australia

A 2-stage flood estimation and water quality decision support tool (DST) was developed, calibrated, and applied to a field site in south-eastern New South Wales (NSW) to simulate tidal restoration in a flood mitigation drain affected by acid sulfate soils leachate. The first stage of the DST employs a digital terrain map, geographic information tools, and measured water levels to calculate drain water overtopping due to tidal variations. Simulations using the GIS technique at the study site indicated that the primary drainage network can safely contain full tidal flushing (0.91 m AHD or a 58% increase), whereas at the same level the secondary drainage network overtops along relict drainage channels. The second stage of the DST simulates the change in drain water quality using an ion-specific program code written within the open interface PHREEQC program. The results from the water quality model were calibrated against laboratory titration tests. Drain water pH was shown to increase above 6.0, and soluble aluminium and iron concentrations decreased by 73% and 56%, respectively. The extent of water quality change is directly related to the ionic strength of the intruding water and the ion-specific reaction kinetics of aluminium, iron, and sulfate.

Analysis of the Kinetics of Iron(II, III) Oxide Dissolution in Hydrochloric Acid Using a Generalized Delmon Model

A detailed analysis of the kinetics of iron(II, III) oxide dissolution in hydrochloric acid is performed using a generalized Delmon model, which takes into account changes in the fractal dimension of the surface of dissolving particles.

The effects of pH, ionic strength, and iron–fulvic acid interactions on the kinetics of non-photochemical iron transformations. I. Iron(II) oxidation and iron(III) colloid formation

Flow injection analysis was used to study the effect of a fulvic acid on the kinetics of iron(II) oxidation and iron colloid formation under conditions approximating fresh natural waters. While iron(II) oxidation in high-carbonate inorganic solutions is predicted well by a recently proposed homogeneous model, it overestimates the oxidation rate in low-carbonate solutions, possibly due to the formation of an intermediate iron(II) colloid or surface species. Results in fulvic acid solutions are consistent with the formation of an iron(II)–fulvic acid complex at both pH 6.0 and 8.0 which accelerates the overall oxidation rate relative to inorganic solutions. However, iron(III) complexation by fulvic acid greatly slows the formation of iron colloids, stabilizing dissolved iron(III). Decreased pH and increased ionic strength slow and decrease iron colloid formation. Evidence of a kinetic control on the distribution of iron(III) between organically complexed and colloidal forms is presented.

The effects of pH, ionic strength, and iron–fulvic acid interactions on the kinetics of non-photochemical iron transformations. II. The kinetics of thermal reduction

A combination of flow-injection analysis and kinetic analysis was used to examine the speciation of iron(II) and iron(III) in fulvic acid solutions as a function of pH, ionic strength, and time. This methodology was used to follow a shift in iron speciation from faster to slower reacting species over a timescale of several days. This speciation data shows that both iron(II) and iron(III)–fulvic acid complexes are important iron species in humic-containing natural waters and that their amounts and their rates of transformation to colloidal iron are controlled primarily by the kinetics of thermal (dark) reduction and iron(II) oxidation. The kinetic analysis methodology also yielded the rate constants for the thermal reduction of iron by the fulvic acid. These rate constants decrease with increasing pH and are independent of ionic strength. While thermal reduction was found to be too slow to produce large amounts of steady state iron(II) at circumneutral pH, it does provide a mechanism for iron redox cycling in the absence of photochemical or biochemical processes.

Oxygenation kinetics of iron and copper protein active site model complexes

Oxygenation kinetics of iron and copper protein active site model complexes

Competition for oxygen by iron and 2,4,6-trichlorophenol oxidizing bacteria in boreal groundwater

Kinetics of simultaneous iron and 2,4,6-trichlorophenol (TCP) oxidation by groundwater enriched cultures were studied in order to reveal the competition for oxygen in aerobic in situ bioremediation of boreal groundwater. Chemical iron oxidation at near neutral pH in synthetic groundwater depended by the first order on the concentrations of ferrous iron and dissolved oxygen and by the second order on pH. The chemical iron oxidation rate constant was on average 2.2×10 13 mol −2 L 2 atm −1 min −1 . Chemical iron oxidation was insignificantly affected by natural organic matter, 2,4,6-tri-, 2,3,4,6-tetra- or pentachlorophenol in groundwater. Biological oxidation of iron followed zero-order kinetics. At pH of 6.3 and dissolved oxygen (DO) concentration of 11.5 mg L −1 , the rate of biological iron oxidation was 3.8×10 −4 mmol L −1 min −1 and up to one order of magnitude higher than the chemical oxidation rate, 5.2×10 −6 mmol L −1 min −1 . Biological oxidation of iron was completely inhibited by pentachlorophenol at 23 μmol −1 . With a groundwater enriched culture, oxygen was consumed at higher rates by 2,4,6-TCP oxidizers (2.5−7.6×10 −5 mmol DO L −1 min −1) than the iron oxidizing bacteria (0.8−3.1×10 −5 mmol DO L −1 min −1) at both low and saturated DO-concentrations. The results indicate that in situ iron oxidation is predominantly biogenic in the studied boreal aquifer. 2,4,6-TCP degrading bacteria consumed DO at higher rates than the iron oxidizing bacteria and thereby, favour bioremediation of the polychlorophenol contaminated groundwater.

Studying the Adsorption of an Iron(II) Complex of 1,10-Phenanthroline on Laboratory Glassware Using Thermal Lens Spectrometry

The adsorption of iron(II) tris(1,10-phenanthroline) on the glass surface of laboratory ware from solutions has been studied by thermal lens spectrometry at a level of nanogram amounts. The effect of glass pretreatment on the fraction of the adsorbed substance has been studied, and the most appropriate variant of the pretreatment has been selected. The kinetics of iron(II) tris(1,10-phenanthroline) adsorption on the surface of laboratory glass has been studied, and an adsorption isotherm has been constructed for nanogram chelate contents of the solution. The process is most closely approximated by the Freundlich equation. Based on the obtained data, a procedure has been proposed for the preparation of solutions for constructing calibration relationships that can be used in thermal lens measurements of trace amounts of analytes. This procedure takes into account the loss of substances at the surface of laboratory glassware.

Transport kinetics of zinc, copper, selenium, and iron in perfused human placental lobule in vitro.

Transport characteristics of essential trace elements as zinc, copper, selenium and iron have been studied in maternal-fetal direction in normal pregnancies, using in vitro perfusion of human placental lobules. Solutions of trace elements corresponding to twice the physiological concentrations were injected (100 microl bolus) into the maternal arterial perfusate. Serial perfusate samples were collected every 30 sec from venous outflows for a study period of 5 min. Concentrations of these trace elements and their transport kinetics were determined. Transport fractions (TF) of zinc, copper, selenium and iron averaged 0.21, 0.49, 0.55 and 0.10% of maternal load respectively. Other parameters such as area under the curve, clearance, elimination constant, absorption and elimination rates showed some significant differences between the various elements. Copper and selenium appear to be transported passively in maternal-fetal direction, while for iron and zinc, role of active transport for transfer across the human placental membrane cannot be discounted. We speculate that alterations in copper: zinc TR50 (transport rate for 50% efflux) and TF ratios could serve as useful indicators for assessing placental transport status of these essential elements in complicated pregnancy states.

Maternal-fetal transport kinetics of copper, selenium, magnesium and iron in perfused human placental lobule: in vitro study.

Transport characteristics of certain inorganic elements such as copper, magnesium, selenium and iron have been studied in maternal-fetal direction in normal pregnancies, using in vitro perfusion of isolated placental lobules. Copper, selenium, magnesium and iron salts corresponding to twice physiological concentrations were injected as a 100 microl bolus, into the maternal arterial perfusate. Serial perfusate samples were collected from venous outflows for a study period of 5 min. Concentrations of various inorganic elements and their transport kinetics were determined. Transport fractions of copper, selenium, magnesium and iron averaged 0.14, 0.19, 0.06 and 0.23% of maternal load respectively. The pharmacokinetic parameters such as area under the curve, clearance, elimination constant, and time for maximum response showed some significant differences between the various elements. We speculate that copper and selenium share the same transport pathway along a concentration gradient in maternal-fetal direction, while for iron and magnesium, active transport plays a predominant role for element transfer across the human placental membrane.

The oxidation, fate and effects of iron during on-site bioremediation of groundwater contaminated by a mixture of polychlorophenols.

Kinetics of simultaneous iron and polychlorophenol (CP) oxidation by groundwater enriched cultures were studied in laboratory and during actual remediation in order to reveal the fate and effects of iron on aerobic on-site bioremediation of boreal groundwater. 2,4,6-tri- (TCP), 2,3,4,6-tetra- (TeCP) and pentachlorophenol (PCP) were degraded in fluidized-bed bioreactor (FBR) by over 99%, over 99%, and over 96%, respectively. The oxygen consumption rate for CP-biodegradation was 1.31 micromol DO L(-1) min(-1) and 0.29 micromol DO L(-1) min(-1) for iron oxidation, i.e. approximately 12% of the oxygen was consumed by iron oxidation during normal FBR operation. Mineralization of CPs was confirmed by DOC removal and chloride release of 158% and 78%, respectively. Excess DOC removal was due to partial degradation of the natural organic matter (NOM) (1.1 mg L(-1) or 24% DOC removal) in the groundwater. Removal of NOM consumed 0.91 micromol DO L(-1) min(-1). Iron oxidation in the FBR was over 94% of which chemical Fe(II) oxidation accounted for up to 10%. Fe(III) partially accumulated (58 to 69%) in the system. The TCP- and CP-biodegradation consumed DO at two times higher rates than the Fe(II)-oxidation in both, laboratory and full-scale, respectively. The batch assays at various TCP and Fe(II) ratios and DO concentrations showed simultaneous oxygen consumption by TCP and Fe-oxidizers and that increased Fe concentrations do not outcompete the bioremediation of CP's for available oxygen.

Microbial and hydrothermal aspects of ferric oxyhydroxides and ferrosic hydroxides: the example of Franklin Seamount, Western Woodlark Basin, Papua New Guinea

Deposits of Fe-Si-Mn oxyhydroxides are commonly found on the seafloor on seamounts and mid-ocean spreading centers. At Franklin Seamount located near the western extremity of Woodlark Basin, Papua New Guinea, Fe-Si-Mn oxyhydroxides are being precipitated as chimneys and mounds upon a substrate of mafic lava. Previous studies have shown that the vent fluids have a low temperature (20–30°C) and are characterized by a total dissolved iron concentration of 0.038 mM kg-1, neutral pH (6.26) and no measurable H2S. The chimneys have a yellowish appearance with mottled red–orange patches when observed in situ from a submersible, but collected samples become redder within a few hours of being removed from the sea. The amorphous iron oxyhydroxides, obtained from active and inactive vents, commonly possess filamentous textures similar in appearance to sheaths and stalks excreted by the iron-oxidizing bacteria Leptothrix and Gallionella; however, formless agglomerates are also common. Textural relationships between apparent bacterial and non-bacterial iron suggest that the filaments are coeval with and/or growing outwards from the agglomerates. The amorphous iron oxyhydroxides are suggested to precipitate hydrothermally as ferrosic hydroxide, a mixed-valence (Fe2+-Fe3+) green–yellow iron hydroxide compound. Consideration of the thermodynamics and kinetics of iron in the vent fluid, suggest that the precipitation is largely pH controlled and that large amounts of amorphous iron oxyhydroxides are capable of being precipitated by a combination of abiotic hydrothermal processes. Some biologically induced precipitation of primary ferric oxyhydroxides (two-XRD-line ferrihydrite) may have occurred directly from the fluid, but most of the filamentous iron micro-textures in the samples appear to have a diagenetic origin. They may have formed as a result of the interaction between the iron-oxidizing bacteria and the initially precipitated ferrosic hydroxide that provided a source of ferrous iron needed for their growth. The processes described at Franklin Seamount provide insight into the formation of other seafloor oxyhydroxide deposits and ancient oxide-facies iron formation.

Influence of Microalloying and Heat Treatment on the Kinetics of Bainitic Reaction in Austempered Ductile Iron

The effect of different contents of alloying additions and austenitizing temperature on the transformation kinetics of austenite in a ductile iron austempered at 300 and 400 °C has been investigated in the present study. X-ray diffraction, optical microscopy, and hardness measurements were used to determine the transformation kinetics of low Ni iron, low Mo iron and low Ni, Mo iron during austempering at 300 and 400 °C for 1 to 480 min after austenitizing at 850 and 930 °C for 120 min. Nickel and molybdenum in used contents are shown to delay the bainitic transformation without the undesirable features. Decreasing the autenitizing temperature is shown to increase the driving force for stage I of reaction but to have only a small effect on stage II kinetics. This shifts the position of the processing window to short periods of time and leads to opening of the processing window, which is closed for higher autenitizing temperatures. A more uniform austempered microstructure can be obtained with a decrease of autenitizing temperature. Decreasing the autenitizing temperature has the disadvantage of reducing the austemperability.

Thermal dependence of austempering transformation kinetics of compacted graphite cast iron

The evolution of the relative fraction of high-carbon austenite with austempering time and temperature was analyzed in a compacted graphite (CG) cast iron (average composition, in wt pct: 3.40C, 2.8Si, 0.8Mn, 0.04Cu, 0.01P, and 0.02S) at five different austempering temperatures between 573 and 673 K. Samples were characterized by Mossbauer spectroscopy, hardness measurements, and optical microscopy. During the first stage of transformation, the kinetics parameters were determined using the Johnson-Mehl’s equation, and their dependence with temperature in the range from 573 to 673 K indicates that the transformation is governed by nucleation and growth processes. The balance between growth-rate kinetics and nucleation kinetics causes the kinetics parameter (k) to have a maximum at ≈623 K of 3.9×10−3(s−1). The evolution of the C content in the high-carbon austenite was found to be controlled by the volume diffusion of carbon atoms from the ferrite/austenite interface into austenite, with a dependence of t 0.40±0.05 on the austempering time (t).

Reaction Kinetics of Desulfurization of Molten Pig Iron Using CaO-SiO2-Al2O3-Na2O Slag Systems.

Desulfurization kinetics of molten pig iron were studied using CaO–SiO2–Al2O3–Na2O quaternary slag sys-tems at 1 350°C. The concentration of Na2O in slag decreases with time due to evaporation. The rate of desulfurization increases by increasing the Na2O content in slag, decreasing Al2O3 content, increasing the slag basicity, i.e., the ratio of CaO to SiO2, and increasing the temperature. A mathematical model has been developed which enables the effect of decrease in Na2O content over time to be taken into consideration. The model provides a rate equation that can represent all conceivable rate controlling steps, such as interfacial chemical reaction, mass transport in the metal phase, and in the slag phase. The apparent rate coefficient—a parameter employed in the model—was dependent on temperature and slag composition, especially Na2O content. An equation is suggested which relates the coefficient to the sulfide capacity of slag. The activation energy of the apparent rate coefficient was found to be 127 kJ mol-1 . It was concluded that the desulfurization of molten pig iron using the present slag system is controlled either by the interfacial chemical reaction or slag phase mass transfer.