Oxidation Of Ferrous Ions Research Articles

The Correlation Between Urinary 8-Iso-Prostaglandin F2α and Hydrogen Peroxide Toward Renal Function in T2DM Patients Consuming Sulfonylurea and Combination of Metformin-Sulfonylurea.

Renal dysfunction is a common complication in type 2 diabetes mellitus patients associated with oxidative damage which could be characterized by 8-iso-prostaglandin F2α and hydrogen peroxide level as oxidative stress markers. The aim of our study is to determine if there is a difference in 8-iso-prostaglandin F2α and hydrogen peroxide levels between sulfonylurea and combination of metformin-sulfonylurea in diabetic patients. We also wanted to determine if these oxidative stress markers correlate with the estimated Glomerular Filtration Rate (eGFR). We conducted a cross-sectional study with inclusion of 55 patients with type 2 diabetes mellitus in Dr. Sitanala Tangerang Hospital, Indonesia with purposive sampling. The value of eGFR was obtained by serum creatinine levels, while the level of 8-iso-prostaglandin F2α was measured by ELISA and urinary hydrogen peroxide using FOX-1 (Ferrous Ion Oxidation Xylenol Orange 1). There was no difference in 8-iso-prostaglandin F2α and hydrogen peroxide level between the two groups (p=0.088 and p=0.848). Moreover, there was no difference in eGFR values between the two groups, measured by Cockroft-Gault, MDRD, and CKD-EPI. 8-iso-prostaglandin F2α (n=55) was positively correlated with eGFR based on Cockroft-Gault (r=0.382; p=0.009), whereas urinary hydrogen peroxide (n=47) also generate significant positive correlation with eGFR based on the MDRD equation (r=0.326; p=0.021). Linear regression analysis showed that 8-iso-prostaglandin F2α is the most predictive factor and the only significant factor for eGFR in Cockroft-Gault, MDRD and also CKDEPI, even after controlled by gender, age, BMI, HbA1c, systole, and H2O2. The two treatments did not have any significant differences in antioxidant activity. However, an increase of urinary 8-iso-prostaglandin F2. and hydrogen peroxide which correlates with eGFR in the total sample may play a significant role in the pathophysiology of diabetic nephropathy.

Hexagonal-shaped aminosilane magnetite nanoparticles: Preparation, characterization and hybrid film deposition

Hexagonal amino-functionalized magnetite nanoparticles were successfully produced by two-step method: initially, bare Fe3O4 nanoparticles were obtained by partial oxidation of ferrous ions in alkaline conditions, followed by hydroxyl groups interchanging with (3-aminopropyl) triethoxysilane (APTES) moieties. The products were evaluated for possible water repellent applications. Hybrid ternary films were prepared by spray coating in a layer-by-layer configuration: the hybrid polymeric matrix first, followed by modified iron oxide nanoparticle dispersion, both mixed with the third component, pre-hydrolyzed/precondensed sol–gel solution of hexadecyltrimethoxy silane (HSi). The found results demonstrate the ability of the hexagonal amino-functionalized magnetite nanoparticles to self-assembly and generate hierarchical roughness.

An Investigation of Facile One-Pot Synthesis of Li2FeSiO4/C Composite for Li Ion Batteries

Li2FeSiO4 and its carbon composite are prepared by an urea-assisted combustion method. The synthesis has been carried out in different urea concentrations, namely 1 Molar (M), 2 M and 3 M urea in the cost-effective ambient atmospheric condition. The x-ray diffraction analysis confirms the orthorhombic structure of Li2FeSiO4 compounds. The urea-assisted combustion reaction enhanced the phase purity of the compound and prevented the oxidation of ferrous ions in Li2FeSiO4. The x-ray photo electron spectroscopy analysis further confirmed the reduction of Fe3+ concentration in Li2FeSiO4 while adding urea. The Li2FeSiO4 compound formation in the presence of urea occurred at a temperature < 623 K. The one-pot synthesis of Li2FeSiO4/C with the help of starch and urea in ambient atmospheric condition resulted in Li2FeSiO4 with an orthorhombic crystal structure. The carbon coating in an amorphous nature is observed and the lattice dimension values of Li2FeSiO4/C are 6.248 A, 5.330 A, and 5.029 A. The lattice parameter has remained unchanged with carbon addition. The addition of 5% carbon to Li2FeSiO4 improves the electrical conductivity and lithium diffusion coefficient to 7.24 × 10−4 S cm−1 and 5.54 × 10−6 cm2, respectively. The coulombic efficiency and capacity retention after 50 cycles of Li2FeSiO4/C composite are around 83% and 95%, respectively.

Microbial Ferrous Ion Oxidation versus Ferric Ion Precipitation at Low Temperature Conditions

Ferric ion precipitation in a typical bioleach operation is known to be inevitable. However, its management has been emphasized as critical to efficiently maximize the potential that bioleach technique offers, especially in heap bioleach systems. Although there are some studies on ferric ion precipitation, limited studies exist in the context of a cold condition which often prevails in some operations. This study investigated ferrous ion biooxidation and ferric ion precipitation under cold temperature conditions. The results showed that maximum ferrous ion oxidation rates of 1.05, 1.25, 1.51 and 1.60 mmol/L/h at 6, 7, 8 and 10°C respectively were achieved in packed column reactor. The results further showed a simultaneous ferric ion precipitation during the oxidation process. The kinetics of ferric ion precipitation follows a first order kinetics with the rate constants of 0.0066, 0.0074, 0.0080 and 0.011 h-1. Activation energies of 68 and 77 kJ/mol were obtained for both ferrous ion biooxidation and ferric ion precipitation respectively. Although slow kinetics are expected for both processes, the kinetics information may be useful for design management consideration at least to predict when bioleach liquor would likely run out of dissolved ferric ion.

Novel GTA-PVA Fricke gels for three-dimensional dose mapping in radiotherapy

One of the most recent and promising developments in radiotherapy dosimetry was the introduction of 3D radiation-sensitive gels. These gels present tissue equivalent composition and density, so they also serve as phantoms, and their response is largely independent of radiation quality and dose rate. Some gels are infused with ferrous sulfate and rely on the radiation-induced oxidation of ferrous ions to ferric ions (Fricke-gels). These formulations suffer from spontaneous-oxidation and diffusion of ferric ions after irradiation; chelating agents such as xylenol-orange significantly reduces the latter. Other gel types consist of dispersed monomers, and rely on radiation-induced cross-linking; they form stable polymer structures, but they are typically affected by significant toxicity. In a large multicenter study, we developed and investigated new formulations of Fricke-gels based on poly-vinyl alcohol chemically cross-linked with glutaraldehyde. The formulation is safe and easy to manufacture, with a sensitivity of 0.073 Gy-1 and a diffusion coefficient of 0.17 mm2/h, it arguably offers the best all-around performance of current Fricke-infused gels. The main original outcomes of the study are described in this work, while reference is made to separate reports for specific procedures and results.

A new method for dosimetry standardization using 137Cs biological irradiator based on Fricke solution

Radiobiological experiments such as small animal whole or partial body irradiation, cell culture irradiation, tissue culture irradiation, require accurate and reproducible irradiation dosimetry to allow the work to be interpreted and repeated and for valid comparisons to be made by other laboratories. Limited standardized protocols are available for small animal dosimetry when using 137Cs irradiators.Methods for mapping dose distributions and to determine the regions of isodose such as Gafchromic film, ionization chambers or arrays of Thermoluminescent Dosimeters (TLDs) may result in low-resolution mappings, is very laborious, time-consuming and allows for dosimeter placement inaccuracies in regions of high-dose gradients. Our new approach takes advantage of Fricke solution properties and has been adapted so that it can be performed in 96-well plates. Fricke dosimetry depends on the oxidation of ferrous ions (Fe2+) to ferric ions (Fe3+) by ionizing radiation. The increased concentration of ferric ions is measured spectrophotometrically at 304nm. The Fricke dosimeter is 96% water by weight; therefore, it lends itself well to a determination of absorbed dose to water. This dosimeter is used in a dose range of 5–400Gy and for dose rates of up to 106Gy/s.This new methodology approach allow us to have an absolute dosimetry system, with proven performance, having 96 independent dosimeters on plates of small dimensions. A 3D array of hundreds of independent dosimeters analyzed with a mathematical software to create 3D-surface plots lead that absorbed dose can be estimated in virtually any area of the chamber.Our method could be used for standardization of dosimetry within and between laboratories and for intercomparison programs, which is becoming clear that is needed to be implemented for the radiobiology research procedures.

Urinary Hydrogen Peroxide and Renal Function Parameter of Type 2 Diabetes Mellitus Patients Consuming Metformin and Metformin-Sulfonylurea

Objective: Diabetes is one of the primary causes of kidney failure. About 40% people with diabetes will get Chronic Kidney Disease (CKD). The previous study reported that oxidative stress played an important role in diabetic patients with kidney damage. However, the study did not take consideration for the therapeutic treatment of the patients. This study purpose to determine urinary hydrogen peroxide concentration as a biomarker of oxidative stress in type 2 diabetes patients consuming metformin and metformin-sulfonylurea and to know its correlation with estimated Glomerular Filtration Rate (eGFR) and Urine Albumin to Creatinine Ratio (UACR) as a parameter of the renal function. Methods: Blood and urine were collected from 114 type 2 diabetes outpatients in Pasar Minggu Community Health Center. The concentration of urinary hydrogen peroxide (H2O2) was measured using Ferrous Ion Oxidation Xylenol Orange 1 (FOX-1) method and was normalized with urine creatinine measured with kinetic Jaffe method. The value of eGFR was calculated based on serum creatinine using Cockroft-gault, MDRD, dan CKD-EPI equation. Results: There were no significant difference in concentration of urinary H2O2 (p = 0.228), eGFR (Cockroft-Gault p = 0.936; MDRD p = 0.779; dan CKD-EPI p= 0.671), and UACR (p = 0.838) between the two groups of treatment. There was no correlation between urinary H2O2 with eGFR in all equations and between urinary H2O2 and UACR. In the other hand, moderate positive correlation showed in analysis between urinary H2O2 and UACR in patients with albuminuria (r=0.457; p=0.001). Results of linear regression analysis showed that H2O2 was the most and the only significant factor for increased UACR, even after controlled by age, gender, IMT, systolic blood pressure, HbA1c, hypertension status, smoking habit, exercise habit, and medicine. Conclusion: There was no significant difference in concentration of urinary H2O2 in type 2 diabetes patients consuming metformin and metformin-sulfonylurea. Urinary presumably will increase significantly together with the present of albuminuria, so it can not be used in early detection of renal function in patients without albuminuria. Key words: Metformin, Sulfonylurea, Diabetes Mellitus, Estimated Glomerular Filtration Rate, Urine Albumin to Creatinine Ratio, Urinary Hydrogen Peroxide.

The Oxidation of Fe(II) in Acidic Sulfate Solutions with Air at Elevated Pressures. Part 1. Kinetics above 1 M H2SO4

The oxidation of ferrous ions in acidic sulfate solutions at elevated air pressures was investigated. The effect of the Fe2+ concentration, initial H2SO4 concentration and partial oxygen pressure on the reaction rate were determined at three different temperatures, that is, T = 90, 70, and 50 °C. The effect on the reaction rate of the components that H2SO4 dissociates into, that is, HSO4–, H3O+, and SO42–, was established as well. A second order of reaction in Fe2+ and a first order of reaction in O2 were determined. No clear order in either H2SO4 or the components H2SO4 dissociates into, could be established. For the experiments with initial concentrations of H2SO4 of 1 M and higher the oxidation rate was not affected, that is, a zero order of reaction in H2SO4 for these concentrations. Therefore, the kinetic rate expression for the oxidation of Fe2+ at concentrations of H2SO4 of 1 M and higher can be calculated with RFe2+ = d[Fe2+]/dt = k[Fe2+]2PO2, where the activation energy EA was determined to be 60.3 kJ/mol.

The Oxidation of Fe(II) in Acidic Sulfate Solutions with Air at Elevated Pressures. Part 2. Influence of H2SO4 and Fe(III)

The oxidation of ferrous ions in acidic sulfate solutions at elevated air pressures was investigated. The effect of the Fe2+ concentration, Fe3+ concentration, H2SO4 concentration, and partial oxygen pressure on the reaction rate were determined at three different temperatures, that is, T = 90, 70, and 50 °C. A second order of reaction in Fe2+ and a first order of reaction in O2 were determined, respectively. A slight inhibition by Fe3+ on the Fe2+ oxidation reaction was observed. The reaction is first order in Fe3+ in the kinetic term for the inhibition by Fe3+. Concentrations of H2SO4 up to 1 M result in a fractional negative order of −0.6; concentrations of H2SO4 above 1 M result in a zero order. One kinetic equation for the oxidation of Fe2+ was postulated, in which the order of reaction in H2SO4 is changed depending on the H2SO4 concentration. RFE2+ = −d[Fe2+]/dt = k[Fe2+]2PO2[H2SO4]c/(1 + A[Fe3+]), with c = −0.6 for [H2SO4] < 1 M, and c = 0 for [H2SO4] > 1 M. The activation energy was determined to be EA = 62.1 kJ/mol. The order c in H2SO4 is either −0.6 or zero, depending on the H2SO4 concentration.

Influencing Mechanism of Calcium Peroxide Pre-treatment on Dewatering Performance of Waste Activated Sludge

The evolution of sludge filteration dewaterability, floc structure and hydrolytic kinetics with calcium peroxide oxidation pre-treatment was investigated in this study. The effect of sludge characteristics with combined process of ferrous ion and calcium peroxide was deeply analyzed and the result suggested that the sludge dewatering performance was improved first and then worsened after CaO2 addition. When the dosage was 20 mg·g-1, sludge reached its optimal dewaterability. At the same time, sludge was effectively dissolved and the floc structure became loose and broken with the increase of organic matters in the supernatant. Moreover, sludge solubilization process followed the pseudo-zero-order kinetic equation well and the reaction rate of sludge with CaO2 treatment was 15.2 mg·L-1·h-1. In addition, sludge floc lysis was enhanced by the treatment of ferrous ion and calcium peroxide oxidation, whilst sludge dewaterability was improved due to the reconstruction of sludge floc structure by the iron ions produced. This study provided theoretical basis for application of calcium peroxide pre-treatment and its combining technique in sludge treatment.

Fricke Gel Dosimeters

Fricke gel dosimeters are based on the aqueous ferrous sulfate solution that has been used as a reliable chemical dosimeter for more than 90 years. The amount of radiation-induced oxidation of ferrous ions to ferric ions could be evaluated three-dimensionally via optical computed tomography (OCT) or magnetic resonance imaging (MRI). Three-dimensional dosimetry is expected to be a useful tool, in particular, for the verification of complex radiation dose planning in advanced radiation cancer therapy. Compared with other 3D gel dosimeters, there are several problems such as retention of dose distribution or dose sensitivity; however, they can easily be prepared in a chemistry laboratory. In addition, a unique gel dosimeter was also reported for heavy-ion beam irradiation. In this review, recent papers concerning the Fricke gel dosimeter and its application in 3D dosimetry are summarized.

Ferrous Ion oxidation monitoring by using magnetic resonance imaging for bio-oxidation laboratory testing

A non-invasive, non-destructive monitoring approach using three-dimensional (3D) Magnetic Resonance Imaging (MRI) is proposed to study the iron oxidation process driven by Ferrooxidans’ bacterial activity. This activity is related to the oxidation of Fe2+ into Fe3+. Fe3+ ion has paramagnetic properties that could be used to visualize its presence using MRI. A novel MRI methodology has been implemented to visualize Fe3+ in solution with the aim to be used as a marker of iron oxidizer bacteria activity. A proof of concept test has been performed with bacteria in solution and in two solids media: an inert vegetal material (luffa) and solid particles, both dipped in acid solutions. The samples were scanned using a clinical 1.5T MRI scan at several time points to test the capabilities of detecting different Fe3+ concentrations in the solution in time, while Ferrous Ion oxidation is driven by Ferrroxidans. The measurements were contrasted with titration methods to account for Ferrous Ion consumption during the process. The result reveals that a characteristic parameter obtained with MRI imaging, known as R1 relaxivity time measured in Hertz, correlates with Fe2+ oxidation (increment in Fe3+ concentration). 3D images of the distribution of Fe3+ production in the samples were acquired. Results are promising and open opportunities to continue complementary laboratory research at the network porous level to capture the spatial 3D distribution of Ferric Ions as distributed inside the porous network during a bio-reaction test.

Agent-based Model of Oxidation Reactions of Ferrous Ions

Molecules in comets are formed through chemical oxidation reactions induced by radiation. Thesereactions can be simulated in laboratory experiments applying gamma radiation to samples at low temperatures. The kinetics of the induced reactions can be modeled by a system of coupled non-linear ordinary differential equations describing the mass balance of all of the species involved. However, finding a traditional solution to this system is difficult because of the large number of reactions involved, the need to solve all of the equations simultaneously, and the strong dependence on the initial conditions due to the non-linear character of the equations. For each species, the mass-balance equation includes all of the reaction rates leading to production (source terms) and to destruction (sink terms). In this sense, each equation is analogous to the prey-predator model, with the sink terms consider to be the “prey” and the source terms as the “predators”. Due to this, we can use an agent-based model to follow the kinetics of the chemical reactions. In this paper, we present a code in Python for an agent-based model of the chemical oxidation of ferrous ions (Fe2+) induced by gamma radiation and in the presence of molecular oxygen. We compare the results that this code produces for molar concentrations of Fe3+over time with those obtained in the laboratory.

TH-CD-BRA-08: Novel Iron-Based Radiation Reporting Systems as 4D Dosimeters for MR-Guided Radiation Therapy

Purpose: To compare novel radiation reporting systems utilizing ferric ion (Fe3+) reduction versus ferrous ion (Fe2+) oxidation in gelatin matrixes for 3D and 4D (3D+time) MR-guided radiation therapy dosimetry. Methods: Dosimeters were irradiated using an integrated 1.5T MRI and 7MV linear accelerator (MR-Linac). Dosimeters were read-out with both a spectrophotometer and the MRI component of the MR-Linac immediately after irradiation. Changes in optical density (OD) were measured using a spectrophotometer; changes in MR signal intensity due to the paramagnetic differences in the iron ions were measured using the MR-Linac in real-time during irradiation (balanced-FFE sequences) and immediately after irradiation (T1-weighted and inversion recovery sequences). Results: Irradiation of Fe3+ reduction dosimeters resulted in a stable red color with an absorbance peak at 512 nm. The change in OD relative to dose exhibited a linear response up to 100 Gy (R2=1.00). T1-weighted-MR signal intensity (SI) changed minimally after irradiation with increases of 8.0% for 17 Gy and 9.7% after escalation to 35 Gy compared to the un-irradiated region. Irradiation of Fe2+ oxidation dosimeters resulted in a stable purple color with absorbance peaks at 440 and 585 nm. The changes in OD, T1-weighted-MR SI, and R1 relative to dose exhibited a linear response up to at least 8 Gy (R2=1.00, 0.98, and 0.99) with OD saturation above 40 Gy. The T1-weighted-MR SI increased 50.3% for 17 Gy compared to the un-irradiated region. The change in SI was observed in both 2D+time and 4D (3D+time) acquisitions post-irradiation and in real-time during irradiation with a linear increase with respect to dose (R2>0.93). Conclusion: The Fe2+ oxidation-based system was superior as 4D dosimeters for MR-guided radiation therapy due to its higher sensitivity in both optical and MR signal readout and feasibility for real-time 4D dose readout. The Fe3+ reduction system is recommended for high dose applications. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. LH-102SPS.

Acidithiobacillus ferrooxidans's comprehensive model driven analysis of the electron transfer metabolism and synthetic strain design for biomining applications

Acidithiobacillus ferrooxidans is a gram-negative chemolithoautotrophic γ-proteobacterium. It typically grows at an external pH of 2 using the oxidation of ferrous ions by oxygen, producing ferric ions and water, while fixing carbon dioxide from the environment. A. ferrooxidans is of great interest for biomining and environmental applications, as it can process mineral ores and alleviate the negative environmental consequences derived from the mining processes. In this study, the first genome-scale metabolic reconstruction of A. ferrooxidans ATCC 23270 was generated (iMC507). A total of 587 metabolic and transport/exchange reactions, 507 genes and 573 metabolites organized in over 42 subsystems were incorporated into the model. Based on a new genetic algorithm approach, that integrates flux balance analysis, chemiosmotic theory, and physiological data, the proton translocation stoichiometry for a number of enzymes and maintenance parameters under aerobic chemolithoautotrophic conditions using three different electron donors were estimated. Furthermore, a detailed electron transfer and carbon flux distributions during chemolithoautotrophic growth using ferrous ion, tetrathionate and thiosulfate were determined and reported. Finally, 134 growth-coupled designs were calculated that enables Extracellular Polysaccharide production. iMC507 serves as a knowledgebase for summarizing and categorizing the information currently available for A. ferrooxidans and enables the understanding and engineering of Acidithiobacillus and similar species from a comprehensive model-driven perspective for biomining applications.

Pulsed electric discharge treatment of uranium leaching solutions: A method for accelerated extraction

Depletion of uranium ore deposits is leading to a need for more efficient uranium extraction techniques. In this study, gas-phase electric discharge is applied to an aqueous leaching solution dispersed between electrodes as a technique for enhancing acidic extraction of uranium. Application of the electric discharge treatment resulted in a 1.5 to 2.0 times increase in the leaching rate and an improvement in uranium recovery of 4%. The enhanced extraction method was found to involve oxidation of ferrous ions in the acidic aqueous solution by nitrogen-containing ions generated in the spark discharge channels.

Remote Control Electrodeposition: Principles for Bipolar Patterning of Substrates without an Electrical Connection

We describe electrolyte design for bipolar electrochemical growth and patterning of a range of materials on an electrically floating substrate using the scanning bipolar cell (SBC). In the SBC, bipolar electrodeposition is driven by local potential variation generated beneath a rastering microjet anode connected to a far-field cathode. Metal reduction occurs beneath the microjet when the substrate is approached, provided the electrolyte possesses a suitable reducing agent that undergoes oxidation across the substrate far-field. We use a series of metal reduction reactions (Ni, Cu, Au, Ag) that cover a wide range of nobility, and couple them to the oxidation of ascorbic acid or ferrous ion, depending upon the metal used. The reversibility or irreversibility of the local metal reduction reaction dictates details of the required electrolyte thermodynamics. For irreversible deposits (Ni, Au), there is a wide thermodynamic operating window for the bipolar counter reaction. Reversible deposits that are easily etched (Cu, Ag) have tight thermodynamic windows; deposit stability requires the use of metastable electrolytes. We provide a simple scaling relationship that incorporates the electrolyte thermodynamics, interfacial charge transfer kinetics, and SBC operating conditions, then demonstrate its use through a 10X reduction in the spatial dimensions of local nickel reduction chemistry.

Effect of calcium oxide on the efficiency of ferrous ion oxidation and total iron precipitation during ferrous ion oxidation in simulated acid mine drainage treatment with inoculation of Acidithiobacillus ferrooxidans.

Calcium oxide was added into ferrous ion oxidation system in the presence of Acidithiobacillus ferrooxidans at concentrations of 0-4.00 g/L. The pH, ferrous ion oxidation efficiency, total iron precipitation efficiency, and phase of the solid minerals harvested from different treatments were investigated during the ferrous ion oxidation process. In control check (CK) system, pH of the solution decreased from 2.81 to 2.25 when ferrous ions achieved complete oxidation after 72 h of Acidithiobacillus ferrooxidans incubation without the addition of calcium oxide, and total iron precipitation efficiency reached 20.2%. Efficiency of ferrous ion oxidation and total iron precipitation was significantly improved when the amount of calcium oxide added was ≤1.33 g/L, and the minerals harvested from systems were mainly a mixture of jarosite and schwertmannite. For example, the ferrous ion oxidation efficiency reached 100% at 60 h and total iron precipitation efficiency was increased to 32.1% at 72 h when 1.33 g/L of calcium oxide was added. However, ferrous ion oxidation and total iron precipitation for jarosite and schwertmannite formation were inhibited if the amount of calcium oxide added was above 2.67 g/L, and large amounts of calcium sulfate dihydrate were generated in systems.

Kinetics of the pressure leaching of enargite in FeSO4–H2SO4–O2 media

The pressure leaching of enargite in FeSO4–H2SO4–O2 media was studied with the aim to determine the role of the ferrous ions on the rate of arsenic dissolution in the temperature range of 140–200°C. Thus, the effect of ferrous sulfate addition into the leaching of enargite was determined under partial pressure of oxygen in the range of 207–1379kPa. The results showed that the addition of ferrous ions greatly enhanced the leaching rate of enargite, which confirmed that the ferric ion generated in the solution is the major oxidant of enargite while the role of the oxygen in this system was essentially to regenerate the ferric ion. It was also determined that the cupric ions from the enargite dissolution catalyzed the oxidation of ferrous ions to ferric. The kinetics data of the enargite dissolution in this system was analyzed by using the shrinking particle model for monosized particles considering a surface chemical reaction control. The apparent activation energy determined with this model was 111.8kJ/mol for the temperature range 140 to 200°C.

Interaction mechanisms and kinetics of ferrous ion and hexagonal birnessite in aqueous systems.

BackgroundIn soils and sediments, manganese oxides and oxygen usually participate in the oxidation of ferrous ions. There is limited information concerning the interaction process and mechanisms of ferrous ions and manganese oxides. The influence of air (oxygen) on reaction process and kinetics has been seldom studied. Because redox reactions usually occur in open systems, the participation of air needs to be further investigated.ResultsTo simulate this process, hexagonal birnessite was prepared and used to oxidize ferrous ions in anoxic and aerobic aqueous systems. The influence of pH, concentration, temperature, and presence of air (oxygen) on the redox rate was studied. The redox reaction of birnessite and ferrous ions was accompanied by the release of Mn2+ and K+ ions, a significant decrease in Fe2+ concentration, and the formation of mixed lepidocrocite and goethite during the initial stage. Lepidocrocite did not completely transform into goethite under anoxic condition with pH about 5.5 within 30 days. Fe2+ exhibited much higher catalytic activity than Mn2+ during the transformation from amorphous Fe(III)-hydroxide to lepidocrocite and goethite under anoxic conditions. The release rates of Mn2+ were compared to estimate the redox rates of birnessite and Fe2+ under different conditions.ConclusionsRedox rate was found to be controlled by chemical reaction, and increased with increasing Fe2+ concentration, pH, and temperature. The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite. The presence of air accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days. As for the oxidation of aqueous ferrous ions by oxygen in air, low and high pHs facilitated the formation of goethite and lepidocrocite, respectively. The experimental results illustrated the single and combined effects of manganese oxide and air on the transformation of Fe2+ to ferric oxides.Graphical abstract:Lepidocrocite and goethite were formed during the interaction of ferrous ion and birnessite at pH 4-7. Redox rate was controlled by the adsorption of Fe2+ on the surface of birnessite. The presence of air (oxygen) accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite