Catalytic wet peroxide oxidation of phenol solution over Fe–Mn binary oxides diatomite composite

Mn–Fe binary oxides incorporated into diatomite (denoted as FM-diatomite) was prepared by the redox reaction of KMnO₄ and FeSO₄ with pH ranging from 3 to 9. The catalytic activities of FM-diatomite were studied for phenol oxidation and were compared with iron oxide modified diatomite (F-diatomite) and manganese oxide modified diatomite (M-diatomite). The obtained catalysts were characterized by scanning electron microscope, powder X-ray diffraction, energy dispersive spectroscopy, transmission electron microscope, X-ray photoelectron spectroscopy, and nitrogen adsorption/desorption isotherms. The results show that Fe–Mn binary oxides were highly dispersed on the diatomite surface in which manganese oxide and iron oxide displayed multiple oxidation states including Mn⁴⁺, Mn³⁺, Fe²⁺ and Fe³⁺. The phenol oxidation by H₂O₂ through the use of Mn–Fe-diatomite as a catalyst was conducted. FM-diatomite exhibited as an excellent catalyst for the total oxidation of phenol and main intermediates (catechol and hydroquinone). The conversion of phenol and main intermediates by means of FM-diatomite was 100 % under 50 min while that by F-diatomite also was 100 % after 110 min but other intermediates still remained. While phenol conversion by M-diatomite was close to zero due to speedy hydroperoxide decomposition over the manganese oxide catalyst. These results show that there was a synergized effect of iron and manganese oxide present in FM-diatomite.     

Bio‐oxidation of ferrous ions by Acidithioobacillus ferrooxidans in a monolithic bioreactor

BACKGROUND: The bio‐oxidation of ferrous iron is a potential industrial process in the regeneration of ferric iron and the removal of H₂S in combustible gases. Bio‐oxidation of ferrous iron may be an alternative method of producing ferric sulfate, which is a reagent used for removal of H₂S from biogas, tail gas and in the pulp and paper industry. For practical use of this process, this study evaluated the optimal pH and initial ferric concentration. pH control looks like a key factor as it acts both on growth rate and on solubility of materials in the system. RESULTS: Process variables such as pH and amount of initial ferrous ions on oxidation by A. ferrooxidans and the effects of process variables dilution rate, initial concentrations of ferrous on oxidation of ferrous sulfate in the packed bed bioreactor were investigated. The optimum range of pH for the maximum growth of cells and effective bio‐oxidation of ferrous sulfate varied from 1.4 to 1.8. The maximum bio‐oxidation rate achieved was 0.3 g L^?1 h^?1 in a culture initially containing 19.5 g L^?1 Fe²⁺ in the batch system. A maximum Fe²⁺ oxidation rate of 6.7 g L^?1 h^?1 was achieved at the dilution rate of 2 h^?1, while no obvious precipitate was detected in the bioreactor. All experiments were carried out in shake flasks at 30 °C. CONCLUSION: The monolithic particles investigated in this study were found to be very suitable material for A. ferrooxidans immobilization for ferrous oxidation mainly because of its advantages over other commonly used substrates. In the monolithic bioreactor, the bio‐oxidation rate was 6.7 g L^?1 h^?1 and 7 g L^?1 h^?1 for 3.5 g L^?1 and 6 g L^?1 of initial ferrous concentration, respectively. For higher initial concentrations 16 g L^?1 and 21.3 g L^?1, bio‐oxidation rate were 0.9 g L^?1 h^?1 and 0.55 g L^?1 h^?1, respectively. Copyright © 2008 Society of Chemical Industry     

Pro‐oxidant activity of Fe2+ in oxidation of cod phospholipids in liposomes

This work examines how different factors such as temperature, amount of injected Fe²⁺, lipid concentration, pH, concentration of NaCl and concentration of dissolved oxygen influenced the lipid oxidation rate of liposomes made from cod phospholipids. The rate of lipid oxidation was measured by consumption of dissolved oxygen by liposomes in a closed vessel. The rate of oxygen consumption in liposomes was proportional to the concentration of iron and the lipid concentration in the assay mixture. The oxygen consumption rate was dependent on pH, with a maximum observed between pH 4 and 5. The addition of salt (final concentration 0.04–0.8 M) decreased the rate of oxygen consumption. The rate of oxidation was independent of the concentration of dissolved oxygen (in the range of 230–5 μM). The oxygen consumption rate followed Arrhenius kinetics, and the variation in activation energy found (60–87 kJ/moles×K) might be due to variations in the composition of raw materials used in the experiments and different susceptibility to oxidation.     

Influence of process variables on biooxidation of ferrous sulfate by an indigenous Acidithiobacillus ferrooxidans. Part II: Bioreactor experiments

The oxidation of ferrous iron in solution using Acidithiobacillus ferrooxidans has industrial applications in the regeneration of ferric iron as an oxidant agent for the removal of hydrogen sulfide from waste gases, desulphurization of coal, leaching of non-ferrous metallic sulfides and treatment of acid mine drainage. The aim of this attempt was to increase the biooxidation rate of ferrous sulfate by using immobilized cells. Rate of ferrous iron oxidation was determined in a packed-bed reactor configuration with low density polyethylene (LDPE) particles as support material in order to find the most practical system for scale-up. The present work studies the influence of basic parameters on the ferrous iron biooxidation process using an indigenous iron-oxidizing microorganism, namely A. ferrooxidans, in a 2 L packed-bed bioreactor. Effects of several process variables such as initial pH, temperature, dilution rate, initial concentrations of ferrous and ferric ions on oxidation of ferrous sulfate were investigated. Experimental results indicate that in the temperature range of 31–34 °C the biooxidation of ferrous ions to ferric ions could be resulted efficiently. A pH range of 2–2.2 was optimum for the growth of the culture and effective bacterial activity for oxidation of ferrous ions to ferric ions. The highest oxidation rate of 2.9 g Fe²⁺ L⁻¹ h⁻¹ was obtained using a culture initially containing 25 g L⁻¹ Fe⁺² at the dilution rate of 0.4 h⁻¹. This rate is very high compared to that achieved in other bioreactors found in the literature. In addition the biooxidation of Fe²⁺ to Fe³⁺ conversion could be achieved effectively in the presence of the Fe³⁺ in the concentration range of 0.1–0.7 g/L.     

Removal of high concentrations of H2S from simulated natural gas by Acidithiobacillus ferrooxidans immobilized on polyurethane foam

A chemo‐biochemical process for desulfurization of simulated natural gas containing hydrogen sulfide (H₂S) was investigated. The results showed that using polyurethane foam as a support for immobilization of Acidithiobacillus ferrooxidans obtained good biological oxidation performance and the maximum oxidation rate of ferrous iron was 4.12 kg m^?3 h^?1. Moreover, a semi‐empirical formula was set up for calculating theoretical ferrous oxidation rate as a function of influent Fe²⁺ and Fe²⁺ concentration in the bioreactor. The integrated chemical and biological process achieved removal efficiencies of about 80% when treating high concentrations of H₂S (15 000 ± 100 ppmv). © 2012 Society of Chemical Industry     

Generation and characterization of catalytic nanocomposite materials of highly isolated iron nanoparticles dispersed in clays

Nanostructured metallic iron particles in montmorillonite matrix have been prepared at ambient temperature through iron intercalation followed by reduction of resulting iron pillared montmorillonite with potassium borohydride. The resulting nanocomposites have been characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), UV–VIS-diffuse reflectance spectrometer (UV–VIS). The catalytic performances of resulting nanocomposites have been evaluated by probe phenol oxidation reaction with hydrogen peroxide. The results reveal that the nanosized iron polyoxocations intercalated clays can be successfully obtained by conventional synthesis of pillared clays, and after reduction of pillars, the highly dispersed zero-valent iron nanoparticles in clay matrix with diameter in the range of 3–10 nm can be successfully yielded. Over the nanocomposites catalyst prepared at a molar ratio of [CO ₃ ²⁻ ]/[Fe³⁺] = 0.5, the catalytic conversion of phenol oxidation is 49.5% with a 67.4% of selectivity to carbon dioxide and tar. The iron species dispersed in clay matrix may provide the catalytic active sites and the size of iron species has an effect on selectivity. More highly isolated iron nanoparticles dispersed in clays could lead to higher catalytic deep oxidation.     

The effects of ferrous iron,dissolved oxygen,and inert solids concentrations on the growth of thiobacillus ferrooxidans

The effects of suspended, inert solids concentration, ferrous iron concentration and dissolved oxygen concentration on the kinetics of iron oxidation by Thiobucillus ferrooxidans are reported. It is shown that the maximum specific growth rate for this organism, oxidizing ferrous iron, is of the order of 0.1 h^?1. Competitive inhibition by femc iron is demonstrated. The dissolved oxygen concentration below which the bacteria will not grow is 0.20 mg/L. The dissolved oxygen concentration below which O₂ availability is limiting is around 0.29-0.7 mg/L. 10.4 millimols of CO₂ are fixed by the bacteria per mol of ferrous iron oxidized. 0.0185 mg of bacterial carbon are generated per mg of O₂ consumed. Comparative mass transfer rates for O₂ and CO₂ are discussed. Oxidation rates decreased significantly in shake flasks as suspended solids concentrations rose above 0.5%, whereas in stirred tanks solids concentrations up to 15% had little effect on oxidation rate.     

The oxidation of Fe(II) with Cu(II) in acidic sulfate solutions with air at elevated pressures

The oxidation of ferrous ions in acidic sulfate solutions in the presence of cupric ions at elevated air pressures was investigated in a high-intensity gas–liquid contactor. The study was required for the design of the regeneration steps of the novel Vitrisol^® desulphurization process. The effects of the Fe²⁺ concentration, Cu²⁺ concentration, Fe³⁺ concentration, initial H₂SO₄ concentration, and partial oxygen pressure on the reaction rate were determined at three different temperatures, i.e., T?=?50?°C, 70?°C, and 90?°C. Most of the experiments were determined to be affected by the mass transfer of oxygen, and therefore true intrinsic kinetics could not be fully determined. An increase in Fe²⁺ and Cu²⁺ concentrations, as well as the partial pressure of oxygen and temperature, increased the Fe²⁺ oxidation rate. H₂SO₄ did not influence the Fe²⁺ oxidation rate. An increase in Fe³⁺ concentration decreased the Fe²⁺ oxidation rate. Although determined from experiments partially affected by mass transfer, a first order of reaction in Fe²⁺ was observed, fractional orders in both Cu²⁺ and O₂ were measured, a zero order in H₂SO₄ was determined, and a negative, fractional order in Fe³⁺ was obtained. The activation energy was estimated to be 31.3?kJ/mol.     

Process intensification in wastewater treatment: ferrous iron removal by a sustainable membrane bioreactor system

Biooxidation of ferrous iron (Fe²⁺) from strongly acidic industrial wastewater with a high Fe²⁺ content by Thiobacillus ferrooxidans in a packed bed reactor and subsequent removal of ferric iron (Fe³⁺) by a crossflow microfiltration (membrane) process have been investigated as functions of wastewater flowrate (54–672 cm³ h^?1), Fe²⁺ concentration (1.01–8.06 g dm^?3), and pH (1.5–5.0). A natural (vegetable) sponge, Luffa cylindrica, was used as support matrix material. The fastest kinetic performance achieved was about 40 g Fe²⁺ dm^?3 h^?1 at a true dilution rate of 19 h^?1 corresponding to a hydraulic retention time of 3.16 min. Steady state conversion was observed to be about 10% higher at pH 2.3 than that at pH 1.5. Increasing the flowrate of the inlet wastewater caused a reduction in conversion rate. The oxidation rate reduced along the reactor height as the wastewater moved towards the exit at the top but conversion showed the opposite trend. Increasing Fe²⁺ concentration up to a critical point resulted in an increased oxidation rate but beyond the critical point caused the oxidation rate to decrease. Luffa cylindrica displayed suitable characteristics for use as a support matrix for formation of a Thiobacillus ferrooxidans biofilm and showed promising potential as an ecological and sustainable alternative to existing synthetic support materials. Membrane separation was shown to be a very effective means of Fe³⁺ removal from the wastewater with removal changing from 92% at pH 2.3 to complete removal at pH 5.0. Copyright © 2003 Society of Chemical Industry     

Catalytic property of Fe-Al pillared clay for Fenton oxidation of phenol by H2O2

Clay pillared with Fe-Al was synthesized as a catalyst for Fenton oxidation of phenol by hydrogen peroxide (H₂O₂). The pillaring process altered the basal space of clay, which is related to the amounts of aluminium and iron in the pillaring solution. The catalytic activity of the pillared clay was attributed to the accessible iron species, whose amount is regulated not only by the introduced iron species but also by the basal space that subsequently depends on the introduced aluminium species. The heterogeneous Fenton reaction exhibited an induction period followed by an apparent first order oxidation of phenol by H₂O₂. The induction period was proposed as an activation process of the surface iron species, which is thus enabled to complex with the reactants. The induction time (t_I) depended on temperature (T) and pH condition but irrelevant to the concentrations of phenol and H₂O₂ and the amount of catalyst. The rate of the oxidation process was evaluated with respect to the concentrations of phenol and H₂O₂, the amount of catalyst, pH and temperatures. During the catalytic reaction the trend of iron leaching showed an ascending period and a descending period, which was related to the presence of ferrous ions and ferric ions. The Fe-Al pillared was recovered through two procedures, dry powder and slurry, which have different effect on the induction period.     

Mössbauer Spectroscopy of Fe Xanthates

Abstract

Mössbauer spectroscopic studies indicate that, depending on pH, two different precipitates are formed when appropriate solutions of iron ions are mixed with ethyl xanthate solutions. Below pH 3.5, ferric ethyl xanthate is obtained, regardless of whether ferric or ferrous reactants are used; ferrous xanthate can be obtained only with highly concentrated solutions and in strictly neutral or even reducing conditions. Above pH 3.5 a ferric hydroxy-xanthate, with one or more OH groups replacing the xanthate groups, is formed. No analogy with the Cu²⁺ → Cu⁺ reduction and the accompanying stoichiometric oxidation of xanthate to dixanthogen could be observed in the Fe³⁺ → Fe²⁺ systems, in which dixanthogen is detected only as a product of ferric xanthate decomposition in alkaline pH's.     

Advanced oxidation processes for the degradation of p‐hydroxybenzoic acid 2: Photo‐assisted Fenton oxidation

Oxidation of p‐hydroxybenzoic acid in aqueous solution by the photo‐assisted Fenton reaction (Fe²⁺ + H₂O₂ + UV) has been studied. The effects of ferrous ion concentration (0.05, 0.14 and 0.29 mmol dm^?3), temperature (10, 20, 30 and 40 °C), and initial hydrogen peroxide concentration (0.7, 1.4, 2.2 and 2.9 mmol dm^?3) on the p‐hydroxybenzoic acid conversion were established. Experimental results indicate that the kinetics of this oxidation process fits pseudo‐first‐order kinetics well. The overall kinetic rate constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidation by free radicals (mainly OH·) generated in the system. The importance of these two reaction paths for each specific value of ferrous ion concentration, temperature and initial hydrogen peroxide concentration was evaluated. A semi‐empirical expression is proposed for the overall reaction rate which takes into account both oxidation pathways and is a function of operating variables. © 2001 Society of Chemical Industry     

Redox cycling of iron and lipid peroxidation

Mechanisms of iron-catalyzed lipid peroxidation depend on the presence or absence of preformed lipid hydroperoxides (LOOH). Preformed LOOH are decomposed by Fe(II) to highly reactive lipid alkoxyl radicals, which in turn promote the formation of new LOOH. However, in the absence of LOOH, both Fe²⁺ and Fe³⁺ must be available to initiate lipid peroxidation, with optimum activity occurring as the Fe²⁺/Fe³⁺ ratio approaches unity. The simultaneous availability of Fe²⁺ and Fe³⁺ can be achieved by oxidizing some Fe²⁺ with hydrogen peroxide or with chelators that favor autoxidation of Fe²⁺ by molecular oxygen. Alternatively, one can use Fe³⁺ and reductants like superoxide, ascorbate or thiols. In either case excess Fe²⁺ oxidation or Fe³⁺ reduction will inhibit lipid peroxidation by converting all the iron to the Fe³⁺ or Fe²⁺ form, respectively. Superoxide dismutase and catalase can affect lipid peroxidation by affecting iron reduction/oxidation and the formation of a (1∶1) Fe²⁺/Fe³⁺ ratio. Hydroxyl radical scavengers can also increase or decrease lipid peroxidation by affecting the redox cycling of iron. Based on a paper presented at the Symposium on Metals and Lipid Oxidation, held at the AOCS Annual Meeting in Baltimore, Maryland, April 1990.     

Oxidation of cod phospholipids in liposomes: Effects of salts,pH and zeta potential

This work examines how different salts and pH influence both the zeta potential and the lipid oxidation rate of liposomes made from cod phospholipids. The rate of Fe²⁺‐induced lipid oxidation was measured by consumption of dissolved oxygen by liposomes in a closed vessel. Cations (Na⁺, K⁺, Ca⁺, Mg⁺) did not influence the rate of oxidation in the tested range [ionic strength (I) 0–0.14 M). Among the tested anions, sulphates and nitrates did not significantly change the oxygen uptake rate, but chlorides (KCl, NaCl, CaCl₂) reduced the oxidation rate down to approximately 45%, and dihydrogen phosphate down to 14%, when I = 0.14 M. The effect of Cl^? and H₂PO4₄^? was additive. Addition of salts increased the zeta potential of the liposomes, divalent cation salts even resulted in a positive zeta potential. When the liposomes contained different concentrations of chlorides, a linear relationship between oxygen uptake rate and zeta potential was observed. When phosphate was added, the oxygen uptake rate was not related to the changes in zeta potential. The decrease in pH was followed by an increase in zeta potential. The oxygen uptake rate did not change significantly at different positive zeta potentials (pH <3). When the zeta potential was negative, the oxygen uptake rate was influenced by the zeta potential and may also be influenced by iron solubility. Absolute values of the zeta potential alone cannot be used to predict oxidation rates.     

Phenol Removal through Chemical Oxidation using Fenton Reagent

In this study, phenol, aromatic, and non‐biodegradable organic matter were investigated and found to be removed from the model solution through chemical oxidation using Fenton reagent. The effects of the initial phenol concentration, hydrogen peroxide, and ferrous sulfate concentrations on the removal efficiency were investigated. Performance of the chemical oxidation process was monitored with phenol and COD (Chemical Oxygen Demand) analyses. In the experimental studies, phenol removal of over 98 % and COD removal of nearly 70 % were achieved. The optimum conditions for Fenton reaction both for initial phenol concentrations of 200 and 500 mg/L were found at a ratio [Fe²⁺]/[H₂O₂] (mol/mol) equal to 0.11. According to the results, chemical oxidation using Fenton reagent was found to be too effective, especially for phenol removal. However, this method has limited removal efficiency for COD.     

Hydrosulphide oxidation pathways in oxic alkaline media containing iron/cerium oxide‐hydroxide

The oxidation kinetics of hydrosulphide by iron/cerium oxide‐hydroxide (FeCeOx) and dissolved oxygen (DO2) was studied at 0.1 MPa and 298 K in a batch slurry reactor. The oxidation of hydrosulphide by the FeCeOx/DO2 system proceeded via a combined heterogeneous–homogeneous pathway to yield zerovalent sulphur and thiosulphate. The role of dissolved oxygen was twofold: (i) it reoxidized the iron from Fe(II) to active Fe(III), (ii) it prompted the homogeneous oxidation of hydrosulphide to polysulphides and of polysulphides to thiosulphate. The Fe(III) in situ regeneration by DO2 showed that FeCeOx holds promise for a redox scrubbing process targeting the elimination of H₂S from the Kraft mill effluents.     

Fenton‐ and Fenton‐Like AOPs for Wastewater Treatment: From Laboratory‐To‐Plant‐Scale Application

Abstract

Fenton‐and Fenton‐like AOPs systems have been utilized for the oxidative degradation of some chlorinated pollutants such as chloral hydrate or 1,1,1‐trichloroethane, and for the treatment of real industrial wastewaters. Both ferrous sulfate (FeSO₄ · 7 H₂O) and Mohr's salt (NH₄)₂Fe(SO₄)₂. 6 H₂O have been used as Fe²⁺ ion sources. With Mohr's salt (MS) the Fenton‐and Fenton‐like reaction has been successfully carried out under acidic (pH 3) and neutral (pH 7) reaction conditions. The new Fenton‐like system utilizes zero‐valent iron (Fe^o) instead of ferrous sulfate has been applied for the 1,1,1‐trichloroethane and chloral hydrate degradation. Similarly, the application of catechol‐ and hydroquinone‐driven Fenton reaction for the degradation of chloral hydrate under acidic and neutral pH is a new Fenton‐like AOPs approach. The photo‐Fenton‐like reactions such as Fe³⁺/hν, Fe²⁺/H₂O₂/hν, and ferrioxalate system have been also studied for the degradation of chloral hydrate. As an irradiation source a daily light or sun light have been used. In comparison with photoreactor experiments the best system was observed to be Fe³⁺/hν. In some experiments the influence of standing time prolongation after Fenton reaction on the final degradation efficiency due to hydrolysis of intermediates such as phosgene (CCl₂?O) has also been studied. The Fenton reaction was successfully utilized for the treatment of real industrial wastewaters, in two cases even in plant‐scale applications.     

Electrogenerative oxidation of ferrous ions with graphite electrodes

Electrogenerative oxidation of ferrous ions in Fe²⁺/O₂ cells to regenerate ferric ions for further use is demonstrated and some results for a hybrid type laboratory-scale reactor are presented. The use of graphite particle, packed-bed anodes for ferrous oxidation with gas diffusion type cathodes for oxygen reduction enables these cells to produce ferric ions at moderate current densities and low cell voltages in sulphuric acid solutions. These cells which utilize the rapid electrochemical, ferrous oxidation rate on graphite catalytic electrodes without any need for an external power source have potential application in hydrometallurgical leaching systems as well as in sulphur dioxide cleanup processes which incorporate the use of ferric ions. Continuous feed stream operation under mild conditions is a special advantage.To whom correspondence should be addressed.     

Kinetics of Multi‐Step Redox Processes by Time‐Resolved In Situ X‐ray Diffraction

The kinetics of redox reactions of iron oxide in oxygen carrier 50Fe₂O₃/MgAl₂O₄ are examined using different time‐resolved techniques. Reduction kinetics are studied by H₂ temperature‐programmed reduction (H₂‐TPR) monitored by time‐resolved in situ XRD. In contrast to conventional TPR, in situ XRD distinguishes the three‐stage reduction of Fe₂O₃ → Fe₃O₄ → FeO → Fe. It also shows that the oxidation of Fe → Fe₃O₄ by CO₂ has no intermediate crystalline phases, explaining why its kinetics can easily be investigated by conventional CO₂ temperature‐programmed oxidation (CO₂‐TPO). A shrinking core model which takes into account solid state diffusion allows describing the experimental data.