Effect of sulfite on reduction kinetics of Fe(III)NTA chelate

The reduction of Fe(III)NTA (ferric ion coordinated to nitrilotriacetic acid) by sulfite has been found to be first-order with respect to Fe(III)NTA and of order minus one with respect to Fe(II)NTA (one of the reaction products). The order of reaction with respect to HSO^?₃ has been determined to be unity when the molar ratio of Na₂SO₃ to total Fe(III) is less than five. In this paper, the role of sulfite in the reduction scheme is reconsidered, and the reduction rate expression in which the coordination of Fe³⁺ to HSO^?₃ is incorporated, is newly presented. The proposed rate equation covers all reaction data for molar ratios of Na₂SO₃ to total Fe(III) in the range of 1 to 25.     

Oxidation kinetics of Fe(II)NTA to Fe(III)NTA by oxygen

The oxidation of aqueous solutions of Fe(II)NTA was investigated in a bubble column reactor. The rate of the oxidation reaction was found to be proportional to the partial pressure of oxygen and to have an order of 0.5 with respect to the Fe(II)NTA concentration. The overall transfer of oxygen appears to be predominantly reaction controlled for Fe(II)NTA concentrations in the order of 1 mmol l⁻¹, whereas for high concentrations (100 mmol l⁻¹) mass transfer becomes the controlling factor. Overall mass transfer coefficients and reaction rate constants were determined in the range between 25 and 60°C and for a wide range of Fe(II)NTA concentrations (5-250 mmol l⁻¹).     

Denitrification in aqueous FeEDTA solutions

The biological reduction of nitric oxide (NO) in aqueous solutions of FeEDTA is an important key reaction within the BioDeNOx process, a combined physico‐chemical and biological technique for the removal of NO_x from industrial flue gasses. To explore the reduction of nitrogen oxide analogues, this study investigated the full denitrification pathway in aqueous FeEDTA solutions, ie the reduction of NO₃^?, NO₂^?, NO via N₂O to N₂ in this unusual medium. This was done in batch experiments at 30 °C with 25 mmol dm^?3 FeEDTA solutions (pH 7.2 ± 0.2). Also Ca²⁺ (2 and 10 mmol dm^?3) and Mg²⁺ (2 mmol dm^?3) were added in excess to prevent free, uncomplexed EDTA. Nitrate reduction in aqueous solutions of Fe(III)EDTA is accompanied by the biological reduction of Fe(III) to Fe(II), for which ethanol, methanol and also acetate are suitable electron donors. Fe(II)EDTA can serve as electron donor for the biological reduction of nitrate to nitrite, with the concomitant oxidation of Fe(II)EDTA to Fe(III)EDTA. Moreover, Fe(II)EDTA can also serve as electron donor for the chemical reduction of nitrite to NO, with the concomitant formation of the nitrosyl‐complex Fe(II)EDTA–NO. The reduction of NO in Fe(II)EDTA was found to be catalysed biologically and occurred about three times faster at 55 °C than NO reduction at 30 °C. This study showed that the nitrogen and iron cycles are strongly coupled and that FeEDTA has an electron‐mediating role during the subsequent reduction of nitrate, nitrite, nitric oxide and nitrous oxide to dinitrogen gas. Copyright © 2004 Society of Chemical Industry     

Reductive transformation of 2-nitrophenol by Fe(II) species in γ-aluminum oxide suspension

Fe(II) adsorption onto γ-Al₂O₃ surfaces was studied in view of its high reactivity towards the aqueous reductive transformation of 2-NP. Kinetic measurements demonstrated that rates of 2-NP reduction were highly sensitive to pH, Fe(II) concentration and reaction temperature. An increase in pH, Fe(II) concentration or reaction temperature gave rise to an elevated density of Fe(II) adsorbed to mineral surfaces, which further resulted in an enhanced reaction rate of 2-NP reduction. By using the diffuse double layer (DDL) surface complexation model, the dominant Fe(II) surface complex that was responsible for the high reactivity was predicted to be the strongly bound ≡ SOFe⁺ functional group (represented by ≡ Al_stOFe⁺) onto γ-Al₂O₃ surfaces. In addition, cyclic voltammetry tests showed that the enhanced activity of Fe(II) species was attributed to the negative shift of the redox potential of Fe(III)/Fe(II) couple, resulted from the enhanced concentration of ≡ Al_stOFe⁺ complex.     

The characterization and bioelectrocatalytic properties of hemoglobin by direct electrochemistry of DDAB film modified electrodes

Direct electrochemistry of hemoglobin can be performed in acidic and basic aqueous solutions in the pH range 1-13, using stable, electrochemically active films deposited on a didodecyldimethylammonium bromide (DDAB) modified glassy carbon electrode. Films can also be produced on gold, platinum, and transparent semiconductor tin oxide electrodes. Hemoglobin/DDAB films exhibit one, two, and three redox couples when transferred to strong acidic, weak acidic and weak basic, and strong basic aqueous solutions, respectively. These redox couples, and their formal potentials, were found to be pH dependent. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ deposition of DDAB on gold disc electrodes and hemoglobin deposition on DDAB film modified electrodes. A hemoglobin/DDAB/GC modified electrode is electrocatalytically reduction active for oxygen and H₂O₂, and electrocatalytically oxidation active for S₂O₄²⁻ through the Fe(III)/Fe(II) redox couple. In the electrocatalytic reduction of S₄O₆²⁻, S₂O₄²⁻, and SO₃²⁻, and the dithio compounds of 2,2′-dithiosalicylic acid and 1,2-dithiolane-3-pentanoic acid, the electrocatalytic current develops from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in neutral and weakly basic aqueous solutions. Hemoglobin/DDAB/GC modified electrodes are electrocatalytically reduction active for trichloroacetic acid in strong acidic buffered aqueous solutions through the Fe(III)/Fe(II) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in weak acidic and basic aqueous solutions. The electrocatalytic properties were investigated using the rotating ring-disk electrode method.     

Kinetics of the Complexation of Ferric Iron with 8-Hydroxyquinoline and Kelex-100

Abstract

The complexation reactions of ferric iron with 8-Hydroxyquinoline and KELEX-100 in both aqueous and methanol solutions were studied by using a stopped-flow spectropho to meter. In the aqueous solutions, the observed rate law was found to be first-order with respect to both iron(III) and oxine and inverse-first-order with respect to the hydrogen ion. While in the methanol-solution, the rate law was first-order with respect to iron(III) and KELEX-100₂₊ Reaction pathes .with the formation of the first complex, FeA²⁺, from either Fe³⁺ or Fe(OH)²⁺ were proposed to explain the observed rate law. The activation energies were found to be 5.5 kcal/g-mole and 15 kcal/g-mole for the aqueous and methanol solutions, respectively.     

Green and efficient synthesis of an adsorbent fiber by preirradiation‐induced grafting of PDMAEMA and its Au(III) adsorption and reduction performance

N ,N ‐Dimethylamino ethyl methacrylate (DMAEMA) is covalently bonded on a commercial polyethylene‐coated polypropylene skin‐core structure fiber (PE/PP) in aqueous and MeOH/H₂O solutions by a one‐step green reaction using radiation‐induced graft polymerization. The effects of the absorbed dose and solvent system on grafting yield are investigated, while the chemical and physical properties of the functionalized fiber are also evaluated. The fiber with a D_g of 51.6% exhibited good adsorption capacity of Au(III) ions over a large range of concentrations (from 10 to 2.5 g L^?1) in both batch and flow‐through adsorption tests. The highest capacity of Au was 949.3 mg g^?1. After elution, the adsorbents can be reused without any further regeneration for at least five adsorption‐desorption cycles. Additionally, the fibers show high selectivity for Au(III). The distribution coefficient of Au(III) is 10⁴ to 10⁵ times higher than that for Cu(II), Fe(III), Ni(II), and Pb(II) even at 100 times lower Au(III) concentration compared to the co‐existing metal ion concentration. This study provides an effective and novel approach for gold recovery from aqueous solutions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44955.     

Application of crosslinked carboxymethyl konjac glucomannan in speciation of dissolved Fe(II) and Fe(III) in water samples

A new solid‐phase extraction technique has been developed for the speciation of trace dissolved Fe(II) and Fe(III) in environmental water samples with a microcolumn packed with crosslinked carboxymethyl konjac glucomannan (CCMKGM) prior to its determination by flame atomic absorption spectrometry (FAAS). Various influencing factors on the separation and preconcentration of Fe(II) and Fe(III), such as the acidity of the aqueous solution, sample flow rate and volume, and eluent concentration and volume, have been investigated systematically and optimized. Fe(III) could be quantitatively retained by CCMKGM in the pH range of 3.0–7.0, then the retained Fe(III) on the CCMKGM was eluted with 5.0 mol L^?1 HCl after cleaning with 0.01 mol L^?1 HCl to eliminate Fe(II) and determined by FAAS. Total Fe was determined after the oxidation of Fe(II) to Fe(III) by H₂O₂, and Fe(II) concentration was calculated by subtracting Fe(III) from total iron. The adsorption capacity of CCMKGM for Fe(III) was found to be as high as 162.3 mg g^?1. The detection limit (3σ) for Fe(III) was 1.5 μg L^?1 and the RSD was 3.5% (n = 11, c = 20 μg L^?1) with an enrichment factor of 50. The proposed method has been applied to the speciation of iron in water samples with satisfactory results. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Regeneration of [Fe(II)-NTA]− catalyzed by activated carbon in the simultaneous removal of sulphur dioxide and nitric oxide

The combined control of NO and SO₂ can be finished with the [Fe(II)-NTA]⁻ solution because [Fe(II)-NTA]⁻ is capable of binding NO. However, the ability of [Fe(II)-NTA]⁻ to bind NO may be lost quickly due to the fast oxidation of [Fe(II)-NTA]⁻ to [Fe(III)-NTA] by oxygen in the flue gases. To make it possible to put this technology into commercial application, efficient measures should be taken to regenerate [Fe(II)-NTA]⁻ to maintain the NO removal efficiency for a long time. The catalytic activity of activated carbon in the reproduction of [Fe(II)-NTA]⁻ has been investigated in a fixed-bed reactor. The experiments indicate that [Fe(II)-NTA]⁻ reproduction increases with [Fe(III)-NTA] and SO₃²⁻ concentrations as well as temperature. Fast flow and high pH are unfavourable for the reproduction of [Fe(II)-NTA]⁻. An NO removal efficiency of 80.11%–89.78% is sustained for a long period of time with the [Fe(II)-NTA]⁻ reproduction catalyzed by activated carbon. The reaction orders with respect to [Fe(III)-NTA] and SO₃²⁻ are 0.784 and 0.336, respectively. The apparent activation energy for this catalytic reaction is estimated to be 41.01 kJ mol⁻¹.     

The Mutual Effect of Iron(III) and Silver(I) Species in Concentrated Chloride Medium

Abstract

Earlier studies carried out to evaluate the selectivity of solvating extractants towards silver(I) in concentrated chloride media revealed that an intriguing situation occurs if a given excess of iron(III) concentration is present in the aqueous solution: the extraction of silver(I) becomes almost quantitative and independent of the initial chloride content. On the assumption that this effect may be due to a phenomenon occurring in the aqueous phase, a systematic study involving solutions containing different Ag(I), Fe(III), and HCl concentrations was carried out by solvent extraction and capillary electrophoresis. Capillary electrophoresis suggests that the AgCl₃ ^2? amount in solution decreases in the presence of Fe(III), whereas FeCl₃ seems to be partially converted onto FeCl₄ ^?. From the experiments performed, it can be concluded that the presence of Fe(III) seems to facilitate the formation of less anionic Ag(I) species, which are in turn more easily extracted by solvating extractants. Furthermore, the presence of FeCl₄ ^? has been detected in the organic phase of triisobutylphosphine sulfide (TIBPS) by UV‐Vis spectrophotometry, after equilibration with HCl solutions containing both Ag(I) and Fe(III), which was not identified during similar experiments carried out in the absence of Ag(I). Speciation of silver(I) and iron(III) in concentrated chloride medium has also been worked out by a numerical methodology.     

Homogeneous Catalyzed Ozone Decomposition in the Presence of Co(II).

The homogeneous decomposition of ozone in the presence of a Co(II) catalyst has been investigated in aqueous solution. Under the conditions investigated (Co(II) concentration: 0.0 – 2.0?ppm, pH: 1.6- 8.4, O₃ concentration: 5 10^?5 – 2.0 10⁴?M) the process can be assumed to follow pseudo first order kinetics with respect to ozone. Cobalt concentration dependency also obeys first order kinetics although it may be considered to reach a steady state concentration. pH exerts a positive influence on the decomposition rate from 1.6 to 7.1, the process leveling off at pH 8.4. An Arrhenius analysis of the temperature effect gave a moderate activation energy of the global reaction (E=10917?cal mol^?1). A more detailed radical mechanism than a simple pseudo first order reaction can be postulated for simulation purposes. By numerical optimization of some unknown kinetic constants the influence of several operating variables can be adequately predicted.     

Electrochemical oxidation of aliphatic hydrocarbons promoted by inorganic radicals. I. OH radicals

The OH initiated oxidation of aliphatic hydrocarbons by the simultaneous electrochemical reduction of O₂ and of Fe(III) at controlled potential was investigated in the liquid phase over a Fe(III) concentration range 0.5–5 mM. OH radicals were generated by the reaction: Fe(II)+H₂O₂Fe(III)+^.OH+OH^– The compounds studied were the linear alkane hydrocarbons from C₅ to C₁₀ and 3-methyl pentane. The results showed that the ketones are the only reaction products and that the yields decrease with increasing number of carbonium atoms of the hydrocarbon. Decreasing yields were also observed with increasing Fe(III) concentration.     

Osmium(VIII) catalyzed oxidation of a sulfur containing amino acid—a kinetics and mechanistic approach

The kinetics of osmium (VIII) catalyzed oxidation of DL-methionine by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm^?3 was studied spectrophoto-metrically. The reaction between hexacyanoferrate(III) and DL-methionine in alkaline medium exhibits 2:1 stoichiometry (2HCF:DL-methionine). The reaction is of first order each in [HCF] and [Os(VIII)], less than unit order in [alkali] and zero order for [DL-methionine]. The decrease in dielectric constant of the medium increases the rate of the reaction. The added products have no effect on the rate of reaction. The main products were identified by spot test. A free radical mechanism has been proposed. In a prior equilibrium step Os(VIII) binds to OH^? species to form a hydroxide species and reacts with [Fe(CN)₆]^3? in slow step to form an intermediate species(C₁). This reacts with a molecule of DL-methionine in a fast step to give the sulfur radical cation of methionine and yields the sulfoxide product by reacting with another molecule of [Fe(CN)₆]^3?. The rate constant of the slow step of the mechanism is calculated. The activation parameters with respect to slow step of the mechanism are evaluated and discussed.     

New Inorganic–Organic Hybrid Materials and Their Oxides for Removal of Heavy Metal Ions: Response Surface Methodology Approach

In this paper, Cu(II), Fe(III), Pb(II), and Zn(II) heavy metal ions were removed from their aqueous solutions by using novel inorganic–organic hybrid materials, Al-GPTS-H and Al-GPTS-NaOSiMe₃-H (hybrid material-1 and 2, respectively), and their oxides (calcined-1 and 2) as adsorbents. These ions removal by adsorption was optimized by using response surface methodology (RSM). Central composite design (CCD) method was used in order to investigate the effects of initial pH, initial metal concentration of solutions and adsorbent quantity on the adsorption efficiency (R, %). As a result of the experiments under optimum conditions, the maximum % R values were obtained by hybrid material-1 for Fe(III) (99.89%) and by calcined material-1 for Pb(II) (97.14%), respectively. These quite high adsorption efficiency values have shown that these hybrid materials and their oxides are suitable to use for heavy metal ions removal from aqueous solutions.     

Comparative Equilibrium Studies on the Sorption of Metal Ions with Macroporous Resins Containing a Liquid Ion-Exchanger

Abstract

The distribution of five metal ions (M ^m+) including Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) between dilute sulfate solutions and macroporous resins containing di(2-ethylhexyl) phosphoric acid (D2EHPA, HR) was investigated. Experiments were carried out as a function of aqueous pH, D2EHPA concentration in the resin phase, and temperature. The equilibrium data were numerically analyzed. It was shown that the sorption reaction could be described by assuming the formation of metal complexes with a general composition MR _m (HR) _n in the resin phase. For several systems a change of complex stoichiometry with temperature was observed and discussed. The apparent thermodynamic data for the formation of these complexes were also calculated.     

Removal of Cu(II) from Aqueous Solution by Oil-Water Interfacial Emulsion Technique with Adsorbing Colloids

Abstract

Experimental investigations on the removal of Cu(II) from an aqueous solution were carried out by an interfacial emulsion technique with an adsorbing colloid (Al(OH)₃, FE(OH)₃), Cu(II) from the aqueous solution was segregated into a compact emulsion between water and a water-immiscible oil phase by an interfacial emulsion technique that uses the adsorptive power of the oil-water interface. Trimethylamine was effective as a surfactant for the removal of Cu(II), and the optimum pH for the removal of Cu(II) was found at 9.0 when using Fe(OH)₃ and at 10.0 when using Al(OH)₃ as an adsorbing colloid, respectively. The effects of pH, mixing time, initial surfactant concentration, initial Fe(III) concentration, and foreign ions (Na⁺, Ca²⁺, CI^?, NO₃ ^?, HPO₄ ^2?) on the removal efficiency were investigated. The adsorption and separation mechanisms for the removal of Cu(II) by the interfacial emulsion technique of adsorbing colloids were observed.     

LIQUID-LIQUID EXTRACTION OF GOLD(III) AND ITS SEPARATION OVER COPPER(II), IRON(III), AND ZINC(II) USING THIOUREA DERIVATIVES FROM CHLORIDE MEDIA

ABSTRACT

Selective liquid-liquid extraction of Au(III) from aqueous chloride media (1 mol/L NaCl) into cumene by thiourea derivatives namely 2a-c (N-thiocarbamoylbenzamidine derivatives), 3a-f (N-benzoylthiourea derivatives) has been investigated in detail. Marked differences in the metal extraction are noted using these organic compounds with respect to their structural variation. The extraction behaviour of Au(III) with extractants 2a-c and 3a-f followed the order : 2b> 2a>2c and 3e≈ 3c≈ 3d >3a >3f≈3b, respectively. The organic reagent 2a and 3c were selected for further detailed studies owing to their better strippability behaviour. Optimum conditions such as structure of the organic extractant, aqueous phase pH, diluent, time of equilibration, metal concentration, extractant concentration, effect of other metal cations were established for extraction separation of Au(III). Experimental data have been treated graphically and numerically by means of the computer programme LETAGROP-DISTR, and can be explained by assuming the formation of the species AuCl₃L and AuCl₃L₂ for 2a-c and AuCl₃L₂ for 3a-f derivatives. The lack of interference from even appreciable amounts of possible base metals such as Cu(II), Zn(II) and Fe(III) may be considered an outstanding advantage of the method for separation of gold from these metals using 2a and 3c.     

A Model for The Recovery of Titanium From Mixtures of Ilmenite and Hematite by Hydrochloric Acid Leaching

Abstract

A partial equilibrium model has been developed to describe the leaching of FeTiO₃-Fe₉O mixtures by aqueous HC1. The model couples the rates of leaching of the minerals to changes in the solution species concentrations; 23 species concentrations were calculated as a function of leaching time. Solution reactions included in the model include (1) the redox reaction converting Ti(IV) and Fe(II) to Ti(III) and Fe(III); (2) formation of chloro complexes; (3) hydrolysis; and (4) dissociation of H₂O. Ilmenite is more rapidly depleted than hematite, and available data indicate that the time dependence of the leaching reactions is different. Modeling results show that the Ti/Fe concentration ratio drops steeply initially but then gradually rises as the leaching rates change. Of the two oxides, FeTiO₃ is consumed first, and thereafter the Ti/Fe ratio again declines. The Fe(II)/Fe(III) concentration ratio behaves similarly. The Ti/Fe and Fe(II)/Fe(III) ratios have simultaneous extrema and plots of these ratios vs. time can, with appropriate adjustments in vertical scale, virtually be superimposed. These changes are greatest when the initial molar amounts of FeTiO₃ and Fe₂O₃ are approximately equal. They are qualitatively the same, but of much smaller magnitude, when the initial FeTiO₃ /Fe₃O₃ molar ratio is far from 1.0. The species distributions change in a complex way during leaching; typically, hydroxo species become more important but chloro species become less so. Implications of these results for the selective recovery of titanium will be discussed.     

MECHANISM OF POLYMER-BASED SEPARATIONS. III. METAL ION LOADING CAPACITIES OF REACTIVE POLYMERS WITH SPECIFIC RECOGNITION MECHANISMS

The metal ion selectivity series displayed by a reactive polymer, the phosphinic acid ion exchange/redox resin, was determined from equinormal solutions of 1 milliequivalent metal ion per milliequivalent of polymer ligand sites and compared to results from trace ion solutions. It was found that intervention by the recognition mechanism (i.e., reduction) with Hg(II) and Ag(I) ions from pH 2 aqueous solutions led to high resin loading capacities. Thus, the phosphinic resin/Hg(II) interaction displayed a log D of 3.88, compared to 3.80 from a 10^-4 N solution, indicating that the recognition mechanism obviated any influence of a loading effect. The loading effect was apparent in Fe(III) complexatign wherein a log D of 4.94 was found from a 10^-4 N solution and 0.40 from the equinormal solution. The solution acidity was also an important determinant of selectivity: the series was Fe > Hg > Mn > Ag from 4N HNO₃ and Hg > Ag > Mn > Fe from 0.01N HN0₃. The performance of the phosphinic acid resin was contrasted to that from the non-reactive (i.e., solely ion exchanging) phosphonic acid resin.     

Oxidative absorption of hydrogen sulfide using an iron‐chelate based process: chelate degradation

BACKGROUND: Oxidative absorption of hydrogen sulfide into a solution of ferric chelates is studied in a stirred cell glass reactor. The experiments were performed to investigate the degradation of chelates sodium salt of nitrilotriacetic acid (NTA) (Merck), ethylenediaminetetraacetic acid diadisodium salt (EDTA) and diethylenetriaminepentaacetic acid (DTPA) at 313 K, pH 6, iron concentration 10 000 g L^?1 and Fe:chelate molar ratio 1:2. RESULTS: Oxidative absorption of hydrogen sulfide into a solution of Fe‐NTA was found to be more successful, therefore, further experiments with 10%, 50% and 100% concentrations of hydrogen sulfide were performed. It was shown that this process is applicable for removal of low and high concentrations of hydrogen sulfide. The effect of antioxidants using sodium thiosulfate was also studied in order to minimize degradation of NTA. The kinetics were studied and it was observed that the reaction appeared to be first order in ferric chelate with rate constants for 100, 50 and 10% hydrogen sulfide concentration: 0.035, 0.013 and 0.019 h^?1, respectively. CONCLUSIONS: Gas sweetening processes have commercial importance in natural gases, refinery of gases and biogas processing. Desulphurization and cleaning (i.e. removal of H₂S and CO₂) of petroleum gas and biogas is important to make the gas methane rich and to increase the calorific value of fuel. The same techniques of desulphurization and cleaning can be used for treating natural gas or petroleum gas. The desulphurization and cleaning processes can minimize the atmospheric emission of gases like SOx, NOx and CO. As the iron chelate based process is based on the principle of redox reaction of metal chelate with hydrogen sulfide, this method is very useful for desulphurization of petroleum gas and biogas. This work studied the effective use of Fe‐NTA solution for removal of high to low concentrations of H₂S as found in biogas and industrial waste gases. © 2012 Society of Chemical Industry