Initial Fe Concentration Research Articles

Oxidation of sulphide in abandoned mine tailings by ferrate

In this study, Fe(VI) was applied to treat three mine tailings containing different amounts of sulphides and heavy metals. Oxidation of sulphides by Fe(VI) was studied at pH 9.2 with variation of solid to solution ratio, Fe(VI) concentration and injection number of Fe(VI) solution. The major dissolved products from the treatment of mine tailings with Fe(VI) solution were sulphate and arsenic. Oxidation efficiency of sulphides was evaluated by reduction efficiency of Fe(VI) as well as by measurement of dissolved sulphate concentration. Even though inorganic composition of three mine tailings was different, reduction fraction of Fe(VI) was quite similar. This result can suggest that Fe(VI) was involved in several other reactions in addition to oxidation of sulphides. Oxidation of sulphides in mine tailing was greatly dependent on the total amount of sulphides as well as kinds of sulphides complexed with metals. Over the five consecutive injections of Fe(VI) solution, dissolved sulphate concentration was greatly decreased by each injection and no more dissolved sulphate was observed at the fifth injection. While dissolved arsenic was decreased lineally up to the fifth injection. Sulphate generation was slightly increased for all mine tailings as Fe(VI) concentration was increased; however, enhancement of oxidation efficiency of sulphides was not directly proportional to the initial Fe(VI) concentration.

Disintegration of waste activated sludge by different applications of Fenton process

Oxidative disintegration of municipal waste activated sludge (WAS) using conventional Fenton (Fe2++H2O2, CFP) and Fenton type (Fe0+H2O2, FTP) processes was investigated and compared in terms of the efficiency of sludge disintegration and enhancement of anaerobic biodegradability. The influences of different operational variables namely sludge pH, initial concentration of Fe2+ or Fe0, and H2O2 were studied in detail. The optimum conditions have been found as catalyst iron dosage=4g/kg TS, H2O2 dosage=40g/kg TS and pH=3 within 1h oxidation period for both CFP and FTP. Kinetics studies were performed under optimal conditions. It was determined that the sludge disintegration was happened in two stages by both processes: rapid and subsequent slow disintegration stages and rapid sludge disintegration stage can be described by a zero-order kinetic model. The effects of oxidative sludge disintegration under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential (BMP) assay in batch anaerobic reactors. Total methane production in the CFP and FTP pre-treated reactors increased by 26.9% and 38.0%, relative to the untreated reactor (digested the raw WAS). Furthermore, the total chemical oxygen demand reductions in the pre-treated reactors were improved as well.

In situ precipitation: a novel approach for preparation of iron-oxide magnetoliposomes.

BackgroundConventional methods of preparing magnetoliposomes are complicated and inefficient. A novel approach for magnetoliposomes preparation was investigated in the study reported here.MethodsFeCl3/FeCl2 solutions were hydrated with lipid films to obtain liposome-encapsulated iron ions by ultrasonic dispersion. Non-encapsulated iron ions were removed by dialysis. NH3 · H2O was added to the system to adjust the pH to a critical value. Four different systems were prepared. Each was incubated at a different temperature for a different length of time to facilitate the permeation of NH3 · H2O into the inner phase of the liposomes and the in situ formation of magnetic iron-oxide cores in the liposomes. Single-factor analysis and orthogonal-design experiments were applied to determinate the effects of alkalization pH, temperature, duration, and initial Fe concentration on encapsulation efficiency and drug loading.ResultsThe magnetoliposomes prepared by in situ precipitation had an average particle size of 168±14 nm, zeta potential of −26.2±1.9 mV and polydispersity index of 0.23±0.06. The iron-oxide cores were confirmed as Fe3O4 by X-ray diffraction and demonstrated a superparamagnetic response. Encapsulation efficiency ranged from 3% to 22%, while drug loading ranged from 0.2 to 1.58 mol Fe/mol lipid. The optimal conditions for in situ precipitation were found to be an alkalization pH of 12, temperature of 60°C, time of 60 minutes, and initial Fe concentration of 100 mM Fe3+ + 50 mM Fe2+.ConclusionIn situ precipitation could be a simple and efficient approach for the preparation of iron-oxide magnetoliposomes.

Effects of Ni, Fe chemicals and hydrogen on deposits formed on Zirlo fuel cladding material in nuclear primary water chemistry conditions at 325 °C

The morphology and amount of deposits formed on the surface of a Zirlo fuel cladding material were investigated in terms of the concentration of Ni, Fe chemicals and hydrogen after testing using a test loop simulating an AOA, since these deposits can have an influence on an AOA. Porous deposits with some needle-like whiskers were observed after testing in a solution containing 3.5ppm Li as LiOH and 1500ppm B as H3BO3. Ni and Fe acetates were added for this test intermittently to increase the deposits formed on the surface of the fuel cladding material. The pore sizes are from 0.1 to 0.3μm. To minimize the pH change during the tests, Ni EDTA and Fe EDTA were used in the same solution instead of Ni and Fe acetates. Polyhedral structures were found, when both of Ni EDTA and Fe EDTA coexist significantly. These polyhedral structures are nickel ferrites analyzed by SEM–EDS. A number of whiskers with about a 0.05μm diameter were detected, when the ratio of Ni/Fe increased due to decrease of Fe concentration during the test, even though the initial Fe concentration was high. However, some short whiskers are formed, when initial Ni concentration was high. These whiskers seem to be NiO by SEM–EDS. It was reported that the formation of fine whiskers might be one of the major causes for an AOA in connection with SNB. These whiskers were observed, when the hydrogen concentrations were 5 and 25cc/kg H2O in the test conditions at 325°C. No whiskers were found in the conditions at above 25cc H2/kg H2O. In addition, it was found that the concentration of hydrogen does not greatly affect the amount of deposit formed on the surface during testing.

Characterization of the physiology and cell-mineral interactions of the marine anoxygenic phototrophic Fe(II) oxidizerRhodovulum iodosum- implications for Precambrian Fe(II) oxidation

Anoxygenic phototrophic Fe(II)-oxidizing bacteria (photoferrotrophs) are suggested to have contributed to the deposition of banded iron formations (BIFs) from oxygen-poor seawater. However, most studies evaluating the contribution of photoferrotrophs to Precambrian Fe(II) oxidation have used freshwater and not marine strains. Therefore, we investigated the physiology and mineral products of Fe(II) oxidation by the marine photoferrotroph Rhodovulum iodosum. Poorly crystalline Fe(III) minerals formed initially and transformed to more crystalline goethite over time. During Fe(II) oxidation, cell surfaces were largely free of minerals. Instead, the minerals were co-localized with EPS suggesting that EPS plays a critical role in preventing cell encrustation, likely by binding Fe(III) and directing precipitation away from cell surfaces. Fe(II) oxidation rates increased with increasing initial Fe(II) concentration (0.43-4.07 mM) under a light intensity of 12 μmol quanta m(-2) s(-1). Rates also increased as light intensity increased (from 3 to 20 μmol quanta m(-2) s(-1)), while the addition of Si did not significantly change Fe(II) oxidation rates. These results elaborate on how the physical and chemical conditions present in the Precambrian ocean controlled the activity of marine photoferrotrophs and confirm the possibility that such microorganisms could have oxidized Fe(II), generating the primary Fe(III) minerals that were then deposited to some Precambrian BIFs.

Kinetics of Fe<sup>2+</sup> Oxidization at Different Initial Fe<sup>2+</sup> and Fe<sup>3+</sup> Concentration in the Presence of Moderate Thermophilic Bacteria

In the bacterial leaching, the oxidation of Fe2+ is very important process. According to the results of this paper, Fe2+ and Fe3+ concentration effect on the growth of moderate thermophile. The optimum conditions for growth of moderate thermophile are the initial concentration of Fe2+ at 0.16mol/l. It indicates the existence of the optimum conditions including initial concentrations of Fe2+ and Fe3+ for the bio-oxidation Fe2+. To increase the initial concentration of Fe3+ can enhance the oxidation rate of Fe2+. The dynamic model of the moderate thermophile oxidation Fe2+ has been established by analyzing and calculating test data with the Matlab software.

Anaerobic Nitrate-Dependent Iron (II) Oxidation by a Novel Autotrophic Bacterium, Citrobacter freundii Strain PXL1

Anaerobic Fe(II) Oxidizing Denitrifiers (AFODN), a type of newly found Fe(II)-oxidizing bacteria, play an important role in iron and nitrogen cycling. In the present study, a novel AFODN strain PXL1 was isolated from anaerobic activated sludge. Phylogenetic analysis of 16S rRNA gene sequence revealed similarity between this strain and Citrobactor freundii. The strain reduced 30% of nitrate and oxidized 85% of Fe(II) over 72 h with an initial Fe(II) concentration of 3.4 mM and nitrate concentration of 9.5 mM. Oxidation of iron was dependent on the reduction of nitrate to nitrite in the absence of other electron donors or acceptors. Nitrate reduction and Fe(II) oxidation followed first-order reaction kinetics. Iron oxides accumulated in the culture were analyzed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The strain recovered deposited oxidized Fe in the form of amorphous Fe oxides.

Photo-Fenton degradation of phenol, 2,4-dichlorophenoxyacetic acid and 2,4-dichlorophenol mixture in saline solution using a falling-film solar reactor

In this work, a saline aqueous solution of phenol, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4-dichlorophenol (2,4-DCP) was treated by the photo-Fenton process in a falling-film solar reactor. The influence of the parameters such as initial pH (5–7), initial concentration of Fe2+ (1–2.5 mM) and rate of H2O2 addition (1.87–3.74 mmol min−1) was investigated. The efficiency of photodegradation was determined from the removal of dissolved organic carbon (DOC), described by the species degradation of phenol, 2,4-D and 2,4-DCP. Response surface methodology was employed to assess the effects of the variables investigated, i.e. [Fe2+], [H2O2] and pH, in the photo-Fenton process with solar irradiation. The results reveal that the variables’ initial concentration of Fe2+ and H2O2 presents predominant effect on pollutants’ degradation in terms of DOC removal, while pH showed no influence. Under the most adequate experimental conditions, about 85% DOC removal was obtained in 180 min by using a reaction system employed here, and total removal of phenol, 2,4- and 2,4-DCP mixture in about 30 min.

Degradation of Ammonium butyl-dithiophosphate by Fe<sup>2+</sup>/NaClO Process

The initial pH, initial concentration of Fe2+and NaClO on the degradation of ammonium butyl-dithiophosphate using Fe2+/NaClO process have been investigated in this paper. The results shows that under the optimum reaction conditions of a temperature 28°C, pH 4.0, the initial concentration of Fe2+and NaClO is 15 mg/L and 5.33 mL/L, respectively, about 87.86% ammonium butyl-dithiophosphate removal can be achieved within 150 min by using a Fe2+/NaClO process. The degradation of ammonium butyl-dithiophosphate under different NaClO concentration conditions follows the first order exponential decay equations. The Fe2+/NaClO can efficiently oxidation of ammonium butyl-dithiophosphate in aqueous solution and can be an effective process for the treatment of ammonium butyl-dithiophosphate wastewater.

Comparative study of advanced oxidation for textile wastewater

ABSTRACT It was conducted to evaluate the efficiency for oxidations of a typical azo dye by advanced oxidation such as Fenton process and Fenton-like process. The ratio parameters affecting the decolorization efficiency of C.I. Basic Red 22 such as initial concentration of Fe2+, Fe3+ and H2O2, initial pH of dye solution, and reaction temperature were investigated. The results showed that the decolorization efficiency of C.I. Basic Red 22 in Fenton oxidation was much higher than that of the Fenton-like oxidation in the initial stages and the decolorization efficiency was similar but trends to the similar level for both systems after 45 min. For the two oxidation systems, the decolorization efficiency of C.I. Basic Red 22 depended on [Dye]0, [Fe2+]0 or [Fe3+]0, [H2O2]0, pH, and temperature.

A Discussion on the Influence Mechanism of Iron to Algal Blooms in Natural Raw Water

Through designing orthogonal tests, the influence mechanism of iron to the growth of fresh water algae was studied. The results indicated that the initial Fe concentration of 0.3mg/L or above can lead to high algae relative growth rate while the initial Fe concentration under 0.3mg/L can only generate low algae relative growth rate. The consumption of iron in Group LNLP under low initial Fe concentration and Group HNHP under high initial Fe concentration was in synchronism with the consumption of nitrogen and phosphorus. However, in Group HNHP under low initial Fe concentration and Group LNLP under high initial Fe concentration the concentration of iron decreased with the increase of algal biomass before reaching the peak value of algal biomass and it increased after reaching the peak value in contrary. Among all those 25 groups the order of the peak value of algal biomass from big to small is as follows:All-rich Group>Nitrogen-lacked Group>Phosphorus-lacked Group>Iron-lacked Group>All-lacked Group. The lack of Fe content will restrain the growth of algae. In certain concentration rage algal biomass increased with the increasing of Fe content while Fe content will restrain the growth of algae in contrary if beyond the concentration rage.

Longitudinal measurements of exhaled nitric oxide in children–what is a significant change in FENO?

The principle aim of this study was to describe the variability of exhaled nitric oxide (FE(NO)) concentrations over 10 months in children with and without asthma. FE(NO) was measured on six occasions at 2-month intervals in a community-based cohort of children with and without asthma. There were 178 children recruited, 47 had asthma, mean age 9.6 yr. A total of 851 FE(NO) measurements were made. The change in FE(NO) values was positively associated with the initial FE(NO) concentration (p < 0.001) and duration between paired measurements (p = 0.016) but not asthma diagnosis; there was an interaction between initial FE(NO) and duration between measurements. As an approximate rule-of-thumb, a child's FE(NO) may rise by up to 100% of their current FE(NO) over 2 and 4 months, independent of asthma. Both the baseline FE(NO) and interval between repeated FE(NO) measurements are relevant to FE(NO) values, independent of asthma. These findings may be useful to clinical interpretation of FE(NO) results in children.

Kinetic of C.I. Reactive Black 5 by Fenton-Like Oxidation

The decolorization kinetic of C.I. Reactive Black 5 was studied using Fenton-like oxidation. The effect of the major system parameters, such as initial pH of the solution, concentration of H2O2, concentration of Fe3+ and reaction temperature on the kinetics was determined. The results indicate that the operating parameters, such as initial pH of dye solution, initial concentration of Fe2+ and H2O2, reaction temperature, have strong influences on the degradation of C.I. Reactive Black 5 by Fenton-like oxidation process. In addition, it was also found that the decolorization of C.I. Reactive Black 5 followed the first-order kinetics well.

Coordination of Polyacrylic Grafted Polytetrafluoroethylene Fiber with Fe (III) Ions in Aqueous Solution

The grafted polytetrafluoroethylene (PTFE) fibers were prepared with acrylic acid and then coordinated with Fe (III) ions. The effect of initial Fe (III) ion concentration and temperature on coordination process was investigated. In addition, the kinetics of the coordination process was also evaluated. The results indicated that increasing initial Fe (III) concentration and temperature significantly improve the amount of Fe (III) ions coordinated onto the fiber. The coordination between them can be described by Langmuir and Freundlich isotherm equations. On the other hand, coordinating process also follows a pseudo-second order model. Moreover, a higher initial Fe (III) ion concentration gives rise to an enhanced initial Fe (III) ion coordination rate.

Dechlorination of liquid wastes containing chlorinated hydrocarbons by a binder mixture of cement and slag with Fe(II)

Iron-based degradative solidification/stabilization (DS/S-Fe(II)) is a modification of conventional solidification/stabilization (S/S) that incorporates degradative processes for organic contaminant destruction with immobilization. This study investigated the effectiveness of a binder mixture of Portland cement and slag in a DS/S-Fe(II) system to treat trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride (VC), trichloromethane (CF), and dichloromethane (MC), which are major chlorinated hydrocarbons contained in waste oils and waste organic solvents. For TCE, 1,1-DCE, and VC, degradation experiments were conducted using three different binder combinations with Fe(II) (cement/Fe(II), slag/Fe(II), and cement/slag/Fe(II)). When cement and slag were mixed at a 1:1 ratio (% wt), the TCE and 1,1-DCE dechlorination rate was enhanced compared to that when cement or slag was used alone with Fe(II). Also, batch experiments were conducted in the solid phase consisting of cement, slag, sand, and Fe(II) to treat liquid wastes that contain chlorinated compounds at high concentrations. TCE was completely removed after 5days in the cement/slag/sand/Fe(II) system, in which the initial TCE concentration was 11.8mM, with Fe(II) concentration of 565mM. While the CF concentration was decreased by 95% after 5days when the initial CF and Fe(II) concentration was 0.25mM and 200mM, respectively. However, MC was not degraded with the cement/slag/Fe(II) system.

Degradation of bisphenol A in aqueous solution by persulfate activated with ferrous ion

Degradation of bisphenol A (BPA) in aqueous solution was studied with high-efficiency sulfate radical (SO4(-·)), which was generated by the activation of persulfate (S2O8(2-)) with ferrous ion (Fe(2+)). S2O8(2-) was activated by Fe(2+) to produce SO4(-·), and iron powder (Fe(0)) was used as a slow-releasing source of dissolved Fe(2+). The major oxidation products of BPA were determined by liquid chromatography-mass spectrometer. The mineralization efficiency of BPA was monitored by total organic carbon (TOC) analyzer. BPA removal efficiency was improved by the increase of initial S2O8(2-) or Fe(2+) concentrations and then decreased with excess Fe(2+) concentration. The adding mode of Fe(2+) had significant impact on BPA degradation and mineralization. BPA removal rates increased from 49 to 97% with sequential addition of Fe(2+), while complete degradation was observed with continuous diffusion of Fe(2+), and the latter achieved higher TOC removal rate. When Fe(0) was employed as a slow-releasing source of dissolved Fe(2+), 100% of BPA degradation efficiency was achieved, and the highest removal rate of TOC (85%) was obtained within 2 h. In the Fe(0)-S2O8(2-) system, Fe(0) as the activator of S2O8(2-) could offer sustainable oxidation for BPA, and higher TOC removal rate was achieved. It was proved that Fe(0)-S2O8(2-) system has perspective for future works.

Photocatalytic Reduction of Hexavalent Chromium Induced by Photolysis of Ferric/tartrate Complex

Photocatalytic reduction of hexavalent chromium (Cr(VI)) in ferric-tartrate system under irradiation of visible light was investigated. Effects of light resources, initial pH value and initial concentration of various reactants on Cr(VI) photocatalytic reduction were studied. Photoreaction kinetics was discussed and a possible photochemical pathway was proposed. The results indicate that Fe(III)-tartrate system is able to rapidly and effectively photocatalytically reduce Cr(VI) utilizing visible light. Initial pH variations resulte in the concentration changes of Fe(III)-tartrate complex in this system, and pH at 3.0 is optimal for Cr(VI) photocatalytic reduction. Efficiency of Cr(VI) photocatalytic reduction increases with increasing initial concentrations of Cr(VI), Fe(III) and tartrate. Kinetics analysis indicates that initial Fe(III) concentration affects Cr(VI) photoreduction most significantly.

A novel sequential process of bioleaching and chemical leaching for dissolving Ni, V, and Mo from spent petroleum refinery catalyst

Two step leaching experiments were carried out to extract nickel, vanadium, and molybdenum present in spent refinery catalyst. A bioleaching process was applied in the first step. Pulp density, initial Fe(II) concentration, initial pH, particle size, and temperature were varied to optimize the bioleaching process. Ni, V, and Mo were leached out with maximum recoveries of 97%, 92% and 53%, respectively, at an optimized bioleaching condition of initial ferrous ion of 2g/L, initial pH of 2, pulp density of 10% (w/v), particle size of (−106+45) μm, and a temperature of 35°C. As the Mo leaching rate was very low, a second leaching step for the bioleached residue was applied with different concentrations of (NH4)2CO3, Na2CO3, or H2SO4. The second step leaching was optimum at a concentration of 30g/L (NH4)2CO3 with respect to Mo extraction. The rate of Mo dissolution with respect to concentration of lixiviant in the second leaching step was evaluated. The percentages of Ni, V, and Mo leached were 97%, 97% and 99%, respectively, by combining the first step under optimized conditions and the second step with 30g/L (NH4)2CO3.

Simultaneous oxidation and immobilization of arsenite from refinery waste water by thermoacidophilic iron-oxidizing archaeon, Acidianus brierleyi

The use of a thermophilic acidophilic iron-oxidizing archaeon, Acidianus brierleyi, was investigated for oxidation and immobilization of As(III) from acidic refinery waste water. Some As(III) oxidation was measured in all Ac. brierleyi cultures independently of the presence or concentration of Fe(II) in bulk solution; the exception was at initial Fe(II) concentration ([Fe(II)]ini) of 1000mgl−1 where As(III) oxidation became markedly facilitated and consequently approximately 70% of As was immobilized as amorphous ferric arsenate. Providing 1000mgl−1 Fe(III) instead of Fe(II) did not show the same effect, implying the importance of Fe(III) be microbially-produced and complexed in the archaeal EPS (extracellular polymeric substances) region for effective As(III) oxidation. The reaction towards secondary mineral formation shifted from ferric arsenate to jarosite at [Fe(II)]ini of >1000mgl−1. Furthermore addition of jarosite seed crystals retarded the As(III) oxidation rate at [Fe(II)]ini of 1000mgl−1. The observations indicate that by setting the appropriate bulk Fe(II)/As(III) ratio in Ac. brierleyi culture to achieve a certain concentration of Fe(III) within the EPS region, but at the same time to avoid jarosite formation, it is possible to maximize the As(III) oxidation rate and thus As immobilization efficiency. This study describes for the first time microbially-mediated simultaneous oxidation and immobilization of As(III) as ferric arsenate, using a thermoacidophilic iron-oxidizing archaeon, Ac. brierleyi.

Fenton Oxidation of Methyl Violet in Aqueous Solution

In this study, oxidative discoloration of methyl violet (MV) dye in aqueous solution has been studied using Fenton (Fe2+/H2O2) process. The parameters such as concentration of Fe2+, H2O2, MV, temperature, and Cl− and ions that affected of discoloration in Fenton process were investigated. The rate of degradation is dependent on initial concentration of Fe2+ ion, initial concentration of H2O2, and pH of media. Discoloration of MV was increased by increasing the temperature of reaction. Optimized condition was determined and it was found that the obtained efficiency was about 95.5% after 15 minutes of reaction at pH 3. TOC of dye sample, before and after the oxidation process, was determined. TOC removal indicates partial and significant mineralization of MV dye. The results of experiments showed that degradation of MV dye in Fenton oxidation can be described with a pseudo‐irst‐order kinetic model. The thermodynamic constants of the Fenton oxidation process were evaluated. The results implied that the oxidation process was feasible, spontaneous, and endothermic.