Initial Fe Concentration Research Articles

Ozonation of Phenol with O3/Fe(II) in Acidic Environment in a Rotating Packed Bed

The treatment of acidic phenolic wastewater by ferrous-catalyzed ozonation (O3/Fe(II)) process in a rotating packed bed (RPB) was studied, and the O3/Fe(II) process was compared with the O3 process. It was observed that the phenol degradation rate in the O3/Fe(II) process was roughly 10% higher than that of O3 process in acidic environment in the RPB. It is also found that the degradation efficiency of phenol was significantly affected by the rotation speed and inlet ozone concentration. Phenol degradation efficiency increased with increasing initial pH of the phenolic solution, rotation speed, and concentrations of the inlet ozone gas, as well as a decreasing liquid flow rate and initial concentrations of phenol. Phenol degradation efficiency reached maximum at a temperature of 25 °C and an initial Fe(II) concentration of 0.4 mM. The result of the contrast experiment showed that the biological oxygen demand/chemical oxygen demand (BOD/COD) of the phenol solution increased from 0.2 to 0.59 after the solut...

Photo-Fenton oxidation of phenol and organochlorides (2,4-DCP and 2,4-D) in aqueous alkaline medium with high chloride concentration

A highly concentrated aqueous saline-containing 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 system composed of an annular reactor with a quartz immersion well and a medium-pressure mercury lamp (450 W). The study was conducted under special conditions to minimize the costs of acidification and neutralization, which are usual steps in this type of process. Photochemical reactions were carried out to investigate the influence of some process variables such as the initial concentration of Fe2+ ([Fe2+]0) from 1.0 up to 2.5 mM, the rate in mmol of H2O2 fed into the system (FH2O2,in) from 3.67 up to 7.33 mmol of H2O2/min during 120 min of reaction time, and the initial pH (pH0) from 3.0 up to 9.0 in the presence and absence of NaCl (60.0 g/L). Although the optimum pH for the photo-Fenton process is about 3.0, this particular system performed well in experimental conditions starting at alkaline and neutral pH. The results obtained here are promising for industrial applications, particularly in view of the high concentration of chloride, a known hydroxyl radical scavenger and the main oxidant present in photo-Fenton processes.

Both initial concentrations of Fe(II) and monovalent cations jointly determine the formation of biogenic iron hydroxysulfate precipitates in acidic sulfate-rich environments

In order to accurately predict the types of biogenic iron hydroxysulfate precipitates in acidic, sulfate-rich environments facilitated by Acidithiobacillus ferrooxidans, different initial concentrations of Fe2+, K+, Na+, and NH4+ are selected and tested in batch experiments for the formation of the precipitates. The critical equations of jarosite formation in FeSO4–K2SO4–H2O system or FeSO4–(NH4)2SO4–H2O system could be described as Y=−22120.8077−0.04257x+0.006170x2 (R2=0.9979) or Y=0.03540−0.002950x+7.407E−5x2 (R2=0.9934), respectively, where Y is the threshold or critical values of the molar ratio of Fe/K or Fe/NH4 for jarosite formation, and x (mmol/L) is the initial concentration of Fe(II). Schwertmannite is the sole biogenic secondary ferric mineral when molar ratio of Fe/K or Fe/NH4 is higher than Y in the system with a given initial Fe(II) concentration. The precipitates are an admixture of schwertmannite and jarosite, or pure jarosite when the Fe/M molar ratio is lower than Y. The crystallinity of the secondary ferric minerals increased with the increase of initial Fe(II) concentration in the medium with a fixed K+ concentration. It is observed that the capacity of monovalent cation in promoting jarosite formation is K+>NH4+>Na+, as exhibiting that the capacity of K+ in this process is about 75 and 200 times greater than NH4+ and Na+, respectively. Obviously, both the initial concentration of Fe(II) and molar ratio of Fe to monovalent cation determine the types of biogenic iron hydroxysulfate precipitates.

Effect of fertilization with Fe chelates on the state of iron nutrition of greenhouse tomato

A greenhouse experiment aimed at investigating the effect of four chelates, differing in percentage of Fe content and the kind of Fe bonding ligand: Fe 8 Forte (EDTA+ +HEEDTA), Fe 9 Premium (DTPA), Fe 13 Top (EDTA) and Librel Fe DP7 (DTPA), on the state of iron nutrition of Merkury F 1 cultivar greenhouse tomato grown traditionally in peat substrate. The second factor was iron content in the growing medium, which was established to reach the following levels: 50, 75 and 100 mg Fe⋅dm -3 , while in the control object Fe values ranged 17.9 Fe⋅dm -3 (after peat liming). The experiment was established in a two-factorial design with three replications including four plants cultivated on one plot. The iron content was assayed in plant index parts according to the ASA method. On the basis of the results, significant differences were found in the state of greenhouse tomato nutrition under the influence of the examined iron chelates. The highest content of iron in tomato leaves was determined when chelate Fe 9 Premium (DTPA) was used, which points to the fact that it was the best source of Fe. The lowest iron level was recorded after the application of Fe 13 Top (EDTA). The highest mean Fe content for the years and dates of analyses appeared in leaves of plants cultivated in the growing medium containing 75 mg Fe⋅dm -3 . In June, after the plants began to yield, there was a considerable decrease in the Fe content in plant index parts in comparison to the stage of fruit maturation and the end of yielding. The study did not demonstrate any symptoms of phytotoxicity or visible disorders regarding tomato growth and development due to the examined Fe chelates introduced in the doses of 32.1, 57.1 and 82.1 mg Fe⋅dm -3 to the substrate, whose initial Fe concentration after peat liming was on average 17.9 mg Fe⋅dm -3 .

Controlled synthesis of superparamagnetic iron-oxide nanoparticles by phase transformation

A synthesis procedure for generating a uniform distribution of iron-oxide nanoparticles from an amorphous precursor is reported. The investigation suggests no evidence of the formation of unwanted surface oxide layers, internal stress, and multiple phases. This is likely because the physical properties of the diffusion fields surrounding the nanoparticles are self-limiting by Fe(II) depletion. Inside the diffusion field surrounding the nucleation site, decreasing Fe(II) concentration results in a decrease in the diffusion rate that continues to decrease until self-limiting kinetic arrest occurs. The initial Fe(II) concentration is established by reducing a system abundant in Fe(III) by means of exposure to CO/CO2 gas at high temperature.

Efficient Degradation of TCE in Groundwater Using Pd and Electro-generated H2 and O2: A Shift in Pathway from Hydrodechlorination to Oxidation in the Presence of Ferrous Ions

Degradation of trichloroethylene (TCE) in simulated groundwater by Pd and electro-generated H(2) and O(2) is investigated in the absence and presence of Fe(II). In the absence of Fe(II), hydrodechlorination dominates TCE degradation, with accumulation of H(2)O(2) up to 17 mg/L. Under weak acidity, low concentrations of oxidizing •OH radicals are detected due to decomposition of H(2)O(2), slightly contributing to TCE degradation via oxidation. In the presence of Fe(II), the degradation efficiency of TCE at 396 μM improves to 94.9% within 80 min. The product distribution proves that the degradation pathway shifts from 79% hydrodechlorination in the absence of Fe(II) to 84% •OH oxidation in the presence of Fe(II). TCE degradation follows zeroth-order kinetics with rate constants increasing from 2.0 to 4.6 μM/min with increasing initial Fe(II) concentration from 0 to 27.3 mg/L at pH 4. A good correlation between TCE degradation rate constants and •OH generation rate constants confirms that •OH is the predominant reactive species for TCE oxidation. Presence of 10 mM Na(2)SO(4), NaCl, NaNO(3), NaHCO(3), K(2)SO(4), CaSO(4), and MgSO(4) does not significantly influence degradation, but sulfite and sulfide greatly enhance and slightly suppress degradation, respectively. A novel Pd-based electrochemical process is proposed for groundwater remediation.

Communities of neutrophilic iron-oxidizing microorganisms of ferruginous springs of various types and their involvement in fractionation of stable iron isotopes

Abundance and structure of the communities of neutrophilic lithotrophic iron-oxidizing bacteria (FeOB) inhabiting four low-mineralized ferruginous springs of the Marcial Waters Resort (South Karelia, Russia) and the brackish chalybeate spring of the Staraya Russa Resort (Novgorod region, Russia), were investigated, as well as the physicochemical conditions of these environments. In fresh iron-containing precipitates collected near the spring outlets and within the spring-discharge areas, as well as along the spring watercourses, the numbers of unicellular FeOB enumerated on nutrient media ranged from 105 to 107 cells per 1 mL of sediments irrespective of the initial Fe(II) concentration (11–126 mg L−1). In the spring waters and along the spring watercourses inhabited by iron-oxidizing bacteria, the concentration of dissolved oxygen did not exceed 0.05–0.1 mg L−1. Unicellular FeOB were predominant in three springs, while in the springs with relatively low Fe(II) concentrations (11–22 mg L−1), various morphological forms of Gallionella and uncultured forms of the iron-oxidizing bacterium Toxothrix trichogenes prevailed. In the model experiments with the water samples collected in the ferruginous springs and bogs under controlled conditions, the fractionation of stable iron isotopes and the rate of iron oxidation were found to depend on the oxygen regime and, to a lesser extent, on the initial Fe(II) concentration. The maximum enrichment of the iron oxides formed during the simulation experiments with the light 54Fe isotope was observed during bacterial oxidation under microaerobic conditions at O2 concentrations of 0.1–0.3 mg L−1 and in the cultures of iron-oxidizing bacteria. During the abiogenic oxidation of Fe(II), the extent of stable isotope fractionation was 1.5–2 times lower. Enrichment of Fe(III) oxides with the light 54Fe isotope (3- to 5-fold) was considerably lower at high rates of both the biogenic and abiogenic processes of iron oxidation under aerobic conditions; however, it was more intense during the bacterial processes. Comparison of the rates of enrichment of Fe(III) oxides with the light isotope during the model experiments with pure and enrichment cultures of iron-oxidizing bacteria from the sediments of ferruginous springs and bogs revealed that the biogenic factor plays a key role in the oxidation processes of the iron cycle, as well as in the differentiation of the composition of stable iron isotopes in the studied ecosystems.

Ultrasmall superparamagnetic iron oxide (USPIO)-based liposomes as magnetic resonance imaging probes

BackgroundMagnetic liposomes (MLs) are phospholipid vesicles that encapsulate magnetic and/or paramagnetic nanoparticles. They are applied as contrast agents for magnetic resonance imaging (MRI). MLs have an advantage over free magnetic nanocores, in that various functional groups can be attached to the surface of liposomes for ligand-specific targeting. We have synthesized PEG-coated sterically-stabilized magnetic liposomes (sMLs) containing ultrasmall superparamagnetic iron oxides (USPIOs) with the aim of generating stable liposomal carriers equipped with a high payload of USPIOs for enhanced MRI contrast.MethodsRegarding iron oxide nanoparticles, we have applied two different commercially available surface-coated USPIOs; sMLs synthesized and loaded with USPIOs were compared in terms of magnetization and colloidal stability. The average diameter size, morphology, phospholipid membrane fluidity, and the iron content of the sMLs were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), fluorescence polarization, and absorption spectroscopy, respectively. A colorimetric assay using potassium thiocyanate (KSCN) was performed to evaluate the encapsulation efficiency (EE%) to express the amount of iron enclosed into a liposome. Subsequently, MRI measurements were carried out in vitro in agarose gel phantoms to evaluate the signal enhancement on T1- and T2-weighted sequences of sMLs. To monitor the biodistribution and the clearance of the particles over time in vivo, sMLs were injected in wild type mice.ResultsDLS revealed a mean particle diameter of sMLs in the range between 100 and 200 nm, as confirmed by TEM. An effective iron oxide loading was achieved just for one type of USPIO, with an EE% between 74% and 92%, depending on the initial Fe concentration (being higher for lower amounts of Fe). MRI measurements demonstrated the applicability of these nanostructures as MRI probes.ConclusionOur results show that the development of sMLs is strictly dependent on the physicochemical characteristics of the nanocores. Once established, sMLs can be further modified to enable noninvasive targeted molecular imaging.

Treatment of TFT-LCD wastewater containing ethanolamine by fluidized-bed Fenton technology

The objectives of this study are: (1) to determine the effect of pH, initial concentration of Fe2+ and H2O2 dosage on the removal efficiency of MEA by fluidized-bed Fenton process and Fenton process, (2) to determine the optimal conditions for the degradation of ethanolamine from TFT-LCD wastewater by fluidized-bed Fenton process. In the design of experiment, the Box–Behnken design was used to optimize the operating conditions. A removal efficiency of 98.9% for 5mM MEA was achieved after 2h under optimal conditions of pH3, [Fe2+]=5mM and [H2O2]=60mM.

Optimization of physicochemical parameters for bioleaching of sphalerite by Acidithiobacillus ferrooxidans using shaking bioreactors

Bioleaching processes for extraction of zinc from sphalerite are more environmentally friendly and consume less energy than conventional technologies but are as yet less economic. One necessary step towards arriving at a cost-effective sphalerite bioleaching process is the use of appropriate methodology for the optimization of pertinent factors in such processes. Previous studies on Zn bioleaching systems have reported a fairly wide range of values as the optimum level of relevant physicochemical parameters for Zn bioleaching processes. This is partly due to the different strains and Zn source type employed but another reason could be that important parameters in this process interact with each other. In order to shed more light on this matter, in the present work Response Surface Methodology was employed for the study and optimization of important factors in a sphalerite bioleaching process by Acidithiobacillus ferrooxidans using shaking bioreactors. The effect of change in the levels of temperature, pH, initial Fe(II) concentration and pulp density – in the range 30–36 °C, 1.4–2.0, 3–11 g L −1 and 4–6% wt/vol respectively – on the rate Zn bioleaching was studied using a Central Composite Design. The results showed a statistically significant effect of pH and pulp density – and to a lesser extent temperature and initial Fe(II) concentration – on the rate of bioleaching of Zn. A statistically significant interaction was found between pH and temperature, which means that the optimum values of these two parameters can only be correctly obtained through the use of factorial design of experiments. Additionally, the optimum level of temperature and pH was found to depend on the level of pulp density. This means that when employing shaking bioreactors for optimization of these parameters the level of pulp density should be carefully chosen. However, there was no statistically significant interaction between initial Fe(II) concentration and the other three factors studied.

Optimal performance assessment for a photo-Fenton degradation pilot plant driven by solar energy using artificial neural networks

Artificial neural networks (ANN) were proposed as a multivariate experimental design tool for monitoring a photo-Fenton treatment of wastewaters containing a synthetic mixture of pesticides. ANN and Nelder-Mead simplex methods were used to find out the optimum operating parameters of a photo-Fenton pilot plant. ANN was developed to predict the most important operating parameters (e.g., the total organic carbon and the initial mineralization kinetic rate constants of the reactions), which determine the photo-catalytic degradation efficiency in photo-Fenton processes. Experimental measurements of temperature, pH, hydrogen peroxide (H2O2) consumption, initial concentration of Fe2+, and the AE were used as input data for the ANN learning. A feed-forward with one hidden layer, a Levenberg–Marquardt learning algorithm, a hyperbolic tangent sigmoidal transfer function and a linear transfer function were used to develop the ANN model. The best fitting of the training database was obtained with an ANN architecture constituted by seven neurons in the hidden layer. The simulated results were validated with experimental measurements, showing an acceptable agreement (R2 > 0.99). The ANN was subsequently coupled with a Nelder–Mead simplex method to obtain the optimum operating parameters of the photo-Fenton pilot plant. The H2O2 consumption was used as key variable for evaluating the optimization procedure. Errors less than 1% between simulated and experimental data were found. The obtained results showed that the use of ANN provides an excellent predictive performance tool with the additional capability to assess the influence of each operating parameter on the removal process of water pollutants. Copyright © 2011 John Wiley & Sons, Ltd.

Iron Uptake Kinetics and Magnetosome Formation by Magnetospirillum gryphiswaldense as a Function of pH, Temperature and Dissolved Iron Availability

The dynamics of iron uptake and magnetosome formation by the magnetotactic bacteria (MTB) Magnetospirillum gryphiswaldense was investigated at a broad range of pH, temperature and iron availability to evaluate the role of MTB in the iron biogeochemical cycle. Except at pH 5.0, all incubations have shown significant bacterial growth. However, magnetosome formation was limited at pH 8.0 and 9.0 as well as at 4°C, 10°C and 35°C. At optimal conditions (i.e., pH 7 and 28°C), the uptake rates of dissolved Fe(III) as a function of initial Fe concentration can be described by a Michaelis-Menten-type kinetic model with a maximum iron uptake rate, Vmax ,, of 11 × 10−12 μmoles cell−1 h−1 and an affinity constant, Ks of 26 μM Fe. High resolution imaging of magnetosomes synthesized at the different pH values, revealed a large range of morphologies and sizes, which illustrate the impact of environmental conditions on the formation of magnetite crystals by MTB.

Iron redox cycling in hydroxyl radical generation during the photo-Fenton oxidative degradation: Dynamic change of hydroxyl radical concentration

Effects of Fenton reagents, iron and hydrogen peroxide, on the generation of hydroxyl radicals (OH) during photo-Fenton degradation of acetaldehyde dissolved in water were examined. The dynamic change in OH radical concentration during the acetaldehyde degradation by the photo-Fenton process was measured using a coumarin fluorescence probing technique. The OH radical concentrations increased with increasing initial Fe concentrations within the Fe dosage range examined in this study. With increasing acetaldehyde loading the OH radical concentration decreased. The OH radical concentration changed rather complicatedly as the acetaldehyde degradation by the photo-Fenton oxidation process proceeded. The dynamic change in OH radical concentration could be divided into four phases: the OH radical concentration instantaneously and significantly increased just after the start of photo-Fenton oxidation process (Phase I), subsequently decreased (Phase II), increased again after reaching its minimum value (Phase III), and gradually decreased after the OH radical concentration reached a maximum point (Phase IV). This complicated change in OH radical concentration during photo-Fenton degradation of acetaldehyde could be rationally described by the Fe-redox cycle via the Fe–organic complex formation and its oxidation by dissolved oxygen besides the Fenton and photo-Fenton reactions. It was found that the oxidation of iron–organic complexes formed by ferric iron with acetaldehyde and its degradation products accelerated the rate of Fe-redox cycle. On the other hand, the formation of Fe–organic complexes led the decrease in Fe ions available for the Fenton and photo-Fenton reactions.

Study on ion exchange property of removing Mn2+ and Fe2+ in groundwater by modified zeolite

This study selects two types of modified zeolites used as the ion exchanger to treat the groundwater for removing Fe2+ and Mn2+, the column experiments of modified zeolites are conducted, the performance of ion exchange and regeneration of modified zeolites are investigated, and the operation parameters and regeneration conditions are established. The results illustrate that the modified zeolites have excellent performance on removal of Fe2+ and Mn2+, the effluent of modified zeolites contains 8 × 10–3 mg/l Fe2+ and no content of Mn2+. The flow rate and initial concentration of Fe2+ and Mn2+ affect the effective cation exchange capacity of modified zeolites. The flow rate has no obvious impact on the performance of modified zeolite for removing Fe2+ and effects sharply the performance of modified zeolite for removing Mn2+, the flow rate is 30 m/h for modified zeolite for removing Fe2+ and 20 m/h for modified zeolite for removing Mn2+. And solution concentration influences the effective capacity of both of the modified zeolites. The cation exchange capacity of zeolite regeneration by sodium chloride (NaCl) is twice times than hydrochloric acid (HCl) for removing Fe2+ and NaCl is also regeneration agent for zeolite for removing Mn2+. The dosage of NaCl solution for regeneration of zeolite to remove Fe2+ is 0.92 l/(mol/l) and the ratio of dosage of NaCl and the effective capacity is 17.1, the dosage of NaCl solution for regeneration of zeolite to remove Mn2+ is 0.92 l/(mol/l) and the ratio of dosage of NaCl and the effective capacity is 19.9, respectively.

Bioleaching of metal concentrates of waste printed circuit boards by mixed culture of acidophilic bacteria

Metal concentrates of printed circuit boards (PCBs) are the residue valuable metals from which non-metallic components are removed. The non-metallic components show bacterial toxicity in bioleaching process and can be recycled as well. In this study, the effects of initial pH, initial Fe(II) concentration, metal concentrate dosage, particle size, and inoculation quantity on the bioleaching were investigated so as to determine the optimum conditions and evaluate the feasibility of bioleaching of metal concentrates of PCBs by mixed culture of acidophilic bacteria (MCAB). The results showed that the initial pH and Fe(II) concentration played an important role in copper extraction and precipitate formation. Under the optimized conditions of initial pH 2.00, 12 g/L initial Fe(II), 12 g/L metal concentrate dosage, 10% inoculation quantity, and 60–80 mesh particle size, 96.8% the copper leaching efficiency was achieved in 45 h, and aluminum and zinc 88.2% and 91.6% in 98 h, respectively. All findings demonstrated that metals could be efficiently leached from metal concentrates of waste PCBs by using the MCAB, and the leaching period was shorten from about 8 days to 45 h.

Abiotic Reductive Dechlorination of cis-Dichloroethylene by Fe Species Formed during Iron- or Sulfate-Reduction

This study investigated reductive dechlorination of cis-dichloroethylene (cis-DCE) by the reduced Fe phases obtained from in situ precipitation, which involved mixing of Fe(II), Fe(III), and S(-II) solutions. A range of redox conditions were simulated by varying the ratio of initial Fe(II) concentration ([Fe(II)](o)) to initial Fe(III) concentration ([Fe(III)](o)) for iron-reducing conditions (IRC) and the ratio of [Fe(II)](o) to initial sulfide concentration ([S(-II)](o)) for sulfate-reducing conditions (SRC). Significant dechlorination of cis-DCE occurred under highly reducing IRC and iron-rich SRC, suggesting that Fe (oxyhydr)oxides including green rusts are highly reactive with cis-DCE but that Fe sulfide as mackinawite (FeS) is nonreactive. Relative concentrations of sulfate to chloride were also varied to examine the anion impact on cis-DCE dechlorination. Generally, slower dechlorination occurred in the batches with higher sulfate concentrations. As indicated by higher dissolved Fe concentration, the slower dechlorination in the presence of sulfate was probably due to the decreased surface-complexed Fe(II). This study demonstrates that the chemical form of reduced Fe(II) is critical in determining the fate of cis-DCE under anoxic conditions.

Degradation of Rhodamine B in Aqueous Solution by Fenton’s Reagent

The degradation of rhodamine B (RB) in aqueous solution by Fenton’s reagent was studied. After 30 min, the 96.2% removal of RB in water (pH = 3.0, T = 25 °C) was achieved when the initial concentrations of Fe2+, H2O2 and RB were 0.5 mM, 5 mM and 10 mg/L, respectively. A higher initial concentration of Fe2+ and H2O2 resulted in a higher efficiency in RB discolorization. The removal of RB was dependent strongly on the pH value of solution. Increasing the reaction temperature was beneficial for the RB degradation. Based on the Arrhenius equation, the activation energy (Ea) was calculated to be 16.78 kJ/mol from rate constants at different temperatures. The degradation of RB by Fenton’s reagent was inhibited by the presence of oxalic acid.

Combinatorial Parameter Space As an Empirical Tool for Predicting Water Chemistry: Fe(II) Oxidation Across a Watershed

Fe(II) oxidation kinetics in surface waters are a complex function of the concentration of several dissolved species that vary geographically and temporally across watersheds. This work reports an empirical, combinatorial investigation of Fe(II) oxidation that simultaneously evaluated these variations across the pH, Fe(II), PO₄³⁻, Cl⁻, Br(-), CO₃²⁻, and natural organic matter (NOM) axes. The work assayed the effects of independent and dependent variables through application of a novel experimental design that varied Fe(II), PO₄³⁻, Cl⁻, Br⁻, and CO₃²⁻ along the pH axis. Each factor was varied across concentration ranges corresponding to the natural variation between typical fresh and salt water. The system was designed to describe the oxidation of Fe(II) that occurs when Fe(II)-rich groundwaters are mixed rapidly with oxic overlaying waters as a result of tidal movement, bioturbation, dredging, and other mixing/resuspension events. Factors and interfactor interactions were statistically evaluated to determine their importance to Fe(II) oxidation at the 95% level of confidence. Significant factors were retained and used to construct predictive numerical models of Fe(II) oxidation rates. Two models (M1 and M2) were constructed to represent the conditional endmembers of unrestricted Fe cycling (M1) and restricted Fe cycling (due to forced precipitation of Fe(III), M2). The models were challenged to predict net Fe(II) oxidation rates across a watershed (the Congaree/Santee rivers, sampled at ten different locations in South Carolina). The models were generally capable of predicting Fe(II) oxidation rates to within the 95% confidence interval, although M2 consistently overpredicted the rate relative to M1. The minimum initial Fe(II) concentration needed to observe Fe cycling is estimated based on the model output.

Removal of chelated Cu(II) from aqueous solution by adsorption–coprecipitation with iron hydroxides prepared from microelectrolysis process

Iron hydroxides prepared from microelectrolysis process were applied to remove EDTA-chelated copper from aqueous solution through adsorption–coprecipitation. To eliminate the occurrence of adverse reactions, Fe(II)-rich effluent of microelectrolysis was pretreated by continuously flushing N 2 for 15 min to eliminate dissolved oxygen, then iron hydroxides were generated in less than 30 s. The experimental results showed that Fe(II) yields could achieve 530.00–748.00 mg/L after 60-min operation of microelectrolysis process at the initial pH of 2.0–2.3. The uptake rate of Cu(II) by iron(II) hydroxides was so rapid under nitrogen-aerated condition that 100% of Cu(II) was removed within only 5 min at an initial Fe(II) concentration of 374.0 mg/L. However, Cu(II) would desorb from iron hydroxides when iron(II) hydroxides were gradually oxidized into iron(III) hydroxides by oxygen, indicating that iron(II) hydroxide had much higher adsorptive capacity for chelated Cu(II) than iron(III) hydroxide. In addition, iron(II)/(III) hydroxides prepared from microelectrolysis process exhibited a higher removal efficiency of Cu(II) than iron hydroxides prepared from FeSO 4·7H 2O, especially under air-aerated condition. This research provided a novel method for efficient removal of both Cu(II) and EDTA from Cu(II)-chelated wastewater.

Influence of organic acids, complexing agents and heavy metals on the bioleaching of iron from kaolin using Fe(III)-reducing bacteria

Nutrients in leaching solution play an important role in removal of iron impurities from kaolin when using dissimilatory Fe(III)-reducing bacteria (DIRB). However, the effect of organic acids, complexing agents and heavy metals on Fe leaching from kaolin when added to the leaching solution was not well understood and was investigated in this study. The results showed that the removal of iron impurities increased in the presence of oxalic acid in the leaching solution where the removal of iron reached 3.76 mg Fe g clay −1. In contrast, acetic and salicylic acids inhibited or ceased microbial growth. Furthermore, iron dissolution was enhanced by nitrilotriacetic acid (NTA), while the addition of EDTA to the solution medium had little impact on iron reduction. The reduction of Fe(III) was completely inhibited by the addition of 0.08 g L −1 Cu(II) to the solution, while dissolved iron was enhanced by the addition of Mn(II) and Fe(II). Low concentrations of Fe(III) caused a slight decline in iron reduction, but reduction of Fe(III) was significantly inhibited at an initial Fe(III) concentration of 0.08 g L −1. Fourier transform infrared analysis (FTIR) and differential thermal analysis–thermogravimetry (DTA–TG) techniques were used to characterize kaolin before and after bioleaching demonstrating that there was no major change in structural composition or physicochemical properties.