Generation Of Ferrate Research Articles

Toward Continuous Electrochemical Synthesis of Ferrate

AbstractFerrate (Fe(VI)) is of great interest in energy storage solutions, organic synthesis, and wastewater treatment due to its decent oxidation potential and non‐toxic end‐product formation, making it a green oxidizer. The electrochemical generation of ferrate in NaOH at current densities of j ≥ 100 mA cm−2 is presented using low‐cost sacrificial iron anodes, mild steel, and spheroidal graphite cast iron (ductile iron). Under optimized reaction parameters with 40 wt.% (14 m) NaOH and a ZrO2‐based diaphragm, spheroidal graphite cast iron shows no signs of passivation in 5 h experiments even at j = 150 mA cm−2. The results are used in a novel electrolysis cell with a combined geometric anode surface area of 230 cm2, incorporated in a mini‐plant suitable for continuous synthesis. This setup produces a peak ferrate concentration of 10.1 g L−1 (84 mm) after 5 h in 1.6 L anolyte volume, resulting in a total ferrate mass of 16.2 g. Optimal electrolysis temperatures are between 35 and 50 °C. The highest current efficiency is 63.0%, and the lowest specific energy consumption is 9.2 kWh kg−1 ferrate. The presented work is an essential step toward the continuous electrochemical synthesis of ferrate using sacrificial anodes under basic conditions.

Novel use of the electrocatalytic oxidation process with Fe-DSA dual anode configuration for leachate treatment: Significance of in situ ferrate generation

The leachate produced by waste transfer stations (WTSs) contains substantial amounts of refractory organic matter and ammonia, necessitating on-site treatment. In this study, a novel electrocatalytic oxidation (ECO) process with Fe-DSA dual anode configuration was established for leachate pretreatment. In this configuration, chloride in the leachate was converted to active chlorine by the DSA anode, while ferric hydroxide (Fe(OH)3) was produced from Fe anode. As a result, Fe (VI) was in situ formed through the reactions between active chlorine and Fe(OH)3. Simultaneous and efficient removal of COD and NH4+-N in the ECO process with Fe-DSA dual anode configuration was achieved, significantly improving leachate biodegradability compared with the Fe–Fe and DSA-DSA dual anode configurations. The transformation characteristics of organic compounds in the ECO process were investigated through the electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) analysis. The ECO process with Fe-DSA dual anode configuration promoted the removal and transformation of lignins/carboxylic rich alicyclic molecules (CRAM)-like and tannins compounds with biologically refractory properties, as well as S-containing compounds with biological toxicity. Further X-ray photoelectron spectroscopy (XPS) analysis revealed that iron oxides, amorphous Fe-(oxy) hydroxide, and amorphous Fe(OH)3 produced by Fe (VI) decomposition in the ECO process with Fe-DSA dual anode configuration enhanced removal performance through coagulation. In addition, the contribution of different active species to organic matter removal in the ECO process was quantified by quenching experiments. High-valent iron oxidation dominated the ECO process with Fe-DSA dual anode configuration, while active chlorine oxidation, •OH oxidation and coagulation synergistically contributed to organic matter removal.

Novel Synthesis Pathways for Highly Oxidative Iron Species: Generation, Stability, and Treatment Applications of Ferrate(IV/V/VI).

Difficulties arise related to the economy-of-scale and practicability in applying conventional water treatment technologies to small and remote systems. A promising oxidation technology better suited for these applications is that of electro-oxidation (EO), whereby contaminants are degraded via direct, advanced, and/or electrosynthesized oxidant-mediated reactions. One species of oxidants of particular interest includes ferrates (Fe(VI)/(V)/(IV)), where only recently has their circumneutral synthesis been demonstrated, using high oxygen overpotential (HOP) electrodes, namely boron-doped diamond (BDD). In this study, the generation of ferrates using various HOP electrodes (BDD, NAT/Ni-Sb-SnO2, and AT/Sb-SnO2) was investigated. Ferrate synthesis was pursued in a current density range of 5-15 mA cm-2 and initial Fe3+ concentrations of 10-15 mM. Faradaic efficiencies ranged from 11-23%, depending on operating conditions, with BDD and NAT significantly outperforming AT electrodes. Speciation tests revealed that NAT synthesizes both ferrate(IV/V) and ferrate(VI), while the BDD and AT electrodes synthesized only ferrate(IV/V) species. A number of organic scavenger probes were used to test the relative reactivity, including nitrobenzene, carbamazepine, and fluconazole, whereby ferrate(IV/V) was significantly more oxidative than ferrate(VI). Finally, the ferrate(VI) synthesis mechanism by NAT electrolysis was elucidated, where coproduction of ozone was found to be a key phenomenon for Fe3+ oxidation to ferrate(VI).

Research on the Formation Mechanism of MgO and Al2O3 on Composite Calcium Ferrite Based on DA-RBF Neural Network.

Calcium complex ferrate is an ideal binder phase in the sintered ore phase, and a detailed study of the whole process of calcium complex ferrate generation is of great significance to improve the quality of sintered ore. In this paper, we first investigated calcium ferrate containing aluminum (CFA), which is an important precursor compound for the generation of complex calcium ferrate (SFCA), followed by a series of composite calcium ferrate generation process phase XRD detections and data preprocessing of data. Data correlation and data fitting analysis were combined with composite calcium ferrite phase diagram energy spectrum analysis to obtain the effect of MgO and Al2O3 on the formation of composite calcium ferrite. Then a modified RBF neural network model using the resource allocation network algorithm (RAN) was used to predict the generation trend of complex calcium ferrate. The parameters of the neural network are optimized with the Dragonfly algorithm, compared with the traditional RBF neural network. The prediction accuracy of the improved algorithm was found to be higher, with a prediction result of 97.6%. Finally, the predicted results were based on comparative metallurgical experimental results and data analysis. The validity and accuracy of the findings in this paper were verified.

Simultaneous electrochemical oxidation and ferrate generation for the treatment of atrazine: A novel process for water treatment applications

A novel process involving the simultaneous electrochemical-oxidation (EO) and electrosynthesis of ferrate has been investigated for the treatment of the commonly detected and recalcitrant pesticide, atrazine. The present study considered the electrosynthesis of ferrate, in neutral pH, using low concentration iron (Fe2+) representative of raw water levels and its subsequent effect on atrazine degradation. Ferrate synthesis was unaffected by current density (10–80 mA cm−2), indicating mass transport limitations. Synthesis was affected by the initial iron concentration, whereby 0.051, 0.108 and 0.332 mg L−1 was generated with an Fe2+ concentration of 0.5, 1.0 and 3.0 mg L−1, respectively. When operating under simultaneous EO and ferrate oxidation, atrazine degradation exceeded that of a solely EO process. From an initial concentration of 2.00 mg L−1, atrazine was degraded to 1.34, 1.05 and 0.51 mg L−1 during 10, 40 and 80 mA cm−2, characterised by pseudo-first-order kinetics. Degradation with electrochemically-generated ferrate could be described by second-order kinetics, and yielded a degradation rate constant of 23.5 M−1 s−1. The effect of natural organic matter (NOM) on atrazine degradation was also investigated. Ferrate was observed to be mostly scavenged by resorcinol, a representative NOM compound, having a second-order reaction rate constant of 9.71 × 102 M−1 s−1.

Towards in situ electro-generation of ferrate for drinking water treatment: A comparison of three low-cost sacrificial iron electrodes

This work studied the mechanisms governing the electrode processes along with the structure and impact of the passivation layer on the electro-generation of ferrate using three low-cost sacrificial iron materials: mild steel (MS), grey cast iron (GCI) and white cast iron (WCI) electrodes in highly alkaline media. Cyclic voltammetry studies showed that the mechanisms controlling the electrode reactions depend on its alloy composition as it influences the iron species formed in the passivation layer. The presence of silicon in the GCI electrode reduced the stability of the latter, significantly enhancing the ferrate electro-generation due to the persistence of γ-FeOOH in the passivation layer. The instability/dissolution of this layer contributed to a 54%-higher generation of ferrate with GCI when compared to the other electrodes, reaching a maximum titre of 37 mM of ferrate in 10 M NaOH solution with a current efficiency of 45% and the lowest specific energy consumption of 8 kWh kg−1.

Direct and indirect electrochemical oxidation of ethanethiol on grey cast iron anode in alkaline solution

In this study, the electrochemical generation of ferrate (Fe(VI)) from grey cast iron anode in sodium hydroxide (NaOH) solution was utilized in situ to degrade the malodorous pollutant of ethanethiol (C2H5SH). During electrolysis, C2H5SH was oxidized by the combination of direct anodic oxidation and Fe(VI) oxidation (indirect oxidation). The direct anodic oxidation process, which played an important role in the decontamination process but was often disregarded in related studies, was investigated in detail. The electrochemical generation of Fe(VI) was investigated, and the maximum current efficiency of Fe(VI) generation was obtained in 14 M NaOH solution. The voltammetry studies of the grey cast iron anode in NaOH solutions containing and without C2H5SH revealed that the dissolution of anode was improved in the presence of C2H5SH. A decrease in NaOH concentration increased the contribution of direct anodic oxidation but decreased the electrochemical generation of Fe(VI). C2H5SH was degraded on the grey cast iron anode at a higher rate in less concentrated NaOH solution (k = 4.15 × 10−2 min−1 in 2 M NaOH solution), which could be ascribed to the enhancement in direct anodic oxidation as well as in the oxidizing power of Fe(VI). Higher current density promoted the degradation rate of C2H5SH in both direct and indirect oxidation processes, but it also decreased the current efficiency due to the improvement of the side reactions. Additionally, the in-situ and on-line applications of the electrochemical generated Fe(VI) in recent studies were presented and discussed. This study provides a comprehensive understanding of C2H5SH oxidation on grey cast iron anode, and offers a feasible electrochemical scrubbing approach using grey cast iron as the anode for C2H5SH odors control.

Simultaneous Electrochemical Generation of Ferrate and Oxygen Radicals to Blue BR Dye Degradation

In this study, electro-oxidation (EOx) and in situ generation of ferrate ions [Fe(VI)] were tested to treat water contaminated with Blue BR dye (BBR) using a boron-doped diamond (BDD) anode. Two electrolytic media (0.1 M HClO4 and 0.05 M Na2SO4) were evaluated for the BDD, which simultaneously produced oxygen radicals (•OH) and [Fe(VI)]. The generation of [Fe(VI)] was characterized by cyclic voltammetry (CV) and the effect of different current intensity values (e.g., 7 mA cm−2, 15 mA cm−2, and 30 mA cm−2) was assessed during BBR degradation tests. The discoloration of BBR was followed by UV-Vis spectrophotometry. When the EOx process was used alone, only 78% BBR discoloration was achieved. The best electrochemical discoloration conditions were found using 0.05 M Na2SO4 and 30 mA cm−2. Using these conditions, overall BBR discoloration values up to 98%, 95%, and 87% with 12 mM, 6 mM, and 1 mM of FeSO4, respectively, were achieved. In the case of chemical oxygen demand (COD) reduction, the EOx process showed only a 37% COD reduction, whereas combining [Fe(VI)] generation using 12 mM of FeSO4 achieved an up to 61% COD reduction after 90 min. The evolution of reaction byproducts (oxalic acid) was performed using liquid chromatography analysis.

Exploiting water contaminants: In-situ electrochemical generation of ferrates using ambient raw water iron (Fe2+)

Many complexities arise when applying conventional water treatment processes to small and remote systems. A significant challenge is the difficulty and impracticality of supplying chemicals needed for oxidation processes. A burgeoning, yet currently under-utilised, type of treatment are electrochemical technologies, which are receiving considerable research attention and innovation at present. In particular, through the advancement of high oxygen overpotential electrodes, the ability to synthesise highly oxidative chemical species under circumneutral pH conditions has become possible. In this study, the generation of highly oxidative iron-based species, specifically ferrate (Fe6+), has been explored utilising a boron-doped diamond (BDD) electrode and low concentrations of Fe2+ typically found in raw water, thereby eliminating the chemical supply chain required for conventional oxidation processes. Electrochemical ferrate generation experiments were performed in a batch-recycle configuration and were found to be mass transfer limited, whereby the rate-limiting step was the diffusion of Fe2+ to the electrode surface. This was evidenced by very little variation in ferrate generation at the three current densities tested, specifically 3.1 ± 0.2, 2.6 ± 0.2 and 3.3 ± 0.2 μM were generated at 10, 40 and 80 mA/cm2, respectively. Measured Fe6+ concentrations correlated well with those predicted by a mathematical process model, which assumed a completely mass transport limited process. While cyclic voltammetry confirmed ferrate generation by direct oxidation at the BDD surface, the contribution of hydroxyl radicals was indicated by the presence and absence of methanol, an OH scavenger, with ferrate generation decreased by greater than 50 % with methanol, compared to non-scavenged experiments. The results provide one of the first quantitative studies regarding the oxidation mechanisms of ferrate generation by electro-oxidation, and the first example of ferrate generation at circumneutral pH from Fe2+ at levels representative of raw water.

Efficient electrochemical generation of ferrate(VI) by iron coil anode imposed with square alternating current and treatment of antibiotics

Anode passivation is still a main challenge for the electrochemical generation of ferrate(VI, Fe(VI)), leading to the reduction of Fe(VI) production efficiency. In this study, cyclic voltammetry, scanning electronic microscopy, and electrochemical impedance spectroscopy were used to select better anode electrode configurations (iron wire, iron gauze, and iron coil). The results indicate that iron coil had the least degree of passivation. Different imposed current waveforms during the electrochemical generation of Fe(VI) were also investigated, and the iron coil imposed with square alternating current (AC) wave can mitigate the anode passivation, resulting in higher Fe(VI) production efficiency. The optimum conditions for the electrochemical generation of Fe(VI) were evaluated and the optimum temperature (40 ℃), current density (10 mA/cm2), AC cycle period (15 s) and electrolyte concentrations (14 M NaOH) were identified. As a result, 0.12 mol/L Fe(VI) concentration and over 50% of current efficiency can be achieved after 3 h electrolysis. The generated Fe(VI) solution was further applied to oxidize doxycycline(DOX) and sulfadiazine(SDZ) as typical antibiotics. Over 80% of DOX can be removed at a Fe(VI) to DOX molar ratio of 5:1 (pH = 4–9), whilst a higher Fe(VI) to SDZ molar ratio of 20:1 (pH = 7) was needed to obtain 75% SDZ removal.

Enhanced electro-generated ferrate using Fe(0)-plated carbon sheet as an anode and its online utilization for removal of cyanide.

Efficient electrochemical generation of ferrate (Fe(VI)) is still challenged by the passivation of iron materials. Herein, we employed Fe(0)-plated carbon sheet as an anode to enable an efficient production of Fe(VI) with its concentration reached up to 55 mM, which was 8 times higher than that with iron sheet of the same size as an anode. The SEM results showed that the close and uniform dispersion of tapered Fe(0) particles on the surface of carbon sheet helped prevent the formation of passivated layer. The preparative process of electro-deposited Fe(0) affected the generation of Fe(VI). The increase of electroplating time to 40 min and electroplating temperature to 30 °C promoted the production of Fe(VI), and the change in the concentration of Fe2+ in electroplated solution showed little impact on Fe(VI) generation. However, the addition of additives inhibited Fe(VI) generation. As well, an effective removal of cyanide was achieved using on-line production of Fe(VI), comparable to that by NaClO and higher than that by other traditional oxidants containing H2O2, O3, and KMnO4. This study would provide an simple and promising iron anode for efficient production of Fe(VI) by electrochemical method.

Unravelling the mechanisms controlling the electro-generation of ferrate using four iron salts in boron-doped diamond electrodes

This article studies the mechanisms of electrochemical production of ferrate (VI) using a boron-doped diamond (BDD) electrode. Ferrate was synthesized using different current densities, electrolysis time and concentrations of Fe(NO3)3, FeSO4, FeCl3 and FeCl2. The ferrate generation rate was highly affected by the initial concentration and the type of iron salt. The results suggest that diffusion is the controlling mechanism at the BDD electrode. However, for iron salts with oxidation state +2, electron charge also takes place. Cyclic voltammetries showed that the oxidation peak that correlated with ferrate generation is close to the potential where •OH radicals occur. This indicates that a direct electron transfer from the BDD and an indirect oxidation through •OH radicals influenced the generation of ferrate. Although Fe(NO3)3 and FeSO4 oxidation does not perform as well as iron chloride salts in the generation of ferrate, they do not form chlorate and perchlorate. This study demonstrates that it is possible to produce a powerful oxidant that could be used for water treatment purposes without generating toxic by-products.

Electrochemical Ferrates for Drinking Water Treatment: Quantification, Synthesis and Degradation Studies

Ferrate ions are highly oxidizing and unstable species which are challenging to quantify and analyze. They are, however, becoming increasingly recognized as an excellent candidate for a number of applications such as water treatment. Development of ferrate-based technologies for drinking water treatment in remote area requires: a) an accurate assay of the produced ferrates, b) better understanding of the stability properties and c) in-situ electrochemical generation at neutral pH conditions. In order to investigate the possibility of using on-site generated ferrates for treatment of drinking water, we conducted a thorough research program covering the following topics: 1) Quantification of Electrochemically generated Ferrates. Four analytical methods (existing and new) for quantification of ferrates were investigated and compared. These methods include titrimetric analysis, and spectrometric techniques such as direct colorimetric, measurements of ABTS or NaI colorimetric. In terms of accuracy, cost, simplicity and time required the modified indirect UV-Vis/NaI method is shown to be the most effective of all the four methods investigated. 2) Electrochemical ferrate stability. Stability of ferrate species, produced electrochemically for on-site treatment of drinking water, was studied for a number of conditions including: pH, temperature, initial concentration effects, and presence of impurities in order to assess the degradation process quantitatively. Degradation of ferrates for the pH range of 5 to 13 appears to have a first order kinetics behavior. Degradation of ferrates over a temperature range of 5 ºC to 60 °C shows an Arrhenius-type behavior with an activation energy of 348 kJ mol-1. Initial rate analysis of degradation reveals a reaction order of about 1. Impact of potential impurities, such as salts and natural organic matter (NOM), source of water (e.g., tap, deionized and water from natural lake) were also studied and results will be presnted. 3) Electrochemical generation of ferrate species at neutral conditions. Undivided batch (100 mL) cell. An undivided batch cell was used to study the electrochemical generation of ferrate species at neutral conditions (pH ~ 7) using boron-doped diamond (BDD) electrodes and iron (III) salts for applications in drinking water treatment. The impact of several relevant variables, including current density (5-55 mA cm-2), pH (5-9), type and concentration of the dissolved iron salts on the production of ferrates were examined. In addition, linear sweep voltammetry (LSV) studies were conducted using buffer electrolytes with and without the presence of iron (III) to decouple the parasitic oxygen evolution reaction. The LSV measurements in the presence of iron (III) and with a neutral electrolyte exhibit oxidation peaks centered ~ 2.0 V (vs. SHE), indicating the production of ferrates at this pH. The rate of ferrate generation is not strongly affected by the pH condition; however, current density and the source of iron were found to have a higher impact on the production rate of ferrates. The efficacy of the process was higher using FeCl3 compared to other salts such as Fe2O4 and FeO(OH).Semi-batch (2 L) reactor. This approach provided a number of improvements over the batch cell, including: recirculation, proper temperature control, lower cell resistance, excellent mixing, provision for the use of ion exchange membrane, and in-situ pH control. The preliminary results from this benchtop semi-batch reactor showed an improvement in the current effiency from 8% (batch cell) to 75% (semi-batch cell). Overall, about 8 mmol of ferrates was generated during a 2 hour electrosynthesis period exceeding the water treatment targets of about 14 µmol of ferrates. Figure 1

Wastewater treatment via electrochemically generated ferrate and commercial ferrate

This paper presents the results of wastewater treatment using electrochemically generated ferrate and commercial potassium ferrate (supplied by Sigma–Aldrich). Two electrolytes were used for the electrochemical generation of ferrate; NaOH at 8.0, 10.0, and 12.0 M and KOH at 12.0 M, the ferrate solutions produced were used for the treatment of wastewater samples from a wastewater treatment plant. The experimental results of removal of organic matter in wastewater by electrochemically generated and by commercial ferrates were measured. In this work, the pH, chemical oxygen demand, and turbidity were determined for the treatment of wastewater using ferrate from different source. Experimental results revealed that the treatment with electrochemically generated ferrate was more efficient than the treatment with commercial ferrate. The commercial ferrate was found to be chemically unstable when dissolved in water prior to its application on wastewater treatment. The concentrations of potassium and sodium ferrate electro-generated were determined with a UV–visible spectrophotometer throughout this work.

Removal of CH3SH with in‐situ generated ferrate(VI) in a wet‐scrubbing reactor

AbstractBACKGROUNDA wet scrubbing process with in‐situ electro‐generation of ferrate(VI) has been developed for removing odour from foul gas in wastewater treatment plants. In this process, methyl mercaptan (CH3SH) in synthetic gas is removed through absorption and oxidation by contacting the gaseous stream with aqueous NaOH electrolyte that offers in‐situ generation of ferrate(VI).RESULTSThe process parameters including electrolyte concentration, applied current density, initial CH3SH concentration, gas flow rate and gaseous CH3SH compositions were investigated to determine the best operating conditions and design parameters for a scale‐up design. Under all the experimental conditions, gaseous CH3SH was completely removed by the wet scrubbing process at room temperature and atmospheric pressure. The process proved to be quite effective for dissolved CH3S‐ degradation under the optimum experimental condition at the NaOH concentration of 6 mol L–1, current density of 2.22 mA cm‐2 and CH3SH loading below 30 g m‐3 h‐1. A very short contact time of 0.06 s between the gas and the liquid phases was achieved in this in‐situ ferrate(VI) generation reactor.CONCLUSIONSThis process is effective for CH3SH control, and holds great promise for industrial applications due to its high efficiency, simplicity and stability. © 2013 Society of Chemical Industry

Kinetics of CH3S− reaction with in situ ferrate(VI) in aqueous alkaline solution

This study introduced a new treatment process named “in situ ferrate(VI) oxidation (IFO)” in which odorous compounds such as CH3S− can be quickly degraded by in situ freshly generated ferrate(VI) through electrolysis in aqueous alkaline solution. Two kinetic models to describe the in situ ferrate(VI) generation and its reaction with CH3S− were established mathematically by considering three main reaction mechanisms of ferrate(VI) electrochemical generation, ferrate(VI) self-decomposition and CH3S− degradation in aqueous strong alkaline solution. The effects of three key factors: (i) NaOH concentration, (ii) applied current density, and (iii) initial CH3S− concentration on the performance of the IFO process were investigated by conducting three sets of experiments and the kinetic models were validated by fitting the experimental data. The goodness of the fittings demonstrated that the new models could well describe both the kinetics of ferrate(VI) generation reaction and CH3S− degradation reaction. The experimental results confirmed that the higher NaOH concentration and current density applied would be beneficial to the electrochemical generation of ferrate(VI) and also elimination of its self-decomposition, but the experiments also demonstrated an optimum NaOH concentration at 10M to achieve the best performance of CH3S− degradation reaction in such an IFO system.

Ferrate(VI) synthesis at boron-doped diamond anode

The oxidation of iron compounds from alkaline 10 M KOH electrolytes on a boron doped diamond electrode is examined by cyclic voltammetry between the potentials of hydrogen evolution reaction and oxygen evolution reaction, due to ferrate(VI) electrochemical synthesis. It is shown that the anodic current peak that appears in iron free electrolyte at a less positive potential than the potential of oxygen evolution probably coincides with oxidation of hydrogen in >CH2 groups and C-sp2 graphite impurities with formation of >C=O groups at C-sp3 diamond structure. Addition of Fe(III) compounds to the electrolyte provoke formation of the anodic wave on cyclic voltammograms in the potential region which correlates with generation of ferrate(VI). It is concluded that the direct electrochemical synthesis of Fe(VI) at the boron doped diamond anode is possible because of the less positive potential of ferrate(VI)FeO2-4 formation in respect to the potential of oxygen evolution reaction. Presence of ferrate(VI) in electrolyte, formed after anodic polarization of boron electrode in 10 M KOH electrolyte saturated with Fe(III) at + 0.9 V against Hg|HgO electrode, has been proven by UV-VIS spectrometry.

Oxidation of CH3SH by in situ generation of ferrate(VI) in aqueous alkaline solution for odour treatment

This study demonstrated a new approach of odorous gas treatment in a wet scrubbing-oxidation system with in situ generation of ferrate(VI), in which gaseous CH3SH can be quickly absorbed by aqueous alkaline solution and rapidly oxidized by liquid ferrate(VI) generated through electrochemical synthesis in situ. In this study, the electrochemical generation of ferrate(VI) in aqueous NaOH solution was studied and the experiments demonstrated that a maximum current efficiency to generate ferrate(VI) occurred at 14M NaOH concentration, while an applied current density of 14.06mAcm−2 was applied. Then the self-decomposition of ferrate(VI) in such strong alkaline solutions was studied, and the results showed that ferrate(VI) behaved more stable in the stronger alkaline solution. Furthermore, the reactivity of ferrate(VI) with CH3SH in this highly-concentrated NaOH solution was investigated under different reaction conditions as the first time. The experimental results confirmed that CH3SH can be fully oxidized by ferrate(VI) to sulphate ion as a final product. The second-order reaction model is suitable to describe the kinetics of CH3SH reaction with ferrate(VI) in the strong alkaline solution. Meanwhile, stoichiometry of ferrate(VI) reaction with CH3SH in aqueous solution was determined with a minimum molar ratio of 2.20:1 (Fe(VI):CH3SH) to destruct CH3SH effectively and a higher molar ratio of 4.53:1 to convert CH3SH to sulphate ion completely. The experiments also demonstrated that the NaOH concentration in aqueous solution would be a key parameter and the best performance of CH3SH removal was achieved at the optimum NaOH concentration of 6M under our experimental conditions due to an optimum balance between the oxidation potential of ferrate(VI) and its generation rate in this wet scrubbing-oxidation system.

Electrochemical generation of ferrate (VI): Determination of optimum conditions

Abstract The optimum conditions for the electrochemical generation of ferrate were analysed using a laboratory scale electrochemical reactor and using NaOH as the electrolyte with a reaction duration of 25 min. The criteria used for comparison are the current efficiency and the energy consumption. The conducted experiments in this project showed that the optimum current density of the 10 studied applied currents was 36 A/m 2 ; the optimum concentration of NaOH of the four different studied concentrations was 16 M and the optimum carbon content (C%) of the three studied steels was 0.11%.

Engineering Aspects of Electrochemical Generation of Ferrate: A Step Towards Its Full Scale Application for Water and Wastewater Treatment

The objective of this paper is to design a pilot plant electrochemical reactor and to prove the operational concept of the electrochemical production of ferrate in situ and its online application for sewage treatment. To that end, the first part of this paper focuses on the analysis of the main engineering aspects of the reactor and the electrochemical process that affect the ferrate production, using laboratory scale experiments such as the interelectrode gap, the space-time yield, the area/volume (A/V) ratio, the current efficiency, and the energy consumption. The second part focuses on the production of ferrate using a pilot plant scale to prove the operational concept of the electrochemical generation of ferrate in situ and its online application as a step towards its full scale application for water and wastewater treatment.