Steel Anode Research Articles

Application of electro-Fenton process for treatment of water contaminated with benzene, toluene, and p-xylene (BTX) using affordable electrodes

Electro-Fenton (EF) process was utilized for degradation of benzene (B), toluene (T), and p-xylene (X) (BTX) in aqueous solutions using different electrodes. The cathode was made from carbon felt, while different materials were used as anodes including carbon, stainless steel, and nickel. Complete degradation of BTX was attained within 30 min under favored conditions. However, TOC removal of BTX in the mixture was only 75% at early stages of the EF process due to the remaining organic by-products. The effects of operational conditions at different initial concentrations of BTX were assessed in-depth. The EF process was able to attain 95.4%, 88.7%, and 87.6% TOC removal efficiencies at an initial concentration of 150 mg/L using sacrificial stainless steel, carbon, and nickel anodes respectively in 60 min. The stainless steel anode in the mode of the sacrificial electrode was favored due to the continuous production of Fe2+ in the solution. The precipitated sludge during the EF process was treated and used to improve the degradation of BTX. A cost estimation study showed that treatment of one cubic meter of BTX contaminated water by electro-Fenton process costs $1.40 under certain conditions.

Electrocoagulation using stainless steel anodes: Simultaneous removal of phosphates, Orange II and zinc ions.

Two stainless steel anodes, AISI 420 and AISI 310, and pure iron were compared in an electrocoagulation study for the simultaneous removal of phosphates, Orange II and Zinc ions from a synthetic wastewater at a current density of 11.7 mA cm-2 and a surface area to volume ratio of 19.4 m-1. High removal efficiencies were observed with AISI 420 and pure iron, reaching values between 88% and 99%, while significantly lower values, approximately 30%, were obtained with AISI 310. The AISI 310 performed well in the removal of Zn2+ due to its removal as Zn(OH)2. The variations in the performance of the steel anodes were attributed to the lower chromium content of the AISI 420, which gives less passive behaviour. This was supported using polarisation data, where a 10-fold increase in the corrosion current was obtained for AISI 420 compared to AISI 310. Furthermore, Cr(VI) was observed in the solution phase when AISI 310 was employed as the anode, illustrating the importance of the alloying concentrations. While rust particles were seen during the non-continuous use of the iron anode, they were not observed with the AISI 420 anode.

Anode ablation and performance improvement of microcathode arc thruster

This article presents the results of a study into the new concept of the microcathode arc thruster; a thruster with an ablative anode (AA-μCAT). Such a thruster uses a triggerless discharge initiation, and has a coaxial electrode configuration where the central miniature anode is made of an ablative material (brass, solder, copper, etc), and an outer annular cathode, with optional magnetic coil. We show that the use of an ablative material (brass) increases the ion-to-arc current ratio from ∼2 to ∼4% without any focusing magnetic field, and up to 7% with a magnetic field of 0.33 T, compared with the case where the central anode is made of nonablative stainless steel, for the same pulsing power circuitry and parameters. For the first time, we demonstrate that even without a magnetic field, the AA-μCAT has a higher thrust (7 μN) and a higher thrust-to-power ratio (5.5 μN W−1) with respect to the thruster with a nonablative refractory stainless steel anode (5.5 μN and 4.8 μN W−1, respectively). This fact is direct evidence of possible improvements to the microcathode arc thruster thrust-to-power ratio due to anode ablation.

Influence of salt content on clay electro-dewatering with copper and stainless steel anodes

The electro-dewatering technique is an effective method to reinforce soft clay. Electro-dewatering experiments were conducted to assess the impact of salt content on electro-dewatering behaviors and effects with copper and stainless steel anodes. The changes in the current, accumulated drainage volume, and electro-osmotic flow velocity reflect the “catch point” phenomenon between the copper anode and the stainless steel anode. Moreover, the higher the salt content was, the earlier the appearance of the “catch point,” which means that the effect of the copper anode was better in the early stages and then worse in the following stages than that of the stainless steel anode. Based on photographs of anode surface, SEM-EDS (Scanning electron microscopy-Energy dispersive spectrometry) and XRD (X-ray diffraction) results, we found that the copper anode surface produced green product, which observably decreased the conductivity of the copper anode and then reduced the effective electrical potential gradient. On the other hand, there were no added elements on the stainless steel anode surface after the electro-dewatering experiments, and the conductivity of the stainless steel anode was similar to its initial status. The above two points led to the appearance of the“catch point” phenomenon. The pH value of the stainless steel anode was lower than that of copper anode, and the concentration of Cl− had the opposite relationship. Because the effective electrical potential gradient of the stainless steel anode was higher than that of the copper anode after the “catch point,” the water content of the stainless steel anode was lower than that of the copper anode.

An enhanced treatment efficiency for diluted palm oil mill effluent using a photo-electro-fenton hybrid system

Photocatalysis, electrolysis and Fenton process are three important advanced oxidation processes (AOPs) which produce hydroxyl radical in order to degrade organic matter in wastewater within 4-6 hours under ambient conditions. A photocatalysis, electrolysis and Fenton (photo-electro-Fenton) process hybrid system has been carried out to treat the diluted palm oil mill effluent (POME) in this study. An electrolytic cell was set up with a stainless steel anode and a platinum wire cathode with the applied cell voltage of 1.5 V. The diluted POME was then treated in the cell with the mixture of titanium oxide as the photocatalyst, sodium sulfate solution as the electrolyte, hydrogen peroxide and iron sulfate as the Fenton reagents. The effects on the duration, pH, concentration of TiO2 and different light conditions on the removal efficiency of the chemical oxygen demand (COD) of the diluted POME were studied. The optimal conditions for the photo-electro-Fenton hybrid system were found to be 4 hr contact time at pH 4 with 60 mg/L TiO2 under sunlight. With such conditions, the COD removal efficiency was able to achieve 97 %. On the other hand, the photo-electro-Fenton hybrid system gave the highest COD removal efficiency, compared to the electro-Fenton hybrid system, Fenton and photocatalyst, respectively.

A dual TiO2/Ti-stainless steel anode for the degradation of orange G in a coupling photoelectrochemical and photo-electro-Fenton system

A dual-anode consists of stainless steel and TiO2/Ti electrodes is used to study the kinetics of the degradation of hazardous chemicals exemplified by azo dye orange G (OG) using a coupling photoelectrochemical catalytic and photoelectro-Fenton (PEC/PEF) system. Concurrent generation of hydroxyl radicals on the TiO2/Ti photocatalyst and in-situ generation of Fenton reagents on the stainless steel electrode greatly enhances the performance of the PEC/PEF electrodes over that of the PEC and the PEF alone process. The efficiency of the PEC/PEF process is a function of Fe2+ and H2O2 concentration OH⋅ in the solution bulk, which promotes the oxidative degradation of OG and its byproducts. The mean carbon oxidation state (COS) is estimated to reflect the degree of mineralization. Based on the pseudo first-order kinetics with respect to OH, OG, Fe2+, the corresponding reaction rates is established. UV–Vis spectrometry reveals the presence of four major intermediates, which helps establish the OG degradation pathways.

Carbon nanotubes (CNT) market worth $9.84 bn by 2023

With carbon capture and utilization (CCU) technologies, it is possible to take CO2 from air and transform it into valuable carbon products, such as graphene and nanotubes. In this study, CO2 was reduced to solid carbon by molten lithium carbonate salt electrolysis. The reactor used for the electrolysis was a coaxial-type unit, where a cylindrical nickel cathode was placed inside a cylindrical stainless steel vessel; such a coaxial-type reactor has not been used before for molten salt electrochemical reduction of CO2. This reactor design allows studies of voltage-current characteristics, which have previously not been conducted for this specific process. As a result, voltage efficiency of this process could be determined along with effect of temperature to cell voltage. Based on these results it is evident that accurate temperature control is crucial in terms of energy efficiency of the process. Data monitoring revealed a high accuracy of temporal temperature control. Great temperature differences were observed spatially. Thermoneutral voltage from the process was determined to be 1.02 V. For this electrochemical process studied, carbon nano-onions (CNOs) were obtained as a main product. Identification of the product was carried out based on Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) analyses. Results also showed that iron, chromium and nickel metals are released during electrolysis. Iron and chromium can only be released from the stainless steel anode, as nickel can come from anode or cathode.

Study of plasma induced nanostructure formation and surface morphology changes on tungsten and stainless steel at atmospheric pressure

The formation of nanostructures such as “fuzz,” holes, and flakes was observed on tungsten and stainless steel anodes in a 1 atm glow discharge with helium as the feed gas. The structures exhibited morphology similar to the tungsten fuzz growth observed in experiments that simulate wall conditions in fusion reactors, suggesting that similar physics may be present in both scenarios. The anode surface temperature ranged between 1000 and 1300 K with an ion fluence rate of order 1024 s−1 m−2. In this work, scanning electron microscope and transmission electron microscope were used to characterize the evolution of nanostructure formation as a function of time. Observed nanostructures were found to vary with the morphology of the discharge plasma attachment. The composition of the structures was found to be predominantly the native metal by using energy dispersive x-ray spectroscopy. This work gives some insight into the formation of nanostructures at atmospheric pressure, which not only has applications for material processing, but also provides potentially another avenue to study fuzz formation processes relevant to fusion plasma-wall interactions.

Corrosion inhibition of N80 steel in 10% HCl + 8% HBF4 solution

PurposeThis paper aims to analyze the corrosion and corrosion inhibition of N80 in 10 per cent HCl + 8 per cent fluoroboric acid (HBF4) solution for acidizing operation.Design/methodology/approachThe corrosion rate, kinetic parameters (Ea, A) and thermodynamic parameters (ΔH, ΔS) of N80 steel in fresh acid and spent acid, 10 per cent HCl + 8 per cent HBF4, 10 per cent HCl and 8 per cent HBF4 solutions were calculated through immersion tests. The corrosion and inhibition properties were studied through X-ray diffraction and electrochemical measurements. The corrosion morphology of the corrosion product was examined by scanning electron microscopy (SEM).FindingsThe results demonstrated that the spent acid was the main cause of acidification corrosion, and the HBF4 would cause serious corrosion to N80 steel. The results showed that the N80 steel was more seriously corroded in the spent acid than in fresh acid, and the hydrolysis of HBF4 accelerates the dissolution process of N80 steel anode to control the corrosion reaction. The results showed that the acidification will definitely cause serious corrosion to the oil tube; therefore, necessary anti-corrosion measures must be taken in the acidification process.Originality/valueThe results showed that acidizing the formation with 10 per cent HCl + 8 per cent HBF4 will definitely cause serious corrosion to the oil tube, especially when the spent acid flows back. Therefore, necessary anti-corrosion measures must be taken in the acidification process, especially in the spent acid flowback stage.

Development of a High-Performance Mediatorless Microbial Fuel Cell Comprising a Catalytic Steel Anode

The present paper reports for the first time the construction of a sugar cane bagasse-mediated double-chambered microbial fuel cell (MFC), consisting of a novel bioanode of an iron/titanium Ni-P composite. This anode could facilitate uninterrupted extracellular electron transfer (EET) from bacteria (mixed culture). The Ni-P composite anode had a significant corrosion resistance and enhanced electrocatalytic activity. The corrosion rate was reduced to 0.187 mmpy, which was 3 times less than that of the noncomposite anode. A steady decrease in internal resistance from 3.84 × 103 Ω to 2.94 × 102 Ω was achieved with the incorporation of the iron/titanium-based composite on the anode surface. The presence of Fe (III) ion centers in the composite surface favored electroactive biofilm formation and enhanced the capacitive nature of the anode, thereby accelerating EET. The constructed MFC showed an internal resistance as low as 1.12 × 10-2 Ω in comparison with the control MFC. This led to a very high power density of ∼2.1 W/m2, which was 20% higher than that of the control MFC, while a stacked MFC obtained a maximum open-circuit potential of 3.2 V with power density and current density outputs of 6.3 W/m2 and 2.7 mA/m2, respectively. Even though an extensive amount of literature is available in this field, this report is the first of its kind because it includes such a simple reproducible system that can be extended to other similar systems.

Sulfate removal from acid mine water from the deepest active European mine by precipitation and various electrocoagulation configurations

Sulfate removal from mine or process water is a key issue in the mining industry. In this paper, precipitation with lime (calcium oxide) was integrated with electrocoagulation for sulfate removal from Pyhäsalmi/Finland mine water. Sulfate precipitation with calcium oxide decreased the sulfate concentration from 13,000 mg/L to 1600 mg/L. Various current densities were applied to the pre-treated mine water with various electrodes and aluminium and iron anodes. It was found that 25 mA/cm2 was the best tested current density for both anode types. At the second stage, this current density was used for different iron and aluminium anodes in various monopolar and bipolar configurations. It was found that this hybridisation is effective for sulfate removal, and that a bipolar configuration showed better results than the monopolar configuration. The best result was gained from 25 mA/cm2 with a two aluminium and two stainless steel anode–cathode configuration and calcium oxide pre-treatment to reach pH 12. The removal efficiency reached 84.4% and 63.8% with aluminium anodes in bipolar and monopolar configurations, respectively. This setup was able to decrease sulfate concentrations from 13,000 mg/L to 250 mg/L, which meets mine water discharge limits. Kinetic studies showed that iron and aluminium anodes obey pseudo-second order kinetic. Finally, the energy consumption was calculated.

Utilizing Lemon Balm extract as an effective green corrosion inhibitor for mild steel in 1M HCl solution: A detailed experimental, molecular dynamics, Monte Carlo and quantum mechanics study

Abstract This study concerns with mild steel corrosion inhibition in 1M HCl solution protected with different concentrations of Lemon Balm extract. Electrochemical and theoretical approaches are utilized for approaching this goal. The type of functional groups in the active components present in the Lemon Balm extract (LB.E) was examined through UV–visible analysis, Fourier Transform Infrared (spectroscopy) (FT-IR) and Raman spectroscopy. According to the electrochemical impedance spectroscopy (EIS) test results the maximum inhibition efficiency of about 95% was obtained in the solution containing 800 ppm LB.E. Potentiodynamic polarization test results revealed that in the presence of LB.E the rates of anodic steel dissolution and cathodic hydrogen evolution reactions significantly decreased and a mixed inhibition effect was obtained. Surface studies were done by contact angle test, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results revealed that the steel surface damage as a result of HCl solution attack significantly decreased by addition of 800 ppm LB.E. In addition, deposition of a highly hydrophobic film composed of organic compounds of inhibitors on mild steel surface was demonstrated by contact angle test results. The excellent corrosion inhibition effect of LB.E on mild steel in HCl solution is related to the adsorption of active inhibitive compounds such as caryophyllene, germacrene, citral, luteolin, chlorogenic acid and rosmarinic acid on the anodic/cathodic places of mild steel surface. Furthermore, the theoretical results derived from Monte Carlo, molecular dynamics and quantum mechanics techniques evidenced the inhibitors adsorption onto steel substrate through donor-acceptor interactions.

Electrokinetic behaviour of conducting polymer modified stainless steel anodes during the enrichment phase in microbial fuel cells

Two of the major bottlenecks in achieving large-scale power generation with MFCs to date are the low power output and the usually long start-up time, both of which are mainly associated with poor bacterial kinetics and inefficient anode electrode materials. We have demonstrated in this study that the electron transfer kinetics of stainless steel (SS) can be significantly improved by modification with polyaniline (PANi) and polypyrrole (PPy). Furthermore, we have demonstrated that the kinetics of the bacterial growth can be significantly enhanced by the application of a carefully selected external resistance (Rext), resulting in significantly shorter start-up time. The half-cell reactors used for the investigations were enriched under different conditions including without Rext (Open circuit mode), with Rext = Rint (Ohmic region), and with very low Rext (mass transfer region). The MFC anodes enriched under Rext = Rint gave maximum exchange current density (j0max) on the 4th day of operation. The calculated j0max for SS wool, PANi-wool, and PPy-wool anodes were 0.3 ± 0.2 A m−2, 10.5 ± 0.4 A m−2 and 5.0 ± 0.4 A m−2, respectively. The lowest charge transfer resistance (Rct) of 0.23 Ω cm−2 was obtained with SS/PANi-wool anode which exhibited the highest electron transfer kinetics and better compatibility than SS/PPy-wool. The high current drawn from the system during the biofilm establishment phase did not support electroactive biofilm formation because it prevented the growing anode-respiring bacteria (ABR) from providing sufficient electron flow to the counter electrode.

Performance Improvement of Zebra Batteries By Using a Simple and Functional Planar Architecture

ZEBRA batteries (Zero Emission Battery Research Activities) for their high energy and power density are one of the possible solutions to electrical storage for stationary applications. These systems are based on nickel chloride-sodium cells operating at high temperatures (about 270°–350 °C), and rely on a ceramic β”-alumina tube or planar membrane as solid electrolyte. In this work, recent results generated from 3 cm2 button cells, including base line cell performance, cell design and chemistry will be presented. The activity was directed to the realization of two new planar configuration of a beta sodium battery, that means the study of a planar sealing between the metal and the ceramic components. This battery, as many other electrochemical storage technologies, may play an important role for the transmission and distribution of electricity, because it can satisfy, in a very flexible way, many different needs (voltage and frequency control, self consumption of stochastic renewable energy, peak shaving etc.). For this purpose the storage system has to be characterized not only by a suitable energy capacity, but by quick response and high power performance too. A planar configuration could optimize the battery in terms not only of energy density (already satisfactory for this kind of batteries), but also of power density (still to be improved). The planar configuration could also provide a better stack design and thermal regulation. This battery utilizes a ceramic material as the ionic membrane between the anodic and cathodic semi cells and so it has to operate at 300°C. The current form of the β”-alumina membrane is “glass shaped” in order to contain the reagents, so the possible planar shape has to include a sealing system able to contain the reagents, which are in liquid status at the high temperature of the battery and they are also highly chemical reactive, especially the liquid sodium. In particular the research activity was previously directed to the study of the components of the seal between the metal bodies of the semi cells and the ceramic beta alumina and afterwards to a new configuration of the sealing system. The studied materials were insulating paints, ceramic pastes and glass seals and they were tested in order to assess their chemical stability in presence of sodium and their mechanical stability during thermal cycling. The research activity was addressed to define the right geometry of the ceramic support of the β”-alumina. Another purpose was to define a mechanical seals between the ceramics support and metallic body of the two, anodic and cathodic, electrodic compartments. A new activity was started to realize a new configuration in which also the body of battery was realized in ceramic material (α-Alumina), which allows a greater wettability in the anodic compartment. The mono cell was realized with a new sealing system, composed by a new geometry of a ceramic ring to contain the beta alumina membrane and to guarantee the mechanical stability. In both planar configurations of the cell made, it has been noticed that this type of design reduces the volume of the cathodic and anodic semi cell; in this way, not only the energy density is increased but also the power density is improved. Furthermore, the planar design would improve the stack geometry and its thermal distribution. The problems faced in this work were the material resistance to the chemical attack of liquid sodium at high temperature, the mechanical resistance and the compensation of the different thermal expansion coefficient between the solid electrolyte (β-alumina) and the metallic body. The first button cell consisted of two battery cases (stainless steel) for cathode and anode sides, a Nichel network cathode current collector, a stainless steel anode current collector, an α-alumina (99.5% purity) fixture and a planar composite yttria-stabilized zirconia (YSZ)/ BASE (3 cm2 active area) disc. The second buttom cell consisted of battery cases (α-Alumina) for cathode and anode sides, a steel plate held by a spring as a current collector both at the anode and at the cathode (the use of springs makes it possible to better exploit cathodic and anodic active materials), an α-alumina (99.5% purity) fixture and a planar composite yttria-stabilized zirconia (YSZ)/ BASE (3 cm2 active area) disc. It is using an inexpensive stacked design to improve performance at lower temperatures, leading to a less expensive overall storage technology. The new design greatly simplifies the manufacturing process, providing a subsequent pathway to the production of scalable, modular batteries at half the cost of the existing tubular designs.

Non-Precious Group Metal Electrocatalysis of Sulfite Electro-Oxidation Reaction for Gold Electrowinning Processes

The electro-oxidation of sulfite and its radicals has a wide range of applications from gold electrowinning to wastewater treatment, hydrogen production and in the food industry (1-4). While efforts have been made to study the electro-oxidation of sulfite ions on noble metals (e.g. Au) as well as carbon surfaces, metal oxides in general have not been thoroughly investigated for this electrochemical reaction (1, 5). During gold recovery from thiosulfate solutions, Au+ ions are reduced to Au from the thiosulphate gold complex on the cathode while oxygen evolution occurs on the anode via the following reactions (6): Au(S2O3)2 3- + e- = Au + 2S2O3 -2, E0= 0.15 V (1) 4OH- = 2H2O + O2 + 4e-, E0= 0.4 V (2) To drive the cathodic reaction, high current densities are used, which result in high anodic potentials on the stainless-steel anodes. Such high anodic potentials may cause transpassive corrosion of the anode as well as significant, and undesirable, changes in solution chemistry (7). This study systematically investigated the effect of operating factors on the corrosion behavior of stainless steel anodes in thiosulfate solutions during gold electrowinning. Further, novel non-precious group materials such as manganese oxides and perovskites were used as electrocatalysts for sulfite electro-oxidation to ultimately enhance the activity and long-term durability of the anodes in the gold electrowinning process (8). A 2n half-fraction factorial design study was performed to find the effect of five important parameters involved in the gold electrowinning process (i.e. thiosulfate concentration, sulfite concentration, sulfate concentration, temperature and applied anodic current density), on the anodic potential of the stainless steel anode. As shown in the Fig. 1A, increasing the sulfite concentration and temperature of the gold electrowinning solution lead to a low anodic potential of 550 mV which is about 250 mV lower than the transpassive corrosion potential for the 316 stainless steel anodes. To further reduce the anodic potential and employ the high sulfite concentration (i.e. 3000-32000 ppm) in the gold electrowinning solution, non-precious metal oxides were tested to facilitate the electrowinning process by catalyzing the following sulfite electro-oxidation reaction instead of the oxygen evolution reaction (eq. 2): SO3 2- + 2OH- = SO4 2- + H2O + 2e-, E0= -0.93 V (3) Fig. 1B shows that a combination of manganese oxide and perovskite electrocatalysts provides promising electrocatalytic activity and durability for sulfite electro-oxidation (i.e. up to 500 mV lower onset-potential over 7 hours of testing at 3.5 mAcm-2) compared to the Ni, commercial Ag/AgO, Pt, carbon, commercial Pb-2 wt% Ag and stainless steel electrodes tested here. Fig. 1 A) Surface plot produced from the 2n half-fraction factorial design study on the effect of five electrowinning parameters on the performance of 316 stainless steel gold electrowinning anode. B) A comparison between the electrocatalytic activity of various electrocatalyst materials for sulfite electro-oxidation in a solution of 100 ppm NaCl + 3000 ppm Na2SO4 + 32000 ppm Na2SO3 at 3.5 mA cm-2 and 45 °C. All MnO2-based catalysts are under the license with Catalyst Square Materials Ltd (8).

A Study on Galvanic Current Variation of Zn Sacrificial Anode Made by Including of Additive in Solutions with Various Conductivities

There have been two cathodic protection methods to inhibit corrosion of the structural steel piles which are being immerged under seawater, or to control corrosion of a hull part of the ship exposed to sea water. One of them is a sacrificial anode cathodic protection method that the steel pile can be protected with galvanic current by potential difference between sacrificial anode and corrosive structural steel. And, the sacrificial anode cathodic protection method have generally merits compared to impressed current method because it can be easily applied to everywhere which is not connected with electricity. However, when the steel piles are being submerged in low conductivity solution mixed with fresh water and sea water, the structural steel piles mentioned above have not been protected occasionally perfectively due to decreasing of galvanic current of zinc anode caused by deposited with oxide film on the surface of anode. In this study, four types of zinc anodes samples which are included with three types of additives such as NaCl, KCl, and ZnCl2were prepared, and galvanic currents, the polarization characteristics of these anodes was investigated using electrochemical methods such as polarization curves, impedance, cyclic voltammogtam and galvanic current in order to evaluate the effect of additive affecting to quality of zinc anode. The sample added with NaCl indicated the highest value of galvanic current density compared to other samples in the case of lower and higher conductivity solutions such as 0.32 and 2.97mS respectively, and the sample added with KCl revealed the smallest galvanic current density in middle value of conductivities such as 1.53 and 2.27 mS. Moreover, Zn sample no added with additive exhibited the smallest value of galvanic current density in the lowest conductivities such as 0.32 and 0.98 mS. Therefore, it is considered that the galvanic current of the sacrificial anode can be increased by adding of additive when the anode is submerged in low conductivity solution mixed with fresh water and sea water.

Experimental investigation and analysis of a new photoelectrochemical reactor for hydrogen production

In this research paper, an experimental investigation of photoactive material titanium dioxide (TiO2) coated on 180 cm2 316 stainless steel anode is undertaken to study the photoresponse on photoelectrochemical (PEC) hydrogen production. The TiO2 nanoparticles are first prepared via sol-gel method. A large surface 316 stainless steel anode is coated with TiO2 nanoparticles by a dip coating apparatus at a withdraw rate of 2.5 mm/s. The nanoparticles are carried on the stainless steel substrate by two-step annealing procedure. The potentiostatic studies confirm the photoactivity of TiO2 nanoparticles in a photoelectrochemical reactor when exposed to solar ultraviolet (UV) light. The photon to current efficiency measurements carried out on the PEC reactor with TiO2 coated large surface stainless steel as photoanode demonstrate a significant increase of photoresponse in UV light compared to the uncoated stainless steel prepared under similar conditions. Upon illumination at a power density of 600 W/m2, the hydrogen production is observed in TiO2 coated stainless steel substrate at a measured rate of 51 ml/h while no illumination conditions show a production rate of 42 ml/h. In comparative assessments, the TiO2 coated substrate shows an increase in photocurrent of 10 mA with an energy efficiency of 1.32% and exergy efficiency of 3.42% at an applied potential of 1.6 V. The present results show a great potential for titanium nanoparticles semiconductor metal oxide in photoelectrochemical hydrogen production application.

Electrocoagulation using an oscillating anode for kaolin removal

Industrial operations such as oil-sands mining results in large volumes of tailings that contains fine clay particles and minerals. The tailing has high turbidity, is difficult to settle and typically contains a mixture of toxic substrates that impact the environment. In the present work, the effectiveness of electrocoagulation with oscillating aluminum or mild steel anodes was investigated for removal of turbidity from synthetic effluents (using kaolin as a model clay). The effect of the operating conditions including anode material (aluminum or iron), potentiodynamic investigation, current density (0.5–2.0 A cm−2), and the pH (3–9), was studied. Oscillation of the anode was found to enhance the treatment performance, due to a combination of improved mass transfer of dissolved coagulants into the bulk solution and pulsation of the current at the electrode surface. Electrode oscillation led to a reduction of the operating cost as well as electrical energy consumption required for >95% turbidity removal of 52% (from 435 to 207 J per L) and 40% (from 603 to 361 J per L) for aluminum and mild steel electrodes respectively. The results indicate that electrocoagulation with an oscillating anode provides an efficient technique for removal of suspended mineral pollutants.

Optimization and modeling of electro-Fenton process for treatment of phenolic wastewater using nickel and sacrificial stainless steel anodes

Sacrificial stainless steel and nickel electrodes were used as anodes in electro-Fenton (EF) process for degradation of phenol in controlled operating conditions. The influence of different operating parameters such as initial concentration of phenol, current intensity, Fe2+ dose, pH and anode material were studied. At optimal operating conditions, the degradation of phenol was 95.2% using sacrificial stainless steel anode in 90 min and 72% using nickel anode in 120 min. The favored current intensity was 900 mA. The optimal Fe2+ doses using stainless steel and nickel anodes were 5 mg/L and 20 mg/L respectively. The production and consumption of iron during the EF process was monitored to interpret the favorability of sacrificial stainless steel anode. Regression analysis was employed to develop a prediction model for phenol removal. The model is dependent on operational conditions and initial phenol concentration with coefficient of determination (R2 = 0.9525). In addition, artificial neural network (ANN) model was developed based on input layer of operating conditions and output layer of phenol degradation efficiency. The ANN model yielded a coefficient of determination (R2 = 0.9742) and (Se/Sy = 0.16).

Electroextraction of heavy metals from wastewater for the protection of natural water bodies from pollution

The most promising methods of eluates recycling are electrolysis and electrodialysis. It is possible to obtain metals and purified regeneration solutions for repeated regeneration in case of application of electrochemical methods. The processes of electrolysis of solutions of cadmium and zinc sulfates and chlorides in electrolysers of different types were explored, the influence of conditions of electrolysis on effectiveness of extraction and separation of metals, obtaining inorganic acids for repeated usage in regeneration processes was determined. Single- and double-chamber electrolysers, in which cathode was made of stainless steel and titanium anode was covered with ruthenium oxide, were used. Cathodic and anodic areas in double-chamber electrolysers were separated by the anion exchange membrane MA-41. Solution of cadmium sulfate or of zinc sulfate was found in the cathodic chamber in double-chamber electrolysers. Solution of sulfuric acid with concentration of 50 mg-equiv./dm 3 was in the anodic chamber. It is recommended to carry out electrolysis for two hours when using a single-chamber electrolyser at a voltage of 5 V with the purpose of removing cadmium from sulfuric acid solution and reusing regeneration solution of sulfuric acid. Almost complete removal of cadmium ions and concentration of sulfuric acid in anolyte is achieved in case of using a double-chamber electrolyser. However, in terms of power saving, release of cadmium should be performed in single-chamber electrolysers. However, it is recommended to perform zinc removal from eluates in double-chamber electrolysers. In this case, zinc ions are almost completely removed within four hours at voltage of 25 V. The maximum current efficiency is 42‒80 %. Conditions of separation of zinc and cadmium in the eluate are associated with acidity of the solutions. A stage-by-stage removal of metals – cadmium followed by zinc, is observed during electrolysis of the mixture of cadmium and zinc chlorides in a single-chamber electrolyser. Current efficiency of metals is 30–68 %. In the case of electrolysis of a mixture of zinc and cadmium sulfates, only cadmium (В=100 %) is removed from the solution, while zinc ions completely remain in solution. Zinc is released only at the transfer of the electrolyte to a double-chamber electrolyser