Control Of Redox Potential Research Articles

Measurements of UF4/UF3 ratio for redox potential control in u-bearing fluoride salt

Redox potential control is important in mitigating corrosion in molten salt reactors (MSRs) during operation. This study has developed a methodology for establishing the operational boundaries, both upper and lower, of the ratio of UF4 to UF3 (UF4/UF3) for redox potential control in U-bearing fluoride salts by measuring the equilibrium quotient. The upper limit for UF4/UF3 is determined by the potential for chromium dissolution, while the formation of uranium carbides governs the lower limit. By applying the methodology, the research experimentally determined the UF4/UF3 ratio in NaF-KF-UF4 salt at temperatures ranging from 873 K to 1023 K. To determine a stable operational range, the range of the operation temperature of the MSR must be considered, the stable range of the ratio is depicted as a trapezoid, with the upper and lower limits serving as the bases of the trapezoid.

The Role and Application of Redox Potential in Wine Technology

In wine technology, the on-line measurement of redox potential is a fast, accurate, and reliable measurement that provides insight into the metabolism of Saccharomyces cerevisiae, its microbial activity, and the oxidation and reduction state of wine, as well as insight into its quality and stability. The significance of the redox potential measurement and control in wine technology as well as the maintenance and regulation of fermentation redox potential using temperature and carbon dioxide fluxes are discussed. Redox potential levels from Eh 100 to 180 mV are typical for non-oxidized wine that is bottling-ready, while levels of Eh 270 to 460 mV represent oxidized wines with typical failures. The relevance of redox potential measurement during the 2-year maturation of Blau Fränkisch wine in 225 L oak barrels at six levels at a temperature 15 °C is presented. The measurement of the redox potential, expressing heterogeneity in redox layers during wine maturation in oak barrels, is represented in various oxido-reductive fermentation zones. On the contrary, the end of the maturation process is indicated by the homogeneity of redox zones, where the matured wine shows no differences in redox measurement on all levels. Using redox potential as a key scale-up criteria ensures comparable and reproducible amounts of the final product even in geometrically non-similar fermenter systems.

Controlling Redox Potential of a Manganese(III)-Bis(hydroxo) Complex through Protonation and the Hydrogen-Atom Transfer Reactivity.

A series of mononuclear manganese(III)-hydroxo and -aqua complexes, [MnIII(TBDAP)(OH)2]+ (1), [MnIII(TBDAP)(OH)(OH2)]2+ (2) and [MnIII(TBDAP)(OH2)2]3+ (3), were prepared from a manganese(II) precursor and confirmed using various methods including X-ray crystallography. Thermodynamic analysis showed that protonation from hydroxo to aqua species resulted in increased redox potentials (E1/2) in the order of 1 (-0.15 V) < 2 (0.56 V) < 3 (1.11 V), while pKa values exhibited a reverse trend in the order of 3 (3.87) < 2 (11.84). Employing the Bordwell Equation, the O-H bond dissociation free energies (BDFE) of [MnII(TBDAP)(OH)(OH2)]+ and [MnII(TBDAP)(OH2)2]2+, related to the driving force of 1 and 2 in hydrogen atom transfer (HAT), were determined as 75.3 and 77.3 kcal mol-1, respectively. It was found that the thermodynamic driving force of 2 in HAT becomes greater than that of 1 as the redox potential of 2 increases through protonation from 1 to 2. Kinetic studies on electrophilic reactions using a variety of substrates revealed that 1 is only weakly reactive with O-H bonds, whereas 2 can activate aliphatic C-H bonds in addition to O-H bonds. The reaction rates increased by 1.4 × 104-fold for the O-H bonds by 2 over 1, which was explained by the difference in BDFE and the tunneling effect. Furthermore, 3, possessing the highest redox potential value, was found to undergo an aromatic C-H bond activation reaction under mild conditions. These results provide valuable insights into enhancing electrophilic reactivity by modulating the redox potential of manganese(III)-hydroxo and -aqua complexes through protonation.

Control and surveillance of redox potential for 233Pa dissolution in 2LiF-BeF2 molten salt.

233Pa, the precursor nuclide of 233U in the thorium-uranium conversion is prone to reductive deposition in 2LiF-BeF2 (66 : 34 mol%, FLiBe) molten salt. We explored the adjustment and control of the redox potential of the FLiBe melt to avoid the 233Pa reduction deposition. The experimental data indicated that the deposited 233Pa can be completely dissolved and reentered into the molten salt with the addition of oxidant NiF2, and the distribution and behaviour of uranium, thorium, neptunium, and most fission products did not have any significant change in the NiF2-oxidised FLiBe molten salt, showing the feasibility of this manner to make 233Pa exist stably in the melt. The effects of NiF2-addition on the behaviour of the fission products 95Nb and 131I in the FLiBe molten salt were also investigated. It was found that 131I could be used as a redox indicator to monitor the redox potential of the oxidation-enhanced FLiBe molten salt. All the information drawn from this study could provide significant support for the control and surveillance of the redox potential of the FLiBe molten salt in the upcoming thorium molten salt reactor (TMSR).

Pyruvate modulation of redox potential controls mouse sperm motility

Sperm gain fertilization competence in the female reproductive tract through a series of biochemical changes and a requisite switch from linear progressive to hyperactive motility. Despite being essential for fertilization, regulation of sperm energy transduction is poorly understood. This knowledge gap confounds interpretation of interspecies variation and limits progress in optimizing sperm selection for assisted reproduction. Here, we developed a model of mouse sperm bioenergetics using metabolic phenotyping data, quantitative microscopy, and spectral flow cytometry. The results define a mechanism of motility regulation by microenvironmental pyruvate. Rather than being consumed as a mitochondrial fuel source, pyruvate stimulates hyperactivation by repressing lactate oxidation and activating glycolysis in the flagellum through provision of nicotinamide adenine dinucleotide (NAD)+. These findings provide evidence that the transitions in motility requisite for sperm competence are governed by changes in the metabolic microenvironment, highlighting the unexplored potential of using catabolite combination to optimize sperm selection for fertilization.

Depletion-driven thermochemistry of molten salt reactors: review, method, and analysis

Molten salt reactors (MSRs) are innovative advanced nuclear reactors that utilize nuclear fuel by dissolving it in a high-temperature liquid salt. This unique feature differentiates MSRs from other types of reactors and allows for enhanced safety and economic performance. The liquid fuel also entails several multiphysics effects that can complicate reactor design and operation. One primary effect termed here as depletion-driven thermochemistry is a driving force in altering the multiphysics behavior of the reactor. Essentially, depletion-driven thermochemistry is the effect that fuel depletion has on changing the chemical redox potential of the fuel salt over time. As the fuel is consumed, the redox potential shifts toward a more oxidizing state. Without active control, the changing chemistry due to depletion increases corrosion thereby limiting reactor component lifetimes. Additionally, the changing redox potential of the fuel salt alters the vapor pressures of chemical species dissolved in the fuel salt. Changing vapor pressures of species in the fuel salt is an important parameter to understand when off-gassing volatile species during normal reactor operation, and for source term characterization during accident scenario transients. The present work represents a fundamental step toward modeling and coupling the driving physics (i.e., neutronics and chemistry) involved in altering the redox potential in an MSR. Here, the neutronic code Griffin models the depletion of the fuel-salt system, while the chemical equilibrium code Thermochimica calculates the thermochemical state of the isotopic inventory, using the Molten Salt Thermodynamic Database - Thermochemical (MSTDB-TC). These two codes are tightly coupled to predict the impact of fuel depletion in altering the chemistry in MSR systems. Redox potential control methods are discussed and can be modeled using this multiphysics approach. The vapor pressures of chemical species that could be extracted to an off-gas system, as determined by the reactor’s thermochemical state, are examined. The neutronics-chemistry coupling developed in this work is expected to have potential application for analyzing corrosion, source term evolution, and material safeguards in MSR systems. Lastly, suggestions for areas of further improvements of the models to expand these capabilities by incorporating other coupled physics effects is provided.

Redox dynamics of 2D crystalline vanadium oxide phases on high-index anatase facets.

Vanadium oxides exist in a multitude of phases with varying structure and stoichiometry. This abundance of phases can be extended through the use of other oxides as supports, and through redox treatments. However, the combined effects of different supports and redox treatments can be difficult to identify, particularly when present as different terminating facets on nanoparticles. Here, we examine structural dynamics of 2D vanadium oxides supported on anatase TiO2 nanoparticles, correlated with changes in oxidation state, using in situ transmission electron microscopy imaging and electron energy loss spectroscopy. As the average oxidation state is reduced below V(IV), an ordered cubic V(II) phase is observed exclusively at the high-index {10l} facets of the support. This local accommodation of highly reduced states is necessary for explaining the observed range of average oxidation states. In turn, the findings show that oxidation states extending from V(V)-V(IV) to V(II) can be simultaneously stabilized by different supporting oxide surfaces during exposure to atmospheres with controlled redox potential.

Direct and remote control of electronic structures and redox potentials in μ-oxo diferric complexes.

Non-heme diiron enzymes activate O2 for the oxidation of substrates in the form of peroxo FeIII2 or high-valent FeIV2 intermediates. We have developed a dinucleating bis(tetradentate) ligand system that stabilizes peroxo and hydroperoxo FeIII2 complexes with terminal 6-methylpyridine donors, while the peroxo FeIII2 intermediate is reactive with terminal pyridine donors presumably via conversion to a fluent high-valent FeIV2 intermediate. We present here a derivative with electron-donating methoxy substituents at the pyridine donors and its diferric complexes with an {FeIIIX(μ-O)FeIIIX} (X- = Cl-, OAc-, and OH-) or an {FeIII(μ-O)(μ-OAc)FeIII} core. The complex-induced oxidation of EtOH with H2O2 provides μ-OAc-, and in acetone, the complex with mixed OH-/OAc- exogenous donors is obtained. Both reactivities indicate a reactive fluent peroxo FeIII2 intermediate. The coupling constant J and the LMCT transitions are insensitive to the nature of the directly bound ligands X- and reflect mainly the electronic structure of the central {FeIII(μ-O)FeIII} core, while Mössbauer spectroscopy and d-d transitions probe the local FeIII sites. The remote methoxy substituents decrease the potential for the oxidation to FeIV by ∼100 mV, while directly bound OH- in {FeIII(OH)(μ-O)FeIII(OH)} with a short 1.91 Å FeIII-OOH bond decreases the potential by 590 mV compared to {FeIII(OAc)(μ-O)FeIII(OAc)} with a 2.01 Å FeIII-OOAc bond. Interestingly, this FeIII-OH bond is even shorter (1.87 Å) in the mixed OH-/OAc- complex but the potential is the mean value of the potentials of the OH-/OH- and OAc-/OAc- complexes, thus reflecting the electron density of the central {FeIII(μ-O)FeIII} core and not of the local FeIII-OH unit.

Advanced Monitoring and Control of Redox Potential in Wine Fermentation across Scales

Combined with real-time monitoring of density and temperature, the control of the redox potential provides a new approach to influencing cell metabolism during growth, cell viability and non-growing yeast activity in wine fermentations. Prior research indicates that the problem of sluggish and incomplete fermentation can be alleviated by maintaining a constant redox potential during the ethanol fermentation. A secondary trait of hydrogen sulfide formation from elemental sulfur also seems to be associated with the development of low redox potentials during fermentation and this might be prevented by the deliberate control of redox potentials in a certain range. While the control of the redox potential during wine fermentations has been demonstrated previously at the research scale (100 L), the ability to control it in larger volumes typically seen in commercial conditions remained unanswered. Wine fermentations from the same load of Cabernet Sauvignon grapes from the 2021 harvest were conducted at three volumes: 100 L and 1500 L in a research winery and 10,000 L in a commercial winery. Using only pulses of air delivery, the redox potential was successfully controlled to −40 mV referenced to a silver/silver chloride electrode throughout the fermentations, at all scales. This appears to be the first published result of a controlled fermentation trial that includes the commercial scale and demonstrates the scalability of control of redox potential in wine fermentations.

ROS: Basic Concepts, Sources, Cellular Signaling, and its Implications in Aging Pathways.

Reactive oxygen species (ROS) are bioproducts of cellular metabolism. There is a range of molecules with oxidizing properties known as ROS. Despite those molecules being implied negatively in aging and numerous diseases, their key role in cellular signaling is evident. ROS control several biological processes such as inflammation, proliferation, and cell death. The redox signaling underlying these cellular events is one characteristic of the new generation of scientists aimed at defining the role of ROS in the cellular environment. The control of redox potential, which includes the balance of the sources of ROS and the antioxidant system, implies an important target for understanding the cells' fate derived from redox signaling. In this review, we summarized the chemical, the redox balance, the signaling, and the implications of ROS in biological aging.

Review of Redox Potential Control Options for Molten Salt Reactors

Redox potential control is a fundamental requirement to minimize corrosion of metals in neutron irradiated molten salts, including fission reactor fuel, fission reactor coolant, and fusion reactor blanket. In this presentation, the focus will be placed upon metallic redox buffers—including beryllium, zirconium, and lithium. The study of beryllium for this function spans several decades and includes use in the Molten Salt Reactor Experiment (MSRE) in addition to proposed use in a fusion blanket. A fascinating aspect of this subject is the phase behavior of the metallic redox buffer. Evidence has been published that some of the metals—including beryllium and lithium actually dissolve into their host salts in the zero oxidation state. This provides the capability for a fast, homogenous reaction sans mass transfer limits. But redox buffering has also been reported from the reaction of molten salt with zirconium metal rods. It is proposed that these reactions can be categorized as either short range (homogenous) or long range (electrochemical cell) electronically mediated reactions. Data on metal solubility, electrochemical measurements, and corrosion control will be presented from the MSRE to very recent work in support of the Versatile Test Reactor. Open questions will be posed with the intention of encouraging the audience to propose new theories and experiments to test those theories.

Understanding the Role of NRF2 Signalling in Cancer.

Nuclear factor erythroid 2 (NFE 2) - related factor 2 (NFE2L2 or NRF2) is one of the transcription factors predominantly related to the expression of antioxidant genes. NRF2 plays a pivotal role in controlling redox potential in several tumor characteristics, including cancer cell metabolism, stem-cell-like characteristics, tumor aggressiveness, invasion, and metastasis. Further, it was recently discovered that the noncanonical pathway of NRF2 activation was involved in carcinogenesis. Cancerrelated changes (e.g., metabolic flexibility) that support cancer progression were found to be redox and NRF2 dependent. The pro or antineoplastic effects of NRF2 are essentially based on the specific molecular characteristics of the type of cancer. Therefore, systematic investigation of NRF2 signaling is necessary to clarify its role in cancer etiology. Understanding the role of NRF2 in triggering gene expressions in different types of cancer is quite challenging, which might be useful to target those genes for better clinical outcomes. To decipher the role of NRF2 in tumor formation and progression, largescale genomic and transcriptomic studies are required to correlate the clinical outcomes with the activity of the NRF2 expression system. This review attempts to give insights into the understanding of the role of NRF2 in cancer.

Control of redox potential in a novel continuous bioelectrochemical system led to remarkable metabolic and energetic responses of Clostridium pasteurianum grown on glycerol

BackgroundElectro-fermentation (EF) is an emerging tool for bioprocess intensification. Benefits are especially expected for bioprocesses in which the cells are enabled to exchange electrons with electrode surfaces directly. It has also been demonstrated that the use of electrical energy in BES can increase bioprocess performance by indirect secondary effects. In this case, the electricity is used to alter process parameters and indirectly activate desired pathways. In many bioprocesses, oxidation-reduction potential (ORP) is a crucial process parameter. While C. pasteurianum fermentation of glycerol has been shown to be significantly influenced electrochemically, the underlying mechanisms are not clear. To this end, we developed a system for the electrochemical control of ORP in continuous culture to quantitatively study the effects of ORP alteration on C. pasteurianum by metabolic flux analysis (MFA), targeted metabolomics, sensitivity and regulation analysis.ResultsIn the ORP range of −462 mV to −250 mV, the developed algorithm enabled a stable anodic electrochemical control of ORP at desired set-points and a fixed dilution rate of 0.1 h−1. An overall increase of 57% in the molar yield for 1,3-propanediol was observed by an ORP increase from −462 to −250 mV. MFA suggests that C. pasteurianum possesses and uses cellular energy generation mechanisms in addition to substrate-level phosphorylation. The sensitivity analysis showed that ORP exerted its strongest impact on the reaction of pyruvate-ferredoxin-oxidoreductase. The regulation analysis revealed that this influence is mainly of a direct nature. Hence, the observed metabolic shifts are primarily caused by direct inhibition of the enzyme upon electrochemical production of oxygen. A similar effect was observed for the enzyme pyruvate-formate-lyase at elevated ORP levels.ConclusionsThe results show that electrochemical ORP alteration is a suitable tool to steer the metabolism of C. pasteurianum and increase product yield for 1,3-propanediol in continuous culture. The approach might also be useful for application with further anaerobic or anoxic bioprocesses. However, to maximize the technique's efficiency, it is essential to understand the chemistry behind the ORP change and how the microbial system responds to it by transmitted or direct effects.

Oxidation-reduction effects in the flotation of copper sulfide minerals and molybdenite – A proof of concept at industrial scale

Redox potential (Eh) control plays a significant role during sulfide mineral flotation by influencing the reactions on the surface of the minerals and accordingly the flotation behaviour. In this study, the metallurgical performance of typical copper sulfide minerals, molybdenite as well as gangue minerals (e.g., pyrite, tennantite, and enargite) under different pH and Eh conditions of the flotation cell were investigated. The copper and molybdenum processing plant at the Sungun complex-Iran were selected as a case study. For this purpose, Eh of flotation cells of phases 1 and 2 of copper and molybdenum processing circuits – Sungun complex – were measured by off-line method. After performing chemical analysis, the mineralogical study of the input load and products of each of the aforementioned flotation circuits in the rougher, cleaner, re-cleaner, and scavenger stages was performed. Based on the results, the potential in cells of phases 1 and 2 of copper concentration plants is in the range of −60 to −100 mV; and for the molybdenum plant, is in the range of −500 to −700 mV. The potentials of more than −100 mV in the phases of copper concentration plants have created suitable conditions for the separation of copper sulfide and molybdenite minerals from gangue minerals, especially pyrite. Adjustment of Eh in the range of −500 to −700 mV in the molybdenum processing plant has also led to the depression of copper minerals and the flotation of molybdenite, resulting in the effective separation of these minerals. However, grade analysis and mineralogical studies indicate the misplaced copper minerals into tailings, the passage of chalcopyrite and pyrite to molybdenum concentrate, the misplaced molybdenite to copper concentrate, and also the presence of minerals containing harmful elements such as arsenic in copper concentrate. Eh fluctuations in phase 1 and 2 of copper plants, the interaction of copper sulfide minerals, especially chalcopyrite with pyrite (and the depression of pyrite in Eh more than −100 mV), are reasons for the misplaced copper minerals into tailings. The interaction of chalcopyrite and pyrite with molybdenite and the high flotation tendency of molybdenite at the potential of +600 mV is the main factor in increasing the Cu and Fe grade in molybdenite concentrate. The interaction of copper minerals with arsenic-bearing minerals and the similar flotation behavior of these minerals in the potential of the rougher cells of the molybdenum processing plant has increased the arsenic grade in the copper concentrate or molybdenum tailings.

Green strategies to control redox potential in the fermented food industry

Lactic acid bacteria (LAB) are important microorganisms in the food industry as functional starters for the manufacture of fermented food products and as probiotics. Redox potential (Eh) is a parameter of the physicochemical environment of foods that influences key oxidation-reduction reactions involved in process performances and product quality. Eh can be modified by different methods, using redox molecules, catalytic activity of enzymes or LAB themselves, technological treatments like electroreduction or heating, and finally gases. Nowadays new applications for food manufacture must undertake green process innovation. This paper presents the strategies for Eh modification in a sustainable manner for production of LAB biomass (starters, probiotics) and fermented food products (fermented milks, cheeses and others). While the use of chemical or enzymes may be subject to controversy, the use of gases offers new opportunities, in combination with LAB. Protection against food-borne microorganisms, an increasing growth and viability of LAB, and a positive impact on food flavour are expected.

Development of the Molten Salt Thermal Properties Database − Thermochemical (MSTDB−TC), example applications, and LiCl−RbCl and UF3−UF4 system assessments

The Molten Salt Thermal Properties Database − Thermochemical (MSTDB−TC) has been developed to support thermodynamic modeling of fluoride- and chloride-based systems for molten salt reactors (MSRs). Utilizing data from available literature and original work, the current MSTDB−TC Ver. 1.2 contains models for 96 pseudo-binary systems, 37 pseudo-ternary systems, 42 solid solutions, 229 stoichiometric compounds, and 130 gaseous species. This includes 67 reassessed systems and 13 original system models. The reassessment of the LiCl−RbCl pseudo-binary system and the original assessment of the UF3−UF4 pseudo-binary system are included as examples of those efforts and provide improved representations of those systems. The database continues to be expanded, adding systems of relevance to the wide variety of MSR concepts. To illustrate applications for MSTDB−TC, phase equilibria were computed to understand the effect of varying uranium content in the KCl−MgCl2−NaCl−UCl3 system. In an example of how such calculations can support corrosion modeling, the control of redox potential by the UF3:UF4 ratio in the LiF−BeF2−UF3−UF4 system is demonstrated and used to assess corrosion potential for typical alloy constituents.

Fermentation redox potential control on the 1,3-propanediol production by Lactobacillus panis PM1

The fermentation redox potential was controlled during the production of 1,3-propanediol (PDO) by Lactobacillus panis PM1. Results show that the best redox potential level was at −200 mV at which had the highest PDO production (23.38 g/L) when compared to that controlled at -250 mV, −150 mV, and without control. For the redox potential level under investigation, the mass PDO yield with respect to glycerol was between 0.66 and 0.82. Potassium ferricyanide was chosen as an oxidant to control the redox potential level. With the addition of oxidant, the batch fermentation time was noticeably reduced compared to the one without the addition of oxidant. Furthermore, co-substrate utilization of glucose and glycerol was observed when potassium ferricyanide was present. It was postulated that such a co-substrate utilization pattern resulted from the redox imbalance where the activities of acetaldehyde dehydrogenase and alcohol dehydrogenase were retarded by the presence of potassium ferricyanide. To overcome the redox imbalance, the glycerol-reductive pathway was triggered to serve as the electron source to fuel the glycolysis pathway and PDO formation. The developed redox potential control strategy may benefit other specifically isolated PDO-producing strains and industrial PDO green processing to further enhance their productivity.

Iodine-assisted chalcopyrite leaching in ferric sulfate media: Kinetic study under fully controlled redox potential and pH

The addition of iodide has been found to significantly accelerate chalcopyrite leaching in ferric sulfate media at ambient conditions. Solution potential is the principal factor determining the leaching performance through controlling the iodine speciation. In order to develop a kinetic equation that incorporates the iodine speciation, a series of leaching tests were carried out in specially-designed sealed reactors that allows the solution potential together with other leaching parameters to be fully controlled. The experimental results showed that the rate of copper dissolution was increased by increasing the solution potential in the range of 669 to 769 mV vs. SHE), increasing the total iodide concentration in the range of 50 to 200 mg/L, and increasing the temperature between 25 and 40 °C. The formation of elemental sulfur and jarosite did not hinder the leaching reaction. A kinetic model was developed that relates the rate of copper extraction to the solution potential with a reaction order of 0.32, the diiodine concentration with a reaction order of 1.17, and temperature with an activation energy of 43.1 kJ/mol. The kinetic analysis supported that the leaching process was controlled by surface chemical reaction.

Theoretical Study on Redox Potential Control of Iron-Sulfur Cluster by Hydrogen Bonds: A Possibility of Redox Potential Programming.

The effect of hydrogen bonds around the active site of Anabaena [2Fe-2S] ferredoxin (Fd) on a vertical ionization potential of the reduced state (IP(red)) is examined based on the density functional theory (DFT) calculations. The results indicate that a single hydrogen bond increases the relative stability of the reduced state, and shifts IP(red) to a reductive side by 0.31–0.33 eV, regardless of the attached sulfur atoms. In addition, the IP(red) value can be changed by the number of hydrogen bonds around the active site. The results also suggest that the redox potential of [2Fe-2S] Fd is controlled by the number of hydrogen bonds because IP(red) is considered to be a major factor in the redox potential. Furthermore, there is a possibility that the redox potentials of artificial iron-sulfur clusters can be finely controlled by the number of the hydrogen bonds attached to the sulfur atoms of the cluster.

The use of pyrite to control redox potential to enhance chalcopyrite bioleaching in the presence of Leptospirillum ferriphilum

Redox potential (ORP) was proved to be a key factor in promoting chalcopyrite (CuFeS2) bioleaching. Though there are some methods for maintaining ORP reported previously, little attention has been given to control it via pyrite. In this work, chalcopyrite bioleaching was investigated in the presence of Leptospirillum ferriphilum (L. ferriphilum) with various amounts of pyrite addition. Bioleaching results showed that the addition of pyrite extremely enhanced the dissolution of chalcopyrite, especially when the mass ratio of pyrite and chalcopyrite was 3:1. In this case, ORP was well maintained at an appropriate range (350–370 mV vs. Ag/AgCl) for 25 days. The results of electrochemical tests indicated that the addition of pyrite did not change the electrochemical dissolution mechanism of chalcopyrite. Thus, the effect of pyrite was mainly a redox potential controlling process, and the reduction of chalcopyrite to secondary copper-iron species like chalcocite (Cu2S) was promoted in the optimum range. Eventually, a high copper extraction (70%) was obtained as a result of the rapid dissolution of formed chalcocite. Based on all the obtained results, a model for illustrating the ORP control of pyrite during chalcopyrite bioleaching in the presence of L. ferriphilum was proposed.