Papers by Keyword: Redox Potential

Abstract: Bioleaching experiments were used in this experiment to study the interaction between marmatite and chalcopyrite. In the sterile system, the copper extraction rate of single chalcopyrite was only 20%, much lower than the copper extraction rate of L. ferriphilum system, which is 95%. The addition of L. ferriphilum can improve the copper extraction rate to a substantial level. In both the sterile and L. ferriphilum system, the single chalcopyrite got a higher copper extraction rate than the mixture minerals of chalcopyrite and marmatite, and with the increase of marmatite, the copper extraction rate decreased. So marmatite may inhibit the dissolution of chalcopyrite. The reason may be that the redox potential of mixture mineral was not in the optimum range.

Abstract: Various methods of controlling redox potential (ORP) with electrochemical bioreactor and others have been investigated to increase copper extraction of chalcopyrite in bioleaching,but less attention has been paid to reducing ferric to ferrous ions. Therefore, in this work, the redox potential of chalcopyrite bioleaching system in the presence of mixed moderately thermophiles containing Leptospirillum. ferriphilum, Acidithiobacillus. caldus and Sulfobacillus. thermosulfidooxidans has been controlled by pyrite. It was found that at a constant pH of 2.0, the addition of pyrite can reduce ferric to ferrous ion to a large extent, and the lower ORP values can be obtained. Bioleaching experiments indicated that the time for adding pyrite caused different bioleaching behaviors of chalcopyrite. The high copper extraction can be obtained by added pyrite at a low ORP values (<420 mV vs. Ag/AgCl). The XRD tests and SEM images showed that the amounts of formed jarosite increased as the pyrite addition, and the loose and porous jarosite can be found at low ORP values.

Abstract: In this work, we present an Electrochemical Impedance Spectroscopy (EIS) study using a carbon paste electrode modified with chalcopyrite (CuFeS₂) containing 50 wt% of the mineral (particle size < 38 μm) and graphite (particle size < 20 μm) in naturally aerated salt acid solutions (pH 1.8) without and with the addition of 0.100 mol L^-1 of ferrous ions. The aim was to evaluate the influence of the solution potential on the behavior of chalcopyrite electrode in the presence and absence of iron (II) ions. Additionally, we evaluated the influence of the bacteria Acidithiobacillus ferrooxidans in the system containing iron (II) ions without applying potential. Therefore, EIS was used to investigate the processes occurring at the electrode/solution interface in the different systems, considering the charge transfer reactions involving chalcopyrite and ferrous ions, the presence of a multicomponent layer, and diffusion. The results showed that the combination of iron (II) ions with the imposition of low potential values (0.100 Fe²⁺ ions with +0.300 V/Ag|AgCl|KCl_3mol/L) activates the chalcopyrite surface and enhances the copper recovery.

Abstract: Commercially available conductive inks are typically made up of precious metal nanoparticles, such as gold (Au) and silver (Ag). Thus, cheaper metals like copper (Cu) are currently being explored as alternative material. Though Cu has a comparable conductivity to that of Ag, they tend to oxidize easily when exposed to air and water, which could limit their application. In this work, oxidation-stable Cu nanoparticles with mean diameter as small as 57 nm were prepared by simple electroless deposition in water. Food-grade gelatin was used as stabilizer, which makes the process more economical and environment-friendly. In situ monitoring of mixed potential was carried out during synthesis to understand the kinetics of the reaction. The mixed potential of the solution shifted negatively as the amount of gelatin was increased. This suggests faster reduction rate.

Abstract: The main sulphidic minerals, contained in the Olimpiada flotation concentrate, are pyrrhotite, arsenopyrite, pyrite and antimonite. Biooxidation of these minerals occurs in the following sequence: Pyrrhotite → Arsenopyrite → Pyrite → Antimonite. Oxidation of pyrrhotite requires acid consumption, oxidation of pyrite is followed by formation of sulphuric acid. The oxidation rate of pyrrhotite is higher and due to this, acid balance of the whole biooxidation process is shifted to the consuming side, and it is required to add acid to the process. The research work has demonstrated, that by regulating oxidation-reduction potential it is possible to reduce pyrrhotite oxidation rate and intensify pyrite oxidation rate; this allows to reduce consumption of sulphuric acid, reduce heating of the slurry inside the reactors and as a result maintain the stable process.

Abstract: Leaching of a pyritic and a pure chalcopyrite concentrate was carried out in stirred tank reactors in the absence and presence of a mixed culture of moderately thermophilic microorganisms at 45°C and pH 1.5. To study the effect of microbial activity on copper dissolution, the abiotic experiments were performed under accurately controlled redox potential conditions to reproduce the same oxidising conditions recorded during the bioleaching experiments. X-ray photoelectron spectrometry (XPS) was used to study the surface of chalcopyrite chips leached for different durations. The results showed that the microorganisms in cases of both concentrates did not have any effect in the copper leaching efficiency other than oxidation of ferrous to ferric ions. Biooxidation of elemental sulphur did not improve the leaching efficiency and bulk and surface jarosite had no negative effect on dissolution. A composite layer composed of mainly elemental sulphur and iron-oxy-hydroxide was found to be responsible for the hindered dissolution.

Abstract: The definition of sub-20 nm electronic devices for the newest generation of smart phones, computer and automotive is calling for very innovative FEOL wet chemical cleans. The electronic properties are very sensitive, in respect of the surface morphology on a Si-wafer. Most of the modern wet cleans are based on the RCA-clean [1]. Innovative cleans, like for example the IMEC-clean [2] and modified RCA clean were developed, using ozone-DIW mixture (O₃-DIW), in order to improve the cleaning performance [3], [4]. Since several years electrolyzed water (EW) is used in semiconductor manufacturing [5]. An electrochemical reaction is induced by an electrode and a small amount of ammonia hydroxide (NH₄OH) or ammonia sulfate and DIW [7].

Abstract: A precise monitoring of reductionoxidation (RedOx) potential is necessary for using molten salts as fuel compositions and coolants in molten-salt reactors as well as for pyrochemical processing of a spent fuel. So, low over-potentials (~10 mV) are required for rigorously selective extraction of impurities out of the molten salt due to a permanent diffusive cathode polarization in galvanic cell. At the same time, a weak identification of cationic disproportionation (M^k+ M^l+) of metal impurities in liquid salts reflects the common defect of all known internal monitoring tools using salt as a sensor: realizing high over-potential and thereby strong polarization of the cathode. It leads to appreciable energy deformation of allowed electron states in the molten salt near the electrodes so that metal components of the basic salt are extracted out of the salt solution together with the selected impurity. Obviously, such the kinetic monitoring of RedOx potential cannot be a precise method since there is impossible eliminating the uncertain polarizing cathode effects in the galvanic cell with the molten salt as an electrolyte. Therefore a monitoring of the RedOx potential of liquid salts by means of an external potentiometer is necessary. This method is based upon the using of a gauge with Na⁺βAl₂O₃ electrolyte as a solid membrane with unipolar sodium conductivity assigned for monitoring a thermodynamic activity, , of neutral sodium atoms (Na⁰) in the molten salt. The principle of operation of such the gauge is based on the e.m.f. method. A measuring electrode, Pb [N (a thin layer of liquid lead on the solid electrolyte), directly contacts with the molten salt, easily exchanges by dissolved sodium atoms, and corrosive protects the solid electrolyte. The e.m.f., E, of this electrode is defined relatively a reference electrode (liquid sodium) located on the other side of solid electrolyte, Na⁺βAl₂O₃, in the four-layer galvanic cell: NaNa⁺βAl₂O₃Pb [Nsalt [], by equation, E = (RT/F) ln, where R is the universal gas constant, T is Kelvin temperature, F is Faraday constant.

Abstract: In this work we present an electrochemical study using carbon paste electrode (CPE) with CuFeS₂ in solutions with different concentrations of Fe²⁺ ions in order to evaluate the possible interaction between these ions and mineral sulfide in the absence and presence of the bacteria Acidithiobacillus ferroxidans.

Abstract: Valuable metals as well as ferrous iron and sulfur compounds are released from ore by ferric iron and sulfuric acid chemical attack. Biomining microorganisms allow the recycling of these products by oxidizing ferrous iron and/or sulfur compounds. The energy released from the oxidation of these substrates is used for the growth of the acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans. The respiratory pathways involved in these respiratory processes have been deciphered and the expression of the genes encoding these redox proteins is dependent on the electron donor present in the medium. Furthermore, in the presence of both ferrous iron and sulfur, the genes involved in iron oxidation are expressed before those involved in sulfur oxidation. We propose that the global redox responding two component system RegBA is responsible for this regulation since (i) the redox potential increases during iron oxidation but remains stable during sulfur oxidation and (ii) the transcriptional regulator RegA binds the regulatory region of a number of genes/operons involved in iron and sulfur oxidation. To understand the mechanism of the At. ferrooxidans RegBA system, the regA gene and the DNA corresponding to the DNA binding domain of RegA were cloned in an expression plasmid in Escherichia coli. The recombinant proteins, RegA and RegA-HTH respectively, were purified. The binding of RegA-HTH, phosphorylated and unphosphorylated RegA on the regulatory region of some target operons have been compared by gel shift mobility assay.