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Electrochemical Processes at Porous Electrodes
Published in Antonio Doménech-Carbó, Electrochemistry of Porous Materials, 2021
The discrimination between the extreme cases (i.e. solution of Aox or Ard) can be made by measuring the open circuit potential of the solution or by recording the initial currents upon starting the potential once on the positive and again on the negative limit. A straightforward and sensitive discriminating method of application was proposed by Scholz and Hermes [23] in CV experiments in the solution phase. The method exploits the shift along the current axis of the entire voltammogram depending on the redox state of the depolarizer and involves the measurement of the currents at the lower (Iλc) and upper (Iλa) limits of the potential range. Simulations indicated that the difference ΔI = | Iλa | – |Iλc| varied linearly on the molar ratio of the reduced (or oxidized) electroactive species of the couple provided that: (i) the potential limits are chosen symmetric to the formal potential, (ii) the potential range is relatively large (at least eight times the peak separation), and (iii) repetitive voltammetry (fifth scan is recommended in order to avoid transient phenomena) is used [23].
Hydrometallurgy — An Introductory Appraisal
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2019
Hence, on substituting the value of [H+] for both [D] and [C], one gets the linear dependence of the rate on the hydrogen ion concentration. In basic medium when dissolution is accompanied by hydrogen evolution, as, for example, in the dissolution of Al in NaOH, H+ ions serve as a depolarizer and the OH− ions as a complexing agent [Al3+ + 4OH− → AlO(OH)2 + H2O]. In this case, substituting [H+] for [D] and [OH−] for [C] in the main kinetic equation, the velocity equation reduces to: () Rate=klk2⋅A[OH−]kl+k2K[OH−]2
Basic Materials Engineering
Published in David A. Hansen, Robert B. Puyear, Materials Selection for Hydrocarbon and Chemical Plants, 2017
David A. Hansen, Robert B. Puyear
Polarization occurs because of ion concentration buildup in the vicinity of the anode and/or cathode. Once the ion concentration reaches saturation, corrosion slows to a virtual stop. Polarization can occur when: Hydrogen ions concentrate at an active cathode in the absence of a cathodic depolarizer. Dissolved oxygen is an example of a cathodic depolarizer.Soluble Fe(++) saturates the electrolyte around an anode in carbon steel, perhaps as the result of the precipitation of an insoluble iron salt which inhibits diffusion of Fe(++).
A Review of Low Grade Manganese Ore Upgradation Processes
Published in Mineral Processing and Extractive Metallurgy Review, 2020
Veerendra Singh, Tarun Chakraborty, Sunil K Tripathy
The other consumers, such as chemical, battery, glass, non-ferrous metal industry, etc. use relatively high grade or processed ores. Chemical industry uses high-grade manganese oxide ores to produce potassium permanganate, hydroquinone, manganese sulfate, manganese oxide, manganese chloride, manganese carbonate, manganese phosphate, etc. Most of these plants consume manganese ores with >78% MnO2, <5% SiO2, and <5% Fe2O3. Glass industry uses high-grade manganese oxides ores as a decolourizer. For this purpose, high-grade manganese ore containing >85% MnO2 with <10% Fe is used. In the battery industry, the high-grade manganese dioxide is used as an oxidizing agent or a depolarizer of hydrogen. Variety of ore compositions are used, e.g. (a) natural ore with 72% MnO2, (b) chemically activated manganese dioxide with 85% MnO2, and (c) electrolytic manganese dioxide (EMD) with 90% MnO2 and small amount of iron and should be free from copper, nickel, cobalt, arsenic, chromium, lead, etc. In general, the battery industry consumes manganese ore with 70–90% MnO2 and low Fe (2.5–4%). Manganese metal is used for refining and as an alloying element for aluminum, copper, magnesium, and zinc alloys. These industries use Mn metal with Mn >95%, Si <1%, Fe <2.5%, C < 0.2%, S < 0.005% and P < .1% (IBM Report 2006). The specifications reveal that first choice of all the industries is to get high grade manganese ores as a raw material.