Electrolysis Step Research Articles

Effect of Water Transport on the Production of Hydrogen and Sulfuric Acid in a PEM Electrolyzer

The thermochemical cycle involving the interconversion between sulfur dioxide and sulfuric acid is a promising method for efficient, large-scale production of hydrogen. A key step in the process is the oxidation of sulfur dioxide to sulfuric acid in an electrolyzer. Gaseous fed to a proton exchange membrane (PEM) electrolyzer was previously investigated and was shown to be a promising system for the electrolysis step. A critical factor in the performance of this gas-fed electrolyzer is the management of water since it: (i) is needed as a reactant, (ii) determines the product sulfuric acid concentration, (iii) affects crossover rate, and (iv) serves to hydrate the membrane. Therefore, we present a coupled mathematical and experimental study on the effect of water on the production of sulfuric acid in a gas-phase PEM electrolyzer. The model is shown to successfully predict the concentration of sulfuric acid as a function of temperature, current density, pressure differential across the membrane, and membrane thickness.

Tritium in water electrolytic enrichment and liquid scintillation counting

A batch of electrolysis cells was developed for tritium in water samples enrichment by at least a factor 10. The cell batch is controlled by a pre-programmable electronic system that interrupts the current through any cell when the planned electrolyte volume is attained. A starting and a final distillation of water samples are carried out before and after the electrolytic enrichment. Both distillations are made to dryness in order to avoid isotopic fractionation. A second electrolysis step allowed the tritium enrichment factor (EFT) to be doubled. The EFT was calculated by means of the deuterium enrichment factor (EFD) that was measured by mass spectrometry. The EFT was also measured by liquid scintillation counting. The calculated and measured EFT values were found in good agreement, especially for samples with significant tritium content.

Hydrometallurgical Recovery of Zinc from Fine Blend of Galvanization Processes

In many factories, which are working in the field of steel industry, there are galvanization units in which steel products are galvanized for corrosion protection. About 15% of the total amount of the used zinc are accumulated as zinc ash and dust at the surface of molten zinc bath and in the chimney respectively. In a previous work, zinc was successfully recovered from the coarse ash by applying pyrometallurgical processing. In this work, zinc fine blend (of fine ash and flue dust) was hydrometallurgically treated using sulfuric acid. Two alternative techniques were applied for producing zinc sulfate salt or pure zinc metal. In the first technique, the salt was separated from the leach solution as zinc sulfate hydrate (ZnSO4 · H2O). It was crystallized by concentrating the leach liquor to a density of 1.52 g/cm3. The purity of the produced zinc sulfate was 99.5%. In the second technique, the leach solution has been purified with respect to the soluble impurities using precipitation. The electrowinning technique was applied for producing a pure zinc metal from the purified solution. Electrolysis was performed at ambient temperature (25–28°C) with current density (c.d.) of 40 mA · cm−2. The recovery of zinc proceeds down to a concentration of 50 g · l−1 with acceptable cathodic current efficiency of 96.5%, and energy consumption for the electrolysis step of 2.75 KWh/Kg. The zinc purity in the deposit obtained from the electrolysis was 99.9%.

Selective recovery of Zn and Fe from spent pickling solutions by the combination of anion exchange and membrane electrowinning techniques

Although the environmental industry has developed many modern techniques to treat spent pickling liquors, including also the membrane separation, still neither of them can be applied alone for the efficient treatment of HCl containing spent pickling solutions originating from hot dip zinc galvanizing plants. In this area, the most frequently applied treatment is still the common precipitation–filtration process. However, this technique generates large amounts of hazardous waste to be deposited at high costs and does not recover the acid. Our novel approach to treat such spent liquors consists of an ion-exchange separation and a membrane electrolysis step to recover HCl, Fe and ZnCl 2 as saleable products. The experimental part of this paper concentrates on the anion-exchange separation of the components in the raw liquor and the cathodic deposition of iron at varied pH, temperature and cathode materials by using potentiodynamic testing technique. As a result, a direct anion-exchange with a strongly basic resin can separate the main components (Fe and Zn) of the raw solution loaded at a moderate flow rate into the column. The recommended conditions for the electrolytic deposition of iron are pH>1 and nickel cathode.

Electrowinning process

Although the environmental industry has developed many modern techniques to treat spent pickling liquors, including also the membrane separation, still neither of them can be applied alone for the efficient treatment of HCl containing spent pickling solutions originating from hot dip zinc galvanizing plants. In this area, the most frequently applied treatment is still the common precipitation–filtration process. However, this technique generates large amounts of hazardous waste to be deposited at high costs and does not recover the acid. Our novel approach to treat such spent liquors consists of an ion-exchange separation and a membrane electrolysis step to recover HCl, Fe and ZnCl2 as saleable products. The experimental part of this paper concentrates on the anion-exchange separation of the components in the raw liquor and the cathodic deposition of iron at varied pH, temperature and cathode materials by using potentiodynamic testing technique. As a result, a direct anion-exchange with a strongly basic resin can separate the main components (Fe and Zn) of the raw solution loaded at a moderate flow rate into the column. The recommended conditions for the electrolytic deposition of iron are pH>1 and nickel cathode.

A Study of Production Process of Uranium Metal by Molten Salt Electrolysis using Zinc Cathode: A Study of Molten Electrolysis Step

A Study of Production Process of Uranium Metal by Molten Salt Electrolysis using Zinc Cathode: A Study of Molten Electrolysis Step

Investigation of mercury-free potentiometric stripping analysis and the influence of mercury in the analysis of trace elements lead and zinc

The application of Potentiometric Stripping Analysis (PSA), without any mercury, to the determination of trace elements lead and zinc, results in linear responses between stripping-peak areas and concentrations within 0 to 2000 ng/g. The best response, as determined by the size of stripping areas, was obtained with an electrode prepared with mercury but without mercury ions in the electrolyte. Lead is analysed by a freshly polished glassy-carbon electrode in 0.09–0.1 mol/L HCl while the analysis of zinc requires an electrode activation procedure. The electrode activation is performed by stripping zinc in an electrolyte containing 0.1 mol/L HCl and 2 μg/g Zn2+ and electrolysis at −1400 mV (SCE). The concentration range of linear response occurs where the electrode is not fully covered by metal clusters during the electrolysis step. The influence of mercury is investigated and a model is proposed which explains the co-deposition of mercury and test metals in the electrolysis step in terms of a charge-distribution parameter. The model explains that the decrease of stripping peak area, as a function of concentration, is entirely due to mercury ions being simultaneously reduced together with the ions of the test metal in the electrolysis step. The influence of hydrogen evolution and oxygen reduction together with possible improvements of the method are discussed.

Influence of Triton X-100 in stripping potentiometry

The influence of a saturated Triton X-100 layer on glassy carbon based mercury film electrodes when used for stripping potentiometry determination of mono-, di- and trivalent ions has been investigated. By using an electrode assembly, permitting medium exchange at a controlled potential, it has been possible to study, separately, the influence of such a layer on the electrolysis step and on the stripping step. The latter step has been carried out either by means of spontaneous chemical reactions using dissolved dioxygen (molecular oxygen) or mercury(II) as oxidants or by means of an applied constant current. Pseudopolarograms, registered in the presence and absence of a saturated layer during electrolysis followed by complete desorption of this layer prior to stripping, show that Triton X-100 had no effect on the monovalent T1(I) ion. The stripping signals obtained for the divalent ions Pb(II), Cu(II) and Cd(II) and trivalent ions Bi(III) and In(III) on Triton X-100 covered electrodes were found to be the same as those obtained from non-covered electrodes, provided the electrolysis potentials were decreased with approximately 0.15 and 0.40V, respectively. It was also found that a Triton X-100 layer, applied on the electrode after electrolysis and prior to stripping, had no effect on the magnitude of the stripping signals in the constant current mode. In the chemical oxidation mode the bismuth stripping signal increased with a factor of five when dissolved dioxygen was used as oxidant, the signal increase for the other elements being less than 30%. When mercury(II) was used as oxidant the increase in stripping signals was less than 20% for all elements studied. It was also found that Triton X-100 could be completely desorbed from the mercury film in acetate buffer containing 60% (v/v) ethanol in the whole potential range −0.10 to −1.70 V vs. SCE.

ChemInform Abstract: Synthesis of 4,4′‐Dipyridyl from Pyridine Using an Electrolysis Step.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Electrolysis of ammonium iodide solution in a Na 2CO 3I 2 hybrid cycle

The electrolysis step in the following hybrid cycle Na 2CO 3+I 2→2NaI+CO 2 1 2 O 2 2NaI+2NH 3+2CO 2+2H 2O→2NaHCO 3 +2NH 4I 2NaHCO 3→Na 2CO 3+CO 2+H 2O ▪ was studied. The solubility of iodine in the anolyte (NH 4I-I 2 solution), steady state compositions of the catholyte (NH 4I-NH 3 solution), polarization characteristics for both electrolyte solutions and the nature of ion-exchange membranes was examined. The polarizations of the anode were very small, in a range up to 1000 mA cm −2, and those of the cathode were also relatively small. An advantageous feature of this electrolysis over NaI electrolysis [1] is that a large current density is obtainable. Decomposition voltages assumed from the polarization curves are small compared with NaI electrolysis. This improvement arises from greater solubilities of electrolytes. Among the ion-exchange membranes tested, Nafion was usable because of durability of the electrolyte solution and low permeation of iodine.

Electrolysis of iodine solution in a new NaHCO3-I2 hybrid cycle

Abstract The electrolysis step (6) in the following hybrid cycle was studied. Reaction (7) has been confirmed experimentally in an earlier paper [1]. Decomposition voltage of the electrolysis is lowered by introducing CO2 into the catholyte to decrease the pH. Polarization characteristics and related phase diagrams of NaI-I2-H2O and Na2CO3-NaHCO3-H2O systems were examined. Both I2 formed in the anolyte and NaHCO3 formed in the catholyte could be separated by cooling and carbonating each electrolyte, respectively. Polarizations of anodic and cathodic reaction are very small in a range up to about 100 mA cm−2. Cell voltage at current density of 100 mA cm−2 on platinum-black at 50°C is estimated to be about 1.6 V. Increasing temperature is effective in reducing concentration polarization.

The Electrochemical Production of Organic Hypochlorite Compounds

The electrochemical synthesis of organic hypochlorite compounds is important as a process for direct production of reactive halofunctionalization agents (1, 2). These materials are useful as intermediates which contain a halogen in the plus one valence state, and applicable to the manufacture of industrial chemicals such as propylene oxide (2) and calcium hypochlorite (3–5). This electroorganic synthesis requires a raw material feed of aqueous brine, organic alcohol, and organic solvent in an undivided cell without separator, and no solvent in a second multi‐chambered cell having a membrane. For example, tertiary butyl hypochlorite can be prepared by the electrolysis of aqueous sodium chloride brine and tertiary butyl alcohol. High product yield, current density, and current efficiency is achieved by the proper choice of anode‐cathode or anode‐membrane gap, proper control of the pH, and cell temperature control. The addition of an organic solvent such as carbon tetrachloride can be used in the “gap‐cell” to extract the organic hypochlorite formed within the aqueous brine phase during or after the electrolysis step, according to the following overall reaction

Photochemical and thermoelectric utilization of solar energy in a hybrid water-splitting system

A hybrid thermochemical water-splitting cycle using solar energy is proposed and experimental results are presented. The cycle consists of a photochemical reaction conducted in a flat cell with a Fresnel lens and concentrating the remaining solar energy on a thermoelectric generator which produces electric power for the electrolysis steps. The photochemical reaction is: 2 Fe 2++ I −+ light→2 Fe 3++3 I − The overall efficiency is estimated to be as high as 15–25%.