Waste, removal anodic oxidation

Nagayama, M. Cohen, M. (1963) Anodic oxidation of Fe in a neutral solution. 1. Nature and composition of the passive film. J. Elec-trochem. Soc. 109 781-790 Nakai, M. Yoshinaga, N. (1980) Fibrous goethite in some soils from Japan and Scotland. Geoderma 24 143-158 Nakazawa, H. Sato, H. Hasebe, S. (1989) Study of the removal of arsenic from hot waste water by the ferrite formation method. Shigento Sozai 105 239-244 Namjesnik-Dejanovic, K. Maurice, P.A. 

Anodic oxidation was shown to be a useful method for the removal of organic pollutants from aqueous solutions [15]. Partial decomposition of hazardous organic compounds to biodegradable compounds or complete decomposition to H2O and CO2 can be achieved by the electrochemical treatment of waste [14]. Two different categories of electrochemical treatment of waste-water or waste can be distinguished ... 

Usually only one electrode product is recovered as a product of commercial value the product of the counterelectrode must be removed as waste or as a low-value byproduct. During anodic oxidations, hydrogen gas is evolved and has to be freed of solvent and low-boiling by-products. In the case of cathodic reductions, the gas given off is oxygen, sometimes containing halogens and acids as impurities. 

The main difference between a fuel cell and a battery is that the fuel and oxidants are not integral parts of the fuel cell, but instead are supplied as needed to provide power to an external load, while the waste products are continuously removed. Where hydrogen is supplied as the fuel to the anode and oxygen to the cathode, this waste product is only water. 

Hexavalent chromium is used in anodizing baths, and in pickling solutions that remove oxide layers from parts. The chromic acid in these solutions eventually enters the waste stream, either through dragout, or when the pickling or anodizing bath is disposed of. Less... 

When the waste contains more complex molecules such as compounds refractory to oxidation with OH radicals, as well as in the presence of inorganic ions which can be precursor of long-life oxidants, the Faradic yield cannot be calculated by (8.3) and different alternatives have been proposed. Faouzi and co-worker (Faouzi et al. 2006) proposed a comparison between electrochemical oxidation at BDD anodes and Fenton and Ozone treatments for the removal of dyes a specific parameter OCC (oxygen-equivalent chemical-oxidation capacity) was proposed which is defined as the kg of 02 equivalent to the quantity of oxidant used in each AOP to treat 1 m3 of wastewater. As highlighted by the authors, the parameter OCC may only give information on the chemical efficiency of the oxidants, but it does not give any information related to the real cost of the treatment, as the oxidants can... 

The cathode reaction generates calcium metal for recycle and the anode reaction yields oxygen which combines in situ with the carbon anode to produce a mixture of CO and CO2. (For simplicity only CO is considered in the mass balances.) Thus, the oxygen is removed from the oxidic fuel not as a large volume solid waste but as a common gas which can be scrubbed for release into the atmosphere. 

The elimination of COC from soil can be achieved by a totally different approach. Instead of removing the contaminants from the soil and accumulating them in the anode or cathode reservoirs, COC can be chemically oxidized or reduced in the soil, transforming the harmful COC into less toxic compounds. An additional advantage of this technology is that no wastes are generated. 

In solid polymer electrolyte cells (Fig. 5.7) the electrolyte is a thin perftuorinated sulphonic acid (Nafion) membrane (c, 0.2Smm thick) having a structure which promotes conduction of hydrated protons. The schematic cell reactions are shown in Fig. 5.7(a). Pure water is supplied to the anode where it is oxidized to oxygen and protons the latter pass through the polymer electrolyte to the cathode where hydrogen gas evolves. In fact, excess water is circulated through the anode compartment to remove waste heat. 

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