Oxalic acids anodizing with

Incinerator ashes are decontaminated simply by loading them into a separate, stirred electrolytic oxidizer tank. The cathode in this tank is partly shielded from the anode and air-sparged to remove nitrous acid. After several hours of leaching at reflux, the excess ceric nitrates may be reduced with oxalic acid, the... 

The process is one of electrolytic reduction and the apparatus is similar to that shown in Fig. 77, p. 144. It consists of a small porous cell (8 cm. x 2 cm. diam.) surrounded by a narrow beaher (ii cm. X 6 cm. diam.). The oxalic acid, mixed w lth too c.f. 10 per cent sulphuric acid (titrated against standard baryl.a solution] forms the cathode liquid and is placed in Iht beakei. The porous cell is filled with the same strength of siilphuiic acid and foims the anode liquid. The electrodes ara made from 01 dinary clean sheet lead. The anode consists of i thiu strip projecting about two inches from the cell and tliu... 

The addition of various Kolbe radicals generated from acetic acid, monochloro-acetic acid, trichloroacetic acid, oxalic acid, methyl adipate and methyl glutarate to acceptors such as ethylene, propylene, fluoroolefins and dimethyl maleate is reported in ref. [213]. Also the influence of reaction conditions (current density, olefin-type, olefin concentration) on the product yield and product ratios is individually discussed therein. The mechanism of the addition to ethylene is deduced from the results of adsorption and rotating ring disc studies. The findings demonstrate that the Kolbe radicals react in the surface layer with adsorbed ethylene [229]. In the oxidation of acetate in the presence of 1-octene at platinum and graphite anodes, products that originate from intermediate radicals and cations are observed [230]. 

P 17] In order to have a catalyst with a sufficiently high specific surface area, pretreatment of the micro channels made of aluminum was necessary [17], Following a cleaning procedure, an oxide layer with a regular system of nanopores was generated by anodic oxidation (1.5% oxalic acid 25 °C 50 V DC 2 h exposure using an aluminum plate cathode followed by calcination). 

A typical example is the synthesis of oxalic acid. Electrochemical synthesis of oxalic acid by reduction of C02 in aprotic media with a Zn sacrificial anode was brought to pilot scale by the Dechema Institute some years ago (1981) [177]... 

When an electrolyte which is without action on vanadium at ordinary temperatures (for example, dilute solutions of mineral acids, of oxalic acid, or of potassium halides) is electrolysed with a vanadium anode, a complex tetravalent vanadium ion is produced. Similarly, electrolysis at 100° C. and in molten chlorides of sodium or zinc gives rise to complex tetravalent vanadium ions. The E.M.F. in each case is found to be independent of the nature of the electrolyte. When, however, solutions of caustic soda or of caustic potash are employed, the vanadium dissolves as a pentavalent ion, irrespective of variations... 

Electrically produced anodic coatings from chromic, sulfuric, or oxalic acid electrolytes are more dense and less porous. Their corrosion resistance is improved by hot-waler sealing, which is even more effective with the inclusion of dichromale. 

All these advanced methods have been compared with anodic oxidation for a 178-ppm 4-chlorophenol solution [140]. The mineralization rate was much faster for the new processes and the substrate was completely transformed into C02 by the Photoelectro-Fenton method, as can be deduced from data given in Fig. 22. In all cases, the initial intermediate was 4-chloro-l,2-dihydroxybenzene, which was further oxidized to yield maleic and fumaric acids with loss of Cl-. The subsequent degradation of these acids gave oxalic acid, which complexes with Fe(III). Such complexes are attacked slowly by OH, but decomposed quickly by UVA light. 

Another process of physical protection is the formation of an oxide layer that makes the metal passive. This procedure is used for aluminium. Aluminium is normally anodized in 10 per cent sulphuric acid with steel or copper cathodes until an oxide thickness of 10-100 pm is obtained. As the more superficial part of the oxide layer has a fairly open structure it is possible to deposit metals (cobalt, nickel, etc.) or organic pigments in the pores and seal with boiling water or with an alkaline solution. The colours after metallic deposition are due to interference effects. Chromic and oxalic acids are also used significantly as electrolyte. 

Studies of the electrochemical detoxification of 1,4-benzoquinone (Pulgarin et al. 1994) showed that the primary oxidation, i.e., elimination of benzoquinone, was obtained with Ti/Ir02 anodes, resulting in an accumulation of carboxylic acids maleic, fumaric, mesoxalic, and oxalic acids that were only poorly degraded at the Ti/Ir02 anode (Fig. 2.5). 

When adsorption of oxalic acid was hindered, either by adsorbed hydroxyl radicals [as at Os electrodes (Sargisyan et al. 1982)] or by a low adsorption capacity (as at glassy carbon or BDD electrodes), the rate of anodic oxidation reached minimum values. However, the same authors underlined that compared with glassy carbon, a... 

Ivandini, T.A., Rao, T.N., Fujishima, A. and Einaga, Y. (2006) Electrochemical oxidation of oxalic acid at highly boron-doped diamond electrodes. Anal. Chem. 78, 3467-3471 Josephy, P. D. (1996) Molecular Toxicology, Oxford University Press, New York, NY Kraft, A., Stadelmann, M. and Blaschke, M. (2003) Anodic oxidation with doped diamond electrodes A new advanced oxidation process. J. Hazard. Mater. 103, 247-261 Kusic, H., Koprivanac, N. and Bozic, A.L. (2006) Minimization of organic pollutant content in aqueous solution by means of AOPs UV- and ozone-based technologies. Chem. Eng. J. 123, 127-137... 

The use of a classical anode such as Pt in anodic oxidation usually leads to a partial mineralization of wastewaters containing aromatics due to the formation of final short-chain carboxylic acids, as oxalic acid, that hardly react with OH. Overall mineralization is feasible with a boron-doped diamond (BDD) anode that possesses a much greater 02 overpotential compared to Pt, thus producing a higher amount of... 

Fig. 19.17 Evolution of oxalic acid concentration during the treatment of 194mgdnW3 4-CPA solutions in a BDD/O2 cell under the same conditions as reported in Fig. 19.16. (Open circle) Anodic oxidation with electrogenerated H2O2 and (filled circle) electro-Fenton with 1 mM Fe2+...

The photoelectro-Fenton method [98] complements the photo-Fenton and electro-Fenton reactions. In the latter, a potential is applied between two electrodes immersed in a solution containing Fenton reagent and the target compound. The recent study of the herbicide 2,4,5-T, performed in an undivided cell with a Pt anode and an 02-diffusion cathode, showed that the photo-electrochemical process was more powerful than the electro-Fenton process, which can yield only about 60-65% of decontamination. The electro-Fenton method provides complete destruction of all reaction intermediates, except oxalic acid, which, as already mentioned, forms stable complexes with Fe3+ that remain in the solution. The fast photodecarboxylation of such Fe(III)-oxalate complexes by UV fight explains the highest oxidative ability of the photoelectro-Fenton treatment, which allows a fast and total mineralization of highly concentrated acidic aqueous solutions of 2,4,5-T at low current and temperature. A similar behavior was found for the herbicide 3,6-dichloro-2-methoxybenzoic acid [99]. 

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