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ePaper created 2017-03-14, 10:25:37 | version 1.49.03
3 4 reason for this is the reducing agent used, as a rule sodium hypophosphite. This cannot be directly precipitated due to its good solubility; it is thus a major problem for a downstream municipal sewage treatment plant. For this reason electroplat- ing facilities have to ind large sums of money for disposal by external companies that then generally incinerate the waste- water. In order to avoid this, in the ECOWAMA plant the hy- pophosphite present in the chemical nickel bath is speciically oxidized in the electrooxidation unit to form a precipitable phosphorus compound. Boron-doped diamond electrodes, which exhibited the best oxidation characteristics in all the trials, are used for this purpose. Results Numerous short- and long-term trials with depleted chemical nickel baths conirmed the complete decomposition of the hypophosphite and the substantial decomposition of the phosphite. In a further step more than 98 percent of the easily precipitable phosphate produced was in each case separated by means of electrocoagulation (Fig. 3). In the treatment of the waste and process water from the electrolytic nickel plating an electric conductivity of 12 µS / cm was achieved, enabling a complete return of the water to the appropriate process baths. Metallic nickel with a purity of over 99.9 per- cent was obtained from the concentrate by means of galvanic deposition; it can therefore be reused for coating purposes. Contact Dipl.-Ing. Maximilian Kotzur Phone +49 711 970-4097 maximilian.kotzur@igb.fraunhofer.de Dr. rer. nat. Thomas Scherer Phone +49 711 970-4091 thomas.scherer@igb.fraunhofer.de Literature [1] Kanani, Nasser (2009) Galvanotechnik – Grundlagen, Ver- fahren und Praxis einer Schlüsseltechnologie: 16 – 18 [2] European Commission (2006) Integrated Pollution Prevention and Control – Reference Document on Best Available Techniques for the Surface Treatment of Metals and Plastics: 164ff Funding This project has received funding from the European Union’s Sev- enth Framework Programme for research, technological develop- ment and demonstration under grant agreement no 308432. Outlook – further applications The robust and modular design of the ECOWAMA pilot plant Project partners and further information enables the use of individual process units for further applica- tions in the treatment of process water. The principal market here consists of other types of waste and process water in the surface treatment industry, followed by special applications in the chemical industry that require strong, chemical-free oxidation. www.ecowama.eu 1 Principle of the circular economy in the ECOWAMA project. 2 Diagram of the ECOWAMA process. 3 ECOWAMA modules: electrooxidation (front), electrocoagulation (rear). 4 Coated workpiece. 9 7