Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1994-02-24
1995-11-07
Niebling, John
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
204109, 204222, C25C 120
Patent
active
054645069
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electrolytic device comprising at least one porous stirring electrode associated with at least one counter-electrode, as well as a method for processing the effluents by means of this device. This electrolytic device and method can be applied, for example, to the recovery, recycling and purification, in a concentrated or dilute solution, of-compounds exhibiting redox properties.
In the case of effluents containing metallic ions, the present invention allows the discharge of these effluents into the sewer, after treatment by means of the device according to the invention, without causing environmental problems. Moreover, the device and method according to the present invention are easy to use technically and are economical. This device and method are particularly effective for treating photographic effluents.
It is known that the efficiency of electrolytic devices can be improved by increasing both the electrolytically active surface, which is the effective surface area on which the electrolytic deposition is performed, and the mass transfer coefficient, which accounts for the matter deposited on the active surface of the electrode, while maintaining good electrical conduction between the electrolyte and the electrode. The prior art proposes various solutions in order to attempt to overcome these different problems.
The electrolytically active surfaces were improved by using for example, cells comprising electrodes consisting of porous or fibrous materials, or cells with volume electrodes consisting of a bed of conductive particles. The mass transfer was increased, for example, by stirring of the electrolyte. This stirring can be obtained by means of moving electrodes, by percolation of the electrolyte through the bed of conductive particles in the case of volume electrodes or by injection of an inert gas into the cell.
European Patent 71,443 discloses an electrolytic device for treating waste waters which consists of porous cathodes associated with perforated solid anodes to allow the electrolyte to pass through the cell. These electrodes are called "moving electrodes" because the fixing of these electrodes on the electrolytic device is performed in order to be able to replace these electrodes very easily when they are clogged up. The cathodes used in European Patent 71,443 are made from polyurethane foam coated with nickel. This device enables the metallic pollutants contained in the waste waters to be removed. The examples illustrating this European patent show that, with the device according to European Patent 71,443, it is possible to treat only waste waters containing, before treatment, less than 1 g/l of pollutant; using such a cell with more concentrated solutions, such as used photographic developing and fixing solutions, would involve a rapid clogging up of the cell equipped with such electrodes.
British Patent 2,078,782 discloses a means for stirring the electrolyte which consists of imparting to the cathode an oscillating motion around a fixed horizontal axis. This oscillating motion is used in order to form a vortex in the whole electrolyte volume, which enables the mass transfer coefficient to be improved. In the device disclosed in British Patent 2,078,782, the cathode used is flat and non-porous and the oscillating speed is less than 60 rotations per minute (1 Hz), with high amplitudes in order to allow the occurence of vortices in the whole volume of the electrolytic cell. It can be assumed that the oscillating frequency is maintained at a value less than 1 Hz, in order to maintain sufficient electrical conduction between the cathode and electrolyte.
Although these methods aim to improve the mass transfer coefficient, they inevitably involve, however, a deterioration of the conduction of electricity within the electrolyte in the cell. Indeed, the stirring of the electrolyte allows an increase in the mass transfer coefficient due to a greater mass supply of material on the electrolytically active surface but this stirring involves also a deterioration of t
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Bernard Patrick E. Y.
Bertorelli Claude R.
Eastman Kodak Company
Leipold Paul A.
Mee Brendan
Niebling John
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