Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1981-02-05
1983-03-08
Williams, Howard S.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
204300R, B01D 5702
Patent
active
043760228
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method for concentrating by electro-osmosis a fluid aqueous sludge formed from fine particles suspended in water. Such sludges are encountered for example in the residues from purification stations, in the working of argillaceous gravel pits, in the by-products resulting from the processing of certain minerals (bauxite), in the paper industry etc.
If it is required to conveniently handle such sludges, for example if they are to be gathered up mechanically in order to load a vehicle with them, it is necessary to previously dehydrate them by dewatering in order to give them the required solid consistency and to reduce their dead weight. In doing this, simple water removal under pressure is not convenient because, due to the fineness of the particles, the filter pores become rapidly blocked, the filtration slows down to an exaggerated extent, and the energy (pressure) expenditure required for extracting the liquid becomes incompatible with the results obtained.
PRIOR ART
These drawbacks have been remedied by filtration methods based on electro-filtration. In this respect, it is known that the majority of the particles of mineral sludges suspended in water become charged negatively on contact therewith, and consequently when placed in an electric field they migrate in the direction of the anode where they accumulate, to create a region depleted in solid materials in the vicinity of the cathode (electrophoresis). By disposing a microporous obstacle (membrane with osmotic properties) between these electrodes, the sludge particles are retained in the anode compartment, whereas the liquid is driven into the cathode compartment by traversing the membrane. The typical cathaphoresis filtration principle is illustrated by U.S. Pat. No. 4,003,811, which describes a method consisting of introducing a particle suspension into the anode compartment of an electrokinetic cell comprising an anode and a cathode, these being separated by a membrane which is permeable to water but is impermeable to the clay particles. A direct current is then applied across the electrodes, this causing the water to pass through the membrane and the particles to deposit on the positive electrode. This process can take place continuously, the solid clay deposit being periodically detached from the anode on which it settles, while the excess liquid of the cathode compartment is evacuated regularly. There are other electro-filtration methods based on the same principle, some also using the action of a pressure to which the sludge to be dewatered in subjected. Among the documents defining this state of the art, the following documents can be mentioned: " The Electrical Dewatering of Clay Suspensions", by C. E. CURTIS, Annual Meeting American Ceramic Society, Cleveland, Ohio, February 1931; "Electro-Osmotic and Electrophoretic Dewatering as Applied to Solid-Liquid Separation" by C. RAMPALEK, in Solid Liquid Separation by J. P. POOLE & D. DOYLE, H.M.S.O. London (1966); "Application of Electro-osmosis in the Consolidation of Clayey Soils" by L. ZARETTI, L'Energia Elettrica 27, 625-31 (1950); "Electro-Chemical Treatment of Clays" by C. M. PANT, A. KUMAR and K. P. SHUKLA, Soils & Fertilizers 16 (1953), Abstract 402; U.S. Pat. Nos. 3,773,640-2,099,328-4,001,100-4,003,819; German Pat. Nos. 163,549-316,444-154,114-124,509-128,085-131,932; French Pat. No. 2,231,627 and British Pat. No. 169,315. Thus, French patent application No. 2,231,627 (27.12.74) relates to a method for dehydrating a sludge in which the sludge is transported on a fluid-permeable belt, a direct current is passed through this sludge between the electro-endosmosis electrodes which are disposed on one side and the other of the sludge layer (i.e. the anode above and the cathode below the permeable belt), and the sludge is simultaneously subjected to pressure.
German patent DPS No. 316,444 (14.2.1918) describes a device for the electro-filtration of aqueous sludges comprising a metal cathode grid on which the sludge to be filtered is dispo
REFERENCES:
patent: 894070 (1908-07-01), Schwerin
patent: 4244804 (1981-01-01), Moeglich
Kulhanek Antonin
Porta Augusto
Battelle (Memorial Institute)
Williams Howard S.
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