The present invention relates to a method of recovering sodium (Na) wherein sodium (Na) is recovered from spent sodium-sulfur cells (hereafter referred to as NaS cells).
NaS cells are charge and discharge capable secondary cells in which molten metallic sodium as an anode and molten sulfur as a cathode are arranged, the two are separated by .beta.-alumina as a selective sodium-ion conductive solid electrolyte, and the cell is operated at a temperature of 300 to 350.degree. C.
The structure of such NaS cells comprises a cylindrical anode container which contains the molten sulfur, a cartridge (inner cylinder) which contains the molten metallic sodium (Na), and a cylindrical solid electrolyte tube with a bottom, which contains the cartridge, and having the function of selectively conducting sodium ions (Na.sup.+). The anode container and the solid electrolyte tube are joined by an insulating ring and a metal anode fitting. A metal cathode fitting is thermocompressively bonded to the upper surface of the insulating ring and a cathode cover is welded in place on this metal cathode fitting.
As NaS cells having a structure of this kind have the capacity of storing large amounts of electrical power, attention is given to them as electrical power storage cells. Accordingly, a trend towards future large scale production and use can be assumed and, as the life of these NaS cells is estimated at approximately 10 years, it can be assumed that a large volume of spent NaS cells, which must be disposed of, will be generated.
The disposal of these spent NaS cells without modification leads to such environmental problems as the generation of public hazards, and constitutes a waste of planetary resources, and it is therefore necessary for spent NaS cells to be recycled.
The present applicant has proposed a method of processing NaS cells and equipment for the same that is capable of automatically recovering the sodium from NaS cells and removing the inner cylinder (Japanese Patent Application Laid-open 6-333606).
According to this method for processing NaS cells and equipment for the same, several NaS cells, the openings of which had been opened, were loaded as one set into a work-set pipe unit. This arrangement of cells was maintained in the interior of a heated oil bath and, after sodium had drained away, the chuck claw of a pipe removing machine was introduced and, by means of chucking the NaS cell from the inside, the inner cylinder of the NaS cell action was removed. This was desirable in so much as it was possible to prevent contact between the sodium and air and to solve sodium evacuation problems resulting from oxidization of the sodium.
However, in the aforementioned method of processing NaS cells and equipment for the same, while it was possible to recover even the Na present outside the inner cylinder of the NaS cell as the result of removing this inner cylinder, and while both recovery ratios and safety were improved, the facilities required a large amount of space. Further, as this method and equipment use work-set containers, handling equipment for such activities as of work-set containers transport and return was required. In this respect also, the overall facilities were large and complicated.
Accordingly, the present invention has been attained in view of conventional problems noted above. It is an object of the present invention to provide a method which can selectively recover sodium alone and which makes possible large scale simplification of the overall facilities.