Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-09-30
2001-02-20
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S227000, C204S269000
Reexamination Certificate
active
06190515
ABSTRACT:
The present invention relates to an installation for refining silver operating according to the Moebius process and designed for treating particulate raw silver, the anodes containing a compartment for receiving the raw silver, an underlying compartment for receiving anode sludge, and, positioned between them, a support permeable to anode sludge and designed for supporting the raw silver charge, the support having at least two mutually mobile conveyor elements with horizontal axes, extending substantially over the support width and defining a gap for the passage of anode sludge.
In the Moebius process raw silver is dissolved anodically and deposited cathodically as refined silver. For this purpose plate-like silver anodes were originally surrounded by anode bags and each of them arranged between stripping-off sheet cathodes. The anode bags retain the gold sludge—when an anode has been used up, it is replaced, the gold sludge being rinsed off the anode bags after they have been turned inside out.
In order to provide for continuous operation, Applicant's prior art Austrian Patent 1751/96 (hereinafter A 1751/96) proposes the use of tank-like anode casings having a gold sludge collecting space with a rigid bottom from which the gold sludge can be sucked off during operation. In this, the anode body is a frame-like or basket-like structure of insoluble metal, e.g. of titanium, and is supplied with raw silver granules so that operation may be continuous. A sieve bottom is provided for separating the raw silver charge from the collecting space for anode sludge. This may lead to the problem of passivation of the anode surface, on the one hand, which may be solved by agitating the electrolyte in the anodic charge according to Austrian Patent A 510/97 of Applicant. On the other hand, there may be the problem of clogging of the sieve bottom, even in case of agitation of the electrolyte, as its passage gaps must be narrow enough so as to permit the passage of anode sludge only.
In this context it was found that the raw silver granules remain solid for the most part of the period of silver dissolution and that their size changes very little—the granules become soft only after the silver content has fallen to about 4% (starting at more than 80%). Then the gold content is about 90%. It is supposed that the palladium content is responsible for this strength, which has been enriched to about 6% by this time. Towards the end the granules fall apart almost by themselves, but during the transition from softening to disintegration, there is the so-called mud phase, when there may be the danger of clogging of the sieve bottoms.
According to applicant's A 896/97 it had surprisingly been found that the Moebius electrolysis may be carried out in a way as efficient as never before by very simple agitation of the granule charge in the final phase of electrolysis and a completely new kind of support instead of the sieve bottom.
Accordingly it had been proposed to provide the support for the raw silver charge in the form of at least two cylinders driven in counter-rotation, the axes of which are parallel to each other and which have conveyor elements, in particular axial conveying ribs for conveying anode sludge through the gap between the cylinders and, as the case may be, between one cylinder and an adjacent immobile wall.
The conveyor elements furthermore have the additional highly important function of bringing about complete disintegration of the granules by movement—for this purpose oscillating movement of the cylinders has been preferred, wherein material may remain in the nip while the conveyor elements move away after having conveyed it to the nip. The same is true for the gap between the cylinder and the bottom container wall.
Now it was surprisingly found that, as compared to applicant's A 896/97, a still improved disintegration effect for the granules is achieved if the conveyor elements are not swivelled with regard to each other, but if moved back and forth in the direction of their axes.
Accordingly, an installation of the kind initially defined, namely where the support comprises at least two conveyor elements being moveable with regard to each other and each having a horizontal axis, said elements substantially extending over the width of the support and defining between them a gap for the passage of anode sludge, is primarily characterised in that said conveyor elements are movable back and forth in axial direction. Thereby, their surfaces contacted by the granular charge are displaced with regard to said charge and provide for the necessary abrasion.
Preferred conveyor elements are straight prisms having triangular or rectangular cross sections and being arranged with the gap between two of their edges so that abraded matter is directed to the gap by converging surfaces.
Its is furthermore advantageous to use straight cylinders as conveyor elements, said cylinders having preferably at least substantially smooth surfaces and their cross-sections possibly differing from a circle. Its is contemplated to also make use of the inventive idea of applicant's A 896/97, namely to also swivel said cylinders in case a more complicated driving mechanism is tolerated. Then after a swivelling stroke conveying material to the gap, several back-and-forth strokes of the conveyor cylinders in axial direction may be provided.
REFERENCES:
patent: 4054503 (1977-10-01), Higgins
patent: 4090935 (1978-05-01), Dunning, Jr. et al.
patent: 4257864 (1981-03-01), Gacki
patent: 4670115 (1987-06-01), Prior et al.
patent: 4728402 (1988-03-01), Prior
patent: 5100528 (1992-03-01), Claessens et al.
Gorgos Kathryn
Prior Engineering AG
Smith-Hicks Erica
Townsend and Townsend / and Crew LLP
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