Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-09-13
2002-03-05
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S284000, C204S278500, C204S286100, C204S288000, C204S290010, C204S290120, C204S290130
Reexamination Certificate
active
06352622
ABSTRACT:
FIELD OF THE INVENTION
A compound electrode relying on lead is disclosed. The lead can form a base for the electrode. The active surface for the compound electrode may comprise valve metal. The electrode is particularly serviceable in an electrolytic cell used for electrowinning of a metal.
BACKGROUND OF THE INVENTION
Historically, lead or lead alloy anodes have been widely employed in processes for the electrowinning of metals, such as copper, from sulphate electrolytes. These lead anodes nevertheless have important limitations such as undesirable power consumption and anode erosion. This anode erosion can lead to sludge production and resulting contamination of one or both of the electrolyte and the electrowon product.
During the time that these lead electrodes have been in use, a major breakthrough in anode advancement led to the development of the dimensionally stable anode, principally for use in the chlor-alkali industry. This anode relied typically on a coated valve metal. There then followed attempts to utilize concepts behind this advance so as to devise an improved lead electrode such as for copper electrowinning.
One conceptual approach was to unite in some way the desirable characteristics of a valve metal, e.g., the excellent acid resistance of a valve metal such as titanium, with the desirable features of the conventional lead anodes, including the presence of an oxide that can be an electroconductor. Using this approach, it was proposed to make a composite anode from a sintered article of one metal, e.g., the titanium, which article is infiltrated with the other metal, i.e., the lead. These anodes have been proposed, for example, in U.S. Pat. No. 4,260,470. The titanium can be ground, compressed and sintered to prepare a titanium sponge as a porous matrix. This matrix is then infiltrated with molten lead or lead alloy. The object is first to provide planar anodes in the form of strips. The strips are then joined together in a parallel, co-planar array to provide a large sheet anode.
The patent teaches employing these anodes particularly for use in electrowinning zinc or copper from sulfate electrolytes. However, if the sintered metal is infiltrated with lead, under the anodic conditions that are present such as in a copper electrowinning cell, the lead is anodically oxidized to lead dioxide. Thus, the anode can present loss of lead to the electrolyte, with resultant sludge build-up, and/or require electrolyte additives to deter such loss. Therefore, these anodes are ostensibly better suited for use in lead-acid batteries. Such utility has been disclosed in U.K. Patent Appln. No. 2,009,491A. In any event, there is today no known utilization of these anodes commercially such as in the copper electrowinning industry.
It has also been proposed to retain the commercially acceptable lead anodes, while fully utilizing the technical advance of the coated valve metal development. To this end, ways have been considered as to how to shield the lead from electrolyte, so as to reduce, to eliminate, lead erosion. Thus, it has been proposed to prepare catalytic particles of a metal such as titanium, which particles are activated with a platinum group metal. These particles are then uniformly distributed over, and partly embedded within, the surface of an anode base of lead or lead alloy. The lead plate is thus covered with a layer of these particles, such as of activated titanium sponge particles. Such an anode has been disclosed in U.S. Pat. No. 4,425,217. Therein it is taught that the anode offers improved electrochemical performance for anodically evolving oxygen in an acid electrolyte, and use is taught such as in the electrowinning of metals. However, it was found to be uneconomically viable to scale up this concept and to provide a uniform layer of small particles on the surface of commercial lead electrodes. In working with a multitude of particles, it was further found that the resulting article was difficult to refurbish. As a result, there is no known commercial use today of this anode.
Despite these developments, there then has not yet been found a commercially practicable anode, as a replacement for lead or lead alloy anodes, in industries such as copper electrowinning from sulfate electrolyte. Even today, decades after the development of the dimensionally stable anode for use in the chlor-alkali industry, the anode of choice for copper electrowinning is still the historical lead or lead alloy anode. There is thus a need for an anode, particularly for electrowinning of a metal, which is serviceable for extended stable operation. As an example of this need, even today it is not unusual to remove from 80 to 100 pounds of sludge, comprised principally of lead oxide and lead sulfate, after only about a week of operation, from a single commercial copper electrowinning cell that uses lead anodes. There is not only still the need for a commercially practicable as well as stable anode, but also the need for one which can be readily prepared for reuse and, in reuse, provide similar, extended operation. Therefore, it would be desirable to provide an anode, as either a fresh or refurbished anode structure, having stability, economy of operation, and economy of preparation as a fresh or refurbished structure.
SUMMARY OF THE INVENTION
There is now provided a compound electrode, particularly for electrowinning of a metal, which is serviceable not only for extended operation, but which can be readily prepared for reuse and, in reuse, provides similar, extended operation. The compound electrode is provided with either a fresh or refurbished lead electrode segment, having economy of preparation as a fresh, or as a refurbished, item. This lead compound electrode can have desirably low operating voltage and can offer enhanced current density in cell operation. It can serve to minimize or eliminate loss of lead to the electrolyte, which usually proceeds due to electrochemical oxidation as well as erosion of the lead. For convenience, such oxidation plus erosion may more simply be referred to herein as lead “corrosion”. This innovative compound electrode can thus provide for desirable electrolyte cleanliness as well as product cleanliness. The electrode can provide for further operating economy such as by reducing to eliminating the need for electrolyte additives, e.g., the elimination of the use of cobalt addition in a copper electrowinning bath. The compound electrode can not only be easy to assemble as a fresh electrode, but also can be spot repaired and, in refurbishing, such may be done by field installation.
In a first aspect, the invention is directed to a compound electrode for electrowinning a metal present in an electrolyte in an electrolytic cell by partially submersing the electrode in the cell electrolyte, such electrode comprising a thin and solid lead electrode base and at least one thin valve metal surface member in mesh form, which lead base is in sheet form and has broad, essentially rectangular front and back surfaces as well as narrow side and bottom surfaces, with each front and back surface having at least substantially parallel side edges, as well as having top and bottom edges, with the electrode comprising exposed lead side surfaces as well as exposed front and back surface portions above an electrolyte-air interface of the cell, and which metal mesh surface member has a multitude of voids exposing the lead base underlying these voids, with the valve metal mesh surface member extending at least substantially from side edge to side edge across at least one of the broad front and back surfaces of the base, while extending from below the top edge of the base, but above said electrolyte-air interface of the cell, to at least substantially the bottom edge of the lead base, which valve metal mesh surface member has a front, active major face presenting an electrochemically active surface in mesh form for the compound electrode, and a back major face which faces a broad surface of the lead base, and wherein the mesh surface member is combined with the lead base in el
Bishara Jeries I.
Brown Carl W.
Ernes Lynne M.
Getsy Andy W.
Hardee Kenneth L.
Bell Bruce F.
Eltech Systems Corporation
Hudak & Shunk
Tyrpak Michele M.
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