US3098019A - Electrolytic production of zinc - Google Patents

Description

Patented July 16, 1963 3,098,019 ELECTROLYTIC PRODUCTION OF ZINC Richard F. Pagel, Believille, IlL, assignor to American Zinc, Lead and smelting Company, St. Louis, Mo., a corporation of Maine No Drawing. Filed Mar. 9, 1962, Ser. No. 178,568 4 Claims. (Cl. 204-55) The invention relates generally to the electrolytic production of zinc, and particularly to a method of lowering the lead content of zinc produced by the electrolytic process.

This is a continuation-in-part of my copending application Serial Number 87,083, filed February 6, 1961, now abandoned.

In the process commonly used for the production of electrolytic zinc, an electric current is passed between an electrode of metallic lead or lead alloy, which is made anodic, and an electrode of aluminum made cathodic, in an acidified zinc-bearing electrolyte, usually a sulfate. Metallic zinc is deposited upon the cathode in a relatively pure form, usually at least 99.9% pure. Of the impurities present, lead is the most troublesome, although normally present in amounts of only a few thousandths of one percent. Even at this level it is considered highly objectionable to the making of zinc base die casting alloys.

The problem of reducing the lead content of electrolytic zinc has been recognized for a long time. Numerous previous inventors have used or devised various means in attempting to decrease the lead content in electrolytic zinc. Both organic, as well as inorganic, additives have been added to the electrolytic solution and both have proved successful in the reduction of the lead content. Similarly, organic materials are Well known as additives for purposes other than for the suppression of lead. However, only by the use of relatively large quantities of these additives can a commercially acceptable process be obtained, whether it be for the suppression of lead or for improving the covering power of the deposited zinc.

Flett, Patent No. 2,195,409, suggests the use of an alkyl aromatic sulfonic acid compound for use in electro-deposition of zinc to improve the covering power of the deposited metal and eliminate pitting and pinholing. Quantities of 0.1 to 0.3 gram of the additive per liter of electrolyte were used in this process. However, no mention is made of the fact that by the addition of this material the lead content of the deposited zinc is decreased.

Wernlund, Patent No. 2,600,352, teaches the use of certain organic ketones of the aliphatic type, such as methyl ethyl ketone and acetone, as additives to an electroplating solution to be used as brightencrs for the zinc electroplated. He states that a concentration of at least about 3 grams per liter of electrolyte is required to obtain a commercially acceptable plate. Here again, no mention is made of the fact that the addition of these organic ketones will lower the lead content of deposited zinc.

Nachtman, Patent No. 2,370,986, suggests the use of nicotine, thiourea, ammonium thiocyanate and the sodium salts of the sulfate ester of a mixture of long chain aliphatic alcohols as additives in a zinc electrolytic bath. However, Nachtman makes no mention of the effect which this additive has on the lead content in the deposited zinc. Large quantities of these additives are used in this process to 42.5 grams of the additive per liter of electrolyte.

Gray, in Patent No. 2,407,489, suggests the use of anthraquinone sulfates to retard the pitting and pin-holing effect of electrolytically deposited zinc. Gray uses quantities of 0.5 to 5 grams of additive per liter of electrolyte, but makes no mention of the fact that the anthraquinone decreases the lead content of the deposited zine.

Lowe, in Patent No. 2,471,965, attempts to reduce the lead content of electrolytic zinc by the addition of 2 to 10 pounds of cresylic acid and up to 6% pounds of pine oil per ton of zinc deposited. Cresylic acid is a mixture of phenol and its homologues. And he suggests that by the addition of these additives in the aforestated amounts the lead content of the deposit of zinc will be below the maximum requirement of zinc purity established by the British Ministry of Supply, which was, at that time, 0.003% lead.

Certain inorganic salts have been suggested as additives to reduce the amount of lead appearing in deposited zinc. Yeck and Lebedelf, in Patent No. 2,539,681, suggest the addition of barium or strontium salts. Strontium is added as strontium carbonate at a rate between 2.2 and 45 pounds of strontium carbonate per ton of cathode zinc produced. By this addition of 45 pounds strontium can bonate to the electrolyte, the lead content was reduced to about 0.00064%, average.

One of the objects of the present invention is to provide a method of producing electrolytic zinc with a low lead content, easily and consistently.

Another object is to provide a commercially acceptable electrolytic process for the production of zinc of low lead content by the use of minute quantities of an organic additive to the electrolyte.

Other objects will become apparent to those skilled in the art in the light of the following description.

In accordance with this invention, generally stated, a process of electrowinning zinc is provided, which includes the addition to the usual zinc electrolyte of a halogenated benzoquinone, of which chloranilic acid (2,5-dichloro- 3,6-dihydroxyquinone) is the preferred example. The electrolyte in this process contains an amount of additive so small as compared with additives known heretofore, as to be of a wholly different order of magnitude.

In the case of halogenated benzoquinones, the preferred operable limits are from about 0.0001 to 0.1 gram per liter of electrolyte. The use of much more of the additives than about 0.1 gram per liter of electrolyte, results in the reduction in current efficiency and blackening of the surface of the zinc deposit.

The following example is illustrative of the process of the present invention:

Example 1 An electrolytic solution taken from a commercial electrowinning plant, having the following metallic content,

G./'liter Zn Mn 2.50 Pb 0.01 Cd 0.001 Fe 0.035 As 0000i was put into a test plant circuit. Electrolysis of this solution was started and for the first six days during which period no lead suppression reagents were added, the lead Beginning with the seventh day, an amount of chloranilic acid amounting to approximately 0.007 pound per ton of cathode zinc (0.0004 gm. per liter of electrolyte was added to the electrolyte in the circuit, at which time there was an immediate reduction in the amount of lead in the cathode zinc deposited thereafter, as shown by the following assays:

Day: Lead assay, percent 7 0.0019 8 0.0018 9 0.0011 10 0.0015 11 0.0015 12 0.0013 13 0.0013 14 0.0013 15 0.0017 16 0.0014 17 0.0014

1 shorted electrode in one cell.

The electrotyte in the test circuit was maintained at a temperature of approximately 43 C.

It has been found that the effectiveness of chloranilic acid as a lead suppressant increases as the temperature of the cells decreases. Thus, cathode zinc assays of approximately 0.0005% lead have been obtained at temperatures of about 32 C.

In normal zinc plant operations the tendency is for the lead assay to drop to 10.004 during the first four or five days after electrolysis is started with clean anodes. After this time, at temperatures of about 40 C. there is little or no decrease in the lead assay unless a suppressing agent is added.

Although the electrolysis in this case was carried out using the lead silver alloy anode that has become the industry standard, the same principle of operation will prevail if a chemical or ordinary lead anode is used.

We have also found that, in both commercial plant and test plant scale operations, greater effectiveness of chloranilic acid as a suppressant is obtained if the man ganese content is held below 2.5 grams per liter. However, even if the manganese content is allowed to be more than this amount, the chloranilic acid would still be active as a lead suppressant, but its efiectivencss will be slightly deterred.

Among the other substituted-p-benzoquinones which have been found useful in the present invention are 2,6- dichloro-p-benzoquinone, chloranil (tetrachloro-pdvenzoquinone) and trichloro-p-benzoquinones. It is believed that other halogenated p-benzoquinones, as well as other di, tri, and tetra substituted p-benzoquinones, may also be applicable in the present invention.

While only a single illustrative embodiment of the process of the present invention has been set forth, it is to be understood that the invention is not limited to the particular material mentioned, or to the particular proportions set out.

Many changes in and modifications in the method set forth may be made without departing from the spirit of the invention or sacrificing any of its advantages.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In the method of electrolytically depositing high quality zinc, the step comprising adding to an acidic zinc electrolyte a quantity of a halogenated p-benzoquinone within the range of 0.0001 and 0.1 gram per liter of said electrolyte.

2. The method of claim 1 wherein the halogenated pbenzoquinone is chloranilic acid.

3. The method of claim 1 wherein the lead content of the deposited zinc is less than 0.002%.

4. The method of claim 1 wherein the halogenated benzoquinone is present in an amount within the range of 0.000 1 to 0.001 gram per liter of electrolyte.

References Cited in the file of this patent UNITED STATES PATENTS Gray Sept. 10, 1946 Wernlund June 10, 1952 OTHER REFERENCES

Claims (1)

1. IN THE METHOD OF ELECTROLYTICALLY DEPOSITING HIGH QUALITY ZINC, THE STEP COMPRISING ADDING TO AN ACIDIC ZINC ELECTROLYTE A QUANTITY OF A HALOGENATED P-BENZOQUINONE WITHIN THE RANGE OF 0.0001 AND 0.1 GRAM PER LITER OF SAID ELECTROLYTE.