US3821096A - Process for electrodepositing manganese metal - Google Patents

Abstract

The present invention relates to a process for producing electrolytic manganese metal. Broadly, the invention comprises adding trace amounts of selenium and zinc to the electrolyte of a manganese electrodeposition cell to increase the current efficiency of the cell. It has been discovered that a combination of zinc and selenium acts synergistically to increase the current efficiency of the cell.

Description

[451 June 28, 1974 PROCESS FOR ELECTRODEPOSITING MANGANESE METAL [75] Inventor: San-Cheng Lai, Edmond, Okla.

[73] Assignee: Kerr-McGee Chemical Corp.,

Oklahoma City, Okla.

[22] Filed: Dec. 22, 1972 [2]] App]. No.: 317,526

[52] 11.8. CI 204/105 M [51] Int. Cl C22d l/24 [58] Field of Search 204/ 105 M [56] References Cited UNITED STATES PATENTS 3,455,799 7/1969 Mantell et al. 204/105 M 3,696.01! lO/I972 Lai 204/105 M FOREIGN PATENTS OR APPLICATIONS 15,610 1/1970 Japan 204/105 M 19,282 9/I966 Japan 204/l05 M Primary Examiner-John H. Mack Assistant Examiner-R. L. Andrews Attorney, Agent, or Firm-William G. Addison 57 I ABSTRACT 7 Claims, N0 Drawings PROCESS FoR ELECTRODEPOSITING MANGANESE METAL BACKGROUND OF THE INVENTION It is well known that in the electrodeposition of manganese metal, that the addition of a small amount of sulfur dioxide to the electrolyte helps to prevent oxidation of the manganous ion in the solution and reduces the undesired formation of manganese dioxide on the anode. However, in commercial practice when sulfur dioxide is used as an additive, it has been found that current efficiencies in the cell are only about 60-65%.

In U.S. Pat. No. 3,455,799 it is suggested that the addition of a small amount of zinc ions to a catholyte in a manganese electrodeposition cell will reduce the current density necessary to produce manganese. Patentees further disclose that their invention enables input requirements of the cell to be reduced whereby operating efficiency is increased. However, in tests using zinc as the additive, it has been found that the current efficiency is increased by only about I to 2 percent.

In an article Effect of Selenious Acid on the Electrodeposition of Manganese, by A. J. Rao, Y.D.P. Rao, and R. Vedaraman, published in the November- December, 1966 (Volume 4) issue of the Journal of Electrochemical Technology it was reported that when The present invention comprises an improved process for the electrodeposition of manganese. The improvement comprises adding to the electrolyte of a manganese electrodeposition cell a combination of zinc and selenium in an amount sufficient to provide from 1 to 8 ppm selenium and from about 1 to 5 ppm zinc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides an improved process for the production of electrolytic manganese. The production of manganese by the electrolysis of an aqueous electrolyte containing manganese ions is well known to those versed in the art. The present invention contemplates those processes wherein the electrolyte is mainselenious acid was used as an additive in place of sulfur dioxide in the electrodeposition of manganese metal that current efficiencies in excess of 90% could be obtained. Further, it has been reported that higher current densities can be used when selenium is used as the additive and that its use results in'lower cell voltages when compared with conventional sulfate bath electrolytes wherein sulfur dioxide is used as the addition agent.

In U.S. Pat. No. 3,696,01 1 it is reported that when a selenium compound is used as the additive, a precipitate of amorphous selenium forms in the electrolyte. This is disadvantageous, of course, because the selenium is thereby removed from the electrolyte solution and the advantages of its presence are lost, thus necessitating a constant replenishment of selenium to the electrolyte. Further, costs are increased because of the necessity of having to replace the selenium which is precipitated out of the solution. Patentees suggest the addition of small amounts of S0 to the,electrolyte to maintain the selenium compound in solution. However, the use of substantial quantities of a selenium compound as an additive to a manganese electrodeposition cell results in selenium contamination of the product manganese.

SUMMARY OF THE INVENTION The present invention provides a process whereby it is possible to use selenium as an additive in the electrodeposition of manganese with substantially no selenium contamination of the electrodeposited manganese. Broadly, the present invention is based upon the discovery that the addition of a combination of zinc and selenium in only trace amounts provides a substantial increase in the current efficiency of a manganese electrodeposition cell. Further, when zinc and selenium are used in the amounts set forth herein substantially no selenium contamination of the electrodeposited manganese is observed.

tained at a pH of from about 7 to 8.5 and contains ammonium sulfate in an amount of from about to grams per liter and from about 11 to 45 grams per liter of manganous ion. Generally, in such processes the manganese is electrodeposited at a cathodic current density of from about 35 to 55 amps per square foot.

In accordance with the present invention it has been discovered that when two known additives, selenium and zinc are added to such an electrolyte they act synergistically to increase the'current efficiency. Thus, it now is possible to obtain a substantial increase in current efficiency while adding only trace amounts of additives to the electrolyte.

The selenium compounds which are suitable for use in the present invention are selenious acid (H SeO or other selenium compounds such as, for example, 5e0 S603, Nagsfiog, (NH4)ZSCO3, Na ScO (NH4)2SeO and the like. Other compounds contemplated herein include Selene-organics such as, for example, selenourea, selenoguanidine, phenylselenourea, tributylselenophosphate and the like. Further, aromatic and quaternary selenium compounds also may be used. These compounds may be added to the electrolyte directly or fed in continuously as aqueous solutions. The concentration of selenium may be present in an amount of from about 1 to 8 parts per million (ppm). However, it is preferred that the concentration of selenium be from about 1 to 5 ppm.

' Zinc also is added to the electrolyte in an amount sufficient to provide a concentration of zinc ion in an amount of from about 0.1 to 5 ppm and preferably in an amount sufficient to provide a concentration of from about 0.3 to 2 ppm. The zinc is added in any form of compound that will disassociate in the electrolyte to provide zinc ions in solution. Examples of such compounds include zinc sulfate, zinc chloride, zinc sulfite and zinc ammonium chloride. The concentration of zinc ion should not be allowed to exceed about 5 ppm, as it has been observed that a higher concentration of zinc may result in a decrease in current efficiency. Particularly, good results have been obtained when the concentration of zinc ion is in the range of from 0.5 to 1 ppm and the weight ratio of zinc ion to selenium is about 1:3.

Advantageously, sulfur dioxide also is added to the electrolyte. It may be supplied by bubbling liquified or gaseous S0 into the electrolyte or by adding to the electrolyte compounds such as H SO Na SO (NH SO and the like which may be converted to S0 in the electrolyte. Generally, the concentration of S0 is maintained within the range of from about 0.1 to 1.0 gm/liter. However, the best results have thus far been obtained when the S is present in an amount of from about 0.1 to 0.5 gm/liter.

EXAMPLE To demonstrate the effectiveness of the present invention, a series of electrodepositions of manganese metal are performed with various amounts of zinc and selenium as additives to an electrolyte. The electrolysis conditions are as follows:

Temp. 34 C.

Current density 45 asf.

The initial electrolyte consisted of:

Mn++ l4 gm/l Oz 4 140 gm/l S0 0.4 gm/] The results of the tests are as shown in the following table.

Selenium content not determined.

From these tests it is seen that the addition of trace amounts of a combination of zinc and selenium to the electrolyte provides an increase in current efficiency that is greater than the sum of the increases in current efficiency obtained when they are used individually. Further, when the concentration of selenium is maintained within the range of from about 1 to 8 ppm substantially no selenium contamination of the electrodeposited manganese is observed.

The composition of the electrolyte is not critical to the operability of the present method. However, it has been noted that the concentration of manganous ion in the electrolyte does have an effect on the amount of synergism observed using the additive combination of the present invention. More particularly, at a manganous ion concentration in excess of about 25 gm/l little synergism is observed. Therefore, to obtain full benefit of the present invention it is preferred to maintain the manganous ion concentration in the range of from about 14 to 25 gm/l.

The foregoing example and description are for the purpose of illustration only and should not be considered as limiting the scope of the instant invention; reference being had to the appended claims for such latter purpose.

What is claimed is:

1. In a process for electrodepositing manganese metal from an ammonium sulfate electrolyte containing manganese as manganous ion in an amount up to about 25 gm/l, the improvements which comprise introducing into said electrolyte a selenium compound in an amount sufficient to provide from about 1 to 8 ppm of selenium and a zinc compound in an amount sufficient to provide from about 1 to 5 ppm of zinc ion based on the total volume of the electrolyte.

' 2. The process of claim 1 wherein the electrolyte contains sulfur dioxide in an amount of from about 0.1 to 1.0 gm per liter of electrolyte.

3. The process of claim 1 wherein the selenium compound is selected from the group consisting of H SeO S603, (NH )2SeO3, (NH4)2SeO3 and 8e02- 4. The process of claim 1 wherein said selenium is present in an amount of about 3 ppm of electrolyte and the zinc is present in an amount of about 1 ppm of electrolyte.

5. The process of claim 1 wherein the electrolyte is maintained at a pH of from about 7.0 to 8.5 and contains ammonium sulfate in an amount of from about 100 to 160 gm/l, sulfur dioxide in an amount of from about 0.1 to 1.0 gm/l and manganous ion in an amount of from about 11 to 25 gm/l, based on the total volume of electrolyte.

6. The process of claim 5 wherein the zinc and selenium are present in an amount within the range of from about 0.3 to 2 ppm and l to 5 ppm respectively.

7. The process of claim 6 wherein the zinc and selenium are present in an amount sufficient to provide a weight ratio of zinc to selenium of about 1:3.

Claims (6)

1. 2. The process of claim 1 wherein the electrolyte contains sulfur dioxide in an amount of from about 0.1 to 1.0 gm per liter of electrolyte.
2. 3. The process of claim 1 wherein the selenium compound is selected from the group consisting of H2SeO3, SeO3, (NH4)2SeO3, (NH4)2SeO3 and SeO2.
3. 4. The process of claim 1 wherein said selenium is present in an amount of about 3 ppm of electrolyte and the zinc is present in an amount of about 1 ppm of electrolyte.
4. 5. The process of claim 1 wherein the electrolyte is maintained at a pH of from about 7.0 to 8.5 and contains ammonium sulfate in an amount of from about 100 to 160 gm/l, sulfur dioxide in an amount of from about 0.1 to 1.0 gm/l and manganous ion in an amount of from about 11 to 25 gm/l, based on the total volume of electrolyte.
5. 6. The process of claim 5 wherein the zinc and selenium are present in an amount within the range of from about 0.3 to 2 ppm and 1 to 5 ppm respectively.
6. 7. The process of claim 6 wherein the zinc and selenium are present in an amount sufficient to provide a weight ratio of zinc to selenium of about 1:3.