US2445826A - Electrolyte purification in manganese electrowinning - Google Patents

Description

Patented July 27, 1948 ELECTROLYTEPURIFICATION IN MANGA- NESE ELECTROWINNING William L. Hammerquist, Knoxville, Tenn., as-

signor to Electro Manganese Corporation, Knoxville, Tenn., a corporation of Delaware No Drawing. Application February 1, 1944,

Serial No. 520,689

10 Claims.

, h ,1 i This invention relates to purification of solutions for use as electrolytes in the electrodeposition including the electrowinning of manganese.

In the electrowinning ofmanganese, electrolytic cells are employed in which the electrolyte is divided into catholyte and anolyte. A type of cell in commercial use at thepresent time contains a plurality of catholyte chambers suspended in a tank containing anolyte liquid. A cathode,

in sheet form is suspended in each catholyte chamber and these chambers include in their structure permeable diaphragms Whichseparate the catholyte liquid from the anolyte liquid. The anodes are suspended in the anolyte liquid in spaced relation to the adjacent diaphragm walls so that the cell comprises a series of anodes and cathodes alternately arranged in a row and separated by the catholyte or diaphragm chambers.

Anolyte containing manganese sulfate, ammonium sulfate, and sulfuric acid is withdrawn from the anolyte chamber and used to extract manganese ore and the extract is then subjected to purification. When purified it becomes catholyte liquid and is suppliedto the catholyte chamber, Metallic manganese is deposited on the cathodes in the cathode chambers. The cathodes are commonly made in sheet form from a suitable metal or alloy. At the end of a predetermined plating period, the cathodes with a deposit of manganese metal thereon are removed from the cathode chambers, the electrolytic deposit is stripped therefrom, and the cathodes after suitable reconditioning are returned to the cell.

In the catholyte chamber the catholyte is partially depleted of its contents of manganese. It then passes to the anolyte chamber partly or wholly by diifusion and/or partly by other means of transfer, as, for example, overflow, and becomes anolyte liquid. There is thus a circulation of liquid from-the anolyte chamber to the catholyte chamber and back to the anolyte chamber, and in the course of this circulation outside the cell, the anolyte liquid is enriched in manganese by contact with suitably prepared managenese ore,

or by the addition of the manganese sulfate from a source other than manganese ore, and subjected to purification.

It will thus be seen that to the circulating stream outside the cell, there is continuously added a source of manganese, and since such sources contain substances other than manganese which may be generally referred to as impurities,

it will be clear that these impurities are being continuously added to the circulating stream. Such impurities may include iron, arsenic, antimony, cobalt, nickel, copper, molybdenum, and zinc, and it has been found necessary either to remove these impurities completely or .else reduce them to such small or insignificant proportions that they do not interfere with the plating process and. the production of suitably pure electrolytic manganese. The latter in its commercial form must be extremely pure, e. g., oi'the order of 99.95% manganese, and in this form has a acteristic bright, metallic luster.

It has been discovered that soluble or colloidal silica is an impurity, the removal or, control of,

which is highly desirable because of its adverse elfects on obtaining satisfactory cathodic deposition. Having arrived at this knowledge, theinvention then proceeds further and appl es" a, remedy, this remedy being the use of a reagent which is eifective in separating silicafrom the solution intendedfor use as catholyte; at least go to an extent sufficient to prevent the abovemen tioned phenomenon; The reagentwhich has so far been found best adaptedfor'th purpose" is aluminum sulfate. This occurs in variousiorms, as, for example, the anhydrous salt, or the salt containing water of crystallization, or in the form of variousdouble salts. In accordance with the invention,,an aluminum sulfate reagent is applied to the solution to be purified atapH rangeof about 5.5 to 7.5. V 1 In the commercial electrowinning process where ore is used as the source of manganese, the latter is extractedwith anolyte at a pH which may be from 1 to 3, after which the pH is raised to about 5.5 to 6.5, and air or other suitable oxidizing'agent is employed to oxidize the iron" to the ferric" condition and cause the precipitation thereof, together with any arsenicpantimony, and the like which may; beqpresent'. The iron be treated for the removal-of cobalt and nickel, for which purpose the pH is raised to about 7.2 to "7.5 and treated with a precipitant, e. g; am-

monium sulfide, for cobalt, nickel, and other heavy metals whose sulfides are insoluble at this pH range. Since it as been fauna desirable to effect the aluminum sulfate treatmentl at a pH of about 5.5 to about 7.5, this treatment may conveniently be carried out on 'theinother liquor after separation of the ironprecipitate and gangue andhaving a pH of about 5.5 to 6.5.

char- Still another variation is to add all or'a part of the aluminum sulfate to the mother liquor after separation of the iron precipitate and gangue at a pH range of about 5.5 to 6.5, and the remainder may be added after the pH has been increased to about 7.2 to 7.5 preparatory to precipitating the cobalt, nickel, etc.

It is also possible to add thealu-minum sulfate 4 said solutions and adapt them for use as catholyte.

It is, of course, entirely possible to replenish the manganese content of the anolyte by enriching it with manganese sulfate obtained from any suitable'source, and the'invention includes, in general, the treatment of solutions containing manganese sulfate in order to purify them to obtain catholyte liquid. Whether or not the solution is obtained by extracting ore, it may well contain silica in soluble or colloidal form, that is to say, silica in a highly dispersed condition,

which. existseitherin the form of a true soluat any time prior to iron precipitation and filtra.

tion, as, for instance, during theore leaching operation. This method, however, is deemed wasteful since aluminum begins to precipitate...as.

hydrous oxide at a pH of 3, and the aluminum thus precipitated amounts of precipitated-iron and gangue cannot perform its function efficiently. To attain maximum efiiciency from the aluminum in removing silicates, it should be precipitated from thesolution-in the absence of .such foreign materials as precipitated iron and gangue and at a pH not lower than about 5.5 or higher than about 7.5. Practical .considerationsdo not always :permit such ideal conditions, and operations may haveto be carried out under less favorable conditions.

The addition of the aluminum sulfate causes the formation of the precipitate of aluminum hydroxide which has been found effective in eliminating soluble orcolloi-dal silica to a sufficient extent.

Proportions of aluminum sulfate varying from about ,10to parts by weight of anhydrous aluminum sulfate for every one hundred thousand parts by weight of solution, have been found adequate. In general, about twenty to twentyfive pounds of 57 per cent. aluminum sulfate to about ten thousand gallons of solution weighing about ten pounds per gallon, have been found suflicient.

However, as shown in column 3 of the table at the' end of the specification and in the paragraph followingthattabl proportions of aluminum sulfate-(calculated as anhydrous aluminum sulfate) as high as 40.0 20=800 "pounds of aluminum sulfate per 10,000 gallons of solution may be used and-since a gallon of said solution weighs 10 pounds, the proportion of said aluminum sulfate maybeas high as 800 pounds per 100,000 pounds of said solution. l

The precipitate formed by the addition of the aluminum sulfate may be separated as such prior to the separation of cobalt, nickel, etc. Preferably, however, theprecipitate of aluminum hydrOXide s f d p or to or concurrently with the sulfide precipitate and the tworemoved at the same time and by the same means, as, for-example, by filtration. In-some cases treatment of the solution with aluminum sulfate may'occur afterseparation of the cobalt, nickel, etc.

There are, of course, numerous specific Variants ofthe manner of adding the aluminum sulfate, and all such variants areintended to be included, provided the precipitation occurs within a pH range of about 5.5 to 7.5..

' It is-tobe .understood that the invention is not limited to the purification of solutions obtained by extracting manganese-containing. era with sulfuric acid solutions or with anolyte, andis generally applicable to the treatment .oisolutions containing manganese sulfate inorder topurify in the presence of large,

tion. or a colloidal solution, and the invention in its-generic aspects is directed to treatment of solutions to. separate. the silica of that type therefrom. While impurities other than silica are commonly present in solutions for the electrodeposition including the electrowinning of manganese, the invention is not in its generic aspects limited tothe removal of silica in conjunction with the elimination of the other impurities, e. g., iron, cobalt, and nickel, but, rather, to the removal-of silica whether or not it may be associated, with other impurities. Therefore, any spe-. cificdescription of embodimentsof the invention which includes the treatment of manganesecontaining ore and the removal of impurities other than silica, are not to be regarded as limitations in respect of the generic phase of the invention. It is also to be pointed out that in some casesv manganese may be electroplated in a cell not provided with a diaphragm, that is to say, in contradistinction to the process of electrowinning 'of manganesefrom solutions containing manganese salts and/or from manganese-containing ores, it is quite possible to carry out a manganese electroplating process in which manganese is deposited asa coating on various objects. I-Iere, also, it is necessary to employ a pure electrolyte, and theinvention is applicable to the purification of solutions for the electrodeposition of manganese Whether that deposition be an electroplating process or an electrowinning process. Therefore, it will be understood that while the specific description of the invention is in terms ofan electrowinning process, that specific description is not to be regarded as a limitation on the .generic features of the invention.

Atypical example of an embodiment of the invention may be describedas follows:

Anolyte liquid having a composition of about 10 to 18 grams per liter of manganese as manganese sulfate, about to grams per liter of ammonium sulfate and a pH of about 1 to 2, is withdrawn from the anolyte chamber of a commercial cell employed for the electrowinning of manganese and ismixed with manganese ore in a digester, the ore being suitably conditioned, if necessary (e. g., by the process described in the co-pendingapplication of Elmer M. Wanamaker et-al., Serialv No. 497,352, filed August 4, 1943, now Patent.2,397,824, granted April 2, 194 6), and, as-a-result of agitation with the are, a mixture of ore and extract is obtained, the extract havinga concentration of manganese of about 20 to 50 grams per liter. The pH of the extract is-ad justed to about 5.5-to 6.5, and airor'other suitable-oxidizing agent is employed to oxidize iron to the-ferric condition and cause precipitation thereof along with any arsenic, antimony, or thelike which may be present. The insoluble gangue and iron precipitate is then separated,

allon, thereis added aluminumsulfate in the proportion of about twelve and one-half pounds, calculated as 57 per cent. aluminum sulfate, for each ten thousand gallons of solution, which is equivalent to a concentration of anhydrous aluminum sulfate of about seven and one-eighth pounds per one hundred thousand pounds of solution. This addition may occur at a pH of about 5.5 to about 7.5, a typical pH value being about 6.3 and a typical range being about 6.0 to 6.5. A precipitate is formed which is preferably allowed temporarily to remain in suspension. Thereafter the pH of the liquid is raised to about 7.2 to about 7.5 and an additional twelve and oneshalf. pounds of 57 per cent. aluminum sulfate is added. Thus the total amount of aluminum sulfate added in the two steps is equivalent -to fourteen and one-quarter pounds of anhydrous aluminum sulfate for each ten thousand gallons of solution. Subsequently a precipitant for cobalt, nickel, etc., e. g., ammonium sulfide, is

added, precipitating the cobalt, nickel, etc., in

the form of their insoluble sulfides mixed with the aluminum hydroxide precipitate caused by the addition of the aluminum sulfate. The mixed precipitate is then removed, as by filtration or other suitable means, and the purified liquid is then in suitable condition for use as catholyte.

In the preferred embodimentof the invention, sufficient precipitant is used to reduce the content of soluble or colloidal silica to not more than about 0.001 gram per liter before using the purifled solution as catholyte. For this purpose the solution to be purified may .be analyzed to determine its content of said soluble or colloidal silica and 'an amount of aluminum sulfate added not less than 4.0 parts by weight ofaluminum sulfate (100%) for each part by weight of colloidal and/or oluble silica, or about 7.0 parts by weight of commercial aluminum sulfate containing 57% AJ2(SO4)3.

The following table shows the minimum concentrations of aluminum sulfate, calculated as anhydrous or 100% A12(SO4)3 and expressed as grams per liter (and pounds per 10,000 gallons of solution), necessary to precipitate varying concentrations of soluble or colloidal silica expressed as grams'per liter: 7

lbs. Ah (S 04): gill, of Soluble g./l. of Al: (S04): per 10,000 galor Colloidal calc. as Anhylens of solution Silica drous calc. as

Anhydrous Larger excesses over the minimum proportions of aluminum sulfate above set forth are desirable, e. g., excesses of, say, 2 to 20 fold.

What is claimed is:

1. The process of treating a solution to be used as an electrolyte in the electrodeposition including the electrowinning of manganese, said solution containing manganese sulfate, ammonium sulfate and soluble silica, which comprises treating said solution at a pH of about 5.5 to'7.5 with aluminum sulfate in the proportion of not less than the electrolyte is divided into catholyte and anolyte and in which process anolyte liquid is withdrawn from the cell and used to extract manganese-containing ore to produce an extract which is subjected to purification for use as catholyte, said purification including precipitation of the iron, separation of the iron precipitate and gangue, and the production of a solution from which said iron precipitate and gangue have been separated, said solution containing soluble silica, the improvement which comprises treating said solution with aluminum sulfate in the ratio of not less than four parts by weight Of aluminum sulfate calculated as anhydrous aluminum sulfate for each part by weight of soluble silica at a pH of about 5.5 to 75, forming 'a precipitate,

and separating said precipitate.

3. In the process of manganese electrowinning involving the use of an electrolytic cell in which the electrolyte is divided into catholyte and anolyte and in which process anolyte liquid is withdrawn from the cell and used to extract manganese-containing ore to produce an extract which is subjected to purification for use as catholyte, said purification including precipita tion of the iron, separation of the iron precipitate and gangue, and the production of a solution from which said iron precipitate and gangue have the electrolyte is divided into catholyte and 65 anolyte and in which process anolyte liquid is withdrawn from the cell and used to extract manganese-containing ore to produce an extract which is subjected to purification for use as catholyte, said purification including precipitation of the iron, separation of the iron precipitate and gangue, and the production of a solution from which said iron precipitate and gangue have been separated, said solution containing soluble silica, the improvement which comprises treating said solution with aluminum sulfate in the ratio of about 10 to 20 parts by weight of aluminum sulfate calculated as anhydrous aluminum sulfate to about one hundred thousand parts of said solution, adding said aluminum sulfate at a pH of about 5.5 to 6.5, then raising the pH to about 7.2

to 7.5, forming a precipitate, and separating said 7. lyte and in which process anolyte liquid is withdrawn from the cell and'used to extract manganese-containing ore to produce an extract which is subjected to purification for use as catholyte, said purification including precipitation of the iron,.separation of the iron precipitate and gangue, and the production of a solution from which said iron precipitate and gangue have been separated, said solution containing soluble silica, the improvement which comprises treating said solution with aluminum sulfate in the ratio of about to parts by weight of aluminum sulfate calculated as anhydrous aluminum sulfate to about one hundred thousand parts of said solution, adding a portion of said aluminum sulfate at a pH of about 5.5 to 6.5, then raising the pH to about 7.2 to 7.5 and adding the remainder of the aluminum sulfate, forming a precipitate, and separating the precipitate from the solution.

6. The process of treating a solution to be used as an electrolyte in the electrodeposition including the electrowinning of manganese, said solution containing manganese sulfate, ammonium sulfate and soluble silica, which comprises treating said solution at a pH of about 5.5 to 7.5 with aluminum sulfate in the proportion of not less thanfour parts by weight of aluminum sulfate calculated as anhydrous aluminum sulfate for each part by weight of soluble silica, forming a precipitate; treating said solution with a precipitant for cobalt and nickel within said pH range to precipitate cobalt and nickel, and separating the combined precipitates.

'7 Process of treating a solution to be used as an electrolyte in the electrodeposition including the electrowinning of manganese, said solution containing manganese sulfate, ammonium sulfate, and soluble' silica, whichcomprises treating said solution at a pH of about 5.5 to 7.5 with aluminum sulfate in the proportion of not less than about 4 milligrams of aluminum sulfate per liter of said solution (0.40 pound per 10,000 gallons of said solution) for each milligram per liter (0.00001 pound per gallon) of said silica, the said aluminum sulfate being calculated as anhydrous aluminum sulfate.

8. Process of treating a solution to be used as an electrolyte in the electrodeposition including the electrowinning of manganesasaid solution containing manganese, sulfate, ammonium sulfate, soluble silica and the sulfatesof cobalt and nickel, which comprises treating said solution at a pH of about 5.5 to 7.5 wit-haluminum sulfate in the proportion of not less than about 4 milligrams of aluminum sulfate per literof said 50-- lution for each milligram per liter of said-silica, the said aluminum sulfate being calculated as anhydrous aluminum sulfate, toform a precipitate of aluminum hydroxide, adding ammonium -ing said solution ata' pH of about 5.5 to 7.5 with aluminum. sulfate in the proportion of aboutIO to 800 parts by weight of aluminum sulfate ca'lculated as anhydrous aluminum sulfate to about 100,000 parts by Weight of said solution, thereby' forming a silica precipitate, and separating said precipitate from said solution.

10. In the process of manganese electrowinning involving the use of an electrolyticcell in which the electrolyte isdivided into catholyt'e and anolyte and in which process anolyte liquid.

is withdrawn from the cell and used to extract manganese-containing ore to produce an'extract which is subjected to purification for use as catholyte said purification including precipita tion of the iron, separation of the iron precipitate and gangue, and the production of a solution from which said iron precipitate and gangue have been separated, said solution containing soluble silica, the improvement which comprises treating said solution with aluminum sulfate in the ratio of aboutlO to 800 parts by weight of aluminum sulfate calculated as anhydrous aluminum sulfate to about,100,000 parts by weight of said solution at a pH of about 5.5 to 7.5 and thereafter treating said solution with a precipitant for cobalt and nickel within said pH range, forming a precipitate, and separating'saidiprecipitate from said solution.

WILLIAM L. I-IAMMERQUIST.

REFERENCES CITED.

The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number Name 7 Date 1,137,005 Jacobson Apr. 27, 1915 1,843,006 Stevens et al Jan. 26, 1932 l 1,989,603 Nicoll; Jan. 29', 1935 2,266,187 Westby Dec., 16, v1941 2,267,831 Liebknecht Dec. 30, 1941 2,325,723 Wanamaker et a1. Aug. 3, 1943 2,340,188 Jukkola Jan. 25, 1944 OTHER REFERENCES Industrial and Engineering Chemistry, vol. 31, July 1939, pp. 859, 860, 861.

Water Works Engineering, Oct. 13,1937, pp.

sulfides of cobalt and"