US3293160A - Electrolytic manufacture of manganates and/or permanganates - Google Patents

Description

Dec. 20, 1966 c. A. MAzzUcHELLx ETAL 3,293,150

ELECTROLYTIC MANUFACTURE OF MANGANTES AND/OR PERMANGANATES Filed Dec. 19, 1962 2 Sheets-Sheet 1 Y: G. L

IFJGZ AT TO 2N EYS Dec. 20, 1966 c. A. MAzzUcHELLl lair/xx. 3,293,160

ELECTROLYTIC MANUFACTURE OF MANGANATES AND/OR PERMANGANATES 2 Sheets-Sheet 2 Filed Dec. 19, 1962 P M U P CQYSTUZER SOLOBHJTY HJ 400 UTER w. wo awr] Fi@ INVENTORS Cnnes A. MAzzUcHELm Yrosevn Snmomoas leo mo g 7" 'rampen-maa P) ATTORNEYS United States Patent O 3,293,160 ELECTROLYTIC MANUFACTURE OF MANGA- NATES AND/R PERMANGANATES Charles A. Mazzuchelli, La Salle, lll., and Joseph Samonides, Tipton, Tenn., assignors to E. J. Lavino and Company, Philadelphia, Pa., a corporation of Delaware Filed Dec. 19, 1962, Ser. No. 245,934 1 Claim. (Cl. 2014-82) This invention 'relates generally to the manufacture of manganates and/or permanganates.

An object of the present invention is to produce manganates and/or permanganates by electrolysing an alkaline solution, using pure, or substantially pure manganese metal as the anode.

More particularly the invention has for one of its objects, the adaptation of a cathode from an electrolytic managanese producing process, to use as an anode in an electrolytic cell for producing manganates and/or permanganates.

Still another object of the invention is to provide a new process of producing manganates and/or permanganates by electrolysing an alkaline solution in which the anode is pure or substantially pure manganese metal deposited upon an electric current conducting core and which anode has been formed or produced as the cathode of an electrolytic manganese production process.

A still further object of the invention is to provide a novel process of producing a permanganate in concentrated solution in an anolyte and recovering crystals of the permanganate directly from such solution.

Still another object is to provide a novel process of producing a manganate in concentrated solution in an anolyte.

In connection with the present invention it has been found that by the use of the combination of an anode of pure manganese and a cathode, in an alkaline solution in accordance with the presen-t process, manganates and/ or permanganates can be produced directly from the anolyte. In such operation the running of the electrolytic cell for a predetermined and sufficiently long period will build up a concentration of the manganate or permanganate in solution to a point where recovery of these compounds directly from the solution can be effected.

In the accompanying drawings the basic elements necessary for the production of the manganates and/ or permanganates, in accordance with the present invention, are illustrated, together with details of such elements and a ow diagram by which to carry out the invention as a continuous process.

In the drawing FIG. l illustrates, in longitudinal section, a suitable type of cell embodying a single anode and a diaphragm or membrane shielded single cathode therein by means of which the Working of the invention may be realized.

FIG. 2 is a View in top plan of the cathode structure and an enclosing or encasing diaphragm and showing one end only ofthe cell.

FIG. 3 is a view taken substantially on the line 3 3 of FIG. 2 and on an enlarged scale.

FIG. 4 illustrates a ow diagram for the continuous production of permanganates in accordance with the present invention.

FIG. 5 is a gra-ph illust-rating the eifect of temperature on potassium permanganate solubility in an anolyte solutlOIl.

Referring more particularly to FIGS. 1 to 3 of the drawings, the numeral generally designates a single cell suitable for carrying out the present invention and which cell may be formed or constructed of any suitable material to contain the selected anolyte solution and inert to or unaffected by such solution.

lthe present manganates or permanganates.

3,293,160 Patented Dec. 20, 1966 Any suitable provision may be made for controlling the cell temperature such as by a bath of flowing water, when necessary, or the cell or a number of cells may be operated at room temperature without cooling, where such procedure is found feasible.

In large scale operation of the invention, provision may be made for continuously removing crystals of the formed compounds as they develop in the anolyte, as by constructting the production cell in a conventional method, such, for example, as by forming the bottom of the cell in a V. Another means of removing crystals might be by providing a suitable channel to allow for the use of a screw conveyor to be mounted in the cell bottom or suitable arrangement may be made in the operation of the cell, as in the hereinafter described system, to remove the crystals as they are formed or suspended in the supersaturated solution to another tank or receptacle to be allowed to settle out or separated from the solution in any other suitable manner.

The method of conducting the electrolyzing current through the anode, anolyte and to the cathode, or through the hereinafter described diaphragm to the cathode, may be of any suitable character most convenient and economical to the installation and operation of the system, and, therefore, is not to be limited to any special type of wiring, etc. Additionally, the cell 10 may be of any desired size or form determined by requirements of the installation and the positions of the anode and cathode are only limited with respect to the relation of the same one to the other.

The numeral 12 generally designates the anode which is suspended in the cell and in the anolyte solution and which solution is generally designated 14.

For the production of the manganates or permanganates according to the present invention, the anode in the form here illustrated, or in any suitable form, consists of pure, or substantially pure manganese metal attached to and supported by a suitable electric current conducting body.

In addition to the foregoing the anode may be in the form of a solid plate of manganese metal or in chips or pie-ces of the manganese metal in or on a suitable carrier and the anode, of course, forms the positive pole of the circuit in which the electrolytic cell is connected.

The solid manganese electrode may also be produced by the process of powder metallurgy.

It is important in any case that the construction of the manganese body and its connection with the electric current conductor be such that the current be conveyed into and through the entire mass of the manganese metal into the electrolyte solution.

The anode 12 in the preferred structural form, -as illustrated in FIG. l, comprises an elongate core 16 of a suitable current conducting material, which may be a metal or non-metal such as titanium, iron, stainless steel, or carbon, upon which the manganese metal, designated 18, is plated.

While the manganese metal may be applied to the core orvcarrier body 16, as illustrated, in actuality, the anode here shown and in the preferred form or embodiment, is formed as the cathode from the electrolytic manganese process, adapted to the present invention as the anode in the electrolytic cell for the production of l In other words, in the process of electrolytically producing the manganese metal, the cathode upon which the metal is deposited, is used in the present process of producing a manganate or `a permanganate, as the positive pole in the electrolytic cell.

Any suitable means may be employed for suspending the anode in the call and in the electrolyte. The means here illustrated may comprise a bridge piece of metallic bar 26, preferably of copper.

or non-metallic material extending across the top of the cell and having the core of the anode fixed thereto in any suitable manner. The core is here illustrated as extending through the bridge piece and carrying suitable means for attaching an electric current conductor 20 thereto.

The numeral 22 generally designates a cathode unit consisting of the cathode element and an enclosing shield or diaphragm.

The cathode element is designated 24. While this element 24 may be constructed in any suitable manner and any suitable material, it is here illustrated as being in the preferred form of a screen or grid supported for suspension in the cell and for extension into the catholyte.

The cathode element 24 is not, of course, restricted in any way, as to its form since it may be in the form of a mesh screen or grid, as stated, or a plate or rod and, of course, of any material either metallic or nonmetallic will conduct the required current load.

The cathode element and the unit as a whole, also is not limited in size but, as hereinafter set forth, there is a prefer-red minimum size ratio between the surface areas of the anode and the cathode element below which the most desirable results in terms of economical operation kof the cell, are not realized.

Acathode unit or structure suitable for working the present invention is here illustrated as embodying a metal The bar 26 is positioned between and has secured thereto the upper ends of the vertical legs of two substantially U-shaped frames 28. These vertical legs of each of the frames, are designated 30 and the lower ends of the legs 30 are connected by the horizontal portions 32.

Any suitable means may be employed for securing the upper ends of the vertical legs 30 of the frames 28, to the bar 26 located therebetween and such means is here shown as a pin or bolt 34 passing transversely through the legs and through the metal bar.

The cathode element 24 is electrically attached or joined to the metal bar 26 to be supported thereby, as hereinafter described, so as to depend into the cell and into the anolyte. When in the form of a screen or grid as here particularly illustrated, such screen or grid may have a construction to be draped over the bar 26 to provide the two side portions or walls 38 and when so draped over the bar 26 it will be located within the area defined by the frames 28 as best seen in the top view of the unit, forming FIG. 2. Thus it will be seen that when the bar 26 is positioned `across the top of the cell, the grid will extend downwardly into the alkaline solution forming the catholyte. It will, of course, be understood that when a cathode element of a form other than a grid or screen such as that illustrated, is employed, it would be lixed or electrically coupled in a suitable manner to the bar to extend downwardly therefrom when the bar is placed in operative position over the top of the cell.

In the illustrated construction, the open mesh metal structure forming the cathode element when draped over the bar 26, may have a spacer 40 interposed between the sides 38 thereof and `at the lower or bottom ends of such sides, as illustrated in FIG. 3.

In the construction of the cell as designed for the manufacture of permanganates, a separating diaphragm Yis interposed between the anode and the cathode element.

This separating diaphragm is here generally designated 42 and in the construction illustrated the diaphragm forms a casing around the cathode element and the diaphragm material extends around the outer sides of the frames 28 and across the bottom elements 32 of the frames thus forming a chamber or enclosed area which is designated 44.

The diaphragm is secured to the frames in any suitable manner, as, for example, by the provision of holding strips 46 between which and the vertical and horizontal members of the frame 28, the diaphragm material is secured.

While the casing or diaphragm material may be placed around the cathode element in contact therewith, it is preferred that it be spaced :from the same so as to allow for the free escape of gases which may be evolved in connection with certain reactions which take place in the enclosed area 44, as hereinafter set forth.

The cathode unit may be mounted in any suitable manner whereby to permit the cathode element and the enclosing diaphragm to depend into the alkaline solution 14 of the cell. The unit is supported so that the top of the diaphragm encasing the cathode element projects above the level of the solution. In the arrangement here illustrated, the bar 26 is disposed across the top of the cell and rests at its ends upon the side walls of the cell above which it may Ibe insulated, if necessary.

Any suitable means may be provided for connecting the bar with an electric current conducting wire forming a part of an electric circuit in which the cell is connected and whereby electrical energy in the form of direct current may be caused to pass from one electrode to the other through the solution. Any suitable means may be provided for furnishing the direct current at the required voltage and amperage.

While a current conductor 36 is here illustrated as attached to an end of the bar 25, this is merely for the purpose of completing the disclosure and is not intended to be in any way limiting as tothe manner in which the bar 26 may be connected in the electric current.

The diaphragm is, of course, formed of a lsuitable material which is inert as regards any reaction with the alkaline solution and it may be in the form of a porous synthetic resin foam, cloth, porous ceramic, asbestos fabric or paper, board, or the like. Examples of synthetic resin foam or liber material which may be employed are polypropylene, polyethylene, and acrylic resins.

The alkaline solution used in the present process of forming the anolyte, may comprise or consist of an alkali or alkaline earth salt which can be electrolyzed. As an example, and without intending to in any way limit the invention, the anolyte may consist of a potassium carbonate solution, a sodium carbonate solution or a solution of any other alkaline earth salt or a mixture of such salt or salts and a hydroxide lsuch as potassium hydroxide, all, of course, aqueous solutions.

The Vfollowing example is -given of the use of potassium carbonate in the production of a permanganate in accordance with the present invention.

Example I An anolyte solution was prepared consisting of approximately 400 grams per liter of potassium carbonate in aqueous solution and placed in the cell 1t), in which the manganese metal anode formed by electrolytic deposition on Va core of titanium, was suspended, together with a suitable cathode element and an encasing diaphragm, also suspended in the solution, substantially as illustrated in FIG. l. A cathode element consisting of a wire grid and using a synthetic iber diaphragm was employed. The anode to cathode element ydistance was about 3 inches and energy was applied at the rate of 5.5 volts and 133 amps. per square foot for a period of about 168.5 hours. At the end of the 168.5 hour period about 91.8 lbs. of potassium permanganate were produced. The yield of this product based on the manganese metalk in accordance with this example is approximately 97%.

The ratio of the anode surface area in solution to the cathode element surface area in solution is approximately 1 to 2 with electrical energy about 14 amps. per square decimeter. Electrical eiiiciency is approximately 32.5%.

For the preparation of manganates the potassium carbonate solution may be replaced by a solution of potassium hydroxide in accordance with the following example:

Example II The production of manganates in accordance with the present invention may be effected without the use of the diaphragm interposed between the anode and the cathode element. In this example an anolyte solution was prepared consisting of approxi-mately 1000 grams per liter of potassium lhydroxide in aqueous solution and placed in the cell 10, in which were suspended the manganese metal anode formed by electrolytic deposition on a core of titanium, and a suitable cathode element as illustrated in FIG. 1, but without the diaphragm. A cathode element consisting of a wire mesh grid was used. The anode to cathode element distance was about 3 cms. and energy was applied at the rate of about 3 volts and 13 amperes for a period of about 5 hours. At the end of the five hour period about 7.3 .grams of potassium manganate were lproduced. The yield of this product based on the manganese metal in accordance with this example, is approximately 57 percent.

The ratio of the anode surface area in solution to the cathode element surface area in solution is approximately l, to 2.1/2 with electrical energy about 40 amperes per square decimeter. The electrical efficiency is approximately 13 percent.

The operation of the cell is such that the cell may be made up of a series of alternate anodes, diaphragms, and cathode elements which can be operated as a cell in series or in parallel. There is no limitation to the number of such anode, diaphragm, and cathode element combinations which may be employed. Neither is the current density of electrical energy applied to the anode limited, but can vary from as low as 2 amperes to 50 amperes or more persquare decimeter.

The energy applied to the cathode may also vary accordingly.

It is found that power requirements for operation of the cell vary in accordance with the ratio of the surface area of the anode to the cathode element. For example, if the ratio of the surface area of the anode to cathode elements is as 1 to 2, the power requirements remain at one factor. If the ratio of the anode as 1 is varied to the cathode element of say 4 times as great, the power requirement or energy necessary for production of the end product will be less. If the cathode element ratio is reduced where the ratio between the anode and cathode element is say l to 1 or 1 to 1A, the power requirements increase proportionately and seem to be in direct ratio to the reduction of the cathode element area to the anode area.

It is also found that the concentration of the anolyte may be as low as 100 grams per liter and as high as its saturation point without impairing the operation of the cell.

power requirements increase while they decrease as the temperature rises.

In addition to the fact that the concentration of the anolyte may vary from 100 to the saturation point of the salt or hydroxide per liter of aqueous solution, the anode to cathode element ratio may vary from 1 to 1A to 1 to 8 or more.

Satisfactory results are obtained with a low current density and a high current density and it has been found that the current density on the anode may vary from as low as 2 amps. to as high as 50 amps. or more per square decirneter.

The main reaction which takes place in the cell as a whole may be shown as:

At the cathode the evolution of hydrogen occurs and this, of course, is well recognized as elementary in electro- 6 lytic dissociation of aqueous solution. At the anode, in addition to the oxidation of the Mn to the MnO4, other reactions take place. The principal side reaction in the cell of the present invention is the formation of possible oxides of manganese and the evolution of oxygen.

In the operation of the cell potassium hydroxide builds up in the catholyte solution and the addition of water or a weak solution of alkali is required to get the potassium hydroxide out and neutralize the bicarbonate to carbonate.

To keep the potassium at the same level in the cell system and prevent the accumulation of bicarbonate equivalent to the potash used in making the permanganate, potassium hydroxide is added. Thus for every 15.8 lbs. of K MnO., produced in the anolyte, 5.6 lbs. of KOH should be added to the anolyte solution to keep the solution in balance. This KOH should be added in a concentrated solution so as to keep down the anolyte dilution.

FIG. 4 illustrates a flow system for producing permanganate crystals in accordance with the present invention, while FIG. 5 is a graph illustrating the effect of the temperature on potassium permanganate solubility in the anolyte solution based on approximately 400 grams of potassium permanganate in the aqueous solution.

The graph illustrates the approximate operating temperature for the cell which will produce in the cell solution the approximate number of grams of potassium permanganate per liter `of solution without crystals forming in the cell. In other words, so long as the cell temperature is maintained for a solution of the concentration indicated, at an indicated degree on the curve, the permanganate will remain in solution and crystals will only be formed by lowering the temperature.

In one run of the process, in a potassium carbonate solution of 600 grams per liter of water, approximatelyl 16 grams of the permanganate form and may be extracted at a solution temperature of 65 C. while at a 70 C., approximately 19 grams per liter of the permanganate are obtained.

Thus operating the cell at say approximately 70 C., when the concentration of permanganate in the cell reaches less than 19 grams per liter, allowing the liquid to run into a cooling tank and reducing the temperature of from about 10 to 20, will cause a good part of the crystals to form and drop out. However, if the cell is operated at this temperature, then the make-up solution tank, hereinafter described, should be heated to this point to keep remaining crystals in solution, the idea being to form the crystals only in the hereinafter described cooling tank.

Referring now to FIG. 4 the numeral 50 generally designates the make-up tank in which the selected alkali is dissolved in water, which alkali is, or may be potassium carbonate, as hereinbefore stated, or any other suit: able alkaline earth salt. In this make-up tank, which is provided with a suitable heating means 52 and agitator 53, the temperature of the solution is raised to the desired degree. The anolyte prepared in the make-up tank flows therefrom as diagrammatically illustrated, into the cell here generally designated 10, as in FIG. 1, where the hereinbefore described electrolytic action is carried out.

The numeral 54 designates a catholyte solution or catholyte make-up and supply tank for addition of catholyte to the cathode element cells which form a part of the ,hereinbefore described unit generally designated 22.1 The catholyte in this tank may comprise a weak alkaline solution or may be water.

The numeral 54a designates a receptacle in which a concentrated potassium hydroxide solution is maintained to be fed as required into the system for mixture with the crystals and liquor passing oilC from the reaction cell 10 into the cooling and crystallizing tank 55.

As hereinbefore stated the addition of potassium hydroxide to the anolyte is required to keep the potash at the same level in the cell system-or in other words to replace the potassium ions removed in the formation of the MnO4. This potassium hydroxide is maintained in concentrated solution in the tank 54a whereby the addi-` tion of the alkali solution will be effective to prevent the accumulation of bicarbonate in the cell Without diluting the solution.

From the reaction cell 10 to the liquor containing the potassium permanganate flows into the cooling and crystalliz'ing tank generally designated 55. After cooling in this tank where the liquor is reduced to the proper degree to effect the formation of the permanganate crystals, the crystals are removed to a centrifuge 56 and the mother liquor is returned by Way of the line 57 to the make-up tank 50.

The crystals from the centrifuge are passed into a tank of Water, generally designated 58, which is heated to about 90 C., and the crystals are there agitated to ensure complete solution of the same. In this solvent tank crystals are added to a sufficient extent to produce a solution having a specific gravity of about 1150-ll60. This solution then passes from the solvent tank 58 to a filter 60 from which it ows as indicated into a crystallizer or receptacle 61 for effecting crystal formation.

In the crystallizer the liquor is allowed to stand without agitation for at least 48 hours for crystals to build up.

The mother liquor extracted in the centrifuge passes from the centrifuge to a receiving tank 62 from which it returns by a line 63 to the anolyte tank 50.

After the crystals are formed, the mother liquor is drawn off and recycled either to the dissolver 58 as shown or it may be returned to the anolyte make-up tank as desired.

The crystals removed from the crystallizer 61 are centrifuged at 64 and the mother liquor is passed from the centrifuge and recycled to the dissolver or the anolyte tank While the crystals are sent to the dryer 65.

As this invention may be embodied in several forms Without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claim rather than by the description preceding them, and all changes that fall within the metes and bounds of the claim or that form their functional as well as conjointly cooperative equivalents, are therefore intended to be embraced by this claim.

We claim:

The process of making a permanganate which comprises providing an electrolyte make-up and supply tank with a solution of an alkali metals salt selected from the group consisting of sodium carbonate and potassium carbonate, heating said solution to about 65 to 70 C., conducting the heated solution into an electrolytic cell,

electrolytically oxidizing an anode body consisting of substantially pure manganese metal suspended in said heated electrolyte solution in said electrolytic cell, suspending a cathode in the said electrolyte, passing a direct current through the said electrolyte in said cell, providing diaphragm a means in the cell for preventing the electrolyte from directly contacting the cathode while electrical energy flows to the cathode, thereby forming permanganate in the anolyte, drawing off the anolyte from the cell into a cooling receiver, adding a concentrated solution of potassium hydroxide .to the anolyte as the anolyte oWs to said cooling receiver to thereby prevent accumulation of bicarbonate Without diluting the solution and to replace potassium ions removed by formation of permanganate, reducing the temperature of the anolyte solution in the cooling receiver from about l0 to 20 to effect formation and precipitation of permanganate crystals, then removing the crystals from the receiver to a centrifuge and returning the mother liquor obtained from the cooling and crystallizing step to the said make-up tank, then centrifuging the permanganate crystals to remove the adhering mother liquor and returning the centrifuged liquor to the make-up tank and -from the make-up tank to the electrolytic cell, dissolving the centrifuged crystals in Water, adding crystals from the centrifuge to the solution of dissolved crystals to give the solution a specific gravity of abouty 1150-1160, filtering the latter solution, then effecting crystallization of the permanganate from the said filtered solution, re-using the solvent for dissolving additional crystals, centrifuging the crystals obtained from the filtered solution to remove all of the solvent therefrom, and finally Adrying the crystals.

References Cited by the Examiner UNITED STATES PATENTS y 1,281,085 10/1918 Shoeld 204-82 1,291,680 l/ 1919 Lovelace et al. 204-82 1,360,700 11/1920 Wilson et al 204--82 3,055,811 9/1962v Ruff 204-98 FOREIGN PATENTS 51,390 7/ 1937 Russia.

OTHER REFERENCES Soobshcheniya Akad. Nauk Gruzin S.S.R., volume 19, No. 3, 285-91 (1957), Chem. Abst. 52:18022i, Chem. Abst. 33167329.

JOHN H. MACK, Primary Examiner.

MURRAY A. TILLMAN, Examiner.

L. G. WISE, H. M. FLOURNOY, Assistant Examiners.

Claims (1)

1. THE PROCESS OF MAKING A PERMANGANATE WHICH CIMPRISES PROVIDING AN ELECTROYTE MAKE-UP AND SUPPLY TANK WITH A SOLUTION OF AN ALKALI METALS SALT SELECTED FROM THE GROUP CONSISTING OF SODIUM CARBONATE AND POTASSIUM CARBONATE, HEATING SOLUTION ABOUT 65 TO 70*C., CONDUCTING THE HEATED SOLUTION INTO AN ELECTRLYTIC CELL, ELECTROLYTICALLY OXIDIZING AN ANODE BODY CONSISTING OF SUBSTANTIALLY PURE MANGANESE METAL SUSPENDED IN SAID HEATED ELECTRLYTE SOLUTION IN SAID ELECTRLYTIC CELL, SUSPEMDING A CATHODE IN THE SAID ELECTRLYTE, OASSING A DIRECT CURRENT THROUGH SAID SAID ELECTROLYTE IN SAID CELL, PROVIDING DIAPHRAGM A MEANS IN THE CELL FOR PREVENTING THE ELECTRLYTE FROM DIRECTLY CONTACTING THE CATHODE WHILE ELECTRICAL ENERGY FLOWS TO THE CATHODE, THEREBY FORMING PERMANGANATE IN THE ANOLYTE, DRAWING OFF THE ANOLYTE FROM THE CELL INTO A COOLING RECEIVER, ADDING A CONCENTRADED SOLUTION OF POTASSIUM HYDROXIDE TO THE ANOLYTE AS THE ANOLYTE FLOWS TO SAID COOLING RECEIVER TO THEREBY PREVENT ACCUMULATION OF BICARBONATE WITHOUT DILUTING THE SOLUTION AND TO REPLACE POTASSIUM IONS REMOVED BY FOR MATION OF PERMANGANATE, REDUCING THE TEMPERATURE OF THE ANOLYTE SOLUTION IN THE COOLING RECEIVER FROM ABOUT 10 TO 20* TO EFFECT FORMATION AND PRECIPITATION OF PERMANGANATTE CRYSTALS, THEN REMOVING THE CRYSTALS FROM THE RECEIVER TO A CENTRIFUGE AND RETURNING THE MOTHER LIQUOR OBTAINED FROM THE COOLING AND CRYSTALLIZING STEP TO THE SAID MAKE-UP TANK, THEN CENTRIFUGING THE PERMANGANATE CRYSTALS TO REMOVE THE ADHERING MOTHER LIQUOR AND RETURNING THE CENTRIFUGED LIQUOR TO THE MAKE-UP TANK AND FROM THE MAKE-UP TANK TO THE ELECTRLYTIC CELL, DISSOLVING THE CENTRIFUGED CRYSTALS IN WATER, ADDING CRYSTALS FROM THE CENTRIFUGE TO THE SOLUTION OF DISSOLVED CRYSTALS TO GIVE THE SOLUTION A SPECIFIC GRAVITY OF ABOUT 1150-1160, FILTERING THE LATTER SOLUTION, THEN EFFECTING CRYSTALLIZATION OF THE PERMANGANATE FROM THE SAID FILTERED SOLUTION, RE-USING THE SOLVENT FOR DISSOLVING ADDITIONAL CRYSTALS, CENTRIFUGING THE CRYSTALS OBTAINED FROM THE FILTERED SOLUTION TO REMOVE ALL OF THE SOLVENT THEREFROM, AND FINALLY DRYING THE CRYSTALS.

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