US2339911A - Manganese electrowinning process - Google Patents

Description

Jan. 25, 1944. 5 H, L. CHAMBERLAIN 2,339,911

- MAGANESE ELEcTRowINNING PROCESS Filed Aug. 19. 1942 6001. Eo A/voLrr;

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Patented Jan. 25, 1944 MANGANESE ELECTBOWINNING PROCESS' Harold L Chamberlain, Knoxville, Tenn., asslgnoxto Electro Manganese Corporation, Knoxville, Tenn., a corporation of Delaware Application August 19, 1942, Serial No. 455,321

7 Claims. (Cl. 2114-105) This invention relates to improvements in the electrowinning of manganese. More particular- 1y it relates to improvements in controlling the purity of the electrolyte and of the manganese deposited therefrom on the cathode.

1n the commercial electrowinning of manganese a body of electrolyte is maintained in an electrolytic cell provided with an anode and a cathode, separated by a permeable membrane or diaphragm into anolyte and catholyte chambers. respectively. From this bo'dy of liquid, specifically from the catholyte in the catholyte chamber, manganese is removed in the form of metallic manganese and deposited on the cathode. To this body of Vliquid a manganese salt is added to replenish the solution with manganese ions and compensate for the removal of metallic manganese. The manganese salt is obtained by leaching a suitably conditioned manganese ore with an acid solution and in practice this acid solution is the anolyte' from the anolyte chamber. Nothing is removed from the electrolyte except metallic manganese and the volatile prod- ?ucts of electrolysis whereas there is a continu- I out or progressive'addition to the electrolyte of the products obtained by leaching ore with the anolyte'liquid.

Consequently the concentration of impurities, specically metallic elements other than manganese,d continuously increases unless steps are taken to prevent this increase in concentration of impurities. Among these impurities magnesium is a common constituent of manganese ores.

l Among the advantages of manganese obtained by the electrowinning thereof are lnot only the low cost of manganese produced by this process as compared with the thermal process and the fact that it is possible to employ low grade manganese ores, but .also thefact that manganese may be produced by electrowinning in a high state of purity. In fact the purity of manganese produced by the electrowinning process must be extremely high as this is one of the outstanding advantages of electrolytic manganese as compared with manganese obtained by other methods. Consequently the control of impurities introduced into the electrolyte is an important matter not only in respect of controlling the iin-4 purities of the manganese deposit but also in preventingside reactions introduced by the impurities and maintaining the eilciency of operation, and has presented a serious problem. Not only do these impurities when less adequately controlled seriously contaminate the deposit of manganese, but also seriously interfere with the successful-operation of the electrolytic process.

The problem is particularly acute in the case of magnesium owing to the difficulty' of successfully separating it from the manganese. Iron can be removed satisfactorily to a large extent by precipitating as ferric hydroxide. Cobalt and nickel can be precipitated to a very large extent by means of ammonium sulfide. Since manganese is commonly in the form of manganese sulfate, the anolyte liquid contains a considerable concentration of sulfuric acid and the relative insolubility of calcium sulfate prevents undue contamination of the electrolyte with calcium. Difficulty has, however, been experienced inadequately separating magnesium.

1f the magnesium content be allowed to build up without control complex sulfates of magnesium with manganese and ammonium ion are formed in the anolyte. These complex sulfates precipitate out in the anolyte and tend to cause clogging of the diaphragm,the anolyte outlet and the anolyte manifolds. In addition Athese complex sulfates cause a loss of manganese and ammonium sulfate which is' obviously undesirable. With clogging of the diaphragm increased voltages are necessary to overcome the increased electrical resistance of the diaphragm with subsequent increase-in the voltage distribution in the cell and a disturbaneeof the necessary cathode potential for the deposit of manganese metal from the catholyte. If the magnesium content were allowed to build up in an uncon- 'trolledamount in the catholyte with increased alkalinity of the catholyte, basicsalts of magnesium tend to be formed which in turn may be mechanically carried to the cathode and depositedfwith the manganese metal thereby contaminating it, or else tend to clog the diaphragm and the overflow pipes connecting the catholyte with the analyte chamber. It is apparent that the deposition of contaminating influences on the cathode will also disturb electrical conditions in the cell.

As previously stated, the problem of controlling the content of magnesium in the electrolyte has been a serious one in the commercial electrowinning of manganese, and a great deal of elort has been expended in attempts to solve the problem without, however, arriving at a' wholly7 satisfactory solution prior to the present invention.

' In general attempts to solve the problem by the addition of reagents to precipitate the magnesium have not been satisfactory, partly at least because oi' side reactions caused by the introduction of the precipitating reagents.

The manganese electrolyte may be considered'- as a solution of manganese sulfate and ammonium sulfate contained as principal ingredients with other sulfates present chief among which are magnesium and calcium sulfates due to the presence of these in the ore along with the manganese. The quantity of calcium sulfate might be considered as small and limited'by the low solubility of the calcium sulfate in comparison to that of the other materials. Magnesium sulfate is thought of as having relatively high solubility. Extensive experimental studies have shown that the solubility of magnesium sulfate is an inverse function of the concentration of ammonium sulfate and manganese sulfate and a direct function of temperature. It has been discovered that Within the ranges of concentration of ammonium sulfate and manganese sulfate employed in the electrolytes for manganese electrowinning, complex sulfates of manganese, ammonium, magnesium, and calcium are formed, which complex sulfates have markedly different solubilities from any of the simple sulfates or Ydouble or4 triple sulfate combinations of these.

A typical analysis of such complex sulfate is as follows:

Percent by weight Moisture 29.11 (NH4) 2504 33.49 MgSO4 19.98 MnSO4 13.91 CaSOl- 2.40

In addition these complex sulfates are not stable over a wide range of `temperature but only exist over rather narrow ranges of temperature and in turn show low solubilities over these temperature ranges as evidenced by the fact that they readily crystallze out. These salts have been discovered to contain a higher proportion of magnesium than does the electrolyte from which y passes from the anolyte chamber to the catholyte chamber via the ore digesting station and purication stations mentioned, the impurities introduced into the electrolyte from the ore are cumulative and will continually build up imless removed, and this of course is true of magnesium as it is with the other impurities. For any given range of composition of electrolyte in termsvof manganese sulfate and ammonium sulfate, separation of complex salts could in theory be prevented by increasing the temperature to a point where these salts are no longer stable and where they are soluble. However, in practice this would be wholly impractical because, due to the accumulation of magnesium and therefore continual increase in the concentration of complex salt, it would be necessariTv to continually increase the electrical resistance, diaphragm potential differences, anode potentials, etc. It is therefore necessary to provide a commercially satisfactory practical method for removing magnesium and controlling the composition of the electrolyte so that the concentration of magnesium may be con-I ltrolled at a point below a desired maximum whereby uniform conditions, including operation within a predetermined range of temperature, may be maintained.

It may be stated at this point that high teml peratures accentuate the harmful eiect of the an enormous amount of water to obtain adequate cooling by the use of cooling coils. One of the outstanding disadvantages is the fact that the complex salt referred to above crystallizes or separates out on the heat exchange surfaces and reduces the heat transfer coeiiicient to such a low value that cooling efficiency is destroyed. Moreover, the removal of the crystals from a pipe cooling system is very diiicult and costly. The most practical Way of effecting this removal is to wash or ilushthem off with hot water. The complex salt is a valuable fertilizer and in order to realize its economic value must be sold in solid or crystalline form.' Therefore the solution resulting from the washing of the crystals from the pipe coils must be concentrated by boiling, a

temperature. With increasing concentrations of magnesium and increasing temperature, electrical ifects enter such as changes in overvoltage,

process which is uneconomical.

As abovedescribed the process of electrowinning of manganese involves a cyclical operation and thecirculation of the electrolyte in a path of circulation from-the--anolyte chamber to the catholyte chamber via certain purification stations.

In accordance with this invention the electrolyte or any predetermined or desired fraction thereof is treated to remove magnesium in the form of a complex salt thereof by cooling said electrolyte or fraction or portion thereof by reducing the temperature of Vsaid electrolyte by evaporative coolingin direct contact with the atmosphere, that is to say, the liquid to be cooled is subdivided into a plurality of parts having a plurality of surfaces. These parts and surfaces are exposed to direct contact with air at atmospheric temperatures. Cooling occurslargely by evaporation. A preferred apparatus element for effecting such cooling is a cooling tower. For example, a cooling towermay be placed at :my desired point in the path of circulation previously described. All 'of the liquid in said path may be passed through the cooling tower or a predetermined portion may be passed through said Atower and the remainder recirculated by returning to the said path. Also all of the cooled liquid from the cooling tower may be sent forward in the circulation path or a predetermined fraction thereof may be sent forward and the remainder returned to the circulation path and thereby recirculated. The proportion of liquid cooled by the method described will depend on without the corresponding penalty of reduction separates out on the bailie surfaces thereof and may be readily removed therefrom in solid form. Since the heat transfer involved is directly from the liquid to the atmosphere as contrasted with the transfer through metallic walls as in the case of cooling coils, the separation of the salt in no way reduces the efficiency of cooling.- Moreover, as will more fully hereinafter be discussed, the cooling by evaporation effects the-desired volume control.

While the principal purpose and advantage of the method and apparatus of this invention are directed to and connected with the removal of magnesium, there are at least two important corollary advantages, one of these being temperature control and the lother volume control. By the method of the present invention it is possible accurately to control the temperature of the electrolyte at any point in the path of circulation thereof. For example, liquid may be withdrawn from the anolyte chamber, a predetermined fraction thereof sent to a cooling tower, cooled and recirculated back to the anolyte chamber, and the remaining portion sent forward to.

the digester. In this way the temperature of the anolyte may be maintained within any desired temperature range. In another case anolyte may be withdrawn from the anolyte chamber, sent to a 'cooling tower and cooled, a portion of the cooled anolyte recirculated back to the anolyte chamber and the remainder sent forward to the ore digester, and by controlling the degree of cooling in the tower and the rate of recirculation not only may the temperature of the anolyte be maintained within a predetermined range, but also the temperature lof the reaction in the'digester may also be controlled. It may be added at this point that temperature control is particularly necessary in manganese electrowinning for reasons already' stated. In respect of controlling the temperature in the .digester, it may be pointed out that in some cases at least it is desirable to be able to cool the liquid delivered to -the digester because of the exothermic reaction occurring in thel digester as a result of reaction between anolyte and certain kinds of ores.

A further important corrolary.Y advantage of this invention is the provision of an eiiicient and economic control for the volume of the, electrolyte. Manganese ores in general contain insoluble portions which must be separated from the leach liquors. These insoluble portions or gangue may occludein their interstices appreciable values of manganese solutions or ammonium sulfate solutions, which for economic reasons should be recovered as far as possible. It is therefore quite desirable to wash these residues with water or dilute solutions. The same situation pertains those precipitates formed in theA course of puncation of the leach liquors. Common examples of the impurities removed are iron, arsenic, antimony, cobalt, and nickelwhich are rendered insoluble in the form of hydroxides or oxides in the case of iron, antimony, and arsenic, and suliides in the case of cobalt and nickel. tive washing it is desirable to employ as large a quantity of water or dilute solutions as possible For most eiecof concentration of manganese sulfate and ammonium sulfate. The concentra-tion of these materials is desired to be maintained within limits because of their effect upon the resulting electrolysis. If, therefore, as a function of cooling an electrolyte there is involved evaporation losses of water, these losses may be restored in the form of wash liquids to treat gangue residue or precipitate impurities without payment of the penalty of reduction ofthe manganese sulfate and ammonium sulfate to an extent greater than restoration of these to their desired values. It is obvious that if an electrolyte be cooled and during such cooling suier evaporation losses, it is likewise concentratedin respect to the initial vquantities of manganese sulfate and ammonium sulfate. The wash water introduced to recover values from the gangue and precipitated impurities is thus a mechanism for the restoration of the manganese sulfate and ammonium sulfate to Y 5. Accurate control over the volume5of the electrolyte in the entire circuit.

6. Effecting this volume control without sub stantial lossAof ammonia.

7. Provision for utilization of wash water to recover values -from gangues and precipitates Without the disadvantage of dilution and without the necessity of discarding solutions or wash waters.

There are Various ways of effecting the subdivision of the liquid and direct contact of the subdivided parts with air. At present, the most convenient apparatus for this purpose is the cooling tower of which there are Avarious designs.

The invention will be denedin the claims and further described and illustrated by reference to the accompanying diagrammatic drawing, in which:

Fig. 1 shows'diagrammatically a form of circulation and recirculation system; and

Fig. 2 shows diagrammatically a cooling` tower.

Referring to Fig. 1, the cell 5 has a cathode I in a catholyte chamber 2 and an anode 3 in an anolyte chamber E, these chambers being separated by diaphragm 20. From chamber 4 theline 'l provided with pump 6 and valve 6A leads to cooling tower 8. From collecting trough 8A the line 9 provided with valve 9AI leads back to chamber 4 via anolyte feed tank 25. Line I0 provided with Valve IIIA leads tothe ore digesting station l I Line I2 leads to mud lter I6 and purifying station I3 and from there, via filter I4, catholyte storage IBA and catholyte feed I1, line I5 leads to catholyte chamber 2. Line 22 provided with valves 22A and 22B leads from anolyte feed tank 25 to digester II.

Referring to Fig. 2, the cooling tower 8 which may be of the natural or forced draft variety, has bailles I8 as shown, collecting trough 8A and feed trough I9.

To illustrate an application of the process of the invention; current is passed-v through the anolyte in chamber I and the catholyte in chamber 2 from anode 3 to cathode I and. coincidental with the deposition of manganese, heat is developed. Anolyte (which may contain for example 150 to 175 grams ammonium sulfate and 5 to 15 grams manganese, as manganese sulfate, per liter and also containing magnesium and sulfuric acid corresponding to a pH of 1.5 to 2 land having a temperature of`35 to 50? C.) is withdrawn by means of pump 6 and line 1 and delivered to cooling tower 8 where it is cooled to a temperature suicient to precipitate magnesium as a complex salt, e. g., 25 to 40 C. The cooled liquid is returned to chamber 4 by line 9, valve 22A being closed and valve 9A open, and thus recirculated and the rate of recirculation is adjusted to maintain the temperature of the liquid in the cooling tower between the desired limits under the prevailing conditions of atmospheric temperature and'humidity. Solid material, e. g., crystals of the complex salt above referred to, are' deposited on the baiiles I8 and may readily be removed therefrom.

Part of the warm anolyte from chamber I is sent forward to the ore digesting station II, via line IU, where manganese ore is extracted. The extract, which may be partly purified in the digester, is'then sent to mud filters I6 and then to purifying station I3 where such further purification as may be necessary is effected by precipitation of impurities which are filtered in filter I4. Washing with fresh Water of the filter cake of lter I 6 (or of the filter cakes produced at any other stage of the process, whether or not specifically shown) may be accomplished with an amount of water equal to that removed by evaporation in the cooling tower without any substantial change in the total volume of liquid.

Solid material separated in the cooling tower is readily and eiciently removable therefrom.

Another example of operation is as follows:

Anolyte from chamber 4 is withdrawn through pipe 1 by means of pump 6 (valve IllA being closed) and all of saidvanolyte sent to cooling tower 8 and then to anolyte feed tank 25 through valve 22A being open to the desired extent).

Instead of a cooling tower, any device which provides 'evaporation by direct contact of liquid with air at normal atmospheric temperatures, by subdivision of the liquid and direct contact of the subdivided parts thereof with air, e. g.,

spraying devices, may be employed.

While anolyte` is commonly contacted with manganese ore to replenish the manganese removed from the electrolyte by cathodic deposition, it will be clear that the anolyte may be contacted with any source of manganese sulfate. Where a manganese carbonate ore is employed the manganese carbonate is the source of manganese sulfate since the carbonate reacts with Y the sulfuric acid of the anolyte to generate manganese sulfate. However, as stated, any suitable source of manganese 'sulfate may be employed instead of manganese ore. For example, manganese sulfate itself may be employed, or any other salt or material which will constitute a source of manganese sulfate.

What is ciaimed is: Y

1. In a process for the electrowinning of manganese employing an electrolytic cell having a Y thode in a catholyte in a catholyte chamber,

said catholyte containing manganese sulfate. magnesium sulfate and ammonium sulfate, and an anode in an anolyte in an anolyte chamber, said anolyte containing manganese sulfate, magnesium sulfate, ammonium sulfate and sulfuric acid, and in which process the anolyte is withldrawn from the anolytechamber, contacted with manganese ore to produce an vextract which is subjected to treatment vto remove impurities and obtain a. purified extract which is delivered to the catholyte chamber, thus establishing a path i of circulation of liquid from anolyte chamber to catholyte chamber and in which process the passage of the electric'current from anode to cathode causes the evolution of heat in the anolyte and catholyte, the improvement which comprises diverting liquid from said path of circulation, subdividing said liquid into a multiplicity of parts having a multiplicity of surfaces adapted for anode in an anolyte in an anolyte chamber, said anolyte Vcontaining manganesesulfate, ammonium sulfate, magnesium sulfate, and sulfuric acid, and in which process the anolyte is Withdrawn from the anolyte chamber, contacted with manganese ore to produce an extract which is subjected to treatment to remove impurities and obtain a purified extract which is delivered to the catholyte chamber, thus establishing a path of circulation of liquid from anolyte chamber to catholyte chamber and in which process the passage of the electric current from anode to cathode causes the evolution of heat in the anolyte and catholyte, the improvement which comprises diverting .liquid from said path of circulation, subdividing said diverted liquid into a multiplicity of parts having a multiplicity of surfaces adapted for evaporation and cooling of said liquid, exposing said parts and surfaces to direct contact with air at atmospheric temperatures whereby evaporation and cooling of said liquid and separation therefrom of a solid complex magnesium salt occurs, returning cooled liquid to said path of circulation and collecting the separated solid complex magnesium salt separate fromV said liquid.

3. In a process for the electrowinning of manganese Vfrom magnesium-containing manganese ore, employing an electrolytic cell having a cathode in a` catholyte in a catholyte chamber, said catholyte containing manganese sulfate, magnesium sulfate and ammonium sulfate, and an Y anode in an anolyte in an anolyte chamber, said anolyte containing manganese sulfate, magnesium sulfate, ammonium sulfate, and sulfuric acid, and in which process the anolyte is withdrawn from the anolyte chamber, contacted with manganese ore to produce an extract which is subjected to treatment to remove impurities and obtain a purified extract which is delivered to the catholyte chamber, thus establishing a path of circulation of liquid from anolyte vchamber to catholyte chamber and in which process the passage of the electric current from anode to cathode causes the evolution of heat in the anolyte and catholyte, the improvement which comprises removing liquid from said electrolytic cell, sub-- returning a portion of said cooled liquid to said v cell and thus establishing a path of recirculation of cooled liquid, and contacting the remainder of said cooled liquid with manganese ore to extract manganese therefrom.

4. In a process for the electrowinning of manganese from magnesium-containing manganese ore, employing an electrolytic cell having a cathode in a catholyte in a catholyte chamber, said catholyte containing manganesesulfate, magnesium sulfate and ammonium sulfate. and an anode in an anolyte in an anolyte chamber, said anolyte containing manganese sulfate, magnesium sulfate, ammonium sulfate, and sulfuric acid, and in which process the anolyte is withdrawn from the anolyte chamber, contacted with manganese ore to produce an extract which is subjected to treatment to remove impurities and obtain a purified extract which is delivered to the catholyte chamber. thus establishing a path of circulation of liquid from anolyte chamber to catholyte chamber and in which process the passage of the electric current from anode to cathode causes the evolution of heat in the anolyte and catholyte, the improvement which comprises removing liquid from said electrolytic cell, subdividing a portion of said liquid into a multiplicity of parts having a multiplicity of surfaces adapted for evaporation and cooling of said liquid, exposing said parts and surfaces to direct contact with air at atmospheric temperatures whereby evaporation and cooling of said liquid and separation of a complex magnesium salt therefrom occurs, and. returning said cooled liquid to said cell, thereby establishing a path of recirculation of said cooled liquid-and contacting the remainder of said liquid with manganese ore to extract manganese therefrom.

5. In a process for the electrowinning of man- 'y ganese from magnesium-containing manganese magnesium sulfate and ammonium sulfate, and 'A an anode in an anolyte in an anolyte chamber, said anolyte containing manganese sulfate, magnesium sulfate, ammonium sulfate, and sulfuric i acid, and in which process the anolyte is with-` drawn from the anolyte chamber, contacted with manganese ore to produce an extract which is into a multiplicity of parts having a multiplicity of surfaces adapted for evaporation and cooling of said liquid. exposing said parts and surfaces to direct contact with air at atmospheric temperatures whereby evaporation and cooling of said liquid and separation of a complex magnesium salt therefrom occurs, and returning at' least a portion of said cooled liquid to said cell and thus establishing a path of recirculation of cooled'liquid.

6. In a process for the. electrowinning of manganese from magnesium-containing manganese ore, `employing anv electrolytic cell having a cathode in a catholyte in a catholyte chamber, said catholyte containing manganese sulfate, magnesium sulfate and ammonium sulfate, and an anode in an anolyte in an anolyte chamber, said anolyte containing manganese sulfate, magnesium sulfate, ammonium sulfate, and sulfuric acid, and in which process the anolyte is withdrawn from the anolyte-chamber, contacted with manganese ore to produce an extract which is subjected to treatment to remove impurities and obtain a. purid extract which is delivered to the catholyte chamber, thus establishing a. path of circulation of liquid from anolyte chamber to catholyte chamber and in which-process the passage of the electric current from anode to cathode causes the evolution of heat in the anolyte and catholyte, the improvement which comprises removing anolyte liquid from said electrolyticA cell, subdividing at least a portion of said liquid into a multiplicity of parts having a multiplicity of` surfaces adapted for evaporation and cooling of said liquid, exposing said parts and surfacesA to direct contact with air at atmospheric temperatures whereby evaporation and cooling of said liquid and separation of a complexmagnesium' salt therefrom occurs, and returning at least a portion of said cooled anolyte liquid'to the anolyte chamber of said cell.

7. In aprocess for the electrowinning of manganese employing an electrolytic cell having a cathode in a catholyte 'in a catholyte chamber, said catholyte containing manganese sulfate, magnesium sulfate and ammonium sulfate, and an anode in an' anolyte in an anolyte chamber, said anolyte containing manganese sulfate, magnesium sulfate, ammonium sulfate and sulfuric acid, and in which process the anolyte is withdrawn from the anolyte chamber, contacted with a source of manganese sulfate to produce an extract which is subjected to treatmentto remove impurities and obtain a purified extract which is delivered to the catholyte chamber,

thus establishing a path of circulation of liquid .electrolyte and in which process the passage of the electric current from anode to cathode causes the evolution of heat in the anolyte and catholyte, the improvement which comprises subdividing said'liquid electrolyte into a multiplicity of parts having a multiplicity of surfaces adapted for evaporation and cooling of said liquid, exposingsaidparts and surfaces to'direct' contact with air at atmospheric temperatures whereby evaporation and cooling of said liquid electrolyte and separation therefrom of a complex magnesium salt occurs, collecting said salt separate from said electrolyte, and returning at least a portion of said'electrolyte to said path.

naaom L. c.

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