US 3065155 A
Description (OCR text may contain errors)
Nov. 20, 1962 J. Y. WELSH 3,065,155
ELECTROLYTIC MANGANESE 'DIOXIDE PROCESS Filed Sept. 2, 1960 5 Sheets-Sheet l ,Q. ATTORNEYS Nov. 20, 1962 1. Y. WELSH ELECTROLYTIC MANGANESE DIOXIDE PRocEss Filed sept. 2. 1960 5 Sheets-Sheet 2 INVENTOR a ATTORNEYS Nov. 20, 1962 J. Y. WELSH ELECTROLYTIC MANGANESE DIOXIDE PROCESS Filed Sept. 2, 1960 5 Sheets-Sheet 3 IgG/777701? fl/71 7 |l 4 Illll'" .n. llllll'"III r IIl wwwa AIII l INVENTOR u ATTORNEYS Nov. zo, 1962 Filed Sepp. 2, 1960 cool/N6 H 0 C. WW
5 Sheets-Sheet 4 @WER WCW/AIG INVENTOR ygw,
BY @a Mfg/@ae Mw 74u', ATTORNEYS Nov. 20, 1962 Filed sept. 2, 1960 gna/NONE J. Y. WELSH ELECTROLYTIC MANGANESE DIOXIDE PROCESS 5 Sheets-Sheet 5 a ATTORNEYS 3,065,155 ELECTRGLYTC MANGANESE DIOXIDE v PRUCESS .lay Y. Welsh, Brainerd, Minn., assigner, by mesne assignments, to Manganese Chemicals Corporation, a corporation of Maryland Filed Sept. 2, 1960, Ser. No. 53,812 4 Claims. (Cl. 204-83) This invention relates to the production of high-quality particulate manganese dioxide especially suitable for use as depolarizer material in Leclanche cells, and is concerned with an improved electrolytic process of making the same.
It heretofore was known to produce manganese dioxide by the electrolysis of an aqueous solution of manganese sulphate, and it was known thatin at least some instancesthe resulting products were, after the necessary grinding and other after-treatments, useful as depolarizer material. In the heretofore conventional electrolytic batch process manganese dioxide was deposited in relatively massive form on the anode (usually graphite or lead), from which latter it had to be stripped; thereafter, the stripped-off deposit had to be ground to suitable particle size and otherwise processed before becoming useful as battery oxide. In a typical procedure of this sort the electrolyte contained 20-l50 g./l. MnS04 and 2-80 g./1. H2804; the temperature of the bath was above normal room temperature (e.g., normally above 80 C. and even up to 100 C.); and the current density was in the neighborhood of to 20 amp/sq. ft.
This combination of conditions precludes the formation of Mn+3ion.
In lieu of the above-described commercial batch process, it has been proposed to eiect the electrolysis of an aqueous (acidic, or neutral) solution of MnS04, in a continuous procedure, in a compartmented cell wherein the feed to the anode compartment contained about 150 g./1. of MnS04 and about 75 g./1. of H280.;= .and wherein the temperature was about 25 C. and the current density was 18-30 amps/sq. ft. The anode product was a scaley and slimy hydrated Mn02, which formed on the anode and sluied off of the latter from time to time: it was brown in color, light in density .and (because of its slimy nature) diicult to wash and process. The process had an eiiiciency of 30%.
This combination of operating conditions (relatively very low current density; relatively high concentration of MnS04; relatively low acid concentration; relatively high temperature) excluded the formation of Mn+3ion in other than trace amounts.
It has been proposed, also, in respect of an electrolytic procedure practiced in a compartmented cell, to neutralize some or all of the acid liberated by the oxidation of MnSCL, in the anode compartment by adding manganous or manganic hydroxide to the content of the anode compartment and maintaining the same in slurry form therein. In this procedure the anode product was hydrated higher oxides of manganese.
It has been determined that such a hydrated higher oxides product not only is diihcult to process but more importantly does not constitute a satisfactory battery oxide.
I have discovered that in order to effect a precipitation of Mn02 in the electrolyte (as opposed to deposition of the same on the anode) and to insure that the precipitate occurs in the form of particles of sucient size to settle and filter easily, the electrolyte must contain a significant concentration of Mn+3ionsay, 3 or preferably about 4 grams per liter-and the reaction Patented Nov. 20, 1952 must be causedby appropriate selection of conditions of temperature, acid concentration and current density` to proceed slowly in the body of agitated electrolyte solution or slurry, the stability of the Mntaion being suiiciently great and the decomposition occurring at a slow enough rate to build large particles of Mn02. I have found that the stability of Mn+3ion (in the electrolyte) decreases with increase in temperature and also with decrease in acid concentration; and that rapid decomposi tion produces a finely subdivided Mn02 product not desirable for use as battery depolarizer.
In broadest aspect, the process of the present invention is a continuous electrolytic procedure wherein an aqueous acidic solution of MnSO4 is passed, in agitated state, through an uncompartmented electrolytic cell provided with a lead anode and lead cathode, the conditions of operation being so selected and controlled 'that Mn+3ion is the substantially sole anode product and that the decomposition of the Mn+3ion is made slow enough to induce the formation of relatively coarse particles of M1102.
The invention will be described in greater particularity and lvith reference to the accompanying drawing, in Whic FIG. 1 is a graph showing the eiect of temperature on the eiiiciency of the process under selected conditions;
FIG. 2 is a graph showing the rate of decomposition of Mn+3ion at selected temperatures;
FIG. 3 is a graph showing the equilibrium concentration of Mn+3ion versus temperature;
FIG. 4 is a graph showing the effect of Mn*-2 concentration on the equilibrium concentration of Mn+3;
FIG. 5 is a graph showing Mnt3 concentration versus H2804 concentration under equilibrium conditions;
FIG. 6 is a representation of a cell for use in carrying out the present process;
FIG. 7 is a flow diagram of the process;
FIG. 8 is a flow diagram of a quinone-producing process integrated into the present process; and
FIG. 9 is a modication of the ow diagram of FIG. 8.
In FIG. 1, which shows the effect of temperature on eiciency, the selected operating conditions were:
(l) 400 amps. per ft2 2) 25-30 gmsJ liter Mn+2 in slurry. 3) 200 gms/liter H2804.
In FIG. 2 showing decomposition of Mai-Sion, the constants were:
Gms./l. (1) H2804 200 (2) Mnt2 120 (3) Mn02 200 In FIG. 3, plotting equilibrium concentration of Mut'3 versus temperature, the constants were:
In FIG. 5, which plots Mn+3 concentration versus H2804 concentration, the selected equilibrium conditions were:
Mn+2 constant at gms./l 20 Mn02 gms./l 200 Temperature C 15 As has been indicated in FIG. 2, the equilibrium concentration of Mn+3ion, in an aqueous slurry of Mn02 (Mn+3 produced) containing 200 g/l. of H2804 and 20 g./l. Mn+2ion and 200 g./l. of MnOz, held at a temperature of about C., is within the range of 0.6-0.7 g./l. This means that if given enough time a solution initially containing more than the equilibrium value of Mn+3ion will undergo decomposition until it reaches this equilibrium value, the interesting aspect of this fact being that it requires a very long time (perhaps a hundred hours or more) for the concentration of Mn+3ion to even approach equilibrium value.
It is to be noticed in FIG. 2, with regard to the decomposition curves for Mn+3ion, that initially the decomposition rate is quite rapid but the curves then flatten out to a very slow decline. This decomposition reaction appears to conform rather closely to a fourth order reaction (i.e., the decomposition rate appears to be roughly proportional to the concentration taken to the 4th power).
The build-up on Mn+3ion, on the other hand, produced when Mn+2ion reacts with active Mn02 (such as is produced by reaction 1) in acid solution, proceeds rapidly to the equilibrium value and then (of course) remains constant, the mechanism of this reaction obviously being quite different from that of the decomposition.
The relationship between Mn+3ion concentration and Mn+2ion concentration in an acidic slurry of Mn02 (250 g./l. H2SO4 and 200 g./l. Mn02), is shown in FIG. 4. From this latter it is to be observed that the ratio of Mn+2 concentration to the square of the (Mni's)2 concentration is roughly constant, as predicted by the equilibrium constant of reaction 1, which is Acid Mn Concentra- Concentration, g./1. tion (or,
Stability) The inuence of temperature is demonstrated in two ways. In FIG. 2 it is evident that the decomposition rate is markedly effected by temperature because the two curves shown are only 4 C. apart. This indicates other things being equal, thatl the Mn'"3 level in an operating cell will be lower at higher temperatures.
FIG. 3 shows the effect of temperature on the equilibrium concentration of-the Mn+3ion in the acid slurry previously described. lIt shows that the Mni'3 concentration (or stability) is roughly reduced by 1/2 in going from 10 to 60 C.
. According to the` flow diagram shown in FIG. 7, an illustrative procedure adapted to the'production of a battery-grade manganese dioxide product involves feeding to an agitated electrolytic cell a cooled slurry resulting from leaching a manganese-bearing feed with an acidic leaching liquor consisting essentially of a filtrate obtained in the process plus make-up H2504 or/ and make-up water, the slurry being cooled during the electrolysis. The effluent from the agitated electrolytic cell is passed through a lter to separate solids from an acidic filtrate (which latter is recycled to the leaching step), after which the resulting ltercake is washed with water, dried and packed.
The nubbin of the process of the present invention is the discovery that under the proper conditions of temperature, acid concentration and current density manganous ion can be efliciently converted to soluble manganic ion which latter undergoes slow decomposition in the body of the agitated solution (or, slurry) to form particulate lvl-m02 having excellent battery depolarized characteristics. The combination of conditions which enable such a process to take place are critical. Optimum cell conditions are as follows:
Temperaturenot over 21 C. and preferably definitely lower than this;
Anode material-lead (or lead alloy);
Anode current density- 400-550 amps./sq. ft. (there is a very marked drop in process efficiency below 200 amps/sq. ft.);
Cathode current density-400-O ampsJ sq. ft. and desirably never lower than the anode C.D.;
Acid-H2804, 15G-250 g./l.-optimum acid level 175- 225 g./l. H2804;
Manganous ion concentrationlO-ZS g./l.
Cell mechanics-strongly agitated, with a cell geometry (ideal) that minimizes solution movement around the cathode and promotes high solution velocity around the anodes.
The process is cyclic, in that the product reaction regenerates Irl-S04 from the MnS04 feed, which HZSO., can then be cycled to leach more manganese (as MnSO4) from a suitable feed material such as MnO, MnSO., or MnC03.
Because of the low temperature criterion above described, in rebuilding the Mn in solution for feeding back to the cell it is desirable if not necessary to carry out the acid leaching step in a separate reaction vessel so as to minimize heat effects. If the feed is MnO, it is not necessary to add heat to effect solution; nevertheless, the solution reaction produces excessive heat. If on the other hand, the feed is Mn304 or MnC03, added heat is necessary for effecting satisfactory solution reaction rates. In either event, the resulting solution or slurry is cooled before being fed to the electrolytic cell.
Moreover, for attaining the desirable low temperature conditions in operating the electrolytic cell the electrolyte is cooled by indirect heat-exchange with a coolant, that is to say, cooled by means of cooling coils. This cooling step may be accomplished by placing electrically isolated cooling coils in the agitated electrolyte cell or advantageously may be effected by (1) using lead pipes as the electrodes (or, lead pipe for at least the anode) and (2) passing a current of fluid coolant-desirably, cool watertherethrough.
In respect of the criticality of high anode current density, it should be mentioned that scaling of the anode surface with M1102 begins at 20() amps/sq. ft. and becomes increasingly worse at lower current densities. The decided drop in efliciency at anode current density of 200 a. (and lower) is believed to be due to the relative increase in the cathodic discharge process.
The following specific examples are illustrative but non-limitative of the present invention:
Example I Agitated 10 liter electrolytic cell, electrode spacing ,1A Ratio of anode-cathode area l/ 1.
Electrodes: 1 0.D. lead pipes, water cooled.
D.C. current a.
Electrode current density 400 a./ft.2
Av. cell voltage 4.2 v.
Acid level in operating cell 200 g./l. H2804 Av.Mn+2 level in operating cell 26 .g./l.
Feed- MnS04 solution containing 100 g./l. Mni'2 as MIISO4 Feed rate 1800 ml./ hr. continuous Operating cell temperature .6 C.
Average electrolytic eiliciency for 28 hr. run-75 .4%
Product: Percent Mn 1 48.2 Mnog H 20.0 Pb v .007 Crystal structuredelta and small gamma component.
Example II Product: Percent Crystal structure-gamma.
In the nal product the Weight ratio of Mn02 from the electrolysis to Mn02 from the disproportionation of Mn304 Was about 2:1.
Example Ill Same cell and current conditions as Examples I and H also same acid level. Average Mn+2 level in operating cell 27 .g./L Average temperature of operating cell 19 C. Feed-MnS04 made from MnC03 containing .7% NH3.
.Feed adjusted to 100 g./l. Mnl'2 as MnS04 Average electrolytic ericiency through run of 48 hrs.
Product: Percent Mn i 49.2 MnOz 72.5 ,H2O 21.1
Examples I, II and UI were carried out in the cell shown in FIG. 6.
In this apparatus (FIG. 6) the cell container 1 was an open topped, generally cylindrical, vessel in which cath- ,odes 2, 2 and an intervening anode 3 were supported, in l substantially parallel relation, by conventional supporting means (not shown). The electrodes were one-inch lead pipes, deeply bent into a U-shape (as shown in the drawing) -to extend substantially the whole distance from top to bottom of the cell container 1. I'he two Cathodes were spaced about one-fourth inch on either side of the anode, being held in this spaced relationship by spacing members 4, 4. An agitator 5, Xed to an agitator shaft 6, was disposed in the lower part of container 1, the agitator shaft extending through apertures 7, 7' in spacing members 4, 4 to a conventional means (not shown) for rotating the agitator. Cathodes 2, 2 were connected to the negative pole and anode 3 to the positive pole of a source of direct current (not illustrated). The Cathodes were connected to a source of relatively cold water, which cooling water Was passed through the Cathodes in such volume and at such temperature to maintain the cell contents at a desirably low temperature below 21 C., eg., at 15-17 C. Cell feed was supplied to the cell through a conduit 10 provided with a constant rate feed pump 11, while a constant level overiiow port 12 provided in the wall of container 1 maintained the electrolyte volume substantially constant.
Example IV Agitated 9-liter electrolytic cell, electrode spacing 1/2.
Ratio of anode to cathode area l/ 1.
Electrodes-anode l 0.D. lead rod. Cathode-our 1A" lead rods. (Separate cooling coils.)
D.C. current 45 a.
Electrode current density 440 a./ft.Z
Av. cell voltage 4.3 v.
Average acid level in operating cell 200 g. H2804 per liter.
Average Mn+2 level in operating cell 20 g./l.
Feed same as Example II.
Average feed rate- 420 ml./hr. continuous.
Operating cell temperature 15 C.
Electrolytic eiiciency: Percent 1st 8 hrs. period 83.7 2nd 8 hrs. period 75.8 3rd 8 hrs. period 74.6 4th 8 hrs. period 75.0 5th 8 hrs. period 73.5 6th 8 hrs. period 73.6 7th 8 hrs. period 68.9 8th 8 hrs. period 69.3 9th 8 hrs. period 1---- 86.2 10th 8 hrs. period 76.0
Product: Same as Example Il.
Dry cell battery data establishing that the product of the process is an exceptional depolarizer material are shown as follows:
Capacities in minutes on the Heavy l'ndustrial Flash Light Depolarizer Composition Test.
to 1.10 v. to 0.90 v. End Point End Point Natural African Battery Grade Ore 319 536 100% Commercial Electrolytic MnOg 625 865 60% Commercial Hydrated MnOi* and 50% African Ore 523 750 50% MnOg from present process and 50% African Ore 652 853 *Made by permanganate decomposition process. Material represents the best commercial battery grade hydrated M1102 available.
Experimental cell runs with acid level as the variable showed that:
At 50 g./l., the Mn02 is formed almost completely on the anode;
Between 50 and 100 g./l., the anode is substantially free from deposited MnOR, but the Mn02 is formed in very close proximity to the anode and therefore at such a rapid rate that particle growth cannot take place and hence the product is a brown collodial mass wholly undesirable for battery use;
Between 100 g./l. and 150 g./l. the cell approaches what I call normal operation in that the Mn+3ion be cornes suiciently stable to be swept into the body of solution (or, slurry) before undergoing decomposition. In the lower part of this range the decomposition rate is still too high to facilitate desirable particle growth, but at g./l. H2S04 the product formation and growth begin to `follow a normal pattern.
As noted above, the optimum acid level is -225.g./l. H2S04.
A comparison run yoli the'cell with 150 g./l. H2S04 butat a temperatureyof 20 C, (instead of 15 showed a brownish product having an undesirably line particle s size, indicating that at higher temperatures and with a minimum acid level the decomposition rate is too fast.
I have found, further, that the precipitated Mn02- produced as described hereinbefore-may be caused to deposit, as it precipitates, on other Mn02. Thus, I have found that particulate African ore may be suspended in the electrolyte feed and carried by the latter through the electrolytic cell, and that in its passage through the cell Mn02 precipitated (from the electrolyte) onto each particle of the ore. Any desired ratio of natural ore to synthetic Mn02 can be easily prepared.
This same observation holds true also in the case of a 1feed produced by acid leaching a Mn304 material Without filtering out the resulting disproportionated Mn02 particles. I take advantage of this phenomenon by feeding the unltered slurry of Mn02 particles suspended in aqueous acidic MnSO4 solution to the cell, and, in the electrolytic step, effect the deposition of the precipitated Mn02 on these suspended particles. The resulting product, when washed and dried, is a battery-grade dioxide.
Laboratory tests have demonstrated that if the H250.,l level is raised to, say, 350 g./l. or higher the apparent Mn+3ion concentration can be in excess of l0 g./l. without a solid phase being present. This is equivalent in oxidizing capacity to 2 g./l. KMn04 solution. According to one aspect of the present invention I may employ the present process in an oxidizing cycle wherein the cell producteither Mn+3 solution or Mn'l'3 solution plus some of the very active precipitated Mn02-is cycled through a system in which an oxidation is carried out, the reduced Mn+3ionthat is to say, Mn+2ionbeing brought back through the cell to complete the cycle. This oxdizing material could replace acid permanganate solution, with significant cost advantage.
In processes where an acidic Mn02 slurry is used as the oxodizing agent (e.g., in the manufacture of hydroquinone and of certain dyestuts) I can substitute the ymixture discharged from the cell, as such, as the oxidizing agent. The MnS04 resulting from the oxidationreduction step thus is not wasted lbut rather is recycled through the electrolytic cell to produce more acidic Mn02 slurry. One particular advantage of this substitution is to be seen in the maintainable high purity of oxidizing agent possible in the present process.
An example of the use of the cell as a primary oxidation source in a commercial process follows:
The commercial production of quinone is summarized by the following sequential chemical reactions:
(l) The neutralization reaction 2C6H5 NH2-l-H2SO4-9 (06H5 NH3 2504 (2) The oxidation reaction Il O Step (Z) may be carried out by reacting previously prepared aniline sulphate in a cold slurry of Mn02 in :sulphuric acid solution, the cold (i.e., unheated) reaction mixture being passed though the cell and the resulting quinone taken off continuously under reduced pressure. The cell temperature is maintained within the 20 70 C. range and as near the lower limit of this range as is economically feasible. This process is illustrated in the FIG. 8 flow sheet, and the course of the reaction, in the 205HA4O; (NHZSOt i (MlSO4-H2SO4 50111171011) In the process just described, the theoretical material balance is:
gms. aniline 100 gms. HQSO4 -f- 155 gms. MnSO4 220 gms. quinone 400 gms. (NH4)2SO4MnSO4-6H2O (crystals) Under the condition that the NH4-tion produced by the oxidation is removed from the operating cell as a 20% slurry of (NH4)2SO.2MnS046H20 crystals, in Icell electrolyte, there ideally are about 200() gms. (or, A1650 ml.) of cell liquor cycled back into the aniline sulphur'ic `acid reaction vessel, to which 190 gms. aniline and 100 gms. H2804 are added, plus heat to produce the aniline sulphate cell feed. However, in actual practice mechanical losses both of MnSO4 and of H2504 and water are incurred when the (NH4)2S04'MnS04-6H20 crystals are separated out, thus requiring make-up additions of each, desirably, by direct additions to the cell. Also, some make-up Water is necessary for replacing the water removed with -the quinone. As is indicated directly in the above material balance, the addition (to the cell) of gms. MnSO4 for each 220 gms. quinone produced is necessary for maintaining the continuity of the reaction, the ammonium sulphate crystallizing out as the double salt, (NH4)2SO4MI1SO46H20, taking MUSC4 Because ofthe greater opportunity of selecting optimum temperature conditions, it is advantageous to conduct the above quinone-producing process as illustrated in the flow `diagram of FIG. 9, the material balance remaining essentially unchanged. Thus, by carrying out, for the most part, the aniline sulphate oxidation in a separate vessel the temperature of this vessel and its contents can be suitably adjusted to the removal of the quinone product. In both instances the cell electrolyte contains MnSO4 and H2804 in the previously mentioned ranges; also, in both procedures the H2804 associated with the cell is cyclic except for handling losses associated with separation of fthe double salt crystals.
The H2804 added with the aniline to the neutralization vessel is entirely consumed and removed as ammonium sulphate. The manganese as MnSO4 is cycled, except for (a) the manganese sulphate lost as the double salt and (b) handling loss connected with the crystals. Since there are 4 moles of MnSO4 formed in the oxidation reduction reaction to only l mole of (NH4)2SO4, it will be apparent that only one-fourth of the MnSO4 is lost as the double salt with each reaction cycle: in terms of the material balance, 155 gms. MnSO4 is lost forevery 220 gms. quinone produced.V This may be compared with procedures, practiced until now, in which a loss' of 620 gms. MnSO4, or more, is suffered for every 220 gms. quinone produced. Since the Mn02 produced vfrom MnSO4 by the presently described process is less expensive than Mn02 from medium grade ores, and since threefourths of the Mn02 employed in the quinone production is made by re-cycle oxidation in the cell, the favorable economics are apparent. Moreover, the one-quarter make-up in manganese per reaction cycle can be added as an Mn02 ore, as opposed to adding MnS04 as shown in the flow sheets.
A further application of the invention is in the field of supported Mn02 catalysts, wherein my process offers unique impregnating advantages. Thus, the particulate catalyst support (e.g., silica or alumina or any other conventional particulate inert material), in the form of a bed or slurry, may be ooded with incipiently decomposing Mnl'3 solution and the precipitating Mn02 be deposited over the surfaces of the support pieces. Or, a cold Mn+3 solution can be decomposed by heat whilst in contact with the support material. This allows a very active Mn02 to be placed in and on the catalyst support in practically any amount desired.
1. In an electrolytic process of producing battery-grade manganese dioxide involving the step of continuously feeding an electrolyte slurry the liquid phase of which consists essentially of an aqueous acidic solution of manganese sulphate through an electrolytic cell and simultaneously eiecting electrolysis in said cell by passing unidirectional current through the electrolyte from a lead anode to a cathode immersed in said electrolyte, the improvement which consists in effecting the precipitation of manganese dioxide solely in the body of electrolyte and in the form of relatively coarse discrete particles by agitating the body of electrolyte and insuring that the body of electrolyte contains a concentration of Mn+3ion of between 0.7 and 4 grams per liter, that Mn+3ion is the substantially sole anode product, and that the MnQ2- producing reaction is caused to proceed slowly, the improved process being further characterized in `that the temperature is maintained at from about to about 30 C., in that the electrolyte contains from about 100 to about 350 g./l. of free H2504 and in that the average Mn+2ion level in the cell is from about 10 to about 30 grams per liter.
10 c 2. The improved process dened in claim l, in which the following conditions are observed:
Temperature of electrolysis-less than 21 C.; Initial acidity of electrolyte--250 grams per liter Mn+3ion concentration-0-7-4-0 grams per liter;
Average Mn+2 level in operating cell-10-30 grams per liter;
Anode current density-300-550 amperes per square foot.
3. The improved process defined in claim 1, in which the electrolyte as fed to the cell is a slurry containing suspended particles of manganese dioxide.
4. The improved process defined in claim 1, in which the precipitation step is carried out in the interstices of a body of catalyst support material in and on the particles of which active manganese dioxide is deposited.
References Cited in the file of this patent UNITED STATES PATENTS 1,352,208 Lovelace Sept. 7, 1920 1,491,498 Tainton Apr. 22, 1924 1,874,827 Storey Aug. 30, 1932 2,299,428 Rossetti Oct. 20, 1942 2,500,039 Magoin et al Mar. 7, 1950