CA1260428A

CA1260428A - Suspension bath and process for production of electrolytic manganese dioxide

Info

Publication number: CA1260428A
Application number: CA000485898A
Authority: CA
Inventors: Geoffrey W. Mellors
Original assignee: Eveready Battery Co Inc
Current assignee: Edgewell Personal Care Brands LLC
Priority date: 1984-11-01
Filing date: 1985-06-28
Publication date: 1989-09-26
Also published as: DE3577999D1; US4549943A; EP0184319B1; JPS61110788A; BR8505427A; EP0184319A1

Abstract

- 22 -Suspension Bath and Process for Production of Electrolytic Manganese Dioxide Abstract A bath for the production of electrolytic manganese dioxide comprising an aqueous solution of a manganous salt and a suspension agent which is an insoluble multivalent element or an insoluble compound of a multivalent metal other than manganese, and having a pH of between about l and about 2, may be electrolyzed at an anodic current density of 10.8 to 21.5 mA/cm2 (10 to 20 A/ft2) to produce battery grade EMD.

Description

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SusPension B~th ~nd Process for Production of ElectrolYtic Man~anese Dioxide Field of the Invention This invention rel~tes to a bath for the production of electrolytic manganese dioxide, which bath comprises at least one suspension agent selected from the 8rouP consisting of insoluble multivalent elements and of insoluble compounds of multlvalent metals other than manganese. In another aspect, this invention relates to a process for producing electrolytic manganese dioxide employing such bath.
Back~round of the Invention The use of manganese dioxide as an active cathode material in dry cells is well known. Among the forms of manganese dioxide which have been found to exhibit desirable electrochemical properties in both aqueous snd non~queous cells is electrolytic manganese dioxide ~''EMD'').IAs is noted in U. S.
Patent No. 4,048,027, in the prior art the production of electrolytic manganese dioxide has typically entailed the feeding of a preheated MnS04-H2S04 bath into an electrolytic cell which is operated wlth direct current under the

2~ following general conditions:
a. electrolytic bath concentration -MnS04: 0.5 to 1.2 mole/liter; H2S04: 0.5 to 1.0 mole/liter;
b. electrolytic bath temperature, 80C to 100C; and "R.,'. ~

1~i()4~8 c. ~n anodic current density of 7 to 12 mA/cm2 (i.e., about 7.6 to 1~.1 Alft2).
The anode employed in such electrolytic process is generally composed of titanium, lead alloy or carbon. The cathode is typically composed of carbon, lead or platinum. During electrolysis manganese dioxide is deposited at the anode. The electrolytic manganese dioxide is removed from the anode and after conventional post-treatment, it is ready for use as an active cathode material in dry cells.
In conventional prior art processes, the current density is the prlncipal factor with respect to productivlty. However, increasing the current density in excess of the range reclted above in order to increase productivity leads to oxygen evolution at the anode with consequent lowering of EMD production efficiency. Such oxygen evolution may result in passivation and/or consumption of the snode. Further, the EMD prloduced by electrolysis at these hlgher current densltles exhiblts undesirable physical properties.
In order to overcome such limitation upon productivlty, it has become known in the art that the current denslty of an EMD production bath may be increased wlthout an adverse effect on voltage if a suspension of manganese oxide particles is employed ln the bath. Thus, U.S. Patent No. 4,405,419 discloses a process for producing manganese dloxide comprising the electrolysis of a slurry of particles of manganese oxides ln an aqueous solution of manganese sulfate at current densltles of up to 16 :

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()4~8 mA/cm2 (i.e., about 14.9 A/ft2). Similarly, Japanese Patent Disclosure No. 1976-104499 published September 16, 1976 discloses a process for the production of EMD by the electrolysis of a solution of manganese sulfate containing sulfuric acid in the presence of a suspension of particles of manganese oxide other than divalent manganese employing anodic current densities of up to 20 mA/cm2 (18.6 A/ft2).
The m~ng~nous salts, derlved from m~ngRnous ores, thst ~re typicaily employed ~8 startlng m~terlsls ln the EMD productlon process gener~lly cont~ln ~ome amount of unde~ir~ble lmpurlties, p~rtlcul~rly pot~sslum. Durlng the electrolysls of these salts pot~sslum 18 lncorporsted lnto the result~nt EMD. ~8 ~8 well known In the art, the presence of potss61um ln ~lectrolytlc m~n8~nese dloxlde ls undeslrsble, hsvln~ ~dver~e effects on the utillzstlon of such msngsnese dloxlde ln slksllne cells. It would therefore be beneflcl~l to provlde ~ process for the m~nuf~cture of EMD, whlch process would reduce th,e ~mount of potssslum lncorpor~ted lnto the product EMD from the m~ng~nese ore st~rtlng msterlal.
It 18 therefore sn obJect of thls lnvention to provlde B b~th for the productlon of EMD whlch bsth wlll sllow an lncressed productlon r~te of EMD.
It 18 B further ob~ect of the ln~entlon to provlde ~ bsth for the productlon of EMD whlch b~th when electrolyzed wlll produce EffD whlch performs deslrQbly when employed ln scldlc, ~lk~llne ~nd nonaqueous bAttery systems.
It 18 ~nother ob~ect of thls lnventlon to provlde ~ b~th for the productlon of EMD, whlch b~th , D-14619 ~, ,~,~ .

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when electrolyzed will produce EMD having a reduced potassium content.
It is yet another ob~ect of this invention to provide a process for the production of EMD, which process will permit rapid production of EMD.
The above and additional ob~ects will become clear from the following description and Examples.
DescriPtion of the Invention This invention relates to a bath for the production of electrolytic manganese dioxide, said bath comprising (a) between about 0.5 and about 1.3 moles/liter of an aqueous solution of at least one manganese salt selected from the group consisting of manganous sulfate, manganous chloride and manganous nitrate; (b) a sufficient quantity of at least one acid selected from the group consisting of sulfuric acid, hydrochloric acid and nitric acid so that the pH of said bath is between about 1 and sbout 2; and (c) at least one suspension agent which is selected : from the group consisting of insoluble multivalent elements and of insoluble compounds of multivalent metsls other than manganese.
In another aspect, the invention relates to a process for the production of electrolytic m~nganese diox~de, which process comprises:
(1) preparing a bath comprising (a) between about 0.5 and about 1.3 moles/liter of an aqueous solution of at least one manganese salt selected from the group consisting of manganous sulfate, manganous chloride and manganous nitrate,(b) a sufficient quantity of at ~ ,.

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least one acid selected from the group consisting of sulfuric acid, nltric acid and hydrochloric acid such that the pH of the bath is between ~bout 1 and about 2, and (c) at least one suspension agent selected from the group consisting of insoluble multivalent elements and of insoluble compounds of multivalent metals other than manganese;
(2) heatin8 said bath to hetween about 90C and about 100C; and

(3) electrolyzing the heated bath in an electrolytic cell having at least one anode and at least one cathode, preferably at an anode current density of between sbout 10 and about 20 amperes per square foot (i.e., between about 10.8 and about 21.5 mA/cm2).
As is employed herein the term "insoluble", when applied to the suspension agent of this invention, refers to materilals having a solubility of no greater than about one gram per liter in the heated suspenslon bath.
The EMD-production bath of this invention is comprised of an aqueous solution of a manganese salt, an acld, and a suspension agent.
The manganese salts which may be employed in such bath are manganous sulfate, manganous nitrate and manganous chloride. Moreover, mixed baths using two or more of these salts may also be utilized. The manganous salts are present in a concentration of between about 0.5 mole/liter and about 1.3 moles/liter of bath, with concentrations 1~i04~:8 of between ~bout 0.7 mole/llter ~nd ~bout l.0 molelliter being preferred.
The acids which msy be employed in the bath of thls inventlon include sulfuric acid, nitric acid, hydrochloric acid and mixtures thereof. The scid is added in a sufflcient quantity such that the pH of the solution prior to the application of current is between about l and sbout 2. Typically, this will involve an acld concentratlon of between about 0.2 and about 0.6 mole of scld per llter of bath.
It is preferred that the ~cid ~nd manganese sslt employed in any particular b~th possess identlcsl anions, i.e., that nitric acid be employed with mangsnous nitrate, sulfuric scid with msnganous sulfste, and hydrochloric acid with manganous chloride. Simllarly, when mlxed manganous salts are employed lt ls preferred that correspondlng mlxed sclds sre used, e.g., hydrochlorlc acld snd nltric ;~ 20 scld when s mlxture of msngsnous chlorlde and msngsnous nltrate ls employed.
The suspenslon sgent of the bath of thls lnventlon ls st lesst one member selected from the group consisting of lnsoluble multlvalent elements snd of insoluble compounds of multlvalent metsls other thsn msn8snese. Illustratlve of the lnsoluble compounds of multlvalent metals other thsn manganese 5 ~ ~ whlch msy be~employed are nloblum borlde, titanium boride, zirconlum carblde, ferrlc oxlde (Fe203), ferrosoferrlc oxlde (Fe304), lron dlsulflde (FeS2), tln dioxide, tln dif}uorlde, lesd dloxlde, lesd dlfluorlde, cobslt oxlde, nlckel oxlde, hafnlum csrblde, boron c~rblde, molybdenum dlsulfide, cerium q ~
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, ~ D-14619 " '; " ' .: ~ , , . . ' ' ' ~, ' ' ~ '' ' ', .. ' ' ,' '' ' ' ~ ' ~ ' ' ' , , '' . ' ~ " ' ' ' ', , ~,, ',, ,' , .
, ~ ' ~ , . . ' " '. ' ,' ' ' ' . ~ '' . ' , ' ".' , ' ~ ;'. ' . . , "' ' ' ' , '"' ' " ~ . ' iO4~8 dioxide, silicon dioxide, bismuth trioxide, titanium dioxide, tungsten trioxide, chromium dioxide, molecul~r sieves including those of the zeolitic type, and the like. Illustrative of t~e insoluble multivalent elements which may be employed are carbon and sulfur. The preferr4d suspension agents are ferric oxide, tin dioxide, iron disulfide, lead dioxide and zeolitic molecular sieves.
It is within the scope of this invention to employ combinations of two or more suspension a8ents such as tin difluoride with tin dioxide, lead dioxide with ferric oxide, tin dioxide with silicon dioxide, and the like. The preferred combination of suspension agents is tin difluoride with tin dioxide.
lS The suspension agent may be present in concentrations of between about 0.05 gram per liter and about 5.0 grams per liter of bath, with concentrations between about 0.1 gram per liter and about 1.0 gram per liter being preferred.
The particles of suspension agent of the EMD productlon bath of this invention preferably possess an average diameter of between about 0.3 micrometers and about 150 micrometers and most preferably possess an average diameter of between about 0.3 micrometers and about 75 micrometers.
The suspension bath of this invention is typically prepared as follows: an aqueous solution of an appropriate manganese salt having a concentration of between about 0.5 and about 1.3 moles per liter is ~repared; a sufficient amount of an appropriate acid is added such that the pH of the solution is between about 1 and about 2; and between about 0.05 and about 5.0 grams per liter of a ., .

~ 8 suspension agent is then added to the acidic solution.
The suspension bath is then typically introduced lnto an electrolytic cell having at least one cathode composed of carbon, lead or platinum and at least one anode composed of le~d alloy, c~rbon, titanlum or tit~nium-mang~nese alloy. Tit~nium, carbon and titanium-manganese ~lloy anodes are preferred.
The b~th is heated to between about 90C
and about 100C, preferably to between about 93C
~nd about 98C. (Optionally, the bath could be heated prior to introduction into the electrolytic cell or prepared, heated and electrolyzed in the same vessel.) The bath is preferably electrolyzed at an anode current density of between about 10.8 mA/cm and about 21.5 mA/cm (i.e., between about 10 and about 20 amperes per square foot), most preferably of between about 12.9 mA/cm and about 19.4 mA/cm2 (i.e., betweenlabout 12 and about 18 amperes per square foot). Electrolysis at anode current densities below about 10.8 mA/cm2 is not preferred as the ma~or advantage of the suspension bath (i.e., the ability to employ higher current densitles with a corresponding higher EMD production rate) i8 not reallzed at such lower current densitles. Electrolysis at anode current densities ~ above about 21.5 mAlcm3 is not preferred as - passivation andlor consumption of the anode may occur at these higher current densities. The application of such current will cause electrolytic manganese dioxide to be deposited at the anode of the electrolytlc cell.

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The EMD so produced is removed from the anode ~nd then typically is crushed, washed with water, and dried (usually at about 110C) prior to being employed in galvanic cells. Optionally, the EMD may be treated with a base, such as sodium hydroxide or ammonia, prior to being wsshed with water snd dried.
The EMD produced using the suspension bath of this invention m~y be m~nufactured at high rates and high efficiencies due to the higher current to which the electrolytic bath may be sub~ected. As shown in Example 1 below, such EMD will typically contain trace amounts of the suspension material, which may be desirable for certain uses of such EMD.
The EMD produced using the suspension bath of this invention exhibits desirable discharge characteristics in galvanic cells comprising acid electrolytes, alkaline electrolytes and, if appropriately heat treated, in nonaqueous electrolytes. In electrolytes contaminated with potassium, several of the suspension agents of this invention have been unexpectedly found to reduce the amount of potassium which may become incorporated into the EMD.
EXAMPLES
The following Examples are intended to further illustrate the invention and are not intended to limit the scope of the invention in any respect.
ExamPle 1 Several solutions containing 0.92 molar MnSO4 and 0.28 molar H2SO4 along with the ~iO4~8 suspension agents llsted in Table I were electrolyzed at 95C with an anode of Ti-Mn alloy (containing 8 weight percent manganese) and a platinum mesh cathode. The area of the anode was 12.8 cm2 and the initial current 207 mA (i.e., 16.1 mA/cm2 or lS.0 A/ft2~. As the anode increased in area with deposition of MnO2, the current was raised to maintain the desired current density. Electrolysis was continued for 40 hours and the EMD produced sub~ected to elemental analysls. The results of such analysls are summarlzed in Table I.

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iO4 The ~bove data lndlc~te that EMD havlng a hlgh peroxld~tlon v~lue may be produced utlllzing a high current density employing the suspension ~gents of this invention. As is known in the art, efflclencies may exceed 100~ because of the productlon of lower valence species and the presence of combined water (see ~. Matsuki, T. Endo and H.
Kumada, SEM Studies of ElectrolYte ManRanese ,Dioxide, Electrochemical Acts, Vol. 29, No. 7, pp.
983-993 (1984)).
ExamPle 2 Several solutions comprising 0.92 M
MnSO4, 0.28 M H2SO4, 1.5 grams per liter of potassium in the form of K2SO4, and 0.2 gram per liter of the suspenslon agent listed in Table II
below were electrolyzed for 40 hours at 95C at an anodlc current density of 16.1 mA/cm2 (except as noted) and the resultant MnO2 analyzed. The results of such anslysis are summarized in Table II.
Table II
Removal of Potassium bv SusPension ARent Weight Percent SusPension AQent ~ MnO2 Peroxidation Potassium in EMD
None* 89.12 1.95 1.05 MnO2 89.01 1.94 1.20 Fe23 89.44 1.95 0.19 SnO2 86.84 1.94 0.40 FeS2 90.00 1.95 0.19 SnF2+SnO2** 89.23 1.96 0.41 ,' 30 * anode current density was 8.1 mAIcm2 - ** 0.1 gram per liter of each component The above results indicate that, unlike manganese dioxide, several of the suspension agents of the bath of this invention will reduce the amount ~`~ 35 of potassium incorporated into the EMD produced, '~ D-14619 ~' ,.;~
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thereby producing EMD which will be more effective in alkaline cells.
ExamPle 3 One tenth of a grsm of several EMD samples produced using a variety of suspension agents (after being ground in a micromill, passed through a 200 mesh screen, washed several times with distilled water, and dried at 110C overnight) were force discharged accordlng to the method described by A.
Kozawa and R.A. Powers in Electrochem. Tech., volume 5, 535 (1967) at 1 mA against a saturated calomel electrode in a 25 weight percent ZnC12 electrolyte. The voltage was monitored until a reading of 0.0 volt against the reference electrode was obtained. The suspension bath which produced the particular EMD tested contained 0.2 gram per liter of the listed suspension a8ent and had been electrolyzed at a current density of 16.1 mAlcm (15 amperes per square foot) at the anode. The results of such testing are summarized in Table III
below.
Table III
Forced Dischar~e of EMD in Acid ElectrolYte EMD Hours to Suspension Voltage (in volts) after hours discharge 0.0 Volt Aqent 0 hrs 5 hrs 10 hrs 15 hrs 20 hrs 25 hrs. Recorded Mn02 .626 .369 .317 .207 .031 - 20 ~eS2 .550 .327 .294 .265 .220 - 24 NiO .614 .359 .313 .281 .237 - 24.5 boron carbide .593 .360 .324 .300 .269 .180 26.5 hafnium carblde .565 .331 .297 .268 .226 - 24.5 The above results lndicate that the electroysis of several of the suspension baths of this invention will produce an EMD which demonstrates improved performance in acidic electrolyte relative to EMD produced using manganese dioxide as a suspension agent.
ExamPle 4 One tenth of a gram of several EMD samples produced uslng a variety of suspension agents (after being ground in a micromill, passed through a 200 mesh screen, washed several times with distilled water, and dried at 110C overnight) were force discharged against an Hg/HgO electrode in a 9N KOH
electrolyte and the voltage monitored until a reading of -0.2 volts against such reference electrolyte was obtained, in accordance with the procedure described by A. Kozawa and R.A. Powers in Electrochem. Tech., Vol. 5, 535 (1967). The suspension bath which produced the particular EMD
tested contained 0.2 gram pler liter of the listed suspension agent and was electrolyzed at an anode current density o$ 16.1 mA/cm2 (15 A/ft2). The results of such testing are summarized in Table IV
below.

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Table IV
Forced Discharge of EMD in Alkallne ElectrolYte Hours to 8MD Suspension Voltage (in volts) after hours discharge -0.2 Volt Aaent 0 hrs 5 hrs 10 hrs15 hrs 20 hrs Recorded MnO2 .109 -.014-.063 -.152 -.208 17 FeS2 .109 -.028-.084 -~146 -.259 18 NlO .126 -.009-.066 -.129 -.242 18 boron carbide.108 -.023-.068 -.117 -.207 20 0 hafnlum carblde .085-.046 -.098 -.163 -.278 16.5 tltanlum carblde .096-.027 -.076 -.130 -.224 19 The above results indicate that the EMD~
produced by the process of this invention exhibit desirable performance in alkaline electrolytes.
Although preferred embodiments of this invention have been described in detail, it is contemplated that modifications thereof may be made and some features may be employed without others, all within the spirit and scope of this invention.

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Claims

What is claimed is:

1. A bath for the production of electrolytic manganese dioxide comprising (a) between about 0.5 and about 1.3 moles/liter of an aqueous solution of at least one manganese salt selected from the group consisting of manganous sulfate, manganous chloride and manganous nitrate;
(b) a sufficient quantity of at least one acid selected from the group consisting of sulfuric acid, hydrochloric acid and nitric acid so that the pH of said bath is between about 1 and about 2; and (c) at least one suspension agent which is selected from the group consisting of insoluble multivalent elements and of insoluble compounds of multivalent metals other than manganese.

2. The bath of claim 1 wherein the manganese salt and the acid possess identical anions.

3. The bath of claim 1 wherein the suspension agent is present in a concentration of between about 0.05 gram per liter and about 5.0 grams per liter.

4. The bath of claim 3 wherein the suspension agent is present in a concentration of between about 0.1 gram per liter and about 1.0 gram per liter.

5. The bath of claim 1 wherein the suspension agent has an average particle diameter size of between about 0.3 and about 150 micrometers.

6. The bath of claim 5 wherein the suspension agent has an average particle diameter size between about 0.3 and about 75 micrometers.

7. The bath of claim 1 wherein the suspension agent is at least one member of the group consisting of niobium boride, titanium boride, zirconium carbide, hafnium carbide, boron carbide, ferric oxide, ferrosoferric oxide, iron disulfide, tin difluoride, cobalt oxide, lead dioxide, lead difluoride, molybdenum disulfide, nickel oxide, tin dioxide, cerium dioxide, silicon dioxide, bismuth trioxide, titanium dioxide, tungsten trioxide and chromium dioxide.

8. The bath of claim 7 wherein the suspension agent is at least one member of the group consisting of ferric oxide, tin dioxide, iron disulfide and lead dioxide.

9. A process for the production of electrolytic manganese dioxide, which process comprises:

(1) preparing a bath comprising (a) between about 0.5 and about 1.3 moles/liter of an aqueous solution of at least one manganese salt selected from the group consisting of manganous sulfate, manganous chloride and manganous nitrate, (b) a sufficient quantity of at least one acid selected from the group consisting of sulfuric acid, nitric acid and hydrochloric acid such that the pH of the bath is between about 1 and about 2, and (c) at least one suspension agent selected from the group consisting of insoluble multivalent elements, and of insoluble compounds of multivalent metals other than manganese;
(2) heating said bath to between about 90°C and about 100°C; and (3) electrolyzing the heated bath in an electrolytic cell having at least one anode and at least one cathode.

10. The process of claim 9 wherein the manganese salt and the acid possess identical anions.

11. The process of claim 9 wherein the suspension agent is present in a concentration of between about 0.05 gram per liter and about 5.0 grams per liter.

12. The process of claim 11 wherein the suspension agent is present in a concentration of between about 0.1 gram per liter and about 1.0 gram per liter.

13. The process of claim 9 wherein the suspension agent has an average particle diameter size of between about 0.3 and about 150 micrometers.

14. The process of claim 13 wherein the suspension agent has an average particle diameter size of between about 0.3 and about 75 micrometers.

15. The process of claim 9 wherein the suspension agent is at least one member of the group consisting of niobium boride, titanium boride, zirconium carbide, hafnium carbide, boron carbide, ferric oxide, ferrosoferric oxide, iron disulfide, tin difluoride, cobalt oxide, lead dioxide, lead difluoride, molybdenum disulfide, nickel oxide, tin dioxide, cerium dioxide, silicon dioxide, bismuth trioxide, titanium dioxide, tungsten trioxide and chromium dioxide.

16. The process of claim 15 wherein the suspension agent is at least one member of the group consisting of ferric oxide, tin dioxide, iron disulfide and lead dioxide.

17. The process of claim 9 wherein the electrolysis of step (3) is conducted at an anode current density of between about 10.8 and about 21.5 mA/cm2.

18. The process of claim 17 wherein the electrolysis of step (3) is conducted at an anode current density of between about 12.9 and about 19.4 mA/cm2.

19. The process of claim 9 wherein the bath is heated to between about 93°C and about 98°C
in step (2).

20. The bath of claim 1 wherein the suspension agent is a molecular sieve.

21. The bath of claim 1 wherein the suspension agent is at least one member of the group consisting of carbon and sulfur.

22. The bath of claim 1 wherein the suspension agent is a zeolitic molecular sieve.

23. The process of claim 9 wherein the suspension agent is a molecular sieve.

24. The process of claim 9 wherein the suspension agent is at least one member of the group consisting of carbon and sulfur.

25. The process of claim 19 wherein the suspension agent is a zeolitic molecular sieve.