US2347451A - Electrolytic deposition of manganese - Google Patents

Description

' Patented A 25, 1944 UNITED STATES PATENT orncs morn/or. onsrosmon or Paul II.

.ccmrationoflllineis No Drawing. Application May 81'. 1989. Serial'lio. 210."!

a m (or. 204-105) ganese sodium citrate. manganese acetate and other manganese salts has heretofore been proposed. The aqueous electrolytes have utilized as such or in coniunction with addition 'agents such asammonium salts and ethanolamine salts, for example, ammonium sulphate, monoethanolamine sulphate, triethanolamine sulphate, and the like. In addition. the prior art suggested the preliminary purification of the aqueous manganese electrolytes by various 188th. ods. Despite all of these efforts to produce fully satisfactory depositions; no one has heretofore successfully produced satisfactorily thick deposits which are substantially free from sulphur. Thus. for example, while good deposits have been reported in connection with the process described in United States Patent No. 2,119,560, the sulphur content of the deposited manganese has ranged from about 0.2% to about 0.8%, repre- :BlqtBtU/C deposits containing of the order of The present invention is based upon new discoveries which enable the formation of exceptionally satisfactory deposits of manganese, of seed thickness, and of substantial freedom from sulphur. In general, these" results are obtained by the utilisation of novel methods of purification of manganese electrolyte solutions coupled with proper control of current density and manganese content of the catholyte.

Aqueous catholyte solutions which are employed in the pmdubtion of electrolytic mangan'ese usually contain relatively large amounts of manganese salts and ammonium salts or salts of organic nitrogenous bases or the like, an illustrative. example being of the order of 70 grams of' manganese sulphate and 200 grams'ol ammonium sulphate per liter as msior constituents. However, the electrolyte also usually contains small amounts of salts of one or more of the elements iron, nickel, cobalt, molybdenum, vanadium, arsenic, copper, zinc, and lead. These impurities seriously interfere with the production of satisfactory deposits of high-purity electrolytic manganese.

In accordance with the present invention, the principal step of purifying the electrolyte is accomplished by the utilization of a sulphide ion to effect precipitation of nickel, cobalt, copper and zinc, the substantial removal of these metals be- Ambrose, Ooilese was, as. asllsnor a Development Oompanr. Ghieaso. ill a ing apparently pkrticuiarly essential if manganese deposits of and density and substantial freedom from sulphur are to be obtained. While these metals are effectively removed in accordance with the practice of my invention, other heavy metals are. likewise at least substantially.

eliminated.

-It has been found that when a sulphide ion is added. for example, to an aqueous solution of manganese sulphate containina' traces of nickel and cobalt and havin: a hydrogen ion concentration greater than about 6.0, pink manganese sulphide and other heavy metal sulphides are essentially precipitated. If filtration to remove such precipitates is carried out under these conditions, it has been found that the filtrate will not be entirely free of nickel and cobalt. If. however, the solutionis permitted to stand for a substantial period of time. at least one hour and preferably several hours in the usual case, the pink manganese sulphide undergoes a change and a black precipitate containing the nickel and cobalt is formed. On filtration, under such conditions, the solution is substantially free from nickel and cobalt.

While good results are obtained by following the procedure describedhereinabove. so far as the initial purification-step is concerned. it has been found that further improvements result from the addition to the electrolyte of a finely divided-material such as infusorial earth. trlpoli, activated charcoal, alumina, silica gel, barium sulphate, titanium dioxide, or anyother inert material presenting a large surface. This sur fees may be produced in other ways, for example. as by forming a=precipitate in the solution itself. for example, by adding barium sulphide thereto. Ex ptionally/satisfactory results are obtained by the use of activated charcoal and it is preferred,

therefore, to employ this material. The activated charcoal or the like reduces materially the length of time that the precipitate of pink manganese sulphide and other heavy metal sulphides is required to be allowed to stand.- Thus, for example, instead of requiring upwardly of an hour and in numerous cases several hours, the addition of activated charcoallor the like reduces the time of standing to only a few minutes, in most instances, to approximately 10 or 15 minutes.

In order to obtain highly pure deposits of electrolytic manganese of desired density, the anode current density should be below twenty amperes per square foot and, for best results, between about sixteen and about eighteen amperes per square foot. Furthermore, the manganese content during electrolysis should be about fifteen grams per liter. In order to accomplish this result, for example. electrolyte containing at least about twenty-five grams per liter of metallic manganese as manganese sulphate may be passed through the cathode compartment at such a rate that the solution leaving the cathode compartment contains of the order oi ten grams of metallic manganese as manganese sulphate per liter. Separate anolyte and catholyte circuits are maintained and they may be separatedby a relatively impermeable diaphragm it it is not desired to make large amounts oi manganese dioxide at the anode.

The following example is illustrative of the practice of my invention. It will be understood that variations may be made with respect to the manganese salt to be electrolyaed, the character of the addition agent or agents, the nature of the cathodes and anodes, current densities and the like, as well as in other ways, all within the scope of the invention in the light oi the guiding principles which have been described in detail hereinabove.

'I'o 10,000 liters of an aqueous solution containing 150" grams of ammonium sulphate and 35 grams of metallic manganese as manganese sulphate per liter, said solution containing traces of nickel, iron and cobalt, one pound of colorless ammonium sulphide and one pound of activated charcoal were added. The solution was stirred and then allowed to standior 15 minutes. The solution was then filtered-through a high silicon iron filter press using an ordinary filter cloth. The resulting solution was free from nickel and cobalt as indicated by tests with dirnethylglyoxime and alpha nitroso beta naphthol. It is particularly preferred that the pH of the solution be maintained between 'i and 8 although good results may be obtained employing a pH of about 5.5 and about 0.5. The resulting solution is then electrolyzed in'a lead lined cell with a heavy canvas diaphragm, sheet steel cathodes and lead anodes, the anode current density utilized being approximately 18 amperes per square foot.

Instead of employing ammonium sulphide,

' other sulphides may be utilized, it being immaterial in what form the sulphide ion is added. Ammonium sulphide, hydrogen sulphide and barium sulphide are particularly preferred because they do not contaminate the solution. It will be understood that the final, purified solution which is to be electrolyzed, when prepared in accordance with the present invention, contains only the amount oi sulphide ion represented by the solubility of manganese sulphide in the particular electrolyte utilized. In general, the sulphide ion is employed in amounts less than or not substantially in excess of, about 1% of the stoichiometric equivalent of the manganese present.

While the practice of the process may be carried out with solutions containing only manganese salts such as manganese sulphate, it is distlnctly preferable to employ aqueous electrolytes containing not only manganese salts but also addition agents such as ammonium salts, for example, ammonium sulphate as well as salts of alkylolamines and related compounds. Where ammonium sulphate is utilized, together with manganese sulphate, there should be present at least about 100 grams of ammonium sulphate per liter oi electrolyte solution in order to obtain the most satisfactory results. a

What I claim as new and desire to protect b Letters Patent oi the United States is:

1. In a method of making high purity manganese which comprises electrolyaing an aqueouesolution containing a soluble manganese seems:

salt, the steps which comprise adding to said aqueous solution a sulphide ion and an inert. solid material having a. high specific surface, the sulphide ion being efiective to precipitate such heavy metals as may be present, allowing the solution to stand for a short period of time, and filtering.

2. The method defined in claim 1 wherein the ineil't, solid material comprises activated charcoa 3, The method defined in claim 1 wherein the inert, solid material is activated charcoal, the sulphide ion added is in an amount less than about 1% oi the stoichiometric equivalent oi the manganese present, the activated charcoal being employed in amounts at least equal to the weight of the added sulphide ion.

4. In a process oi producing electro tic manganese which comprises eleetrolyzing aqueous solution 01' manganese sulphate, the which comprise adding a member selected from the group consisting of ammonium sulphide, hydrogen sulphide, and barium sulphide to said aqueous solution to precipitate such heavy metals as may be present, adding a finely divided inert material to the solution, allowing the solution to stand for at least about 10 minutes, and then filtering the solution.

5. The process defined in claim 4 wherein the aqueous solution of manganese sulphate contains a substantial content oi ammonium sulphate.

6. In a method of producing electrolytic manganese of high purity which comprises electrolyzing an aqueous solution containing at least 15 grams oi manganese as manganese sulphate and at least grams of ammonium sulphate per liter of solution by utilizing an insoluble anode and an anode current density between about 16 and about 20 ampers per square foot, adding ammonium sulphide to said aqueous solution in amounts not substantially in excess of 1% of the stoichiometric equivalent or the manganese present, adding a finely divided inert material to the solution, allowing the solution to stand for at least several minutes. and filtering.

I. In a process of producing electrolytic manganese by electrolysis of aqueous solutions of manganese sulphate containing substantial proportions of ammonium sulphate, the steps which comprise adding a sulphide ion to said solutions at a pH between about 7.0 and 8.0, adding activated charcoal, allowing the solution to stand for an appreciable period of time, and filtering to remove the precipitated sulphides of such heavy metal impurities which may be present.

8. The method 01 claim 7 wherein the sulphide ion is incorporated through the addition oi a member selected from the group consisting of hydrogen sulphide, ammonium sulphide and barium sulphide.

9. The method of claim 7 wherein the sulphide ion is incorporated through the medium of ammonium sulphide and the filtrate is electrolyzed utilizing an insoluble anode and an anode current density between about 16 amperes and about 20 amperes per square foot, the electrolysis being eiiected in a diaphragm cell and the manganese electrolyte being continuously circulated through the cathode compartment at such a rate that there is always present therein at least about 15 grams oi manganese as manganese sulphate per liter.

PAUL M. AMBROSE.