US2325723A - Purification in electrowinning of manganese - Google Patents

Description

ug- 3, 1943- E. M. wANAMAKs-:R E1-AL 2,325,723 PURIFICATIQN IN ELECTROWINNNG 0F MANGANESE vwed Feb. 2v, 1942 1 A rron/Ey;

l peated. Y

Patented .Augr 3,

"UNITED lSTATES PATENT tz( )l"`l",'ICl`.r

2,325,723 y y PURIFICATION 1N ELECTROWINNING 0F 'n MANGANESE l Elmer M. Wanamaker and William D. Morgam Jr., Knoxville, Tenn., assignoi's to Electro 'Manganese Corporation, Minneapolis, Minn.,

acorporation of Delaware The invention ielates to 'the electrowinning of rmanganese, more particularly the purication of electrolyte to be used as the catholyte.

In the electrowinning of manganese, theelecrrolyte is divided into analyte and camente. 5'

Anolyte is continually withdrawn from the anolyte chamber and used for the extraction of manganese from manganese ore, the anolyte being y thereby enriched in manganese. At the same time, however, impuritiesare introduced into the extract from the ore, among which iron, arsenic,

antimony, nickel and cobalt may be mentioned.

The iron, arsenic and antimony are commonly removed by oxidizing the iron `Ato the ferrie condition, following which and at a suitable DH, iron .15

is precipitated, together with arsenic and antimony if a sufiicient amount of iron was present in solution. Following the precipitation ofthe iron, ammonium suliide is used as a reagent for the precipitation oi' other impurities, such as 20 nickel, cobalt and copper, in the form of their suliides. Thenickel and cobalt precipitated in the form of a sulde mud is separated by illtrai tion or otherwise and the filtrate then goes to the catholyte chamber of the cell, thus complet- 2Q 7 ciently adherent lto the cathode to permit its reing the cycle oi the movement and treatment-of the electrolyte, beginningI with the removal of anolyte from the anolyte chamber and ending with the introduction of catholyte into the catholyte chamber.

In the process following this cycle, on which, the process of the present invention is an improvement, a large'excess oi ammonium sulfide over that theoreticallyr` necessary to precipitate antimony have been precipitated, containing 20 40 to grams per liter of manganese as manganese sulfate, ammonium sulfate 140 to 180 grams per liter and which may have a pH of about 7.2 to- 7.5,` about 60 liters ci' a saturated solution of ammonium sulfide are added.- The'prp'ose of f5 using .this large excess o1' ammonium sulfide is to precipitate the nickel, cobalt, etc., as sulildes as' completely as possible. Owing, however, to this large excess, substantial quantities of manganese sulfide are also precipitated.

The mud, which may contain as. much as 5 gement of the manganese in the ore treated, is ither discarded entirely or submitted to a, process comprising treatment'with sulphuric acid to re- This cycle is continuously re- 30 the sulphur as ammonium 'sulfide by Cabsorption of the HzS evolved in aqua ammonia. Y-

This process has certain disadvantages which it is the object of the present invention to .overcome. The recovery of manganese from the mud is troublesome and expensive. The use of the large excess of ammonium suliide represents an economic loss and in turn, re'sults in an excessive precipitation lof manganese as sulfide in the mud.

Moreover the purification which is the objective of the use of this large excess of ammonium sul-A ilde is incomplete and'this incomplete puriiication reflectedin the quality of the cathode deposit.

- In addition to nickel and cobalt there are other impurities the removal of. which is desired'and the efiect of which is evidenced by the physical character of the deposit as a whole as distinguished from the Presence ofnickel and cobalt as metallic impurities in the deposit.

For example, one of the disadvantages isthe tendency of the deposit, during formation 4and ydeposition on the cathode, to peel or crack and in someinstances to actually fall of! in the catholyte chamber, in contrast to the desired character of the deposit which is a coherent coating sumarate the metallic manganese deposit. The preoise nature of these impurities has not been vdeiinitely established although it is believed that l, they are of a colloidal nature and therefore pass through the iilter-membrane. It is believed that they comprise colloidal silicates and compounds -of manganese, cobalt and nickel in dispersed form. f

. It has been discovered that the stated disadvantages can be largely if. not wholly overcome by effecting the precipitation of the nickeL'cobalt; etc., in each Icycle in the presence of a large excess of sulli'de mud obtained in-,a previous cycle. For example, to the extract from which iron, arsenic, antimony and the like have been removed there may be added, at a. pH of about '1.2 to 7.5', not only ammonium suliide but also suliide mud froml the next preceding cycle and r the precipitation of nickel and cobalt'thereby efiected in the presence of that mud. This process is then repeated in each succeeding cycle, sub- 0 stantially the same body of mudbeing continuously reused in the successive treatments or A cycles. Analyses indicate the possibility that'the composition olfV this 'body of mud in these successive treatments progressively changes, the I cover the. manganese as manganese sulphate and V nickel and cobalt content progressively increasarate and independent step of recovering manganese from the mud. In order to avoid too great an accumulation of mud, a fractional part thereof may be removed in each precipitation and discarded or subjected to a process for the recovery of the manganese and other constituents therein. However since, except for this fractional portion, the mud is used over and over again, the lossl of manganese in the event that the excess mud is discarded is greatly reduced and the expense and trouble of recovering manganese from the excess mud is also reduced. In addition and perhaps most important of all, the character of the cathode deposit is improved and it has been found thatby proceeding in accordance with the present invention it is possible to constantly and uniformly obtain smooth adherent deposits free from the previously uncontrolled endency to crack and flake E. It is to be noted that this phenomenon of peeling and flaking oi is to be distinguished from the phenomenon of receding which occurs in the absence of adequate control over cathode potential.

The principles of the invention will be defined in the claims and a specific illustrative embodiment will be described in conjunction with the accompanying drawing showing diagrammatically a ow sheet illustrating steps in the process of the invention and apparatus which may be employed in practicing the same.

' Anolyte having a composition of 10 to 18 grams per liter of manganese as manganese sulfate, about 140 to 180 grams per liter of ammonium `sulfate and a pH of about. 1 to 2 is withdrawn from the anolyte chamber '38 of the cell 40 and passed through line I to the ore extractor or digester 2 where, by agitation with suitable manganese ore, the concentration of manganese in the extract is raised to 20 to 50 grams per literl and the pH raised to about 2 to 5. The pH of the extract is adjusted to about 5.5 to 6.0 and air or other suitable oxidizing agent employed to oxidize theiron to the ferric condition and cause the precipitation thereof along with arsenic, antimony and the like. The precipitate is then ltered in the filter 4 and a volume of filtrate equal to about 32,000 liters is passed through the line 5 to the tank 6 where the pH is adjusted to about 7.2 to 7.5 as, for example, by th addition of ammonia added through the line 1. The contents of the tank 6 is then 'passed through the line 9 provided with valve 8 to the tank I1 in which is retained sulfide mud .(from the previous purification) to level 2l in the tank, the quantity of mud being approximately that which would be tional or excess suliide mud precipitate caused by the addition of the 15 liters of ammonium suliide are siphoned oil. through the riser I9, line I3 provided with valve 29 and line 3i, and ltered in the lter press 32. The filtrate is passed through the line to catholyte storage tank 4I and thence through the line 42 to the catholyte compartment 39 of the manganese electrowinning cell 40. The precipitate of excess suliide mud iilter cake from the filter 32 (corresponding to the 15 liters of ammonium sulfide) is then passed through the line 36 to the mud storage tank 31.

During the treatment of the contents .of tank I1, another batch of 32,000 liters of extract is passed from tank 6 through lin'es 9 and I2 provided with valves I3 and I4 into treatment tank 23 and the treatment therein is the same as that described above in describing the treatment of the contents of tank I1, suliide mud being initially supplied to tank 23 from mud storage tank 31 through line 45 and line 41 provided with valve 48 and thereafter maintained in said tank up to the level 25. The supernatant liquid together with excess mud up to the level 24 is withdrawn from tank 23 through riser ISA, lines 22 and 3| and ltered in lter 32, in the same manner as described in connection with tank I1.

It will thus be seen that in each of the tanks I1 and 23 a substantially constant quantity or volume of suliide m'ud is maintained, indicated in the drawing by the level lines 2l and 25, re-

. spectively. The only portion of the suliide mud obtained by adding 60 liters of 45% ammonium sulfide solution to 32,000 liters of iron-freetextract. In addition, 15 liters of 45% ammonium suliide are added to the contents of the tank I1' I1, is formed and is indicated by the level line 20.

The supernatant liquid, `together' with the acidiwhich is withdrawn from these tanks is the lncreased quantity produced therein by the successive additions of ammonium sulfide (passed through lin'e I5 providedwith valves I6 and ISA) in the successive treatments.

The two tanks I1 and 23 alternate in their functions; that is, while extract is being. purified in one tank puried supernatant liquor is being siphoned oif from the companion tank and delivered to the catholyte storage tank 4I, so that the catholyte storage tank is being continually replenished with puried catholyte. There is always available, therefore, one tank having a suitable body of mud therein into which to charge iron-free extract for purposes of purification. As many separate purification tanks as desired may be used. v

Whereas-in the process in respect of which the present invention is an improvement, it was necessary toV employ about. 60 liters of 45% ammonium suliide for each successive batch of about 32,000 liters of iron-free extract, the present invention makes it possible to reduce the ammonium suliide down to at least 15 liters; and whereas in said previous process it was necessary to discard the entire suliide mud precipitate or work it up for recovery of manganese and other constituents, according to the present invention, except for the increment of sulde mud removed as herein described, the said suliide mud is used over and over again in each of the tanks I1 and 23 and the quantity of mud which it is necessary to work up for vrecovery purposes or discard is very greatly reduced. Finally and perhaps most important, the continuous reuse of the mud in the precipitation of nickel and cobalt e'ects such a puriilcation of the electrolyte thatpthe cathode deposit obtained therefrom is substantially free from the disadvantage of cracking and peeling.

unique adsorptive eiTect or other physicalchemical .action by which the colloidal impurities which are believed to contribute tothe cracking and peeling of the manganese cathode deposit are removed.

' Instead of ammonium sulfide, which is preferred, it is possible to use soluble suldes in y general.

We claim: f 1. In a cyclical process for the purification of catholyte in the eiectrowinning of manganese in which ore is extracted with anolyte and the` extract is treated to remove iron and then with ammonium sulfide to precipitate nickel and cobalt as suliides, whereby a sulfide mud is obtained containing nickel suliide, cobalt sulfide and manganesesulde, the mud' is separated from' the solution and the latter is. used as catholyte, the improvement which comprises precipitating cobalt and nickel suliides by adding ammonium sulfide in the presence of sulfide 5 mud obtained in a previous cycle, and thereby -containing nickel suliide, cobalt sulildel and manganese sulfide, the mud is separated from the solution and the latter is used as catholy'te, the improvement which comprises precipitating cobalt and nickel suliides by adding said soluble suliide in the presence of sulfide mud obtained in a previous cycle, and thereby forming an additional quantity of mud, the proportion of said mud obtained in a previous cycle being `,in exs cess of said additional quantity. y

M. WANAMAKER. WILLIAM D. MORGAN, Jia

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