CA1070122A - Process for manganese removal from metal bearing solutions - Google Patents

Abstract

PROCESS FOR MANGANESE REMOVAL FROM
METAL BEARING SOLUTIONS

ABSTRACT OF THE DISCLOSURE
A process of the preferential removal of soluble manganous ions from a metal bearing solution, particularly a zinc sulfate solution to be subjected to electrolysis for the recovery of zinc, comprising treating said solution with an oxi-dant capable of oxidizing soluble manganous ion to insoluble and filterable gamma-manganese dioxide at a temperature and for a time sufficient to precipitate at least a portion of the mangan-ese present in said solution as gamma-manganese dioxide, said theoretical amount required for substantially total manganese removal from said solution, and separating said precipitate from said solution.

Description

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17 BACKGROUND OF THE INVENTION .
18 Excessive manganese, in solutions containing metals, 19 such as leach extracts, to be treated by electrolysis procedures for the recovery of the metals has caused problems of decreased 21 current efficiencies during electrolytic recovery of the desired 22 metal on the cathodes and manganese deposition on the anodes as well as poor physical and chemical characteristics of the metals recovered.
This problem of manganese and its build-up in the 26 solutions and contamination of the desired metal has been over- :
~7 come to some extent in electrolytic plants by employing a more .
28 "reactive" anode or by bleeding-off part of the solution for 29 neutralization and separation of the desired metal by chemical precipitation prior to further treatment. Thus, for example, ' . ~ .
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~ i` 1070lzz - 1 in electrolytic recovery of ~inc, chemical lead anodes have ; 2 been ~sed in place of the normal lead/silver alloy anodes. Other 3 efforts at overcoming the problems include the method of cleaning the manganese deposit from the anodes and cells more frequently whicll is expensive and time-consuming particularly where high 6 levels of manganese are dissolved in the liquor. Moreover, in some of the procedures dealing with the removal of manganese, 8 there is the undesired removal or loss of significant amounts of the metal desired to be recovered during the manganese removal step.
11 With particular reference to zinc recovery by electroly-12 sis, this problem of manganese contamination of the electrodes ;:~ is aggravated when the "Jarosite Process" is used in the recovery zinc. The "Jarosite Process" is a well-known iron rernoval process employed subsequent to high acid leaching which can in-16 crease the recovery of zinc from roasted sulfide concentrates 17 by the electrolytic zinc process. What transpires is that the 18 roasted zinc concentrate is subjected to a strong sulfuric acid 19 leach followed by treatment using, preferably, an ammonium ion-

- 2~ to precipitate the iron to give a zinc sulfate solution free ~ 21 of the iron and with very little loss of the zinc. With such ~ 22 highly acid leaching, there is even a further solubilization '',~?' 23 of the manganese present in the roasted zinc sulfide concentrate 24 which causes increased problems of electrode fouling and contamin-ation of the desired zinc during electrolytic recovery of the 26 zinc.
` . 27 BRIEF SUMMARY OF Tl]~ _NVENTION
28 The present invention provides a process for the removal 29 of soluble mangAnous ions as insoluble gamma-manganese dioxide 30 j~ from z sulfat~-bearing s 1 tions without a~y excessive loss :.',' ' . .
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.: l 1 lof the zinc which it is desired to recover, particularly with 2 ¦respect to removal of manganese from leach solutions in which

3 ¦said metal is to be recovered by electroytic procedures. The ¦present invention urther provides for the production of readily 5 ¦filterable gamma-manganese dioxide-containing pulp.

6 I Briefly stated, the prcsent invention comprises the 7 ¦stcps of treating said zinc sulfate-bearing solution with an ¦oxidant capable of oxidizing soluble manganous ion to insoluble ¦gamma-manganese dioxide at a temperature and for a time sufficient 10 ¦to precipitate at least a portion and preferably at least about 11 190~ of the manganous ion present in said solution as filterable 12 ¦gamma-manganese dioxide, said oxidant being in an amount of from 13 ¦about 130~ to 1~0% of the theoretical amount required for substan-1~ ¦tially total manganese removal from said solution, and separating 16 ¦said precipitate from said solution. In its preferred embodiment, 16 ¦the instant invention comprises the improvement in the "Jarosite 17 ¦Process" for the recovery of zinc wherein prior to electrolytic 18 ¦recovery of the zinc the leach liquor is treated with a persulfate lg ¦oxidant such as ammonium persulfate so as to oxidize the soluble 20 manganese ion to insoluble gamma-manganese dioxide and after 21 removal of the manganese dioxide to utilize the remaining ammonium 22 ion and sulfate radical in the preparation of the Jarosite precipi-23 tate, which results in the removal of iron from the leach liquors.
24; BRII~F DE:SCRIPTION OF THE DRA~1ING .
The single figure of drawing is a flow diagram of the 2G electrolytic zinc process embodying the "Jarosite Process" and 27 including the improvement of the instant invention relating to 28 the removal of the manganous ion prior to recovery of the zinc 29 ~by rlect lysis.

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DI~TAILr.D D~:SCI~IPTION
2 In the description that follows and in the rxamples 3 there will be discussion of the suitability of the instant inven-tion or the preferential removal of soluble manganous ion as insoluble gamma-manganese dioxide from zinc solutions, particu-6 larly zinc sulfate solutions, wl-ich is the preferred embodiment 7 o~ the invention. It will be understood, however, that the description given herein with respect to conditions which are 9 optimum and/or preferred for preferential removal of manganous ions from zinc sulfate solutions are applicable to the removal 11 of such ions from the solutions containing other metals including 12 copper, nickel, cobalt, cadmium and mixtures thereof.
13 While other manganese containing solutions may be 14 successfully treated in accordance with the process of the instant 15 invention, it is particularly beneficial in the treatment of 16 metal sulfate solutions in general and zinc sulfate leach liquors 17 in particular. Moreover, while it is preferred to treat such 18 leach liquors that are to be subjected to electrolysis for the 19 recovery of zinc, the invention can be used for the treatment 20 of any liquors in which it is desired to preferentially remoYe 21 the manganese.
22 As to the oxidant used in the present invention, it is 23 necessary to use an agent capable bf oxidizing soluble manganous 2~ ion, Mn 2, to insoluble manganese dioxide. There are a number 25 of oxidants whic~ can accomplish this result and the choice is 26 dependent mainly on economic factors and the undesirability, in 27 some cases, of introducing deleterious elements into the solutionO
2~ ln the case oL an electrolytic zinc plant circuit, for example, 29 it would not be appropriate to use lead or bismuth containing 30 oxidants which could contaminate the refined zinc. It would

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1 bc appropriate, howevcr, and advantageous to use in such circuits 2 ammonium or sodium persulfate as oxidants since the ammonium 3 or sodium ions and sulfate radical can subsequently be used in the Jarosite formation step for iron removal from the leach

5 liquors. By way of illustration, suitable oxidants are ammonium ~ersulate, sodium persul~ate, potassium persulfate, sodium 7 bromate, sodium bismuthate, and lead dioxide. Of these the preferred oxidants are the ammonium and sodium persulfates by 9 virtue of their ready availability, ease of handling and produc- I
tion, the fact that they do not contaminate the metal desired 11 to be recovered, and, more particularly, because, as noted above, 12 these persulfates have ~he advantage of a further use for iron 13 removal from the liquors in the "Jarosite Process" step of the 14 electrolytic process for the recovery of zinc.
It is essential for the successful removal of insoluble 16 manganous ions from zinc-bearing solutions that there be substan-17 tially no co-precipitation of the zinc metal with the manganese 18 dioxide since such co-precipation results in an unacceptable 19 and uneconomical loss of the valuable zinc metal O In this regard, 20 while the precise theory is not entirely understood, it has been 21 discovered that when zinc co-precipitates with manganese there 2 results a precipitate comprised principally of hydrated manganous 23 anganite, ZnO-MnO2-2-4~20, containing chemically bonded 2 zinc. Moreover, it has been observed that such hydrated mangan-2 ous manganite is formed to a large extent when the oxidant is 2 employed in an amount substantially above about 1506 of the theo-2 retical amount required or substantially total manganese removal 2 and that under these conditions the hydrated manganous manganite 2 ontains significant zinc, approximately 8-9%, in apparent chemi-3 al substitution for the manganese. Under such conditions the ~ , .
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l amount of zinc that is co-preci~itated with the manganese is 2 unaffected by intensive washing of the precipitate.

, It has similarly been discovered that when the oxidant . ~ is employed in an amount below about 150% of the theoretical 5 amount required for substantially total manganese removal, the resulting crystalline phase precipitate will contain substantially 7 less hydrated manganous manganite and in fact gamma-manganese dioxide, yMnO2, becomes the dominant phase, which, incidentally, is economically desirable for use in the battery industry. Such lO gamma-manganese dioxide retains a minimum amoùnt, or substantially ll no zinc. Thus it can be seen that it is essential for successful 12 operation of the claimed invention that the precipitate be substan .
13 tially in the crystalline form of gamma manganesxe dioxide to l~ the substantial exclusion of the zinc-bonded manganous manganite.
. The identification of the crystalline phases of hydrated 16 manganous manganites and ~amma-manganese dioxide as a function 7 of the amount of oxidant employed is confirmed by X-ray diffrac-]8 tion patterns o the precipitates (oven-dried below 100F.) which l9 show significant variations in crystallinity and phase composition . 20 relative to conditions of oxidation during precipitation. At 21 higher oxidation, i.e., when the oxidant is above about 150%, 22 manganous manganites are formed that display XRD patterns similar 23 to ~MnO2, and that are represented in nature by the mineral, blrnesslte, corresponding to the formula (NaO 7Ca0 3)Mn7Ol4.2.8H2O

A number of metallic ions, including zinc, are reported to be 26 bonded in similar varieties o~ this mineral phase. ~Feitknecht, - ~ 2 W.P. and Marti, W., (19~5a), "Uber die Oxydation von Mangan Hydroxyd mit Molekularen Sauerstoff," Helv. Chim. Acta, Vol. 28, 2 PP 129-1~8; Feitknecht, W.P. and Marti. W., (19~5b), "Uber Manganit 50 ~und ~un ichen Br~unstein, ~]elv. Chim. Actr, Vol. 28, pp 118-156 '~',.
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Buser, W., Graff, P., and Feitknecht, W., (1954~, "Beitrag zur 2 Kenntnis der Mangan (II)-Manganit und des 6Mn02," l~elv. Chim 3 Acta, Vol. 37, pp 2322~2333; Jones, L.ll.P. and Milne, A.A., (195G , "Birnessite, a New Manganese Oxide Mineral from Aberdeenshire, Scotland," Mineral. Mag. Vol. 31, pp 283-288).
In less oxidiz~d precipitates, i.e., when the oxidant i 7- below about 150~, additional lines appear in XRD patterns at 8 2.12, 1.63 and 4.0~A, indicating either a new crystalline phase, 9 or a modification of the manganous manganite phase. XRD data suggest a progressive phase transition to a less hydrated form 11 of MnO2 (incipient ~MnO2). This was subsequently confirmed 12 by the precipitation of major amounts of YMnO2 at lower oxida-13 tion conditions. ~nder such conditions of lower oxidation, dark brownish-black precipitates are formed containing minor amounts of zinc tl-2% Zn) and whose X-ray diffraction patterns bear no 16 resemblance to birnessite and other manganite phases, but corre-17 late closely with those of MnO2.
18 When using lower amounts of oxidant, the manganese pre-19 cipitate, determined by X-ray diffraction analysis to be crystal-2~ ¦ line manganese dioxide o~ the gamma type, is believed to be formec 21 according to the following chemical reaction:
22 MnSO4 + (NH4)2 S2o8 ~ 2H2O ~MnO2 + (NH4)2 SO~ + 21l2SO4 23 Reaction I
When higher quantities of oxidants are used, the zinc-manganese complex ~ormed and identified by X-ray diffraction 26 analysis as manganous manganite containing zinc is believed to ~7 result from the following reaction: `
28 6Mnso4+6(NH~)2s2o8+l3H2o+znso4~ ZnO-6MnO2+6(NH4)2 SO4~131-l2SO4 29 Reaction II
Not only is the production of a sotstantia1ly z~nc-r~ee ¦

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,, gamma-manganese dioxide necessary or successful operation of 2 a commerically viable manganese removal process, but it is also necessary that the resulting precipitate be readily filterable so as to allow the easy separation of the precipitate from the solution. In this regard, it has been discovered that, notwith-

6 standing the requirement that the oxidant should be employed in

7 an amount of from below about 150~ to minimize co-precipitation o zinc and to ensure that the gamma-manganese dioxide crystallin form be predominant, when the amount of oxidant employed is sub-stantially below about 130% of the theoretical amount required fo 11 substantially total manganese removal there results a gamma-man-12 ganese dioxide precipitate, brown to black in color, which is in 13 the colloidal state. Such a colloidal precipitate is of course 14 not readily filterable and therefore tends to be commercially un-satisfactory.
16 Not only does a poorly filterable colloidal gamma-man~
17 ganese dioxide precipitate form under the above-mentioned condi-18 tions of low amounts of oxidant, but it has also been observed 1~ that the precipitate formed under these conditions contains vary-ing amounts of ~inc sulfate which, as the relative amount of oxi-dant is decreased, becomes increasingly difficult to wash out.
22 As is the case of co-precipitation of zinc metal at high oxidant 23 usage, such zinc sulfate loss is also unsatisfactory from an 2~ economical and commercial standpoint.
Thus, it can be seen that when the amount of oxidant is 26 substantially above about 150~ of the theoretical amount required 27 for substantially total manganese removal, the precipitate, though 2 possessing good filterability, neverthelcss is of the manganous 29 manganite crystalline form whereby a substantial amount of zinc 3 metal is co-precipitated. When he oxidant i, substantially "~ ' :,`< . . , :

1 below about 130~, a precipitate is formed which, though being 2 ¦ substantially of the gamma-manganese dioxide crystalline form 3 ¦ and substantially free of co-precipitated zinc metal, is never-¦ theless not readily filterable. ~ccordingly, it is a feature 5 ¦ of the present ~nvention that the oxidant be in an amount of 6 ¦ from about 130% to 150% of the theoretical amount required for 7 ¦ substantially total manganese removal as gamma-manganese dioxide,

8 ¦ and it is preferable that the oxidant be in an amount o~ between

9 ¦ about 130% and 140%.
lO ¦ The temperature of the oxidation reaction can be carriec 11 ¦ out at temperatures ranging from about 90C. to boiling. In 12 ¦ actual plant practice, it would be advisable to keep the temper-13 ¦ ature below boiling.
14 ¦ The reaction times can be as little as about 30 minutes 15 ¦ and preferably about two hours.
16 ¦ The oxidation is preferably carried out at atmospheric ¦ pressure, thus eliminating the need for pressure equipment, such ].8 as autoclaves, although, if desired, pressures at higher than atmospheric can be used. -Lastly, there is the question of hydrogen ion concen-tration of the solution. A wide range of pH is suitable, but 2 it is preferred that the pH be kept within the range of about 23 5 to 12. It has been found that solutions which are highly acidic 24 tend to break down oxidants of the persulfate type and that, consequently, more oxidant must be used to overcome this loss 26 in order to obtain maximum manganese precipitation.
27 ~ithin the parameters discussed above, it will be evi-~ dent that factors such as amount of oxidant, the reaction time, reaction temperature, and pH of the solution can be varied to 30~ give th timum recovery desired for a particalar retal bearing , `
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1 I solution. The conditions noted above as being preferred are 2¦ those most suitable or zinc sulfate solutions, particularly 3 ¦ when the zinc is to be recovered by electrolysis and employing ¦ the "Jarosite Process" and it will be evident that, keeping the 5 ¦ instant invention in mind, it requires but routine experimentatio 6 ¦ by those skilled in this art to find the most optimum conditions ¦ within the ranges noted for the removal of manganese from solu-8 ¦ tions containing other metals such as copper, nickel, cadmium, 9 ¦ and the like.

10 ¦ Reference has been made above to the "Jarosite Process".

11 ¦ This term is used herein to refer to a well-known improvement

12 ¦ in the method of recovering zinc electrolytically from roasted

13 ¦ sulfide concentrates relying on high acid leaching followed by

14 ¦ the precipitation of iron using sodium, potassium, or ammonium

15 ¦ ions prior to electrolytic recovery of the zinc~ A more detailed

16 description appears in the United States Edition of "World ~ining'

17 of September 1972, pp. 26 to 30~

18 Referring to the single sheet of drawing, there is

19 shown a conventional electrolytic system for the recovery of zinc utilizing jarosite precipitation as well as demanganizing 21 in accordance with the instant invention. The removal of the 22 manganese minimizes electrolyte fouling, greatly increases the 23 operating time of the electrolytic cell, and keeps the cathode 24 zinc at the greatest purity~ The process described in the flow sheet is self-explanatory with respect to the overall process, 26 but, for more completeness, will be further described.
27 Zinc sulfide concentrates are conveyed to roaster feed 28 bins and then to roasters, most suitably of the fluid-bed type, 29 where the concentrate lS heated at a teMperature of about 950C.
to convert the zinc sulfide in the concentrate to zinc oxide . ~ . .
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1 (calcine) and sulfur dioxide gas.
2 The zinc calcine is cooled, ground to 90%-200 mesh 3 and conveyed to leach tanks where the zinc oxide and whatever 4 zinc sulfate may be present are dissolved by the use of sulfuric acid. To effect the maximum recovery of zinc, leaching can be carried out in two or more steps: a neutral leaching at a pH o~ about 4.5 to 5 followed by separation of the liquid con-taining the zinc from the solids, and one or more stages of hot acid leach to which ammonium sulfate is added to one of the stage It is at the final phase of these leaching steps that 11 iron is precipitated as the complex compound ammonium jarosite, 12 2NH4[Fe3(SO~)2(OH)5] which is then separated together with the 13 other undissolved materials. The liquid recovered containing the 14 dissolved zinc sulfate is returned to the initial leaching step.
The solution containing the dissolved zinc from the 16 first "neutral" leaching step is purified (the copper and/or 17 cadmium present are removed by precipitation with zinc dust) 1~ and filtered and a portion of the resulting "pure" solution sub-1~ jected to demanganizing with ammonium persulfate in accordance with the present invention, as described above and as further 21 illustrated in the Examples that follow. After separation of 22 the manganese dioxide, the demanganized solution is returned 23 to the hot acid leach circuit where the contained ammonium ion 24 and sulfate radical can be utilized for jarosite formation or fo electrolysis.

26 The remaining pure solution is conveyed to electrolytic 27 cells where, by the application of direct electric current 2~ thereto, the acidified zinc sulfate solution is decomposed and 29 the metallic zinc deposited on the cathode (conventionally aluminum).

The cathode zinc is removed from the cathodel melted '. , . .
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in a furnace, such as an electric low-frequency induction ur-2 nace and cast into slabs, blocks, or ~he other forms utilized commercially.
~ The invention will be further described in connection with the following Examples which are set forth for the purpose 6 of illustration only and in which proportions are by weight 7 unless expressly sta~ed to the contrary.
EXAMPLE I
9 To 50 milliliters of an acid zinc sulfate solution lO containing 40.5g/1 Zn and 4.2i3g/1 Mn (and whose full analysis 11 is set forth in Table I belowj obtained from the leaching of 12 roasted zinc sulfide flotation concentrate with dilute sul-13 furic acid, was added approximately 5 grams of ammonium persul-14 fate and the pH adjusted to slightly acidic with ammonium 15 hydroxide.
16 The solution was boiled for approximately 30 minutes and the resultant precipitate filtered off and washed with 18 distilled water. The filtrate was analyzed for zinc by volume-19 tric titration and for manganese by atomic absorption.
The demanganized solution analyzed 35.2g/1 Zn and 21 0.0026g/1 ~In indicating a selec~ive removal of 99.94% of the manganese with only 13.1% of the zinc.
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, 7 ~ 2 1 X~MPL~ 2 2 Ammonium persulfate was added to samples of the 3 various solutions shown in Table I and agitated at 90C. to boiling for periods ranging from 15 minutes to 2 hours. The 5 arnount of ammonium persulfate added was varied according to G the necessities o manganese content, hydrogen ion concentration, 7 reaction temperature and time, and the other conditions dis-cussed above.
9 The resultant precipitate was removed in each case 10 by filtration and the filter cake washed with water. The fil-11 trate was analyzed for the various elements shown in Table II, 12 and the removal of manganese and other metals calculated.
13 As can be seen from Table II, the solutions which 14 respond to the process covered a wide variety containing 15 major amounts of manganese and metals such as zinc, copper, 16 nickel, cobalt, cadmium and iron. Solutions containing only 17 one of the metals, or several of the metals, were found to be 1~ equally susceptible to the process. -Manganese was removed selectively-from these solu-tions with only minor amounts of the other metals reporting in 21 the manganese precipitate.

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1 EXA~PLE 3 2 Samples of neutral zinc sulate solution containing 3 116.3g/1 Zn and 5.24g/1 Mn (see Table I for full analysis) were hea~ed to boiling for approximately 15 minutes with various oxidants added to the solutions in the amount of 100g/1. The 6 solutions were filtered and the filter cake washed with water 7- and the filtrate analyzed for manganese.
8 The results are shown in Table III and clearly indi-9 cate the near-complete removal of manganese in all cases.
The oxidants used were ammonium per~oxydisulfate (NH4)2S2O8, sodium peroxydisulfate (Na)2S2O8, potassium peroxy-12¦ disulfate KzS2O~ (also known as persulfates), sodium bismuthate ¦ NaBiO3, sodium bromate NaBrO3 and lead dioxide PbO2.

15¦ MANGANESE REMOVAL FROt'l NEUTRF~L ZINC SULFATE SOLUTION
I (5 ~1~;~7~L.OYING DIF~`EREN'r Oi~IDANTS
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¦ Demanganized Solution % Manganese 17l Oxidant Used g/l Mn PreciPitated I
18 ¦ Ammonium Persulfate ; 19 ¦ ( 4)2 2 8 0.0086 99.84

20 ISodium Persulfate -

21 ¦ ( )2 2 8 0.0024 99. 95 IPotassium Persulfate

22 ¦ 2 2 8 0.0095 99.82 ¦Sodium Bismuthate 24 ¦ NaBiO3 0.016 99.69 - ¦Sodium Bromate 25 ¦ NaBrO3 0.0027 99.96 Lead Dioxide ` 27 ¦ 2 0.0005 99 99 28 A series of tests in which samples of neutral zinc sulfate solution were agitated at 90Co for varying periods of 30 ~ time wit iffere~t amounts of ammoniam persulfate are ~hown `.,' :' . . ' .

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1 in Table IV. ~s before, the resultant solutions were filtered and the precipitates washed with water. In these tests, how-ever, both the iltrates and precipitates were analyzed for zinc and manganese. Thc zinc and manganese removal could, 5 th~re~ore, be calculated on the basis of the analysis of both ~ materials.
7 ~s can be seen from the results presented in Table IV, 8 manganese was precipitated from solutions when using a broad 9 range in the amount of oxidant added, iOe., from 50~ to 460%
10 of the theoretical amount needed to precipitate the manganese, 11 as manganese dioxide. The following information is pertinent 12 to each of the tests which are summarized in Table IV:
13 Test 10A
14 Zinc sulfate solution containing 5.24 g/l Mn was agita-15 ted at 90C. for 30 minutes with sufficient ammonium persulfate to 16 precipitate ~60% of the contained manganese. The pulp filtered 17 readily, but the precipitate was found to be principally manganous 18 manganite ZnO-6Mn02-2-4H2O analyzing high in zinc at 8.00~
Zn. X-ray defraction analysis shows that no gamma manganese 20 dioxide was present and only a minor amount of zinc sulfate was 21 found in the precipitate, proving that most of the zinc was chem-22 ically bonded in the manganous manganite.

23 est 11 This test was carried out as for Test 10A, but the amount of ammonium persulfate used was lowered to 230~ of the 2~ theoretical. The pulp filtered readily, but the precipitate 27 was still high in zinc at 9.~0~ Zn and consisted principally 29 of manganous manganite with a small amount of gamma manganese dioxide beginning to show. Zinc sulfate was also present, indi-30 cating that some of the zinc contained in the precipitate was ' , , -15~ '.
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1 due to inefficient washing of the filter cake.
2 Te.st 12 3 This test duplicated Test 11, except that the agitation was extended to ~0 minutes and careful washing of the filter cake was practiced. The results were as for Test 11, but the precipi-6 tate was lower in zinc at 5.60~ Zn, because of the improved filte 7 cake washing technique. Again, the precipitate was principally 8 manganous manganite with some gamma manganese dioxide present.
g Test 13 The conditions for this test paralled those used for 11 Test 12, except that the ammonium persulfate used was reduced 12 further to 130~ of the theoretical requirements for manganese 13 precipitation. The pulp filtered readily and the precipitate 1 consisted entirely of gamma manganese dioxide. No manganous manganite was detected, and the precipitate contained only 1.82%
16 Zn. Manganese removal from solution amounted to 92.65~.
17 Test 14 18 Test 13 was repeated but the reaction time was increased 19 from 60 minutes to 120 minutes. Againr the pulp filtered very readily and the precipitate consisted of gamma manganese dioxide 21 low in zinc at 1.78~ Zn and manganese removal from solution in-22 creased to 99.99%.
23 Test D-8

24 In this test zinc sulfate solution containing 3.90 g/l Mn was used and sufficient ammonium persulfate added to precip 26 itate 133% of the contained manganese. Agitation was effected 27 at 90~C. for 2 hours, and the pulp filtered very readily. The 2~ precipitate consisted principally of gamma manganese dioxide, 29 but some zinc sulfate was present because of inefficient washing.
30 No manganous mangan~te was det ct~d.

. ' i ~

!l ~Lo~OlZ2 1 Tests D-3, ~-~, D-2, D-l These tests were conducted with the same solution used :
3 for Test D-~ and sufficient ammonium persulfate to theoretically 4 precipitate l02%, 102%, ~2% and 50~ of the mangan~se present in solution, respectively. Filtration became increasingly diffi-cult as the amount oE oxidant was decreased; and at 50~ of the 7 theoretical needs, the precipitate was so fine that it passed 8 completely throu~h the filter paper.
9 Agitating the solution for a longer period of 3 hours in Test D-4 ~102% ammonium persulfate) vs. 2 hours in Test D-3, 11 did not improve the situation with respect to filterability.
12 As can be seen, the precipitates consisted mainly of gamma man-13 ganese dioxide with varying amounts of zinc sulfate which became 14 increasingly difficult to wash out as the amount of oxidant was reduced. The manganese dioxide precipitates produced in these 16 tests were very fine; whereas ~hese fine particles had bonded 17 together in the tests using ~130% of the theoretical amount of 18 ammonium persulfate, to form agglomerates, which resulted in 19 rapid and efficient filtration and allowed for efficient washing to remove zinc sulfate.
21 According to XRD data, precipitates from Test 10~ match 22 the reported patterns for birnessite. In less oxidized precipi-23 tates, i.e. Tests 11 and 12, additional lines appear in XRD pat-2~ terns at 2.12, 1.63 and 4.04A, indicating either a new crystalline

25 phase, or a modification of the manganous manganite phase. XRD

26 data suggest a progressive phase transition ~o a less hydrated

27 form of MnO2 (incipient ~MnO2). This was subsequently con-

28 firmed by the precipitation of major YMnO2 at lower oxidation

29 conditions as is summarized in Table IV.
Under conditions of lower oxidation ~i.eO, Tests 13 31 and 14) dark b~ownish-blAck precipitates are formed containing "'.`

7~22 3 ., 1 minor zinc (1~2~ Zn). X-ray diffraction patterns bear no re-2 semblance to birncssite and other manganite phases, but correlate 3 closely with those of YMnO2. Precipitates that are not thorough-4 ly washed contain detectable amounts of ZnS04.H20, which appears as a crystalline phase in dried products. This results 6 in relatively high zinc values, as in the case of Test No. 11 r Minor amounts of ZnS04.H20 were also detected by XRD in Test 8 No. lOA.
X-ray diffraction patterns of the various products lC were developed showing the phases produced at different conditionc 11 of oxidation. A tabulation of "d" spacings of Tests lOA to 14 12 is compared from the major phases in Table IVa.
13 Precipitates from Tests lOA through 14 were thereafter 14 heated for up to an hour at temperatures of 200C. and 450C.
15 in order to evaluate stability phase transformations as an aid 16 to identificationO
17 Dehydration at 200C. resulted only in the collapse 18 of the major spacing near 7.0-7.4 angstroms, apparently the result 19 of removal of interlayered water.
At 450C., decomposition takes place resulting in mix-21 tures of mostly hydrohetaerolite, HZnMn204 and rMnO2.
22 Samples containing higher amounts of structural zinc convert 23 to higher amounts of hydrohetaeriite (Test lOA), wheeeas, unwashed ZnSO~.H20 converts simply to the anhydrous ZnS04, without 25 bonding to the manganese oxide (Test ll).

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i : ~07~2;2 : 1 EX~MP~,E 5 ,........................... __ . Manganese removal from solution was found to be possible : 3 in the temperature range from ambient to boiling, as shown in ~ table V. ~t lower temperatures, however, reaction time was slow.
.. 5 ~t 90C., 2 hours reaction time and 135g of the theoretical oxi-G dant requirements, 99.99% of the manganese was precipitated from I
, 7 purified zinc sulfate solution in Test 16. At 70C., 50C., :~'''! 8 and 25C. with the same amount of oxidant and the same reaction .
9 time, in Tests 17, 18, and 19, the manganese precipitated was lO only 22.66%, 13.48~ and 8.24%, respectively. ~By extending the 11 reaction time at 25C. (ambient temperature) to 24 hours in Test : 12 20, manganese removal was increased somewhat to 14.61%.
13 TABL~ V .
..
14 MANG~NESE R~MOVAL FROM PURIFIED ZINC SULFATE SOLUTION
_ _ . . _ . _ . . ...................... _ _ (5.34 G/l Mn) AT DIFFERENT TE~1PERATURES
16. .Demanganized Manganese Test Time Temp. Solution Removed 17 No. Hours C. ~/1 mn % .
... _ ~ _ .
18 16 2 90 0.000~ 99.9 19 17 2 70 ~ 13 ~2.66 20 18 2 50 4.62 13.48 21 19 2 25 4.90 8.24 22 20 24 25 ~.56 14~61 2~ Tests carried out at 90C. with a large excess of .
25 oxidant showed that a relatively short reaction time could be 26 employed, as shown in Table IV. With 460% of the theoretical 27 amount of oxidant, 99.84~ oE the manganese could be removed 28 ~rom solution in 30 minutes, as shown in Test 10A. With 130%
29 of the theoretical amount of oxidant, however, 2 hours reaction SO time was required to effect this degree of manganese removal, ~: . , . ~ , ~ .
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1 as can be seen in Tests 13 and 14. Example 6 has shown that 2 the temperature of solution is an important factor, when con-3 sidering reaction time.
Economics, coupled with the adverse features oE con-5 tamillating the manganese precipitate with other elements, and the type and size oE precipitation equipment, would dictate the optimum reaction time in the industrial use of the process.
8 T~B~ VI
9 MANGANESE REMOV~L FROM NEUTR~L ZINC SULF~TE SOLUTION
, . ~
~ lO (5.24~1 Mn? ~ITI~ DIFFERENT REACTION TI~ES
', 11 TestTime (NH ) S 8 Demanganized ~ Manganese 12 No.Mins. % Theor.2 Solution g/l Mn Removed 13 lOA 30 130 0.0086 99.84 1~ 13 60 130 0.385 92.65 15 14 120 130 ; <0.0002 99.99 17 Solutions which are highly acidic appear to break down 18 oxidants of the persulfate type and more oxidant must be used 19 to overcome this loss for maximum manganese precipitation.
As shown in Table I, the acid zinc sulfate and 21 neutral zinc sulfate solutions contained similar amounts of 22 manganese, i.e., 4.28g/1 Mn vs. 5.24 g/l Mn, but the hydrogen ~3 ion concentration was very different as the acid solution con-2~ tained 103.6g/1 ~2SO4 vs. pH 5.3 for the neutral solution.
Both solutions were treated with 130% of the theo-26 etical amount of oxidant needed to precipitate all the manganese 27 in 2 hours at 90~C. As can be seen in Tests 14 and 21 in Table 28 II, 99.99~ of the manganese was removed from the neutral solu-29 ion, whereas only 35.51% was removed from the acid solution.

30 ~hen the amount of oxidant was increased to 400% of the theo-. - .

retical in Test 22, with the acid zinc sulfate solution, con-2 sidcrably more manganese was removed, i.e., 61.21%. .

,: . It can be concluded, therefore, that the process .
, ~ will work over a wide range of hydrogen ion concentration .. 5 in solution, but the preferred pH would be close to neutral ~ th r ou9 h alkaline, i.e., pH 5-12.

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l ~X~MPL~ 8 2 ~ test was conducted under the preferred conditions notec3 in the other Exarnples, i.e., with ammonium persulfate as o~idant -- 135~ of the theoretical amount needed to precipitate 5 the manyanese according to Reaction I -- at 90C. for 2 hours --6 using purified zinc sulfate solution with pH 5.5.
r The details of the test conditions were as follows:
8 1 liter of purified zinc solution was agitated 9 2 hours with 30 grams of ammonium persulfate at 90C. The pulp was filtered and the filter 11 cake washed to give l liter of demanganized 12 solution. The cake was repulped and refiltered 13 3 times with l liter of water. Repulping was 14 carried out by agitating for 30 minutes at 70C. The precipitate was dried at 200F.
16 overnight.
17 As can be seen from Table VIII, 99.97% of the manga-18 nese was removed from solution with only 0.16% of the zinc.
The manganese dioxide precipitate was of the gamma crystalline 20 type and analyzed 61.0% Mn and 2% Zn with all other elements 21 in very small amounts.

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Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for removal of soluble manganous ions from a zinc sulfate bearing solution containing the same compris-ing the steps of treating said solution, or a portion of said solution, with an oxidant capable of oxidizing soluble manganous ion to insoluble and filterable gamma-manyanese dioxide at a temp-erature and for a time sufficient to precipitate at least a por-tion of the manganous ion present in said solution as gamma-man-ganese dioxide, said oxidant being in an amount of from about 130% to 150% of the theoretical amount required for substantially total manganese removal from said solution, and separating said precipitate from said solution.

2. The process of claim 1 wherein the temperature is from about 90°C. to the boiling temperature of said solution, and the time is from about 30 minutes to two hours.

3. The process of claim 2 wherein the oxidant is ammon-ium persulfate, sodium persulfate, potassium persulfate, sodium bismuthate, sodium bromate, lead dioxide, or a mixture thereof.

4. The process of claim 3 wherein the zinc sulfate bear-ing solution is at a pH of from about 5 to 12, the oxidant is ammonium persulfate, the reaction time is about 2 hours, and the temperature is about 90°C.

5. The process of claim 3 wherein the manganese-free solution is returned for use in a hot acid leach circuit of an electrolytic zinc recovery process whereby the contained ammon-ium, sodium or potassium ions and sulfate ions are employed for the precipitation of iron as jarosite from an iron containing electrolytic leach solution.

6. In the process of recovering zinc from a manganese containing zinc concentrate wherein the concentrate is roasted and leached with an acid to solubilize the zinc, the resultant solution treated to remove any iron therefrom as jarosite, and then subjected to electrolysis to recover the zinc, the improve-ment comprising admixing with a portion of said solution prior to electrolysis an oxidant capable of oxidizing soluble manganous ion to insoluble and filterable gamma-manganese dioxide at a temp-erature and for a time sufficient to precipitate at least a por-tion of the manganous ion present in said solution as gamma man-ganese dioxide, said oxidant being in an amount of from about 130%
to 150% of the theoretical amount required for substantially total manganese removal from said solution, and separating said precipi-tate from said solution.

7. The process of claim 6 wherein the oxidant is ammon-ium persulfate, sodium persulfate, or potassium persulfate, the temperature is from about 90°C. to the boiling temperature of said solution, the time is about two hours, and the pH of the solution is from about 5 to 12.

8. The process of claim 7 wherein the oxidant is ammonium persulfate, in an amount of 135% of said theoretical amount, the temperature is about 90°C., the time is about two hours, and the pH is about 5.5.

9. The process of claim 7 wherein the manganese-free solution is returned for use in a hot acid leach circuit of an electrolytic zinc recovery process whereby the contained ammonium, sodium or potassium ions and sulfate ions are employed for the precipitation of iron as jarosite from an iron containing elec-trolytic leach solution.