78

DIRECT REDUCTIVE AMMONIACAL LEACHING OF LOW GRADE OXIDE ORES

ABSTRACT

S. ACHARYA S. ANAND 1

S.C. DAS 1

R.F. DAS 1

P.K. JENA 1

Oxidic ores like ocean nodules and nickeliferrous laterites contain todrokite and goethite as the major manganese and iron phases respectively. The valuable metals like Cu, Ni and Co contribute only 1-3% of these minerals and further ｾ｡､｡ｴｩｯｮ＠

ｾｹ＠ beneficiation is usually marginal. During the last decade, direct reductive ammonia leaching of these low grade ores have been reported.

The super-position ｾｦ＠ Eh-pH diagrams of Cu-, Ni-, Co-, Fe- , ｍｮＭｎｈＳＭｈ Ｒ ｯＭｳｯｾＭＬ＠ ｣ｯｾＭＬ＠ cl- systems at 25°C show that at 8,5 < pH < 10,0 and 0,4 < Eh < 0,6 V, selectively Cu, Ni and Co torm-solublP ammine complexes leaving Fe and Mn in the so.lid phase. Below this potential, Fe and Mn also form soluble ammines. This solid-solution phase relationship of Mn and Fe was exploited during leaching by using manganous ion , ferrous ion and pyrrhotite. By controlling Eh, pH, (NH3+NH4l, anions eg., ｳｯｾＭ , coj- , cl- and temperature, selectively the desired metals were extracted using FeS04, MnS04, FeS, so2 and glucose as the reductants. The effect of various pararneters during leaching and a comparison of the merits of the various reductants tested are discussed.

1 Regional Research Laboratory, Bhubaneswar, Orissa, INDIA

79

DIRECT REDUCTIVE AMMONIACALLEACHING OF LOW GRADE OXIDE ORES

S.Acharya, S. Anand, S.C. Das, R.P. Das and P.K. Jena

Regional Research Laboratory, Bhubaneswar, Orissa

INDIA

ABSTRACT

Ckidic ores like ocean nodules and nicke1iferrous 1aterites contain todrokite

and goethite as the major manganes e and iron phas es respective1y. The

va1uab1e metals 1ike Cu, Ni and Co contribute on1y 1-3% of thes e minerals

and further upgradation by beneficiation is usually marginal . During the 1ast ·

decade, direct reductive ammonia 1eaching of these 1ow grade ores have been

reported.

The super-position of Eh-pH diagrams of Cu-, Ni-, Co-, Fe-, Mn-NH -H o-so2--co2-3 2 4' 3

-Cl- systems at 25°C show that at 8.54pH ｾ＠ 10.0 and 0.4 4 Eh ｾ＠ 0 . 6V,

selective1y Cu, Ni and Co form solub1e ammine complexes leaving Fe and Mn in

the so1id phase. Be1ow this potentia1, Fe and Mn a1so form so1ub1 e ammines.

This so1id-solution phase relationship of Mn and Fe was exploited during

1eaching by using manganous ion, ferrous ion and pyrrhotite. By contro11ing + 2- 2-

Eh, pH, (NH3

+NH4

), anions eg., so4

, co3

, Cl and temperature, se1e ctive1y

the desired metals were extracted using Feso4

, MnS04

, FeS, so2

and glucose

as the reductants . The effect of various parameters during leaching anda

comparison of the merits of the various reductants tested are discussed.

l. INTRODUCTION

Cxidic ores like nickeliferrous 1ateritesland ocean nodules 2 are potentia1

sources of nickel and cobalt. ln these iron is associated as goethite, and

manganese as Mn02

and todorkite. The Cu, Ni and Co are present as

CuO, NiO, Ni3o

4, Co

2o

3 etc. which constitute about 1-3% of ore. Since these

ores have high moisture content (10-30%) and are non-amenable to ｢･ｮ･ｦｩ｣ｩ｡ｴｾ＠

ion, a hydrometallurgical route is preferred over other conventional routes

for metal extraction from these ores. One of the lixiviants commonly used

for these oxides is ammonia, which has several advantages3

1ike, (a) non­

diss.olution of iron, sílica and alkaline gangue, (b) selective dissolution

of valuable metals . For effective and rapid dissolution of Cu, Ni and Co

from such oxides, presence of a reductant is necessary2 •4- 12 Numerous

reporta are available on direct reductive ammonia leaching of ocean

nodu1es 2 •6- 12 , but probably no such attempt has been made for leaching of

nickel containing laterites.

ao

The Eh-pH diagrams 4 •5 •13- 22 of unimetal systems provide a good deal of

information regarding various solid-solution equilibria of hydrometallurgical

importance. However, for an understanding of complicated multimetal systems

it is essential to get an insight into the solid-solution relationships. The . . d d b 23-24 d . method of super-pos1t1on as a opte y Osseo-Asare to eterm1ne

approximate Eh-pH relationship in multi-metal systems, was applied in the

present work.

The present paper compares the selectivity and efficiency of various

reductants like (a) Feso4

, Mnso4

, FeS, so2

and glucos e for ocean nodules

and (b) Feso4 and so2f or Ni bearing laterites. The intermetal relationship

during leaching and the relative merits of the reductants tested have been

discussed .

2. THEORY

2 . 1 CHEMISTRY OF REDUCTIVE AMMONIA LEACHING:

The most stable species of metal elements in the natural environment during

nodule formation2 are Mno2

, Fe2o3, FeOOH,CuO, Ni

3o

4 and Co2o3 . Nickel,

Cobalt and iron of nickel laterites are present as NiO, CoO and FeOOH1

The dissolution of the various oxides associated with these ores, during red­

uctive ammonia leaching takes place through the following chemical reactions:

+ 2+ Mn0

2+ 4NH

4+2e - Mn(NH3 \ +2H20

+ 2Mn0

2+2NH

4+2e -- Mn

2o

3+2NH

3+H

2o

+ 3Mn0 2 +4NI\, +4e - Mn

3o

4+4NH

3+zH2o

+ 3Mn

2o

3+2NH

4+2e - 2Mn

3o

4+2NH

3+H

20

3FeOOH - Fe2o3+H20

+ 2+ M'

2o

3+6NH

4+(2n-6)NH

3+z -2M' (NH

3)n +3H

20

+ 3M'OOH+NH

4+e - M' 3

o4

+NH3+2H20

+ 2+ M' 3o4+8NH

4+(3n- 8)NH

3+2 e -- 3M'(NHJ)n +4H

20

2+ M'OOH+3NH4 +(n-3)NH3+e -M' (NH3) +2H2o

where M' ｾ＠ Ni, Co, Mn and Fe

+ Me0+2NH

4 +

2+ ＨｮＭＲＩｎｈｾＭ Me(NH3)n +H20

where Me = Cu, Ni, Co, Mn,Fe and Zn

+ 3+ Co2o3

+6NH4

+(2n-6)NH3 ｾ＠ Co(NH

3)n +3H

2o

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(lo)

(11)

81

Co3

o4

+8NH:+(3n-8)NH3 ｾ＠ ＲｃｯＨｎｈ Ｓ ＩｾＫＫｃｯＨｎｈ Ｓ ＩｾｴＫＴｈ Ｒ Ｐ＠ (12)

+ + Cu0+2NH4 +e - Cu(NH3 )

2 +H20 (13)

- (14)

The dissolution of oxides like MeO in ammoniacal rnediurn is general1y very

2 slow cornpared to Cu2o However, the disso1ution of oxyhydroxídes 1ike

M'OOH is cornparatively faster in presence of a reductant 2• 13 Sorne

of the reductants like Feso4

and Mnso4

directly take part in the chernical

reactions, while others 1ike so2

, FeS, glucose etc. participate directly

or indirectly (depending on the nature of interaction) in the electron

transfer steps.

2.2 SOLID-SOLUTION EQUILIBRIA

The equilibriurn Eh-pH diagrarn for metal oxides in ammonia solutions have been

·drawn by nurnerous investigators 13- 22 According to such diagrarns Fe,Mn,Cu,

and Co etc. are thermodynamically stab1e as ammine cornp1exes at a pH of

9.5 2 . This has been observed experimenta11y in several leaching

investigations 13 •25 - 27 Subsequently with the rea1isation of the importance

of the activity-activity diag4ams, to understand the stability relations invo1ving

the solids, hydroxo-, and ammine species existing in l·!P-NH3

-H2

o syste;;,s,several

diagrams have been deve1oped. So far, these diagrama are 1irnited to unimeta1

systems only. ln practice, while understanding the mu1timeta1 systerns, more

sophisticated mu1tirnetal diagrams have to be considered. ｏｳｳｾｰＭａｳ｡ｲ･ ＲＳ ＲＴ＠

has used the technique of super-position of aC"tivity-activity diagrams to under-

stand the coba1t behaviour in ammonia so1utions.

The super-position Eh-pH diagrams 20- 22 of Mn-, Fe-, Co-, Ni-, ｃｵＭｎｈ Ｓ Ｍｈ Ｒ ＰＭｓｏｾＭＬ＠2--co3 , -c 1 systems (Fig.l to Fig.n) provide sorne insight into the so1id-

so1ution equi1ibr.ia. The various co-existing species at 9.0 4 pH ' 9.5

and 2. O ::,. Eh -0.5V are 1isted in Tab1e I. At 1ower Eh va1ues, the

metal arnmine species become more predominant. However, at 1.0 ｾ＠ ｅｨｾ＠ 0.25V,

Cu, Ni and Co are in solution as ammine comp1exes22 Be1ow this potential

Fe and Mn also form ammine comp1exes 20 •21 and above Eh of l.OV the so1id phase

82

Fig. I Fig.2

ｾＧ ｲＭＭＭｲＭ ＭｲＭＢＢＢＢＧｯＺＭＭＬＭＭＮＮＮＭＭＬＭＭＮ＠I·Dr·--r-·r-o-····,-r·- , ... - ,

-- ... ｾ＠ ·---Hl ｾＭ ＭＭＭ ＭＭｾＭＭＭＭｾＭＭＭ ｾｾ＠

H ]O F• (I(JH

f/ol l IA

n l ｉｉｾｃｃｖｴｬ＠ t'' !1•1 te!

(A

ＭＭｾ＠ . . : ｾｾｾｾｾＭＭ ...L z. ; I ｾ＠ j ｾ＠ ｾＭ Ｍｾ＠ H,

Hn111! j , HM@fi,; : . I 1

ｊｴｴ ｾ ｓｑＧ＠ lbJ I .

- .. SI

ｾｾﾷ＠

-J.S' I I 1!11 t I I :::r:===- I I 61 1 , IDII111JI4

p/1

Fig.3

ｾｯｲＭＭＬｾｾＭＭｾＭＭＬＭＭＭｲＭＭＬＭＭｾＭＭﾷ＠

' ' ｾ ＭＭｪＭＭ ... ｾＭ'

ｳｾ＠ , F. so;:

., ..

ｾ ｾ ＭＭＭＭｾＭＭＭＮｯ ｾｾ＠

HzD FI IDH'J

,, ＭｾｳＬ＠ 1 1 ' ｾ＠ 1

11 Ｑ ｾ＠ ｾｾ＠ A

pH

FtiOH)J

-15

1 1 I , 10 11 11 IJ " pH

Fig.4

c.

ｾｈ＠ __J I 1 ' I I • n U

ｾｾｾ＠

Fig.l Eh-pH diagrama at 25°C : Super- position of ayatems ; (s) Mn-Hf• (.MnJ e 10_\ .

(b) Mn-NH3-a

2o-so!·· ÍMn} • 10-

4M; ( N} • 1.{); ! ｳｯＡｊｾＱＰＭ ; (c) Mn-NH

3- a 2o

2- { l . -4 { t 2- -2 -co

3, 1. Mn.J • lO , ｬｎｾ＠ • l.O, { co

3 i • lO .

Fig.2 Equi1ibrium Eh-pH diagram ·a t 25°C; ( a ) Fe-H20, (Fe} • 10-4 and

(b) Fe-NH3- a

2o, {Fe! a 10- 4 .

Fig.3 Paeudo-equilibrium Eh-pH diagrama at 25°C for aystema; (a) Fe-H20, Fe • 10-4

(b) Fe-NH3-a

2o , !Fej • 10-\ lNf • 1.0; (c) Fe-NHfH

2o-co;. (Fef • ."lo-

3;

(d) Fe- NH3- H

20-so

4, {Fe! • 10-4, {NJ• 1.0, {so

4-J • 10-z

Fig.4 Eh-pH diagrama for the systems; (a ) Co-NH3-a

2o; (b) Co-NH

3-so

4-a

2o and

(c) ｃｯＭｎｈ Ｓ Ｍ｣ｯｾ ＭＭ｡ Ｒ ｯ＠ at 25°C; Ａ｣ｯｾ＠ • 0.01M, {NJ • 5.0 { so!f · ｬＮｯＬ ｻ｣ ｯｾＭＡﾷ＠ 1.0.

Fig.5

Fig.6

Fig.7

. Fig.8

83

1.0

1.0

> . .r::

0.0 UJ

10 14 ·2.0 o

Fig. 7

2 & 8 lO 12 pH

Fig.6

·--_L . _L -

2 4 6 8 lO

pH

Fig.8

Red..clonl> • ｾ･ｾ＠

" MnSO• ＨｬＧｬｈ ＮＬｾ＠

20 -40

% Mn htrod\on

... ----.....

12

Eh-pH diagrama for the Ni-NH3-u2o system at 25°C { Nij = 0.1 , 1N! • 5.0.

Eh- pH diagram for the Cu-NH3-u2o system at 25°C . { Cu! • 0.1 , fNf • 5.0.

Super-position of Mn- , Fe-, Co-, Ni-, Cu-, NH3-so!-- R

20 systems at 25°C;

ｻｍｮｾ＠ = ｬｆ ･ ｾ＠ • 10-4 • \cof • 0.01, fNi i = {cui • 0.1, \Nf • s.o,{so!-j- 10-2 .

Co-Mn dependence during ammoni a leaching of ocean nodules .

"'

84

Table 1: Equilibrium Solid-Solution Predominant Species of Mn, Fe,Co,Ni and

Cu at 25°C and pH of 9.0 to 9.5 Obtained from Superposition Eh-pH

Diagrams.

Eh,V Selectivity Predominant Species

Mn · Fe C o Ni Cu

* * * 2+ 2.00 Mn,Cu Mn0

4 FeOOH Coo

2 Ni0

2 Cu(NH

3)4

3+ Nio

2 2+

l. 25 Mn,Co,Cu ｍｮｏｾ＠ FeOOH ｃｯＨｎｈ Ｓ ＩｾＫ＠ Cu(NH3

)4

1.00 Co,Cu MnOZ FeOOH Co(NH3

)6 Ni02

Cu(NH )2+ 3 4

* o. 75 Co,Ni,Cu . Mn02

FeOOH 3+

Co(NH3

)6

. 2+ 2+ N1(NH

3)6

Cu(NH3

) 4 * 0.35 Co,Ni,Cu Mn

2o

3 FeOOH

3+ Co(NH3),

. 2+ 2+ B1(NH

3)6

Cu(NH3

)4

* 0.25 Co,Ni,Cu Mn3

o4

FeOOH 2+

Co(NH3

)6

. 2+ 2+ N1(NH

3)6

Cu(NH3

) 4

0.00 Mn,Co,Ni,Cu 2+

Mn(NH3

)4

FeOOH 2+

Co(NH3

)6

. 2+ + N1(NH

3)6

Cu(NH3

)2

-0.5 Mn,Fe,Co,Ni,Cu 2+ 2+

Mn(NH3

)4

Fe(NH3

)4

2+ C o (NH3>, . 2+ +

N1(NH3

)6

Cu(NH3

)2

* *Solid phase species; In carbonate medium Mnco3

ｰｲ ･ ､ ｯ ｭｩｮ｡ｾ･ｳ＠ over Mn(II)arnrnine

d Ni becomes more predominant22 Thus, the Eh range of 0.75 to 0.25V is

ideal to keep selectively Cu, Ni and Co in solution (Fig.7). However, in . 1' . ( )2+ carbonate med1um the so 1d Mnco

3 predom1nates over Mn NH

3 4 , hence the

selectivity potential range extends well upto zero volts.

3. EXPERIMENTAL

The Indian Ocean manganese nodule samples were provided by National Institute

of Oceanography, Goa, India. The nickel bearing laterite samples were

obtained from the Sukinda region, Orissa, India. These were crushed, ground

and screened to obtain various sieve fractions. The chemical composition

of the nodules and laterite samples (as received) used for this study are

given in Table II. Feso4

. 7H2o., Mnso

4.5H

2o and glucose were of BDH(Analar)

and dilute H2so

3 (5-6% so

2) were of E.Merck, India make. Other chemicals

used were of reagent grade. Leaching experimenta using glucose and Feso4

for ocean nodules were carried out in a glass set-up27 and all other experi­

ments were carried out. in a Parr autoclave28

. The details of the experimenta

are described elsewhere27

•28

. In all the experimenta samples were collected

at intervals followed by filtration and ｡ｾｩ､ｩｦｩ｣｡ｴｩｯｮＮ＠ After proper dilut­

ions, the samples were analysed for the metal recovery by AAS. The pH values

were recorlded using prestandardised digital pH-meters.

85

Table II: Chemical analysis of ocean nodules and nickel laterite

samples (Basis: as received).

Sample % Moisture %Mn %Fe %C o %Ni %Cu

Ck:ean nodules

Sample I 25 13.0 10.5 0.120 0.56 0.34

Sample II 25 13.0 10.0 0.112 0.64 0.64

Laterite

Ore 12.5 0.66 48.3 0.030 1.12

Roasted ore* o 0.75 55.2 0.034 1. 28

*The ore was roasted at 300°C for l hour

4. RESULTS

4 . 1 FeS04

AS THE REDUCTANT

2+ Ferrous ion ･ｾｩｳｴｳ＠ as soluble ammine, Fe(NH

3)n' (n=l,2,3,4) in ammoniacal

Solutl.ons 21 and 1't d M (IV) 'd M O 0 d M (NH ) 2+ can re uce n ox1 es to n

2 3, Mn

3 4 an n . 3 n'

This probably breaks the nodule matrix, releases Cu, Ni and Co oxides· which

are subsequently reduced to form ammine complexes 8 • 29 During this process

of reductive leaching ferrous •Íon undergoes oxidation as given below:

(15)

(16)

( 17)

These reactions depend mainly on the pH of the medium20

•21

, amount of

Feso4

and teroperature. Accordingly these variables are chosen for optimisation

of leaching conditions.

4 . 1.1. Leaching of ocean nodules 29 . The analysis of the nodule (sample I)

used in this study is given in Table II and results of the leaching experi­

menta (Table III) are suromarised as follows:

(a) by increasing the leaching temperature (30 to 65°C), the extraction of

Cu,Ni,Co and Mn incresse;

(b) when Feso4

used was 1.4 times stoichiometric, all the Cu,Ni,Co and 33%

of Mn dissolved within ten minutes;

86

(c) when the pH of the lixiviant was varied from 9.7 to 11.0 (with ｎｈ Ｓ Ｋｎｈｾ＠5.85M), a maximum recovery of Cu, Ni and Co was achieved at pH of 10.0.

Table III. Results of Ammonia Leaching of Ocean Nodules Using Ferrous Sulp-

hate as the Reductant.

+ pH

(NH3

+NH7) Temp. Stoichio Time % Extraction

(in Mol 1) oC rnetry* (rnin.) Cu Ni C o Mn

10.0 5.85 30 1.40 10 58 54 54 11

10 .0 5.85 65 O.Sn 30 73 51 20

10.0 5.85 65 l. 20 30 97 80 80 14

9. 7 5.85 65 l. 40 10 80 73 74 31

10.0 5.85 65 1.40 10 100 100 100 33

11.0 5 .8 5 65 1.40 10 69 77 69 11

10.2 S. 70 65 l. 40 10 72 77 65 6

10.5 5.55 65 1.40 10 61 76 47 3

*Stoichiometry = Feso4

. 7H20 required to reduce Mn(IV) to Mn(II) of the

nodule (wr/wt).

ｾＱ Ｎ ＲＮ＠ Leaching of laterites: The analysis of the raw ore and r oast ed ore

are given in Table II. The results of reductive amrnonia leaching are given

in Table IV. The % extraction of nickel

total ammonia and the reductant.

increases with the incre as e of

Table IV. Results of Amrnonia Leaching of Nickel Late rite Using Ferrous

Sulphate as the Reductant. Time= 150 min. Temp. = 60°C.

a)

b)

pH

Raw ore

9.87

9.85

9.72

9. 82

9.78

NH3

(Mol)

10

20

50

10

75

Roasted ore

9. 72 50

+ NH

4 (Mol)

10

20

50

10

75

50

FeSO 4

. 7H20

Laterite (g/g)

o .lO

0.20

0.20

0.20

0.30

0.25

Ni

43

56

82

41

85

76

% Extraction

C o Mn

100 100

100 100

100 100

100 100

100 100

100 100

4.2. Mnso4

AS THE REDUCTANT: . . ( ) . 2+ + ( ) 2+ ( ) ln amrnon1acal rned1um Mn II ex1sts as Mn , MnOH , Mn NH3 n n=l,2,3,4 and

( ) . h f 1 420 2- 1- 2- . . .. Mn OH 2

1n t e pH range o to 1 ln so4

, C and co3

med1a 1n add1t1on

to the above species Mnso4

, MnC1!-n (n-1,2,3,4) and Mnco3

respective1y a1so

. 20 ex1st The reducing power

> 2+ 2+

Mn(NH3

) ;t Mn(NH3

)3

>

87

of these species have the 2+

Mn(NH3

) 2

,- MnC03

>

28 order of Mn(OH)

2 2+ + Mn(NH

3) > MnOH

> MnC1 2-n n

All the Mn(II) 2+

Mn species can reduce Mn02

to Mn2

o3

and to Mn 3o4 in ammoniacal media. Below pH of 8.5, Mn2o

3 is stable but above

pH of 8.5 both Mn2o

3 and Mn

3o

4 can co-exist depending on . the Eh 28 . So the

reduction products of Mno2

are not only Mn(II) concentration and Eh dependent

but also strongly pH dependent 28

The results of the leaching of ocean nodules (samples II of Table .II)by manganous

ion are given in Table V, and the following observations are made : (a) Though

the Cu and Ni extractions were ,.90% even at low Mn (II) concentrations, but

cobalt extraction did not exceed 90% even when the Mn(II) concentration was

five times stoichiometric. (b) when Mn(II) concentration was less than two

stoichiometry, the amount of Mn in the leach solution was negligible. Selectively

only about 50% of the cobalt could be leached without dissolution of Fe and Mn

(c) Though in the initial period of leaching, dissolution of a few ppm of Fe

took place but at the end there was no iron in the leach liquor. This is 2+

probably due to the dissolution of FeO and Fe3

o4

producing Fe(NH3

)n species

which are subsequently oxidised and precipitated.

4.3 SULPHITE AS THE REDUCTANT:

The oxidation products of sulphites are dithionate and sulphate which depend

strongly on the pH and the oxidation potential of the oxidant30 . Mn0 2 can 2-

oxidise the sulphite to ＵＲＰｾ＠ 2- 31,32

2-,, and so

4 With the increase of pH,

ＵＲＰｾ＠ becomes the predominant ｾｸｩ､｡ｴｩｯｮ＠ product.

2-2S03 -

2-503 + H20

-0.02fíV (18)

(19)

4.3.1. Leaching of ocean nodules33

: The extraction of metal values from ocean

nodules (Samples II of Table II) at different leaching conditions are given

in Table VI. Some of the observations are summarised as follows (a) Maximum

of 50% of the Co could be leached selectively without extraction of Mn. Any

further attempt to incresse Co recovery leads to Mn dissolution. (b) With the

increase of initial ｓｏｾＭ concentration, the extraction of Cu, Ni and Co

increase. (c) The maximum extractions of metal values are obtained at pH +

of 9.3 with any fixed concentration of (NH3

+NH4

) < SM. (d) The extraction

of metal values incresse with the increase of temperature (40 to 100°C).

4.3 . 2. Leaching of laterites: The optimum conditions established for ocean

nodules were used for the leaching of laterite or e (Analysis in Table II).

The results presented in Table VII show that the roasted ore gives better

recovery of Ni and Co as compared to the unroasted one, which is probably due

to the conversion of the goethite phase to hematite during roasting34

Tab

1e

V &

VI:

R

esu

1ts

o

f A

mm

onia

L

each

ing

o

f oc

ean

N

od

ule

s U

sin

g M

anga

nous

S

u1

ph

ate

and

S

ulp

hit

e

as

the

Red

uct

ants

Red

uct

ant

Sto

ich

io-

(M)

a m

etry

NH

3,M

+

N

H4

,M

pH

Tab

1e

V:

Man

gano

us

Su

lph

ate

as

th

e

Red

uct

ant

o 0.1

2

0.2

4

0.3

6

o. 3

6

0.3

6

0.3

6

0.4

7

0.7

1

1.1

8

o 0.5

0.5

1.5

1.5

1.5

1.5

2.0

3.0

5.0

1.

75

1.

75

1.

75

1.

75

1.

75

2.0

0

1. 5

0

1.

75

1.

75

1.

75

1. 7

5

1. 7

5

1.

75

1.

75

l. 7

5

1. 5

0

2.0

0

1. 7

5

1.

75

1. 7

5

9.2

5

' 9

.25

9.2

5

9.2

5

9.2

5

9.3

7

9.1

2

9.2

3

9.2

3

9.2

3

Tem

p.°C

80

80

100

80

40

80

80

80

80

80

Tim

e H

rs.

4.0

4.0

1).0

4.0

8.0

4.0

4.0

4.0

4.0

4.0

a M

n(I

I)

adde

d/M

n co

nte

nt

of

the

no

du

le;

b %

of

tota

l M

n;

c n

eg

lig

ib1

e

Tab

1e

VI:

S

u1

ph

ite

as

the

Red

uct

ant

o'.z

o o

.4d

z.oo

z.

oo

0.4

0

0.4

0

0.4

0

0.4

0

0.4

0

0.4

0

0.6

0

1.0

0

0.8

0.8

0.8

0.8

0.8

0.8

1.2

2.0

2.0

0

2.0

0

1. 0

0

3.0

0

1. 0

0

3.0

0

2.0

0

3.0

0

2.0

0

2.0

0

1.0

0

3.0

0

3.0

0

1. 0

0

2.0

0

3.0

0

9.3

0

9.3

0

9.3

0

9.3

0

9.3

0

8. 7

8

9.

74

9. 3

1

9.2

9

d S

u1

ph

ite

to

dit

hio

nate

/Mn

(IV

) to

Mn

(II)

.

80

40

80

80

80

80

80

80

80

2.5

2.0

2.0

2.0

2.0

2.0

2.0

1.5

1.5

Cu 5

1)5

92

75

li2

1)3

I) I)

81

94

98

90

7l

95

1)8

91)

72

99

95

99

% E

xtr

acti

on

Ni

Co

4

45

88

72

55

1)2

1)1

83

92

94

80

li2

87

4F,

81)

52

88

88

98

2

20

1)0

58

50

48

52

75

89

90

r, o

40

80

42

75

45

75

81)

91)

b

Mn o c

o 2 r, 3 8 8 20

30

12

20

20

15

30

15

15

33

Fe

o c

o o o o o 1 2 2 o 8 10 8 8

10 8 12

15

())

())

89

Table VII: Results o f Arnmonia Leaching of Laterite using Sulphite as the

Reduc tan t. Temp . ｾ＠ 60°C; P .d . 10% (wt/wt) ; pH ｾ＠ 9.3

Sulphite ｾ＠ 0.5 M; Sulphate 0.5 M;

Laterite sample Time (Min.) % Extraction

Ni C o Mn Fe

Or e o o o 6 o 30 8 37 41

60 10 52 55 2

150 25 80 99 2

Roasted ore o o o 3 o 30 23 83 7F, o 90 50 95 88 o

120 59 99 100 o

4.4: PYRRHOTITE AS THE REDUCTANT:

Natural pyrrhotite, FeS, is easily oxidised to Fe2o

3 or jarosite in oxidative

ammonia cal conditions35

. The Fe (II) and S(II-) can be ox idi sed to Fe( I II)

and .S(VI) respective ly a.nd FeS can yield nine electrons on oxidation .

+ 2FeS+22NH3+llH

20 --. Fe

2o

3+2(NH

4)

2so

4+18NH

4+18e (20)

+ 3FeS+30NH3

+18H2

0 ｾ＠ NH4Fe

3(so

4)

2(0H)

6+ 4(NH

4)2so

4+27NH

4+27e (21)

The studies on the ocean nodules (Sample II of Table II) indi cate that the

extraction of metal values increase with the increase of t emperature and total

concentration of ammonia and ammonium s alt (Table VIII).

Table VIII: Resu1ts of Ammonia Leaching of Ocean Nodules Using Pyrrhotite

Temp. C

60

80

90

NH3

, (g71)

50

50

75

as the Re duc tant. (F eS /Nodule)

Time (Min.) Su

50 10.15 o 10

60 45

120 64

270 85

50 10. 15 75 48

135 59

H> 5 76

50 10. 33 45 31

120 63

180 74

0.15 (wt/wt).

% Extraction Ni C o Mn Fe

2 2 5

42 25 10 2

46 52 8 3

73 76 lO 4

31 35 8 5

56 56 12 4

73 67 12 5

23 28 15 5

56 61 12 6

69 72 8 2

90

4.5 GLUCOSE AS THE REDUCTANT27

:

Glucose can be oxidised to gluconic acid by mild oxidants like oxide minerais.

R-CHO+H20 -+ R-COOH+2H +2e where R=C

5H

11o

5 (22)

Some of the resulta obtained under various leaching conditions using ocean

nodules (sample I of Table II) are presented in Table IX. The following con­

clusions were made: (a) Depending on the leaching temperature, the extraction

of Cu, Ni and Co increases with the increase of glucose concentration upto

certain levels.(upto 0.4g) and 0.2g glucose/g of nodule at 65° and 85°C res­

pectively. (b) The total (NH3

+NH:) concentration has marginal effect on

fue extraction of Cu and Ni and maximum extraction is obtained at a pH 10.

On the other hand the recovery of cobalt increases with the increase of NH3 concentration (NH: constant) upto a pH of 10.3, and also increases with increase

in NH4

Cl concentration (NH3

constant at 2.5M) upto 1.65M corresponding to

pH values of 10.3 and 9.4 respectively. (c) The recovery of Cu, Ni and Co

increases with increase in temperature upto 100°C beyond which the extractions

of Cu and Co decrease. (d) The Cl medium was found to favour higher Cu and

Ni extraction while ｃｏｾＭ medium was better for Co extraction compared to ｓｏｾＭ

Table IX: Results of the Ammonia Leaching of Ocean Nodules Using Glucose

Temp. -c NH3

· NH4 Glucose Time % Extraction

(M) (M) Nodule Hrs. Cu Ni C o (g/g)

65 2.5 0.37a o 2 68 1.2 o 65 2.5 0.37

8 0.2 2 65 56 35

65 2.5 0.378

0.8 2 78 70 40

85 2. 5 0.37a 0.2 2 100 69 60

85 2.5 0.37a 0.3 2 90 66 53

65 2.5 0.37 8 O.li 2 76 fiO 20

65 2.5 l.li58

O.li 2 68 48 42

li5 1. 25 0.37a 0.6 2 42 28 15

65 5.00 0.37a 0.6 2 57 54 32

65 2.5 0.37a 0.6 2 90 72 35

65 2.5 0.37b 0.6 2 49 29 25

6) 2.5 0.37c 0.6 2 57 50 56

65 2.5 0.37a 0.2 1 52 33 18

100 2.5 0.37a 0.2 1 79 81i 42

160 2.5 0.37a 0.2 1 72 100 18

a,b and c are chloride, ｾｵｬｰｨ｡ｴ･＠ and carbonate salts respectively.

Mn

o 3

21

4

o o 2

o o o 2

6

10

91

5. DISCUSSION:

The resulta show almost half the cobalt value in the nodule could be leached

with al l the reductants without any significant dissolution of Mn.(Fig.8).

The rest of the cobalt could be leached only with 30-40% dissolution of Mn.

This observation is partly in agreement with the selectivity and Co-Mn asso­

ciation during acid leaching2

•36

This indicates that about half the cobalt

is associated strongly with Mn in the Mno 2 lattice. However, a reductant

is necessary to dissolve Cu, Ni and Co values in the ammoniacal media unlike

that of acid media where Cu, Ni and 50% of Co dissolve without the use of

any reductant2 •36 •37

Both laterite and nodules contain the valuable metals as oxides but in nodule

the major matrix consist of Fe and Mn oxides 2 while in the former the major

matrix is goe thite 1 (Mn O. 7%). The studies sho.wed that it is not e ssential

t o reduc e the Fe(III) of laterite for Ni and Co extractions whereas in case

of nod ul e Mn ( IV) must be r educed to a lowe r oxidation state for good Co

recovery which justifies the high requirement of reductants for nodule .

However , the liberation behaviour of Ni and Co2 were found to be similar in

both the cases wher e Co is liberated faster as compared to Ni when Feso4

or so2

were used as the reductants .

Table X: Comparison of Ammonia Leaching of Ocean Nodui e s and Laterite Using

Various Reductants.

+ Reductant ＨｎｈｾＫｎｈ Ｔ Ｉ＠ ,pH Time % Extraction

Or e ( ) (Min.) Cu Ni C o Mn (gm/gm)

Nodule Leaching

FeSO 4

. 7H20 (1. 64) 5.85 9. 70 lO a 81 73 74 31

MnS04

.5H20 ( 1. 14) 3.50 9. 25 360b 75 72 71 4

Mnso4

.5H20(2.84) 3.50 9.25 360b 95 93 90 31

so2

(0.40) 4.00 9.74 120c 100 88 75 15

Glucose (0 . 20) 2.87 lO. 01 120d 100 69 60

Glucose (0.60) 2.87 lO .01 l20a 90 72 35 o

Pyrrhotite(O.l5) 3.70 lO .15 165c 76 73 67 12

Laterite Leaching

Fe so4

. 7H20(0.20) 3.70 9.80 150b 85 lO O 100

so2

(O. 16) 4.00 9.33 150b 25 80 100

so2

(0.16)* 4.00 9.33 l50b 68 100 98

a,b,c, and d respectively at 65°,60°,80° and 85°C;

*Roasted laterite ore.

92

The comparison of the optimum results of direct redcutive ammonia leaching

of ocean nodules and laterites (Table X) indicate that the reactivity of the

reductants are in the arder of Feso4 > Glucose > FeS > so2

> Mnso4

for nodules and Feso4

> so2

for nickel laterites. Out ·of all the reductants

tested Feso4

reacts very fast with the nodule, FeS is very efficient in terms

of stoich"iometric requirement and Mnso4

leaches selectively Cu, Ni and Co.

These observations are further substantiated by the followinm facts derived

from comparison of th" ,.u-pH diagrama (Fig._.l to 6) on solid-solution equili-

bria (Fig.7 and Table I): (a) The manganous ammine is comparable to that of

C (NH )+ (b) Ferrous ammine is the most powerful reductant (c) The oxid-u 3 2

2- 2- 2-ation potentials of 2so

3 /S

2o

3 and FeS/Fe

2o

3, 2so

4 are lower than that

+ 2+ of Cu(NH

3)2

, 2NH3

/Cu(NH3

)4

6. CONCLUSIONS:

1. Direct r eductiv· ammonia l eaching has several advantages not only over

the pyrometallurgical / pyro hydrometallurgical routes but also over the acid

leaching.

2 . Almost all Cu and Ni and half of th e cobalt values of the ocean nodules

could be r ecove r e d selectively, To recover the rest of the Co values about

30-40% of Mn has to be dissolve d. The behaviour of Co and Ni dissolution

are similar for nodules and laterites.

3. The arder of reactivity of the various reductants tested

giucose ) FeS > 2-503 > Mnso4 for nodules and Feso

4 >

are FeSO 4

>

2-so3 for ni cke l

laterites on both experimental and theorectical grounds. However, the final

choice of the reductant would depend on various other factors like cost and

availability.

ACKNOWLEDGEMENTS:

The authors are thankful to the National lnstitute of Oceanography for

providing the nodule samples and to the Orissa Mining Corporation for the

laterite samples. The authors are grateful to the Director, Regional Research

Laboratory, Bhubaneswar for his permission to present this paper.

93

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94

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