AN HYDROMETALLURGICAL PROCESS FOH HEC OV l: IUf\iC ,\lANGAN ESE
FROM A WAD TYPE ORE
Carla Abbruzzes e
16 INTRODUCTION
Before 1950 nearly all manganese ore processing plants
c onsisted solely of crushing and screening facilities.
However, since the high-grade depos its have been worked out
it has bec ome ne ce ssa ry to concentrate lean ores by
more
compl e x fl ow-she e t which may in c lude f lotation, heavy -med ia
separation and magnetic separati on . But many manganese ores
are difficult to treat by convent ional metho d s and roasting
under reducing conditions r e quir es large amounts of energy.
Hydrometallurgical process es pe rmit manganese dioxide ores
to be treated without any preliminary preparation, apart
from crushing and grin di ng, while producing a relatively
conc e ntrat erl solut i o n o f ma n g anes e sulphate wh ich can be
pu ri f ied without difficulty.
The r es ea rch r e por ted here was designed to ma ke a systematic
s tudy of manganese r ecovery from a low-grad e ore by means
of a hydrometallurgical process . The ore in question cannot
be concentrated by conventional me tho d s, so it was treated
by leaching with sulphuric acid in the
of
ｰｲ･ｳｐＢｾ＠
some
reduc ing agents
(Feso ,Na so ).
4
2 3
The most appropriate technique of purification to obtain
an electrolyte suitable for the production of metallic
manganese has also rec e ived attention.
CHARACTEHIZATION OF THE ORE
The manganese deposits of north e rn Lati1m occ ur mainly
｡ｾ＠
unevenly spaced beds or lenses of Mno
.L n pumice and tuf3
2
gangue. Two types of orebod ies with dif :' erent man ganese
grades are found. In one type
ore) the oxides of
ＨｬｯｷＭｧｲ｡､ｾ＠
manganese (5-10 % Mn) are associated
ｷｨｯ
ｾ ｬｹ＠
with pyroclistic
materials. In the other type (high-gradc ore) the minr:rals
of manganese (20-40% Mn) are disposed in a s e quence cf clay
593
a n d d iatomac e ous oarth laycrs .
Th e studies have b c en co n cer n ed with th e low- g rad e ore
which has th e appearancc of a blackish e a r thy ma t e rial(wad)
with fra g me nts o f whitish pumice . X-ray diffrac t ion
a n a lysis has r e v e aled t h e pre s e nc e o f albite a nd anorthite
with various aluminium s ilicat es , p robably originating from
we a the red basic plagioclase , associat e d with q uartz
(1).
A small amount of manganese is pres e nt in crystalline form
b irne ssi te) .
Th e fore goi ng findin gs were conf i rmed by th e rmogravimetric
a n a l ysis wh i ch r eve aled a constant weight l oss in the 100-1 000 oc range due to the gradual elimination of the water
o f h y dration
(2).
To summarize, th e results of the miner alog ical and
physico - chemical invest i gat ion indicate that th e manganese
is p resen t
in th e r aw-material as mixed hydrated oxides in
f o rm o f c oll o i da l o r sub-colloidal ge l.
This a cco u n t s for th e u n satisfactory results of previous
tests acl1 i e ved t o upgrade the ore by conve ntiona l mineral
processin g mc thod s
( flotation, magnetic separation ) .
Th e ch e mi c.l. l analys is and the particle-siz e distribution
o f the mampnese ore , ground to minus 3 mm, are shown in
Tab l e 1 .
ACID LEAC HING OF TIIE MANGANESE
Th e o r e
(2 50 g) was leache d in mechanically-stirred glass
r e a c t i o n v e s s els imme r s ed in a thermostatically-controll ed
wa t e r b a t h.
Th e v a r i a ble s s tudied to ass ess recov ery were temperature,
t ime and ac i d c oncentration . The quantity of reducing
) wa s calculated on the basis of the
( Feso , Na so
4
2 3
sto i c hiometric va lues (2). To achieve sing l e -stage l each
age nt
proc e ss,
the slurr y had t o b e d iluted to ensure a 1:4
s olid-liquid r a tio.
Pro g r e s s o f th e manganese d issolution was fo ll owed by the
594
Table 1 - Chemi c al a nd s ize composi tion of
t he man ga nese ore
Size An a l ys i s
Chemical An a lysi s
Eleme nt
We ight
1 3 . 80
Mn
Al
o
2 3
Si0 2
Fe
Na
•
We i gh t
Frac t ion
%
mm
%
1 2 . 50
+1. 65
0 .71-1.65
46 .03
0 . 5 0-0.71
3 .09
0 . 30- 0 . 50
9. 6
1 . 21
0.20-0.30
6.3
o
2 3
o
2
22. 9
29.5
ＹＮ
ｾ＠
K 0
2
CaO
5 . 30
0. 15-0. 20
4. 3
o. 18
0. 075 - 0 .1 5
6.8
ZnO
0.0 3
NiO
o. 01
H20 +
6 .34
-
0.075
11 . 4
Feed
100 .0
measureme nt o f the redox po t ent i al of the leach i ng system
by means o f a combined p l a ti num- calome l electrode connected
t o a pH- meter
( 2) .
At the end of each test the so l id residue and the l each
l i quor , separated by fi l trat i on , were ana l ysed for Mn by
a t omic a b s or pti on s pectrophotome t r y ( 3) .
A p r el i minary ser i es of leach tests run at 25 ° C i n dicated
that after two hours there is li tt l e apprec i ab l e increase
in ma nga nese re cove ry, as it i s ev id ent fr om F i g. 1.
This fact was also con f i rmed by the trend o f the redox
poten ti a l s , as repor t ed i n a previous work ( 2) .
As ma tt er of f act , the pote nti al whi ch :;ta rt s fro m a val ue
c l ose to t hat of the Fe( III )/Fe( II )
ｨ｡ｬ
ｾ Ｍ｣ｯｵｰ
ｬ ･
Ｌ＠
i .e. 0.77
Vo l t , t ends towards the t heoret i ca l lim:.t value of abouc
0 . 90 Volt wh en t h e react i o n is pra cti ca:.ly c omple te.
595
Lcac hin g wi th fct-rous sa l t s
Dissoluti on o f Mn0
in an aci d soiu tion conta inin cr fer rous
2
i ons proccc cls ac cordin'f Lo thc fo llowing rcac tion (4)
ｾＱ
ｮＰ
+ 2Fc
Ｒ＠
'l'wo othc r
2+
+ 4Il
+
2Mn 2 + + 2Fe 3 + + 211 O
2
( 1 ]
r caction s invo lvin q oxida tion of fcr rou s ion a nd
hydroly s i s of fe rric ion als o occ ur at th c s arne time :
4f'c
2Fc J+ + 3 11 0
i s evidc nt fro m thc experimenta l
tests that re acti on
the eff cct o f
[ 1
J
2 ]
+ 2 11 0
2
Fe O + 611+
2 3
2
lt
3+
[ 3 ]
rcs ults o f
th c
leaching
is pract ically complete and tha t
tcmpcra turc in crcasc is minim a l.
ll igh rccovcrics , around 90 % Mn , ar e ach icved rapidl y d u r ing
th e fi rst thi rt.y minu tes of rcactio n, while only a sl i qh t
incr ease
､Ｚ Ｎｾｲ
thc scc ond l eac h hour occurs.
ｩｮｱ＠
Thc in fl u c :ic c of tempera ture a nd a cidi ty on the man ga n e se
ore dis sol ucion with fe rrous i o ns are illustrated in f'iq .2.
'I'he sulph u nc aci d conc entrati on in th e
exert s on l y
ｾ＠
l l mit c d e ffcct.
50- 2 00 g/L ra n ge
Ev e n at r oom t e mperature
rc co veri e s cxccc0 in u 90% Mn ar e o btaincd.
llowcv ec , d lliqiwr h cil tpcratur c fa vours th e ox idation and thc
hydro 1ys i s
rcac Lion. 'i 'he forme r
fc r rous j on act i vity , wll il e
lcad s
to a de crea se in
th c lattcr r cs ults in the
o on t h e
2 3
laycr can b l oc k the active
fo rma t .ion of a q c l atino us film of hyd rat ecl Fe
surfa cc of thc min era l. 'l'hi s
s itc s o[ rcdc tion.
ln Lh e d b sc ncc of ferric i on h y dro l ys i s , acid it y pl ay o nly
a s li q ll t
i n f lucn c c on t h e d i sso lution ra t e of mangan csc .
Ncvcr t h el c ss , t. hc cssc nti .11
dcrnon strat.c ,: Ll'/
than
r,o
p robl c ms
q/L ,
ｴＺｨ
l owc r
i. Jt t h c
｣ｾ＠
fac t
role of th e sulph uric acid ic-;
tll :lt. at c oncen tratio ns o f
less
r ccov cri cs occ ur, whil c the rc ;u c
Li. l t r at ion c, f t h c
59 (
ｲｮ ｯｲ
ｬ ｾ ｣ﾷＺｬ＠
leac h residuc r c tJr cs e ntcd
by hydrates and basic salts of iron:
MnS0
4
+ Fe(OH)
3
+ Fe(OH)S0
4
Leaching with sulphites
Mang a nese dioxid e dissolves readily in acid sulphite
solution ( 5 ):
I 4 l
AG2 98 = -51 . 5 Kcal/mo l e has be e n
cal cul ated for the reaction ( 4 1 at 25"C . Thi s figure is
A value of free energy
mor e than twice thc va lue ca lcul atcc1 fo r the r eact ion
bctween Mn0 and Pc 2 + which , howcvcr , rcsults in high er
2
man ga nese rec ovcry ( 2) . The rcas on is pr obably to be found
in the concurr ent d ithionatc form at ion r eac tion, which
consumes twice th e number of
so 2
moles:
In sulphitc leaching, an increa sc in a c i di ty of s olution
pr oduce s an appr cciab le incre as e in ma ngancse r e cov er y .
Increas e in temperat ure from 25 " C to SO " C has a pos it ive
in f luence on Mn dissolution, but at h i gher tempera tur e a
sharp decrease in rec ovc ry is notcd (F ig . 3 ).
so conce ntration is rai scd
2 4
from 50 q/L to 200 q/L and whcn tcmpcr;: turc is inc reascd
Th e rise in recoveries when 11
to SO" C can bc cxplained by a r cduc tior in thc st:abilit)
of the dithionatc i o n (6). The sharp f Bll in man qa nes e
re cove ry at 70 " C , instead, is attributabl e to the big drop
in the
so 2
shift of ｓＰ
solubility in the so lution, with a co nsequrnt
Ｒ
Ｈｧ｡ｳＩｾｓＰ
Ｒ
Ｈ｡ｱＩ＠
0quilibrium t :) lhe left.
'l' .Ü S
pr oduc es a decrease in availability of re ducing specces .
597
RECOVERY OF MANGANESE
S ince t he man gane s e i s almos t c omp le t ely d issolved, it is
possible to consider successive t r ea tme nt of th e a cidic
solution for the productio n of the meta l.
The filte red pr eg n ant so l ut i on coming from the l eac hing
c on t ains not o n ly Mnso 4 b ut a ls o i mp u riti e s. Th e typical
composition of th c two l ea ch liquo rs , o bta ined re spe ctiv ely
f rom Feso
Table 2.
l e aching and from Na so l eaching , is sho wn in
2 3
4
Tab l e 2. Typica l compos i tion o f
manga nes e p re gna n t l ea ch l iquo rs
Ch e mi ca l Spe c i es
Mn
FeS0 4 -H so
2 4
lea ch sy stem
g/L
Na so -H so
2 3 2 4
l each sys tem
g/L
28 .5
27 . 4
Al
0.23
0 . 27
Si O..,
0 .2 8
K ,C
0 .0 3 7
o. 31
o .17
Na ,, O
0 . 06
3 .84
Zn
0.064
0.076
L
L
L
Fe
44.20
0.66
Cu
0 .0 03
0 .0 02
Ni
o. oo1
0.001
Co
0 . 0002
0 . 0002
Metals more e le c tropo si ti ve t han manganes e
(Zn,Co, Cu,Ni)
will de c r e as e th e cur re nt efficiency and will pollute t h e
c a tho d ic d eposit . The maximum l e ve ls of me tal
contaminants
tol e rated in cell f eed so lution are r eported in Table 3 {7)
Th e co mmercia ll y a ccepted methods for the purif i cation c, f
Mn so
s olution are b a sed o n t he precip ita tion o f i mpurit i c s
4
e i th e r a s me tal ; with meta llic ma n ga n es e powder or as
in solub l e su lph ide wi th ammonium sulphide
(8). Iron i s
c ur ren t l y p rec ipitated as f err ic hydroxiJe .
5 98
Table 3. Maximum concentration of
metal contaminants in Mnso solution
4
Element
Concentration
mg/L
21
15
10
5
1
Siü
2
Fe
Zn
Cu
Ni
Co
0.3
In the actual leach solutions only iron and zinc can give
some trouble. The procedure investigated consisted in the
development of a full solvent extraction operation to
eliminate both metals from the Mnso
liquor.
4
The extraction of iron by means of organo-phosphorous
compounds, as an , alternative
precipitation
route to the conventional
(CaO, Caco ) has
3
be
with a neutralizing agents
been studied since it is well known that Fe(III) can
transferred into organic phase with
coefficients
very high distribution
(9).
However at the high iron concentration present in the leach
liquor ( 40-45 g / L ) a gelatinous precipitaLe has been
observed during the extraction tests. As matter of fact,if
the aqueos iron concentration exceeds 0.1 M,pol yme rization
of the extracted species may occur becanse organic phase
approaches the saturation (10).
So the large amount of iron present in t he leach liquor
. Befor e
3
cleaning up the solution, it must be int en sely aerated to
was eliminated by precipitating the bulky Fe(OH)
oxidize the small amount of Fe(II)
The precipitation of Fe(OH)
still present.
, performed by adding CaO ur to
3
pH 5, play5also an important role in th e purification of
the solution, since most of the silica is
｣ｯｰｲ･ｩｴ｡Ｌｾ､Ｎ＠
When the solution is cooled d own to room t e mperature, Caso
precipitates too .
599
4
The extraction of zinc has be en carried out by means of
di-(2-ethylhexyl)phosphoric acid (DEHPA)
1
recently proposed
to extract zinc 1 copper and cobalt (11).
The experimental work was carried out on a Mnso
solution
4
varying the pH with ammonia at the sarne aqueous-organic
phase ratio A/0=1
The organic phase contained 20% vol.
DEHPA and 5 % vol. TBP 1 as modifier 1 dissolved in kerosene.
High recoveries of zinc are obtainedl while a small amount
of manganese is coextracted into organic phase (about 10 %
for pH = 3.0 (Fig.4).
In the system under investigation zinc is preferentially
extracted over manganese in a wide pH range. High recovery
of zinc is obtained when pH is greater than 4.0 .
Further study is then nec e ssary to set out an appropriate
scrubbing of the loaded organic phase to remove manganese.
Zinc may be stripped by contacting the extract with a
dilute acid solution (5 % H so ) 1 obtaining a purified
2 4
Mnso solution amenable to electrowinning.
4
The electrowinnina of Mnso solutions is a well known
4
process and represents the final step in the production of
the metal. The flow-sheets and the details of the
electrolvsis conditions are reported by Kuhn (12).
The proposed flow-sheet of
the hydrometallurgical process
for the manqanese recovery from a wad type ore is shown in
Fig.5.
CONCLUSIONS
The leaching tests performed have shown that manaanese can
be extracted with high recoveries (over 90 %) from an ore
that cannot be concentrated bv conventional methods owina
to its textural characteristics and the intimate relation
ship between the manganese mineral and the host rock.
Moreover 1 differences in lithological species 1 that may be
encountered in the sarne areal do not pose any feed probl en;s
where a hydrometallurgical plant is concerned.
Operating conditions are not demandinq or costly. since a
temperature of 25-50 C and an average treatment cime of
600
one hour are all that are needed.
SteelworKs pickling solutions (1-10% H2 so ,15-20 % Feso 4 )
4
could possibly be used for leaching rnanqanese ore. 'l'his
would ensure a low-cost reagent,
while reducinq the risk
of environmental pollution that miqht be caused by disposal
of the picklinq solutions.
The results obtained at laboratory scale in the purification
of Mnso
solutions have shown that solvent extraction is a
4
feasible operation for zinc, whereas iron has to be
precipitated as hydroxide. Organo-phosphorous cornpounds
are suitable also for copper, cobalt and nickel eventually
present in the leach liquor.
Though complete dependence on imports of this strategic
metal essential for steelmaking cannot be eliminated in the
short term, it is felt that there is bound interest in
exploitinq dornestic sources of manqanese.
Research work will therefore continue with the optimization
of zinc solvent extraction and with a choice of suitable
scrubbing aqents for manganese ablation frorn the extract.
ACKNOWLEDGEMENTS
The author wishes to express his gratitude to Professor G.
Rinclli for having encouraqed this res earc h. Thanks are
also expr essed to Mr. P.Fornari for his ass istance in the
experimental work.
REFERENCES
1)
P.r-1ASSACCI,P.PIGA.M.SCIOTTI. Mining and b enef iciati o n
probl e ms relat ed to the mangancse deposit in north e rn
Latium. IX World Mining Conqr es s, Istanbul 1979.
2) C.ABBRUZZESE. Est razione d e l manganese da un minerale
povero del Lazio mediante lisciviazione riducente.Boll.
Ass.Min.Subalpina.1980,12,592
3) A.M.MARABINI,M.BARBARO,B.PASSARIELLO. Det erm inati on of
manganese in ores by atomic abso roti o n spectroohotometry. I X Int.Conqress on Atomi c Spectrometry,Tokyo 1981
601
4 ) D. F.KOCH. Kinetics o f the reaction between manganese
d ioxide and ferrous i on, Aus t ral.J.Chem.,1957,10,150
5 ) A .P.HERRING,S.F.RAVI'I'Z. Rate of dissolution of Mnü
sulfurous acid,Trans.Soc.Min.Eng.,1965,3,191.
2
in
6) P.PASCAL. Nouveau Traité de Chimie Minerale,Masson,
Paris 1961.
7) F.E.BACON in C.A.HAMPEL (Ed.) ,The Encyclopedia of Electrochemistry,Reinhold,New York 1964.
8) J.J.HENN,R.C.KIRBY,L.D.NORMAN. Review of major proposed
process for recovering manganese from United States
resources.Bureau of Mines,IC 8368,1968.
9)
10)
ｃＮｆｂａｅｓＬｈｔｋｒｊｐｨｹｳ･ｭＱＹＶＰｾＸ＠
ｔＮｓａｏｊｉｮｯｲｧｎｵ｣ｬｃｨ･ｭＬＱＹＶＵｾＳ＠
11) G.M.RITCEY,B.H.LUCAS. Purification of manganese solu-
tions c o ntaining copper and zinc by liquid-liquid extraction,Can.Metall.Quart.,1971,3,223.
12) A .T.KUHN. Industrial Electrochemical Processes.Elsevier
Amsterdam 1971.
602
'<R
c'i:
ii.....
>=
a:
w
:>
o
u
w
a: 40
o
1
Fig.1 - Kinetics of manganese ore dissolution
when leaching at 25 C with acid Feso solution
4
(H So : 50 g/L)
2
4
40
• Jo·c
• 5o·c
• 1o·c
20
ｯｾＭ＠
50
100
ｾＵＰＴＬＹＯｌ＠
150
200
Fig.2 - Effect of temperature and acidity
during Feso 4 leaching of manganese ore.
603
100
80
'*c
ｳｯ＠ｾ
>
«w
6 40
u
w
• Jo·
• so·
«
20
ｯｾＭｲ＠
4
50
100
70"
150
200
ｾｓｏｱＬＹＯｌ＠
F i g . 3 - Effect o f tempera tu re a n d ac i d ity
during Na so l each i ng of mang ane s e ore.
2 3
100r--------------------,
c:
ｺｾＭ
-
1
- 80
o
ü 60
ｾ＠
)(
w 40,
20
· ＭｾＢＮＬｲ＠
..;•__.-·
o
.
2
4
pH
6
Fig . 4 - Effect of pH on the extra c t i on of Zn
and Mn from Mnso so lu t i o n using DEHPA as e x 4
tracta nt
604
1-l __ SO
Ｚｾ＠
4
FeS O
4
tfJn ore
GR INDING
S/L
SEPARAT:;: ou
LEACHING
DEHPAA
ｾ＠
+-'
'--
Ｍｾ＠
Ai r
SOLVE NT
EXTRAC TJ ON 11------..rUR IFIC ATIO----
X
Fe(OH)
STRI PP lNG
H
Zn SO
4
lvlnSO
4
2
3
so4
Solution
Fig.S - Flowsheet of the proposed process
for manganese recovering.
605