SELECTIVE DISSOLUTION AND DETERMINATION OF
SULPHIDES IN NICKEL ORES BY THE BROMINE-METHANOL
METHOD
URHO PENTTINEN, VEIKKO PALOSAARI and TUOMO SIURA
PENTTINEN, U., PALOSAARI, V. and SIURA, T. 1977: Selective
dissolution and determination of sulphides in nickel ores by the
bromine-methanol method. Bull. Geol. Soc. Finland 49 (2): 79—84.
Bromine-methanol dissolution, which is mainly used in analysis of
metallurgical specimens, has been applied to geological samples. It
has been established that a solution of bromine-methanol dissolves
sulphides and arsenides very selectively but attacks silicates and
oxides only slightly. An exception is pyrite, of which merely 7 to
8 °/o is dissolved under the conditions defined in the analytical
instructions.
Urho Penttinen, Outokumpu Co, P.O. Box 27, SF-02101 Espoo 10,
Finland.
Veikko Palosaari, Outokumpu Co, SF-83500 Outokumpu,
Finland.
Tuomo Siura, Outokumpu Co, SF-29200 Harjavalta, Finland.
Introduction
Economically, t h e most i m p o r t a n t nickelb e a r i n g m i n e r a l s in F i n l a n d a r e p e n t l a n d i t e ,
p y r r h o t i t e , m a c k i n a w i t e , millerite, g e r s d o r f fite, niccolite, v i o l a r i t e a n d b r a v o i t e . In silicates t h e a b u n d a n c e of nickel is distinctly
lower. Olivine, p y r o x e n e s , a m p h i b o l e s a n d
micas, i n c l u d i n g s e r p e n t i n e s , a r e t h e p r e d o m i n a n t silicates in this c o u n t r y in w h i c h
nickel replaces i s o m o r p h i c a l l y o t h e r metals.
T h e c o n c e n t r a t i o n of nickel in olivine is comp a r a t i v e l y high, a v e r a g i n g 1330 p p m (Häkli
1971) in F i n n i s h peridotites. P y r o x e n e s a n d
a m p h i b o l e s a r e only slightly dissolved in
acids, u n l i k e olivine a n d s e r p e n t i n e w h o s e
r e a d y dissolution a f f e c t s a n a l y t i c a l results.
In t h e e v a l u a t i o n of m a r g i n a l deposits, b u t
also in t h e c o n t e x t of some o t h e r r e s e a r c h
p r o g r a m m e s , it is of i m p o r t a n c e t h a t t h e
a b u n d a n c e of s u l p h i d e nickel r e c o v e r a b l e
t h r o u g h c o n c e n t r a t i o n processes b e p r o p e r l y
d e t e r m i n e d . T h u s it w a s essential to develop
a m e t h o d w h i c h allows t h e selective assaying
of nickel f r o m nickel ores in t h e p r e s e n c e of
d i v e r s silicate combinations.
In t h e l i t e r a t u r e , s e v e r a l selective dissolution m e t h o d s a r e r e p o r t e d dealing w i t h t h e
d e t e r m i n a t i o n of s u l p h i d e s in t h e p r e s e n c e of
silicates. M e n t i o n m a y be m a d e of t h e b r o m i -
80
Urho Penttinen,
Veikko Palosaari and Tuomo
Siura
Table 1. Nickel dissolved from olivine in brominated water leach as a function of the sulphur
content in the sample.
S °/o
Percentace of Ni dissolved from
the total Ni in olivine
4
12
20
29
26
72
89
94
p a r t i a l dissolution of silicates. T h e w a t e r
solution of s e r p e n t i n e s h o w s an a l k a l i n e r e action, a n d so t h e n i c k e l p r i m a r i l y dissolved
b y b r o m i n e m a y p r e c i p i t a t e and go u n d e tected in t h e analyses. T h e d r a w b a c k to
m e t h o d of K a t s n e l s o n is t h e v i g o r o u s r e a c t i o n
of some m i n e r a l s d u r i n g dissolution. T h e s e
u n f a v o u r a b l e e f f e c t s a r e listed in Tables 2
a n d 4. T a b l e 1 d e m o n s t r a t e s t h e dissolution
of olivine in b r o m i n a t e d w a t e r f r o m s a m p l e s
containing pyrite.
n a t e d w a t e r leach ( C z a m a n s k e a n d I n g a m e l l s
1970, H ä k l i 1971), t h e dissolution in b r o m i nated water and carbon tetrachloride (Karap e t j a n 1968), t h e use of h y d r o g e n p e r o x i d e
a n d a m m o n i u m c i t r a t e (Katsnelson a n d Osip o v a 1960), t h e h y d r o g e n p e r o x i d e a n d a s corbic acid leach (Lynch 1971) a n d c h l o r i n a t ing r o a s t (Moss et al. 1961 a n d 1967). All t h e s e
methods have certain disadvantages.
The
c h l o r i n a t i n g r o a s t is slow a n d t h u s ill-suited
to e v e r y d a y practice. I n t h e a p p l i c a t i o n s of
m e t h o d s b y C z a m a n s k e , Häkli, K a t s n e l s o n
a n d L y n c h t h e acidity of t h e solution d e p e n d s
on t h e a m o u n t of s u l p h i d e s p r e s e n t .
The
d e v e l o p m e n t of s u l p h u r i c acid in s a m p l e s
c o n t a i n i n g a b u n d a n t s u l p h i d e s m a y lead to
In o u r s e a r c h f o r a s u i t a b l e m e t h o d for t h e
selective dissolution of geological samples, w e
paid p a r t i c u l a r a t t e n t i o n to t h e b r o m i n e m e t h a n o l m e t h o d t h a t K o r a k a s (1962) u s e d
to leach sulphides, a n d K r a f t a n d F i s h e r
(1963) m e t a l l i c i r o n f r o m m e t a l l u r g i c a l p r o ducts. F i l i p p o v a et al. (1973) h a v e s t u d i e d t h e
solubility of synthesized p y r r h o t i t e , p e n t landite, h e a z l e w o o d i t e
and
millerite
in
b r o m i n e - m e t h a n o l a n d o t h e r solvents. Sen
G u p t a a n d C h o w d h u r y (1974) applied b r o m i n e - m e t h a n o l digestion to t h e d e t e r m i n a t i o n
b y A A S of s u l p h i d e nickel a n d cobalt in
c h o n d r i t i c m e t e o r i t e s in t h e p r e s e n c e of
Table 2. The dissolution of nickel in brominated water leach from ultramafic samples, and the pH
in the solution.
Ni, ppm
Sample
Serpentinite
Vuonos
Serpentinite
Vuonos
Ni tailings
Kylmäkoski mine
Peridot'ite
Kotalahti mine
Serpentinite
Hitura mine
Serpentinite
Outokumpu
Lateritic Ni ore
Larymna, Greece
Ni 2 /NiiX100
°/o S
pH
483
25
0.35
6.0
2000
2080
104
1.2
2.6
1620
1230
76
1.2
2.4
1300
15
0.13
7.1
4390
3730
1.1
3.8
508
6
1.2
0.09
7.0
181000
319
0.2
0.08
5.7
1
2
1960
1.2
85
1. total nickel; HNO3, HF and HCIO4 used. 2. nickel dissolved in brominated water.
Selective dissolution and determination of sulphides in nickel o r e s . . .
81
Table 3 Brominated water leach at constant pH. Sample 2000 mg, 2 ml bromine, 20 ml water at 70°C
pH kept constant by means of titration automatics.
Sample
Leaching
time
pH
60
60
60
60
60
60
60
60
60
60
60
60
4.0
5.0
6.0
4.0
5.0
6.0
4.0
5.0
6.0
4.0
5.0
6.0
Peridotite
Kotalahti mine
Lateritic Ni ore
Larymna, Greece
Serpentinite
Hitura mine
Serpentinite
Vuonos
dis.
coexisting m e t a l a n d silicate-oxide phases. As
f a r as w e k n o w , h o w e v e r , b r o m i n e m e t h a n o l
leach h a s n o t b e e n applied to t h e analysis of
geological samples, of w h i c h low g r a d e u l t r a m a f i c nickel m i n e r a l i s a t i o n s , in p a r t i c u l a r ,
c o n s t i t u t e a d i f f i c u l t , y e t i n t e r e s t i n g topic.
F o r m a n y nickel a n d c o p p e r m i n e r a l s of
nickel ores t h e b e h a v i o u r d u r i n g b r o m i n e m e t h a n o l t r e a t m e n t is not r e p o r t e d in l i t e r a ture.
Bromine-methanol dissolution
T h e dissolution w a s c a r r i e d out as f o l l o w s :
A d d 80 m l m e t h a n o l p.a. a n d 5 m l b r o m i n e
into a 500 e r l e n m a y e r f l a s k f i t t e d w i t h a glass
Table 4. The dissolution of serpentinite (Outokumpu) in the brominated water as a fuction
of the concentration of H2SO4.
For the brominated water leach, 5 ml water, 0.5
ml bromine and 1-n sulphuric acid were used.
After the leach, the solution was diluted to 100 ml.
mlH 2 S0 4 ,
1-n
0.5
1.0
2.5
10.0
Nidis./Nitot.
MgOdis./MgOtot.
< 1
< 1
1
16
46
1.4
1.8
2.9
5.8
14
X 100
6.6
6.5
6.2
4.4
1.7
Ni, «/o
tot.
0.028 0.13
0.014 0.13
0.006 0.13
0.069 18.1
0.030 18.1
0.010 18.1
0.15
0.22
0.092 0.22
0.047 0.22
0.14
0.20
0.072 0.20
0.053 0.20
Nidis./Nitot.
X 100
22
11
4.6
0.4
0.2
0.1
68
42
21
70
36
27
dis.
tot.
MgOdis-/
MgOtot.
X 100
0.85
0.59
0.50
0.09
0.06
0.05
4.1
0.8
1.8
0.98
2.2
0.67
28.4
28.4
28.4
1.9
1.9
1.9
35.4
35.4
35.4
35.7
35.7
35.7
3.0
2.1
1.8
4.7
3.2
2.6
12
2.3
5.1
2.7
6.2
1.9
MgO, »/o
stopper. S t i r u n t i l t h e b r o m i n e goes i n t o
solution. Cool to r o o m t e m p e r a t u r e b e f o r e
s t a r t i n g dissolution, to p r e v e n t t h e s t o p p e r
f r o m o p e n i n g d u r i n g s h a k i n g . W e i g h into
t h e e r l e n m a y e r f l a s k 1 g of s a m p l e p u l v e r i s e d
to t h e f i n e n e s s r e q u i r e d b y analysis. S h a k e
g e n t l y f o r 1 h o u r in a s h a k e r . F i l t e r in a
f u m e cupboard through a white-band filter
b y using f i l t e r p a p e r mass. W a s h r e s i d u e a n d
f i l t e r p a p e r six times w i t h m e t h a n o l .
Add
10 m l n i t r i c acid to t h e f i l t r a t e a n d e v a p o r a t e
c a r e f u l l y to dryness. A d d 1 m l conc. h y d r o chloric acid a n d e v a p o r a t e to d r y n e s s . S u b s e q u e n t l y , add 5 m l h y d r o c h l o r i c acid a n d a
little w a t e r , a n d dissolve b y a p p l y i n g heat.
Cool a n d d i l u t e to 100 m l in a v o l u m e t r i c
flask. T h e m e t a l s a r e d e t e r m i n e d b y A A S .
It is not r e c o m m e n d e d to p r e p a r e a stock of
b r o m i n e - m e t h a n o l solution, since t h e dissolving of b r o m i n e l i b e r a t e s so m u c h h e a t
t h a t t h e m i x t u r e m a y s t a r t to boil.
Leaching tests
X 100
T h e solubility of v a r i o u s m i n e r a l s w a s
tested b y s u b j e c t i n g t h e m to t h e b r o m i n e m e t h a n o l leach as d e s c r i b e d above. In a d d i tion to t h e c o m m o n n i c k e l m i n e r a l s , t h e
82
Urho Penttinen,
Veikko Palosaari and Tuomo
c o p p e r m i n e r a l s t h a t a r e u s u a l l y associated
w i t h nickel ores, as w e l l as some sulphides,
w e r e also tested. T h e m i n e r a l s w e r e : p e n t landite, (Fe, Ni) 9 S 8 , p y r r h o t i t e (christal s t r u c t u r e not d e t e r m i n e d ) , m i l l e r i t e NiS, g e r s d o r f f i t e (Ni, Co, Fe)AsS, niccolite NiAs, violarite
(Ni, Fe) 3 S 4 , chalcopyrite,
cubanite
CuFe.,S 3 , p y r i t e a r s e n o p y r i t e F e A s S a n d
s p h a l e r i t e . Most of t h e m i n e r a l s
were
extracted without separation from heavily
m i n e r a l i s e d samples. U n f o r t u n a t e l y , no suitable s a m p l e s of b r a v o i t e w e r e available. T h e
v i o l a r i t e s a m p l e c o n t a i n e d a b u n d a n t pyrite,
a n d t h e c u b a n i t e specimen chalcopyrite. In
t h e leaching test, t h e p e r c e n t a g e of m e t a l
dissolved w a s c a l c u l a t e d on t h e basis of t h e
c o n c e n t r a t i o n in t h e original sample, a n d in
r e s i d u e or solution, or both. T h e dissolution
of nickel and c o p p e r w a s s t u d i e d f r o m
v i o l a r i t e and c u b a n i t e , respectively. F o r
violarite, t h e r e s u l t s w e r e checked b y s u b m i t t i n g t h e r e s i d u e to microscopic e x a m i n ation. F u r t h e r m o r e , t h e dissolution of nickel
oxide, p r e p a r e d f r o m nickel a c e t a t e b y
Siura
roasting, w a s tested. Finally, c o m p a r a t i v e
leaching w a s p e r f o r m e d by using m e t h o d s b y
Häkli, K a t s n e l s o n a n d L y n c h , in a d d i t i o n to
t h a t of b r o m i n e - m e t h a n o l (Table 6).
The
r e s i d u e of t h e b r o m i n e - m e t h a n o l l e a c h w a s
s t u d i e d microscopically a n d it w a s n o t e d t h a t ,
a p a r t f r o m some inclusions and p y r i t e grains,
all t h e s u l p h i d e s h a d g o n e into solution.
Discussion
In t h e leach of a 1 g s a m p l e in a c c o r d a n c e
with
a n a l y t i c a l instructions,
pentlandite,
p y r r h o t i t e , millerite, niccolite, chalcopyrite,
c u b a n i t e and s p h a l e r i t e dissolved c o m p l e t e l y
in b r o m i n e - m e t h a n o l . T h e b e h a v i o u r of
pyrite, g e r s d o r f f i t e a n d a r s e n o p y r i t e , as w e l l
as nickel oxide, n o n e of w h i c h a r e r e a d i l y
soluble, a r e compiled in T a b l e 5. To b r i n g
a r s e n o p y r i t e and g e r s d o r f f i t e c o m p l e t e l y or
n e a r l y into solution t h e s a m p l e s h a d to b e
s h a k e n f o r 4 h o u r s a n d t h e a m o u n t of
g e r s d o r f f i t e r e d u c e d to 0.1—0.25 g. P y r i t e
Table 5. Leaching of minerals not readily attacked by bromine-methanol.
Weight of
sample, g
Leaching
time, h
NiO
1.0
1
Pyrite
1.0
0.5
0.25
0.125
0.25
0.125
1
1
1
1
4
4
Gersdorffite
1.0
0.5
0.25
0.25
0.125
0.125
0.125
1
1
2
4
1
2
4
1.0
0.5
1.0
0.25
0.125
1
1
4
4
4
Mineral
Arsenopyrite
Dissolve
Cu
Ni
in °/o
Co
Fe
0.1
6.8
8.1
7.1
7.5
15.1
12.8
94
95
94
71
74
84
91
78
95
94
57
58
70
80
63
88
95
66
66
77
86
86
86
88
80
87
93
102
101
Table 6. Selective leach by different methods. Legend: 1. dissolved 2. dissolved/total X 100
Concentration: Ni ppm, Mg, Fe and S °/o. For the method of Katsnelson the determinations are by AAS.
Total analysis
Bromine-methanol
Sample no.
Ni
1
2
1940 22.8
5.5 1.3
1860 96
0.24
2190 24.4
4.9 0.50 1710 78
0.54
1300 18.8
8.8 0.25
Mg
2
97
2.8
12
2010
7.8 1530
70
3.4
14
1.6
8.5
489
38
3.2
863 54
0.23
1.7 1160
72
4050 73
1.8
7.9 3420
62
1.1
1350 70
1.1
4.8 1880
2.2
1170 53
1.9
343 26
0.092 0.5
195 15
1610 13.8 10.2 1.4
967 60
0.047 0.3
5550 22.8 11.7 1.3
4410 79
Fe
S
1
Ni
1
1
Mg
Mg
Ni
2
Ni
2
Ni
1
2
2
1
<
Bromine-water
H^OO-ascorbic acid
H 3 O 2 - citrate
Mg
GO
<I>
re
p.
Mg
2
1
2
pH
104
3.3
14
2.3
to
346
16
1.1
4.5 5.5
p.
a>
17
13
1
0.42
2.2 6.3
2.1
15
1230
76
2.0
14
2.2
5.0
22
3370
61
3.8
17
4.2
0.005 0.24 20
6.9
1
o
B
1
2
3
4
5
6
7
Serpentinite
Vuonos
Serpentinite
Outokumpu
Peridotite
Kotalahti mine
Ni tailings
Kylmäkoski mine
Serpentinite
Hitura mine
Lateritic Ni ore
Laryma, Greece
Olivine
188000
1.2
5.3 0.10
278
1.1
4.8
0.1 0.039 3.3
1620
0.9 0.095 7.9 9470
5.0 0.10
8.3
5
0.4 0.092 0.3
9
3p.
•a
cr
720 30.8
5.6
4
0.6 0.006 0.02
36
0.26
0.8
3
m
CO
84
Urho Penttinen,
Veikko Palosaari and Tuomo
t u r n e d out to b e s u r p r i s i n g l y d i f f i c u l t to
dissolve. D u r i n g t h e n o r m a l leach of 1 h o u r ,
only 7 or 8 °/o of t h e m i n e r a l goes into solution. E x t e n d e d leach does not h e l p m a t e r i a l l y .
W i t h t h e m e t h o d of K a t s n e l s o n a n d Osipova,
75 to 90 °/o of t h e p y r i t e in a 1 g s a m p l e w e n t
into solution w i t h i n 2 to 4 h o u r s . In practice,
nickel oxide is insoluble in b r o m i n e - m e t h a n o l .
T h e o u t - c o m e s of d i f f e r e n t m e t h o d s a r e
compiled in T a b l e 6. T h e y s h o w t h a t , as f a r
as nickel a n a l y s e s a r e concerned, t h e r e s u l t s
given by the bromine-methanol and Lynch's
m e t h o d s a r e closest to each o t h e r . T h e m e t h o d
of K a t s n e l s o n g a v e a v e r a g e a b u n d a n c e s 25 °/o
l o w e r t h a n those o b t a i n e d b y t h e b r o m i n e m e t h a n o l m e t h o d . B r o m i n a t e d - w a t e r leach
failed in cases w h e r e p H > 6. Less m a g n e s i u m w a s dissolved in t h e b r o m i n e - m e t h a n o l
leach t h a n in t h e m e t h o d s e m p l o y e d b y
K a t s n e l s o n and L y n c h . Nevertheless, some
Siura
m a g n e s i u m w e n t into solution,
f r o m s e r p e n t i n e a n d oxides.
especially
T h e r e p e a t a b i l i t y of t h e b r o m i n e - m e t h a n o l
method was studied by submitting two
s a m p l e s to 10 leaches each. T h e r e s u l t s w e r e
as f o l l o w s :
S e r p e n t i n e f r o m V u o n o s : T h e solution
c o n t a i n e d 0.299 °/o Mg, SD = ± 0.057 c o e f f i cient of v a r i a t i o n 19.1 %> a n d 1850 p p m Ni,
SD = ± 17.4 p p m , coefficient of v a r i a t i o n
0.95 % .
S e r p e n t i n e f r o m O u t o k u m p u : T h e solution
c o n t a i n e d 0.583 % Mg, SD = ± 0.039 %>,
coefficient of v a r i a t i o n 6.69 °/o a n d 1730 p p m
Ni, SD = ± 16.7 p p m , coefficient of v a r i a t i o n
0.96 °/o.
Acknowledgement
— The authors are indebted
to the Outokumpu Company for permission to
publish this paper.
References
Czamanske, G. K. and Ingamells, C. O. (1970)
Selective chemical dissolution of sulphide minerals: A method of mineral separation. Am.
Min. 55: 2131—2134.
Filippova, N. A., Samokhvalova, L. G., Suminova,
R. I., Slavskaya, A. I. and Bogoslovskaya, E. I.
(1973). Phase analysis of nickel compounds in
the sulfiding products of oxidized nickel ores.
Ind. Lab. 39: 718—720.
Häkli, T. A. (1971) Silicate nickel and its application to the exploration of nickel ores. Bull.
Geol. Soc. Finland 43: 247—263.
Karapetjan, JE. T. (1968) Opredelenie sul'fidnogo
nikelja v sul'fidnyh rudah i kontsentratah.
Zav. Lab. 34. 939 p.
Katsnelson, E. M. and Osipova JE. JA. (1960)
Usoversenstvovannyi metod opredelenija sul'fidnogo nikelja. Obogastsenie rud, n:o 4: 24—
26.
Korakas, N. (1962) Magnetite formation during
copper matte converting. Inst. Min. Met. Trans.
72 (1): 35—53.
Kraft, G. and Fisher, J. (1963) Die Bestimmung
von metallischem, zweivertigem und dreivertigem Eisen nebeneinander in Eisenhüttenprodukten. Z. Anal. Chem. 197: 217—221.
Lynch, J. J. (1971) The determination of copper,
nickel and cobalt in rocks by atomic absorption spectrometry using a cold leach. Geochemical Exploration Spec. 11: 313—314.
Moss, A. A., Hey, M. H. and Bothwell, D. J. (1961)
Methods for the chemical analysis of meteorites. Min. Mag. 32: 802—816.
Moss, A. A., Hey, M. H., Elliot, C. J. and Eston,
A. J. (1967) Methods for the chemical analysis
of meteorites. Min. Mag. 36: 101—119.
Sen Gupta, N. R. and Chowdhury, A. N. (1974).
Determination of nickel and cobalt in chondritic meteorites by atomic absorption spectrophotometry. Z. Anal. Chem., 268. 32 p.
Manuscript received January 13, 1977