95
BEHAVIOR OF ANTIMONY AND ARSENIC IN SULFURIC ACID SOLUTION
ABSTRACT
CHOKO TEREZA ITO 1
TADAHISA NISHIMURA KASUTERU TOZAWA 1
The presence of antimony and arsenic in many mineral sulfides leads to a need to understand the way in which both species react in those processes which have been developed for extracting valuable elements from those minerals.
This paper deals セョ@ particular with the precipitation reactions of antimonious, antimonic, arsenious and arsenic species in sulfuric acid solution in relation to various hydranetàllurgical processes.
The system Sb20 (x:3,5) - As 2o (y:3,5) - so3-H2o has been investigated ッカセイ@ a wide range Óf sulfuric ac1d concentration. The solubility and stability ranges of Sb203 , Sb2o5 , As 2o3 aad compounds formed in the system have been deEermineà at 25 C. Furthermore, the behavior of antimony and arsenic in sulfuric acid solution is discussed.
1 Research Institute of Mineral Dressing and Metallurgy (SENKEN) Tohoku University Sendai, Japan
96
BEHAVIOR OF ANTIMONY AND ARSENIC IN SULFURIC ACID SOLUTION
by Choko Tereza Ito, Tadahisa Nishimura
and Kazuteru Tozawa
Research Institute of Mineral Dressing
and Metallurgy (SENKEN)
Tohoku University
Sendai, Japan
ABSTRACT
The presence of antimony and arsenic in many mineral sulfides
leads to a need to understand the way in which both species react
in tho se processes which have been developed for extracting
valuable elements from those minerals.
This paper deals in particular with the precipitation reactions
of antimonious, antimonic, arsenious and arsenic species in
sulfuric acid solution in relation to various hydrometallurgi cal
processes.
The system, Sb 2ox ( x:3, 5 ) - As 20y ( y:3, 5 ) - so 3 - H20 has
been investigated over a wide ranges of sulfuric acid concentration.
The solubility and stability ranges of Sb 2o 3 , Sb 2o 5 , As 2o 3 and
compounds formed in the system have been determined at 25°C.
Furthermore, the behavior of antimony and arsenic in sulfuric acid
solution is discussed.
INTRODUCTION
ln copper smelters in Japan, various complex sulfide concentrates
are treated. An appreciable quantity of arsenic and antimony is
accompanied in the concentrates. Control of both elements is very
important for producing high grade copper metal. Many new processes
97
for their treatment have been developed and installed in some
smelters(1),(2), but there are still many problems to be solved.
Onahama 5melter(3) has been produced pure arsenic trioxide by
vacuum-cooling the filtrate of liquor( diluted sulfuric acid satu
rated with As 2o3 ) from plant for washing converter gas. It is very
important for production of pure arsenic trioxide to determine the
solubility of arsenic trioxide in concentrated sulfuric acid and to
examine the contamination with antimony.
Recently, arsenic and antimony contents tend to increase in a
conventional electrolyte for the electrorefining of copper. The
elements form often a floating slime which lowers the quality of
electrolytic copper(4).
To clarify the behavior of antimony and arsenic in sulfuric acid
solution for solving such problems in the hydrometallurgical opera-
tions, it is necessary to know the equilibrium for the following
systems.
( 1 ) The system 5b2o 3 - 503 - H20
(2) The system sb2o 5 - 5o3 - H20
(3) The system As 2o 3 - 5o3 - H2o
(4) The system As 2o 5 - 5o3 - H20
(5) The system 8b203 - As 2o 3 - 503 - H2o
(6) The system 5b2o 3 - As 2o 5 - 503 - H2o
(7) The system 5b2o 5 - As 2o 3 - so3 - H20
(8) The system sb2o 5 - As 2o 5 - so3 - H2o
In this paper, the equilibrium for these systems is investigated.
THE EQUILIBRIUM FOR THE SY5TEM Sb(III,V) - As(III,V) - S03 - H20
1. The system Sb20J - S03 - H20
H2o is of great interest in chemical
analytical procedures and in industry of production of various
98
antimony compounds. There is several information in the literature
on the system sb2o 3 - so3 - H2o.
fates are produced by reacting
A variety of antimony(III) sul-
Sb2o 3 and H2so4. The results
reported on the chemical compositinn and solubility of these com
pounds are inconsistent and contradictory.
The equilibrium for the system sb2o 3 - so3 - H2o was examined by
shaking the mixture of antimony trioxide and sulfuric acid solution
( O - 1820 g/1 H2so4 ) at 25°C for one month. The results from
the chemical analysis of solutions and precipitates are plotted
in Figure 1 together with data by Gospodinov et al. (5) at 100°C.
Various compounds are formed in the system Sb2o 3 - so3 - H2o at
both temperatures.
Figu r e 1(a) shows that the so3 /sb2o 3 molar ratio in the precipi
tates is either 0.50, 0.66, 1.0, 2.0 or 3 . 0, indicating the
existence of the five compounds. These compounds are represented
without indicating hydration as 2Sb2o 3 -so3 , 3Sb20 3 ·2S03, Sb203 •S03,
Sb2o 3 ·2so3 and Sb2o 3 ·3S03. At 25°C, Sb2o 3 is stable as a solid in
the range of O - 20 g/1 H2so4 , 2Sb2o 3 ·so3 in 30 - 360 g/1 H2so4 ,
3Sb 2o 3 ·2S0 3 in 400- 560 g/l H2 so 4 , Sb 2o 3·so 3 in 590- 880 g/1
H2so4 , Sb20 3 ·2S03 in 950 - 1280 g/1 H2so4 and Sb20 3 ·3S03 in 1370 -
1800 g/1 H2so4. Below 800 g/1 H2so4 , the results agree well with
those obtained at roem temperature by Hintermann et al.(6).
In Figure 1(b), Sb2o 3 -so3 and sb2o 3 ·2S03 have the highest so1u
bi1ity in 880 g/1 and in 1280 g/1 H2 so 4 at 25°C, respective1y.
Furthermore, the solubility of these compounds wi11 increase with
an increase in temperature.
The data of Figure 1 are a1so shown in Figure 2 as a ternary
diagram of the system sb2o 3 - so3 - H2o at 25°C. The typica1 X-ray
diffraction patterns of their compounds are shown in Figure 3.
99
2. The system 5b2o 5 - 503 - H2o
There is very little data on the system 5b 2o 5 - 50 3 - H2o.
The experiment was carried out by shaking the mixture of antimony
pentaoxide ( amorphous ) and sulfuric acid solution ( O - 1540 g/1
H25o4 ) at 25°C for one month. X-ray diffraction confirmed the
nonexistence of antimony(V) sulfate at 25°C. Figure 4 shows that
5b 2o 5 ( amorphous) is highly soluble at 1100 g/1 H25o 4 at 25°C.
3. The system As 2o 3 - 503 - H2o
The system As 2o 3 - 503 - H2o is of importance in many hydro
metallurgical processes for separation and recovery of arsenic as
arsenic trioxide from acidic solutions.
The equilibrium for this system was examined by shaking the mix-
ture of arsenic trioxide ( cubic and sulfuric acid solution ( O -
1770 g/1 H25o4 ) at 25°C for two weeks. X-ray diffraction confirmed
the existence of As 2o 3 and As 2o 3-5o 3 as a solid between O to 1550
g/1 H2so4 and above 1340 g/1 H2so4 , respectively. X-ray diffraction
pattern of arsenic(III) sulfate, As 2o 3 -so3 , agreed with that pub
lished by JCPDS (Card File No.22-072). The concentration of arsenic
(III) in solutions are plotted in Figure 5 together with data by
Inomata et al.(7) and Zieren Company (7). The solubility of As 2o 3
decreases significant1y with an increase in concentration of su1fu-
ric acid in the range of 100 to 1080 g/1 H2so4 ,
s1ight1y in the range of 1080 to 1280 g/1 H2so 4 .
but increases
Above 1340 g/1
H2so4 in which As 2o 3 -so3 is stable,
(III) is very 1ow.
the concentration of arsenic
On the basis of the chemica1 ana1ysis of so1utions and precipi-
tates a ternary diagram of the system As 2o 3 - 503 - H2o at 25°C was
constructed as shown in Figure 6.
4. The system As 2o 5 - so3 - H2o
There is very litt1e data on the systern As 2o 5 - so 3 - H2o.
100
Menzies et al.(8) reported that arsenic pentaoxide is stable in
water as As 2o 5 ·4H2o below 20°C and as 3As2o 5 ·5H2o above 40°C.
Arsenic pentaoxide is highly soluble in water ( dissolved in water
up to 570 g/1 As(V) at 25°C )(9). It can therefore be presumed that
arsenic pentaoxide is highly soluble in sulfuric acid solution.
5. The system Sb2o 3 - As203 - S03 - H20
Very little is known about the system Sb- As- S0 3 - H20•
The equilibrium for the system Sb2o 3 - As 2o 3 - so3 - H2o was
examined by shaking the mixture of antimony trioxide(orthorhombic),
arsenic trioxide(cubic)( with Sb2o 3 /As 2o 3 molar ratio : 0.10/0.10 )
and · sulfuric acid solution ( O - 1690 g/ 1 H2 so 4 ) at 25°C for one
month.
X-ray diffraction confirmed that sb2o 3 or 2Sb2o3 -so3 and As 2o 3
monoclinic ) exist as a solid in the range of O - 450 g/1 H2so4 ,
while antimony(III) sulfates and As 2o3 (cubic) exist in the range
of 500 - 1600 g/1 H2so4 at 25°C.
The results from the 」ィ・ュゥ」セャ@ analysis of solutions and precipi-
tates are plotted in Figure 7. The stability range and solubility
of antimony(III) sulfates in sulfuric acid solution are invariable
in the presence of As 2o 3 ( monoclinic or cubic ). The solubility of
As 2o 3 lowers in the range of O - 450 g/ 1 H2 so 4 in which the crystal
form of As 2o 3 is changed from cubic to monoclinic by the presence
of Sb2o 3 or 2Sb2o 3 ·so3• But the solubility of As 2o 3 is invariable
in the range of 500 - 1600 g/1 H2so4 in which As 2o 3 (cubic)is stable
even in the presence of antimony(III) sulfates.
The results described above suggest that in the presence of large
amount of antimony(III) in sulfuric acid solution, arsenic trioxide
will be contaminated with antimony (III) because of the very low
solubility of antimony(III) sulfates.
101
6. The system Sb2o 3 - As 2o 5 - so3 - H20
1) The system sb2o 3 - As 2o 5 - H2o
The equi1ibrium for the system Sb2o 3 - As 2o 5 - H2o was examined
by shaking the mixture of antimony trioxide ( orthorhombic ) and
arsenic acid solution ( with Sb2o 3 /As 2o 5 molar ratio : 0.25/0.10 -
0.10/0.10 ) at 25°C for three months. THe results are plotted in
Figure 8 as a function of pH.
Figure 8(a) shows the existence of antimony(III) arsenate having
Sb2o 3 /As 2o 5 molar ratio of 1.0 in the pH range of 1.6 - 2.3. The
formula of the compound will be represented as SbAs04 without
hydrate by the chemical analysis and by the thermoanalysis shown
in Figure 9. The X-ray diffraction pattern of SbAs04 shown in
Figure 10 is in disagreement with that published by JCPDS ( Card
File No.1-728 ).
The solubility of SbAs04 can be characterized by the reaction
SbAs04 (s) + 2H2o = HSb02 + H3As04
The solubility product for SbAs04 is given by
( 1 )
(2)
By calculating from date of Figure 8(b), the value of Kso is
10-6•67 and the value of the standard free energy for formation of
SbAso4 is - 176.2 kcal/mol.
By using this free energy data, the equilibrium log [As(V)] - pH
diagram was calculated and i1lustrated in Figure 11. An increase in
concentration of total antimony(III) in acidic solution leads to
further stabilization of SbAso4•
2) The system sb2o 3 - As 2o 5 - so3 - H2o
The equilibrium for the system Sb2o 3 - As 2o 5 - so3 - H2o was
examined by shaking the mixture of antimony trioxide(orthorhombic),
arsenic acid solution ( with Sb2o 3 /As 2o 5 molar ratio : 0.10/0.10 )
and sulfuric acid solution ( O - 141 O g/1 H2so 4 ) at 25°C for one
102
month. The results are plotted in Figure 12.
Figure 12(a) shows the existence of three compounds having the
5b2o 31As 2o 5 molar ratio of 1.0, 1.5 or 2.0. From the results of
the chemical analysis, the formula of these compounds will be
represented as 5bAso4 formed in the range of O - 930 gll H25o4 ,
SU「 R PセᄋRaウ R P U ᄋTUP S@ in 1020 - 1100 gll H25o4 and 25b2o 3 ·As 2o 5 ·4503
in 1150 - 1370 gll H25o4• X-ray diffraction patterns of these two
antimony(III) arsenate sulfates are shown in Figure 13.
Figure 12(b) shows that the level of antimony(III) in sulfuric
acid solution was reduced by the precipitation of 5bAso4• Further
more, the solubility behavior of 5bAs04 in sulfuric acid solution
( 200 gll H25o4 ) is studied at 25°C. The results are shown in
Figure 14. X-ray diffraction confirmed that only 5bAs04 is formed
at initial 5b2o 3 I As 2o 5 molar ratio in the mixture below 1.0,
while 25b2o 3 ·503 is formed together with 5bAso4 at initial 5b2o 3 I
As 2o 5 molar ratio above 1.5.
Figure 14(b) shows that antimony(III) concentration equilibrated
with the mixture of 5bAso 4 and 25b 2o 3·5o 3 become equal to the solu
bility of 25b2o 3 ·5o3• Corresponding to エィゥセ@ antimony(III) concent
ration, arsenic(V) concentration trends toward a minimum value
which is controlled by the solubility product of 5bAs04•
Therefore, 5bAs04 will be one of. the constitutive compounds in
the floating slime formed during the electrorefining of copper.
7. The systems 5b2o 5 - As 2o 3 - 503 - H2o and
5b2o 5 - As 2o 5 - 503 - H20
The experiments were carried out by varying the 5b2o 51As2o 3 or
As 2o 5 molar ratio in the mixture of 5b2o 5 ·2H20 and arsenious or
arsenic acid solution and sulfuric acid solution ( 200 gll H25o4
at 25°C. The results proved the nonexistence of compounds of 5b2o 5
with As 2o 3 or As 2o 5 in sulfuric acid solution.
103
CONCLUSION
In arder to clarify the behavior of antimony and arsenie in
sulfurie aeid solution, the system sb2ox( x:3,5 )- As 2oy( y:3,5 )-
so3 - H2o át 25°C was investigated by mixing method. Six antimony
one arsenie sulfate in
the system As 2o 3 - so3 - H2o and one antimony arsenate and two
antimony arsenate sulfates in the system sb2o 3 - As 2o 5 - S03 - H20
were identified. The solubility and stability ranges of those
eornpounds, Sb2o 3 , Sb2o 5 and As 2o 3 were determined.
In production of arsenie trioxide from sulfurie aeid solution
eontaining a large amount of antirnony(III) by erystallization, the
produeed arsenie trioxide will be eontarninated with antimony(III)
beeause of very low solubility of antirnony(III) sulfates formed.
Only antimony(III) arsenates are formed as antirnony arsenie
eornpound in sulfurie aeid solution. Therefore, SbAs04 whieh is
stable below 900 g/1 H2so4 , is one of the eonstitutive eompounds
in the floating slirne during the eleetrorefining of eopper. To
further know distinetly the meehanism of formation of the floating
slirne, more detailed studies will also be neeessary in the presence
of bisrnuth and copper at higher temperature.
REFERENCES
(1) Mohri, E. : J. Min. Met. Inst. Japan, 94 451-456 (1978). (2) Yashuda, M. : J. Min. Met. Inst. Japan, W 555-560 (1984). (3) Kono, H., Sugawara, Y. and Hashimoto, M. : Paper presented at
112 th AIME Annual Meeting, Atlanta USA, Mareh 1983. (4) Lindsfrom, N.F.R. : Urlited States Patent, 3,753,877 (1973). (5) Gospodinov, G. and Ojkova, T. : z. anorg. allg. Chem., 472
233-240 (1981 ). (6) Hinterrnann, Jf.E. and Venuto, C.J.: J. Eleetroehern. Soe., 115
10-12 (1968). A -
(7) Menzies, A.W.C. and Potter, P.D. : J. Am. Chern. Soe., 34 1452 ( 1912). -
(8) Broul, M. et al. : Physieal Seiences Data 6, Solubility in Inorganie Two-Component Systems, Elsevier Seientific Publishirig Company (1981).
(9) Inornata, I. et al. : J. Sulphurie Aeid Soe., 9 127-133, 169-175 (1956). -
10.4
! 4
i .!
I
10 イMセセNNNNNNNLN⦅LNNNNLNNNNLNNNLNNNLNNNNNNNMLMLNNMMLMセL⦅LNNNNL@
- ,,.. •• wort, n•c L ャセᄋ |@ ft
s . i = 4
•••• lospodt- t i e1, IOO'C I Gゥセ@ Nセ@I -.,_. セG@ '
,.-4 ' '\ I "
I
l
.............. I , ...
Pセセ G G G NGGG@ ,,,,,,! o 600 1000 1500
H1SO, I t/1 l
Fig. 1 (a) The so3/sb2o3 molar ratio in precipitates
(b) The antimony(III) concentration in solution after equilibrating various mixtures of antimony trioxide and
sulfuric acid solution at 25 and 100°C,
lltO 11 21 11 41 IG 10 1t 10 U wttl
so,
Fig. 2 The system sb2o3 - so3 - H2o at 25°C.
lOS
(E) "'f»·t!l>(>,•"'f' •• Ulo (A)"'f'>(00'-1<) .... • .....
" .... .. .... .. ..... • ,5uc 5u• t.IG • ·- .. ·- " .....
' 1 ... .. J J.L. I
1- • l I III l.d l セ@... .. .. ... - ..
H2so4 20 g11 H2so4 956 g/1
-•• III, .. Ulo •• "'· '·"' • (l) """'' ""
.... .. (f)"'f'>' ..., .... 1 • ._ • ..... • .... >o ... " .....
" ..... " .... .. ..... • ... 11 ..... .. ....
" .... .. ... M ..... ... U\セセセm@ ..... • 1 •• ..
:.- 1- • ..... .. I .III .. I.U '
.... • 1 .... • l .m
" ... ..
I セ@1 ... • .....
" 1.21& • I i ol I ... .. .. .
H2so4 38 g/1 H2so4 1279 911
•• "'• •i UI, •• 111,
. (<) セGBBG G NNNL@10.101 1 <•> '"t'>'"">·'ll 10. ... • '·"' lt ....
' ..... .. ...... .... .... .. .. .. " J.:IQ • t.m . ..... '
J,2ST • 1.t01 "' ..... " J:.Jtt •
セオ」@ 1-·· .. ;til .... • 2. 1 .. • 1 •• • ..... • ...... • 1- 1 ..... "
:t.m • 1 ..... 1 .... .. 1 ...
"
III J • I 1 .... • 1 ... .
J I ., I ·.1.11
• ... .. . .. .. H2so4 l97g/1 H2so4 1463 911
.. •l lllo (M)"'f'>•""J(II •• III, fi· III,
(D) '"f'>' ... ..... .. '·"· " ... 12 ... .. 4-Ul • ... • .... .. . .... I. ... ..
" ..... .. . .... .. .. ... • ..... " . ... • . .... •
s-- ..... .. セ|u@ ·- .. ... .. .... • .. ... • t.l ..
" .... • ... • . .... •
lal I セゥ@ utd ... .. .. .. .. . .. .. H2so4 797 911 H2so4 1714 g/1
Fig. 3 X-ray d,iffraction patterns of compounds in the systern
Sb203 -so3 - H20.
106
ウイッセMイセセセセMイセセセセセセ@
4
セS@::::::. ... セ@ 2
500 1000 1500 H2so. <em
Fig. 4 The solubility of Sb2o5 (amorphous) in sulfuric aci d solution at 25°C.
QUセセセセMMMMMMセセセセMMセ@
-o- pruentwork.25t.2wuh
• ._. Zitttl Co.. 25t
·-<>· 1•••11 .. 111, 40t. 2HtL
·•· • • 2ot • •
i .. c
5
01. ;: Z セLエイセセェ@o 500 1000 1500
HtSO, I g/ 1 I
Fig. 5 The arsenic1III) concentration in solution after
equilibrating various mixtures of arsenic trioxide and sulfuric acid solution at 25°C.
107
l._ft.,Uft. • • . , ___ I I
I..O.·Ift. · •-..-1 ••'- ' IA.O.· liO.
I e MMMMセセRMNッN ᄋ @
12 1\ . \ :? 10
\ \ | M」セ@\
\ \
,, .,,,.. .... ,,'
G BBBG ᄋ M ᄋ セ@P ッ MMセセセ Uセッッセセセ セ LッセッッセセセセLセUセセセ@
H,so, <1/ll
Fig. 7 (a) The Sb2o3/As2o3 molar ratio in the precipitates
(b) The antimony(III) and arsenic (III) concentrations in solution after equilibrating mixture 'of antimony trioxide and
arsenic trioxide at various sulfuric acid concentrations at 25°C.
セ@ 1.5 イMNNNNLNNNMMMNNNMMMMMNMセM
.5 I セ@ 1.0 ' SbAsO, I
1 I PセU@.___.......__.___,_----l..___j
.. ,.......---...----.-......----1
s o .! -2
> i -3
5-4 セ@ ... セ@ -5
\ At(VI
&o-o- SbUIIl
-· セセMMセMMセセセセ@D
pH
108
イMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMセ@;Ã til. ;Á 1/1.
uoe 11 2 •• • .... 100 '·"' • •••• ti 1·111 • Ult 11 .l.tll • 2.121 11 1.13f . 12 un 2S 1.TM 1 , .... 1 1.111 • Sa• 2.102 12 1.111 I
40 2t··
.. . ..
Fig. 9 X-ray diffraction pattern
of SbAs04•
Fig. 8 Relationship between pH and (a) . the Sb2o 3/As 2o 5 molar ratio in the precipitates and (b) the antimony(III) and
arsenic(V) concentrations in solution after equilibrating
various mixtures of antimony trioxide and arsenic acid solution at 25°C.
wッセィエ@
SbAo01 1lo セ@ T 6 925
Rs「。PゥセNMMNYM
ウセNMMMセl@
40
200 coo soo soo 1000 ·c
Fig. 10 Thermoanalytical curves of SbAso4
•
109
セ@ -1 e
g -2
Fig. 11 Equilibrium log [As(V)] - pH diagram for the system
Sb(III) - As(V)- H20 at 25°C.
i .!1
• ii i セセ@ ャMMMMMBZNZZZFZQAAZセ]GMMMNッャMMセ@
j : L........-..1... セ⦅N⦅⦅N⦅N⦅⦅L@ッセセセMtセ セセセ Mイセセ@
--- 111(111) h Sb20,. so,. y QQQセ@
M ᄋセセセセセセセセセセ⦅N⦅@
o 600 1000 1500 H,so, lo/ll
Fig. 12 (a) The Sb2o3/As2o5 molar ratio in precipitates
(b) The antimony(III) and arsenic(V) concentrations in
solution after equilibrating mixture of antimony trioxide and arse
nic acid solution at various sulfuric acid concentrations at 25°C.
u
Su}
110
.. •• lllt •• ,,,,
tllozO,· Aoz01· 4S0, •1 III, 11
lll>:o3 ·ru,o1·&so3 ..... •• l.111 14 .,. .. . . ... e.m • l.l41 • • ••• ' J,41f ..... .. J •• ' '··· .. .... ... ' ... • •••• • 3 .... ... • J ... • Ult 13 セN@ ..
I ••• 11 , ... 14 s:u .... ' . .. UM • J ... 14 ..... 11 ..,. .... 11 J ••• • J.m • ··= U&& a ••• ' •••• • . .. ... IOJ .. ,. ' •••• •
.. .. . .. H2so4 1095 g/1 tt2so4 t254 g/1
Fig. 13 X-ray diffraction patterns of antimony arsenate
sulfates.
i .. •i
I
l -1 セ@ Ao!VI
s ; : -2 セ@c
& -3 4 ;
-4 セ@ DセHQQ@
--- SoMIItllof nbz0l·S03
-5 o 0.5 I. O 1.5 2.0 l5
lnitiat セPN@ lfttlar rttit in fllxt•re
The Sb2o3 /As 2o5 molar ratio in precipitates
lllt • • • • ' • • • 4
..
Fig. 14 (a)
(b) The antimony(III) and arsenic(V) concentrations in solution after equil i brating va.rious mixtures of antimony
trioxide. and arsenic acid solution in sulfuric acid solution,
200 g/ 1 'H2 so4 , at RUセc N@