Solvent Extraction Study of Mercury(II) with Zolon Red ( H Z R )
A . N. P a t e l * a n d A . M. Qureshi
D e p a r t m e n t o f C h e m i s t r y U n i v e r s i t y o f Nigeria, N s u k k a , Nigeria
Z. N a t u r f o r s c h . 3 4 b , 9 8 3 - 9 8 5 ( 1 9 7 9 ) ; received J a n u a r y 11, 1979
Zolon Red, Mercury(II)
T h e e x t r a c t i o n o f m e r c u r y ( I I ) f r o m the a q u e o u s solutions o f m e r c u r y ( I I ) nitrate a n d
m e r c u r y ( I I ) c h l o r i d e w i t h z o l o n red ( H Z R ) dissolved in w-butanol has b e e n studied. T h e
e x t r a c t i o n o f m e r c u r y ( I I ) f r o m t h e a q u e o u s nitrate s y s t e m has b e e n f o u n d t o b e m u c h
b e t t e r c o m p a r e d t o t h a t f r o m t h e a q u e o u s chloride s y s t e m in t h e p H range o f 1 t o 6.
T h e e x t r a c t i o n o f m e r c u r y w i t h z o l o n red is simple, fast a n d selective. T h e c o m p o s i t i o n o f
t h e e x t r a c t e d m e r c u r y z o l o n red c o m p o u n d has also b e e n studied. R e g e n e r a t i o n o f t h e
e x t r a c t i n g s o l u t i o n o f z o l o n red is readily a c h i e v e d b y stripping t h e m e r c u r y ( I I ) w i t h an
a q u e o u s c y a n i d e solution.
Introduction
T h e awareness of the high toxicity of mercury(II)
and
its
role
in
the
environment
has
generated
considerable interest in discovering better methods
for the removal of mercury(II) at micro and macro
levels f r o m the industrial waste solutions.
Solvent
extraction techniques which have been applied very
successfully in the nuclear technology and
copper
extraction are receiving increasing attention in the
search for efficient m e t h o d for the removal
recovery of mercury(II) from the industrial
solutions such as t h e brine effluents f r o m
and
waste
chloro-
alkali plants. T h e n u m b e r of e x t r a c t a n t s for merc u r y ( I I ) r e p o r t e d i n t h e l i t e r a t u r e a r e d i t h i z o n e [1],
tribenzylamine
[2], h i g h m o l e c u l a r w e i g h t
[3], m a c r o c y c l i c
polyethers
[4] a n d
amines
polyurethane
f o a m s [5, 6]. O f t h e s e e x t r a c t a n t s , t h e
successful
a p p l i c a t i o n s o f t h e h i g h m o l e c u l a r w e i g h t a m i n e s [7]
in the nuclear technology attest for their industrial
potential
for
removal
of
mercury
from
aqueous
solutions. This paper describes the solvent extraction study of mercury(II)
w i t h zolon
red
(HZR)
f r o m the aqueous nitrate a n d chloride systems in
the
pH
range
between
1
and
6. Z o l o n
red
has
already been reported to form coloured compounds
w i t h several m e t a l ions including mercury(II)
in
o u r e a r l i e r p a p e r s [8, 9].
Experimental
A l l chemicals used in this investigation were of
standard reagent quality. Zolon red was synthesised
b y t h e m e t h o d r e p o r t e d i n our p r e v i o u s p a p e r s [8,9].
I t s s a t u r a t e d s o l u t i o n o f 0.025 M c o n c e n t r a t i o n i n
* R e p r i n t requests t o D r . A . N . P a t e l .
0 3 4 0 - 5 0 8 7 / 7 9 / 0 7 0 0 - 0 9 8 3 / $ 01.00/0
%-butanol s e r v e d as o r g a n i c p h a s e . T h e s t o c k solutions for mercury(II) nitrate and
mercury(II)
chloride were prepared b y dissolving the respective
salts in distilled water. T h e buffer solutions for the
p H r a n g e b e t w e e n 1 - 6 w r ere p r e p a r e d b y t h e
standard m e t h o d described in t e x t books of practical
i n o r g a n i c c h e m i s t r y [10].
T h e extraction of mercury(II) was carried out by
placing 5 m l of m e r c u r y ( I I ) salts solutions in a
s m a l l flask a n d a d j u s t i n g p H b y a b u f f e r s o l u t i o n
a n d finally adding 25 ml of zolon red solution. T h e
mixture was shaken for about t w e n t y minutes at
a b o u t 2 5 °C a n d w a s a l l o w e d t o s e p a r a t e i n t o t w o
layers in a separatory funnel. T h e aqueous a n d
organic phases were separated and analysed for
m e r c u r y ( I I ) . T h e c o n c e n t r a t i o n of m e r c u r y ( I I ) in
the aqueous phases was determined b y the gravim e t r i c m e t h o d [10] o f p r e c i p i t a t i n g m e r c u r y ( I I ) as
sulphide. T h e mercury(II) concentration in the
o r g a n i c p h a s e s w e r e c a l c u l a t e d b y d i f f e r e n c e bet w e e n t h e i n i t i a l a n d final v a l u e s o f t h e a q u e o u s
phases. T h e mercury(II) concentration in
the
organic phases were also checked b y a m e t h o d
where a k n o w n volume of organic phase was evaporated to dryness followed b y an addition of
concentrated nitric acid and evaporation to dryness
again. T h e residue w a s dissolved in dilute nitric
acid a n d m a d e u p to e x a c t l y 25 m l a n d t h e n
determining the concentration of mercury(II) as in
the case of the a q u e o u s phases.
A saturated alcoholic solution of zolon red was
added to the aqueous solution of mercury(II)
n i t r a t e of 0.1 M c o n c e n t r a t i o n b u f f e r e d w i t h I O - 2 M
solution of sodium acetate. Mercury(II) gave red
precipitates w i t h zolon red w h i c h were soluble in
excess alcoholic solution of zolon red. T h e red
p r e c i p i t a t e s o f m e r c u r y z o l o n r e d w h e n first f o r m e d ,
appeared as colloidals b u t on standing separated as
r e d p r e c i p i t a t e s w h i c h t h e n w e r e filtered o f f , d r i e d
and analysed for a stoichiometric ratio of mercury ( I I ) t o z o l o n r e d ( H g : Z R ) w T hich w a s f o u n d t o
be 1 : 2 .
Infra-red spectra of zolon red, mercury zolon red
in N u j o l m u l l w e r e o b t a i n e d w i t h P e r k i n E l m e r 257
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984
A. N. Patel-A. M. Qureshi • Solvent Extraction Study of Mercury(II) with Zolon Red (HZR)
Infra-red spectrophotometer. Electronic absorption
spectra of zolon r e d a n d m e r c u r y zolon red in e t h a n o l
w e r e d e t e r m i n e d o n U n i c a m S P 500 s p e c t r o p h o t o meter.
100
£
Results and Discussion
90
c
o
T h e extraction reaction of mercury(II) with zolon
red from the aqueous nitrate and chloride solution
o
80
x
£
is of t h e t y p e :
HZR
2 HZR
^ H+ +
+
ZR
Hg2+ -
Hg(ZR)2 +
2 H+
(2)
Zolon red, a w e a k acid dissociates a n d forms red
coloured
compound
70
(1)
with
mercury(II).
The
red
coloured c o m p o u n d to be referred as m e r c u r y zolon
0
2
pH
i
6
8
Fig. 1. The percent extraction of Hg(II) from the
aqueous nitrate (1) and chloride (2) solution as a
function pH. Hg(II) conc. 0.05 M, H Z R conc 0.025 M.
r e d , H g ( Z R ) 2 , is i n s o l u b l e in a q u e o u s s o l u t i o n s b u t
soluble in acids a n d organic solvents. T h e solubility
of
mercury
zolon
precipitation
sodium
of
acetate
red
in
acids
mercury(II)
and
in
buffer suggest
incomplete
the
that
concentration of mercury(II) ions in the
aqueous
of
phase, as m e r c u r y ( I I ) nitrate has a h i g h e r dissocia-
reaction
tion constant than mercury(II) chloride. T h e depent-
absence
the
chloride system. T h i s can be a t t r i b u t e d to a h i g h
b e t w e e n m e r c u r y ( I I ) ions a n d z o l o n r e d is revers-
ence of the extraction of m e r c u r y ( I I ) o n its
con-
ible. T h e r e m o v a l of dissociated h y d r o g e n ion b y a
centration
been
in
the
aqueous
phase
has
also
buffer solution shifts the equilibrium of the reaction
confirmed b y a n increase in t h e distribution coeffi-
t o w a r d s the right a n d results in a complete precipi-
cient of mercury(II) with increase in concentration
tation of mercury(II). A quantitative
of mercury(II)
precipitation
of mercury(II) from an aqueous solution of
chloride in the aqueous
phase
as
mer-
c u r y ( I I ) n i t r a t e o f 10~ 2 M c o n c e n t r a t i o n o c c u r e d a t
0.80
p H 4 with the saturated alcoholic solution of zolon
red. T h e analysis of the m e r c u r y zolon red c o m p o u n d
indicated the stoichiometric ratio of 1 : 2
between
m e r c u r y ( I I ) a n d zolon red. F u r t h e r m o r e , the infrared and electronic absorption spectra in the visible
0.75
o
o*
0.70
region of zolon red and mercury-zolon red favoured
the formation of mercury zolon
red byion-associa-
tion. The infrared spectrum of zolon red h a d a broad
band at 3410 c m - 1 and a strong b a n d at 1435 c m
assigned
to
-OH
stretching
and
-OH
of the mercury
zolon
in
red,
thereby confirming the replacement of the h y d r o g e n
of the hydroxyl group b y mercury(II).
m a x i m u m absorption at 520 n m in t h e
showed
electronic
absorption spectra.
nitrate
and
U.1U
0.15
of
0.20
H g C I 2 (M)
Fig. 2. The distribution coefficient of Hg(II) as a
function of the concentration of HgCl 2 at pH 4.
H Z R conc. 0.025 M.
cient of mercury(II)
decreases w h e n the
concen-
tration of m e r c u r y ( I I ) chloride in t h e a q u e o u s
above
The extraction of mercury(II) from the aqueous
of m e r c u r y ( I I )
0.05
The concentration
s h o w n i n F i g . 2. H o w e v e r , t h e d i s t r i b u t i o n c o e f f i -
B o t h zolon red and mercury zolon red
solutions
ü
bending
vibrations. However, these bands were absent
the infrared spectrum
1
0.65
0.12 M.
This
decrease
in
the
is
distribution
coefficient of mercury(II) m a y be explained b y the
mercury(II)
f o r m a t i o n of a chlorocomplex, (HgCLi)2- as well as
chloride w i t h zolon red dissolved in w-butanol as a
insufficient a m o u n t of zolon red. A s s h o w n in F i g . 1,
f u n c t i o n of p H is s h o w n i n F i g . 1. T h e
the decrease in the extraction of mercury(II) a b o v e
percentage
e x t r a c t i o n of m e r c u r y ( I I ) in t h e case of t h e a q u e o u s
p H 4 m a y be a reflection of increasing t e n d e n c y to
nitrate
f o r m h y d r o x y species of mercury(II). T h e distribu-
system
is m u c h
higher than
that
of
the
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985 A . N . P a t e l - A . M . Q u r e s h i • S o l v e n t E x t r a c t i o n S t u d y o f M e r c u r y ( I I ) w i t h Z o l o n R e d
(HZR)
1.00
cn 0.90
0.80
Log.conc. of H Z R (Ml.
F i g . 3. T h e d i s t r i b u t i o n c o e f f i c i e n t o f H g ( I I ) as a
f u n c t i o n o f t h e p H . A q u e o u s n i t r a t e (1) a n d c h l o r i d e (2)
s o l u t i o n s . H g ( I I ) c o n c . 0 . 0 5 M , H Z R c o n c . 0.025 M .
F i g . 4. T h e d i s t r i b u t i o n c o e f f i c i e n t o f H g ( I I ) as a
function o f the total concentration o f H Z R at p H 4
a n d H g C l 2 c o n c . 0 . 1 0 M . (v = 25 m l o f H Z R s o l n . o f
0.025 M conc.)
tion coefficient of m e r c u r y ( I I ) as a f u n c t i o n of the
cyanide solution, while mercury(II) forms a
p H a n d t h e c o n c e n t r a t i o n o f z o l o n r e d is s h o w n in
c o m p l e x a c c o r d i n g t o t h e r e a c t i o n (3):
F i g s . 3 a n d 4, r e s p e c t i v e l y . T h e d i s t r i b u t i o n coeffi-
Hg(ZR)20rg. +
c i e n t o f m e r c u r y ( I I ) is h i g h e s t a t p H 4, a n d is a l s o
increased w i t h increase in the concentration of H g 2 +
a n d Z R - ions, the concentration of Z R ~ ions being
influenced
by
pH.
The
extraction
efficiency
was
improved considerably w h e n a required volume
of
zolon red solution w a s used in t w o or three fractions
instead
of utilising
the
same
volume
in a
single
4CN-AQ.
Hg(CN)2"4Aq. +
The
mercury(II)
cyano
complex
^
2ZR-org.
was
from
stripped
the
(3)
quantitatively
organic
phase
with
a q u e o u s c y a n i d e s o l u t i o n (0.5 M K C N ) . T h e r e g e n was subsequently reused. Zolon red, thus for process
t i o n s . Z o l o n r e d is a p r o m i s i n g e x t r a c t i n g
Mercury
zolon red
compound
was found to
be
soluble in acids a n d c y a n i d e solutions, h o w e v e r the
zolon
red
regenerated
was
destroyed
whereas it w a s f o u n d to be stable in the
by
acids
aqueous
[1] H . L . F i n s t o n , E . T . W i l l i a m s , a n d R . L i t m a n ,
A n a l . C h e m . 4 9 , 9 8 3 (1977).
[ 2 ] O . V . S i n g h a n d S. N . T o n d o n , A n a l . L e t t . 9 (10),
921 ( 1 9 7 6 ) .
[ 3 ] F . L . M o o r e , E n v i r o n . Sei. 2 T e c h . 6 , 525 (1972).
[4] D . Serdic and H . Meider, J. Inorg. Nucl. Chem.
3 9 , 1409 ( 1 9 7 7 ) .
[ 5 ] P . K n a u e r a n d R . Sala, A n a l . C h e m . 75, 285
(1975).
[6] M. A . Mazurshi a n d A . Chow, Anal. Chim. A c t a
6 5 , 99 ( 1 9 7 3 ) .
as
the
erated zolon red r e m a i n e d in t h e organic phase and
application can be regenerated for recycle
extraction as expected.
cyano
for mercury(II)
and
may
find
application
operareagent
in
the
treatment of mercury pollution and the recovery of
mercury
from
the
aqueous
chloride
solutions
of
industrial waste.
[ 7 ] F . L . M o o r e , N a t . A c a d . Sei. N u c l . Sei, N A S - N S 3101 (1960).
[ 8 ] A . N . P a t e l a n d A . M . Q u r e s h i , P a p e r p r e s e n t e d at
I S E C ' 7 7 , T o r o n t o , C a n a d a , S e p t e m b e r 1977.
[9] A . M. Qureshi a n d A . N . Patel, Z . Naturforsch.
3 3 b , 450 (1978).
[10] A . I. Vogel, A T e x t B o o k of Quantitative Ino r g a n i c A n a l y s i s , p . 4 8 7 , 3rd E d . , L o n g m a n s ,
L o n d o n 1961.
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