STUDIES ON THE DISPOSAL AND TREATMENT OF SOME INDUSTRIAL WASTES DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF i l g i i d I P @ff P)[h)QO@g@p(h)Si' IN CHEMISTRY AKHTAR HUSSAIN KHAN DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA) 1988
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STUDIES ON THE DISPOSAL AND TREATMENT OF SOME
INDUSTRIAL WASTES
DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS
FOR THE AWARD OF THE DEGREE OF
ilgiidIP @ff P)[h)QO@g@p(h)Si' IN
CHEMISTRY
AKHTAR HUSSAIN KHAN
DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY
ALIGARH (INDIA)
1 9 8 8
DS1280
Dr. Mohammad Ajmal Environmental Research Lab. Deptt. of Applied Chemistry Z.U. College of Engg.&Tech. Aligarh Muslim University Aligarh - 202 002 iIndia)
Dated . k: JP.. ^.'^. . .
C E R T I F I C A T E
This is to certify that the work described
in this dissertation entitled "Studies on the Disposal
and Treatment of some Industrial Wastes" is the original
work of Mr. Akhtar Hussain Khan, carried out under my
supervision and guidance. The work included in this disser
tation has not been submitted elsewhere for any other
degree or diploma of any university.
MOHAMMAD AJMAL (Supervisor)
A C K N O W L E D G E M E N T
I am highly thankful to Dr. Mohammad Ajmal, Reader,
Department of Applied Chemistry, Aligarh Muslim University.
Aligarh for his guidance, healthy criticism and worthy
suggestions.
My special thanks are also due to Prof. K.T. Naseem
Chairman, Department of Applied Chemistry, A.M.U, Aligarh,
for providing me all the requisite research facilities
available in the department.
I also render my sincerest thanks to
Dr. Ali Mohammad and Dr. Naim Fatima for their kind and
valuable help and suggestions during these studies.
I am indebted to my senior colleagues
Drs. Sultan Ahmad, Ahsanullah Khan, Mujahid A. Khan,
Raziuddin, Nadeem A. Siddiqui and Abdul Jabbar Khan
for their advice, affections and encouragement from time
to time during the all stages of assignment.
I am also sincerely grateful to my colleagues
Rubina Chaudhry and Shamim Ahmad for their moral support
and all round co-operation during the entire period of
studies.
I am no less thankful to my fellow research scho
lars Shahreer Ahmad, Rais Ahmad and Jamal A. Khan for
their assistance and co-operation.
I express heartfelt regards and reverence to my
parents whose good wishes and love have always been
a great source of inspiration in accomplishing this task.
I, indeed feel proud of dedicating this research work
to them.
v - V ^ . v l i > v y ^ ^ - -
(AKHTAR HUSSAIN KHAN)
CONTENTS
Chapter I GENERAL INTRODUCTION
Chapter II SURVEY OF LITERATURES
Chapter III REVERSED PHASE THIN LAYER CHROMATOGRAPHIC SEPARATION OF HEAVY METAL IONS ON SILICA GEL LAYERS LOADED WITH TRIBUTYLAMINE
Introduction
Experimental
Resvilts and Discussion
Chapter IV USE OF ACIDIFIED SILICA GEL LAYERS AS AN ADSORBENT IN CHROMATOGRAPHIC SEPARATION OF SOME METAL IONS
Introduction
Experimental
Results and Discussion
Chapter V SUMMARY
REFERENCES
Page
1-25
26-48
49-55
54-57
58-82
83
84-86
86-97
98-100
101-104
PUBLICATION
1. Reversed Phase Thin Layer Chromatographic
Separation of Heavy Metal Ions on Silica
Gel Layers Loaded with Tributylamine.
Journal of Planar Chromatography
Volume-1, No. 2, pp. 128-15A (1988).
C H A P T E R - I
GENERAL INTRODUCTION
C H A P T E R I
GENERAL INTRODUCTION
It is difficult to define Environmental pollution
and its defination may change not only from country to
country but also from area to area within the same
country. It is, however, less difficult to describe
Environmental Pollution. Such a pollution inclxjdes the
release of substances, which harm the quality of air,
water or soil into the environment which upset the
biological cycles linking man to animals or plants even
when this damage is subtle and causes no deaths or does
not manifest itself for several decades or generations.
Pollution such as noise and smell which often irritates
is also hazardous to health.
We are on stronger ground if we relate pollution
to the natural cycles of growth and decay which, govern
all life on the planet. Where man's activities feed
into and are accomodated within these cycles, he is not
causing pollution. For example, the discharge of carbon
monoxide into the atmosphere by motor vehicles is unli
kely to cause serious overall damage, because natural
bacteria in the soil can feed on it and convert it to
harmless compounds. Provided we do not release so much
carbon monoxide that there are not sufficient bacteria to
break it down, then pollution cannot be said to occur.
On the other hand, the chemicals xxsed as propellants
in domestic and industrial aerosols are not, so far as
we know, attacked by any bacteria and so do not decay
naturally. They cannot slot into any natural cycles
and are therefore steadily building up in the atmos
phere. While there seems no suggestion that they are in
any way dangeroiis at present, they are most certainly
a form of pollution.
Sometimes man's waste products do not merely fail
to form part of the natural cycle, but positively
overwhelm or poison it. Our rivers for example are well
used to receiving natural organic matter and breaking it
down to compounds which can once again become the buil
ding blocks of new plant and animal tissue. When man
adds moderate quantities of domestic sewage, he merely
increases the total load of organic matter to be decayed.
But the bacteria which mainly bring this about need
oxygen to survive and the more the sewage is added the
more oxygen is consumed. Within limits the river natu
rally reaerates itself. But if too much organic matter
is added, the water becomes totally devoid of oxygen.
Not only do fish and other aquatic life die, but so do the
every bacteria which carryout the decaying process. They
are sometimes replaced by other species of bacteria, which
can survive without oxygen, and which can trigger off
different and often dangerous ecological cycles. Either
way, the river has been overwhelmed by pollution.
Some pollutants are indisputably dangerous either
to human health and welfare or to ecological cycles on
which man depends for his survival. I would like to
stress the point that it is quite inadequate to think
of harm to human beings or human health. Man is integral
part of the highly complex web of living organisms which
we call biosphere. Harm done to any part of the biosphere
may have reperexjssions on human welfare, for man relies
on it for food and other raw materials. Many pollutants
have already damaged agriculture and fisheries. We may
conclude that any substance which weakens any link in
nature s network is potentially harmfvil. Pollutants can
be harmful, harmless or even beneficial depending on
their concentration. Carbon dioxide for example, is
essential for green plants, so are the traces of some
heavy materials, so, probably, are small amounts of sulphur
dioxide. Yet large quantities of any of these can skill
plant or animal life.
Again it is easy to determine the effects of a
single pollutants in the laboratory. But in real life
there are usually many pollutants and they may sometimes
have synergistic effects on one another (combined effect
is much greater than the sum of their individual
effects). For example, nitrogen oxides and hydro
carbons emitted from motor car exhausts are relatively
harmless. Together, under the influence of intense
sxjnlight, they can combine to form an eye-smarting
photochemical smog.
One of the important aspects of pollution
abatement pollutes is to strike a balance. On the one
hand we wish to avoid a pollutant reaching a dangerovis
level. On the other than we must not suppress at
great expense which at present is nowhere near a
harmftil level. However, there are certain pollutants
about which there is no controversy. Any pollution
abatement policy shoxjld concentrate upon them.
The Origin of Waste:
One characteristics peculiar to Man is that he
progressively changes his environment to meet his
biological and social needs. On a socially organized
basis Man provides himself with the materials necessary
of life which he removes initially as raw material
from his environment. It is in the provision and
utilization of these material necessities, that worthless
and sometimes harmful by-products originate. Such pro
ducts comprise wastes of ail descriptions and they are
inev i tab le r e s u l t of Man's i n t e rac t ion with h i s physical
and bio logica l sorroundings. To separa te waste from
environment has been one of Man's o ldes t a c t i v i t i e s .
His tor ica l and Cultural Background:
In primit ive nomad s o c i t i e s the problem of waste
d isposal is a t i t s l e a s t . The nomad separa tes waste
from environment by changing his sorroundings. I t i s
when Man ex i s t in permanent communities t h a t the
removal of his waste products must be condixjted on
an organised bas i s . I t i s of i n t e r e s t t o note t h a t
i t was the t r ans i t i on from Pa laeo l i th ic Society based
on hunting and gathering to Neoli thic soc ie ty based on
farming and agricultixre which heralded the need for
waste d isposal . But i t has been the excesses of the
Indus t r i a l Revolution and i t s aftermath upto the
present day which has resul ted in a q u a l i t a t i v e l y
d i f f e ren t type of problem. Although waste disposal
must, as a minimum requirement, conserve the environ
ment's a b i l i t y to sustain human l i f e , the degree to
which i t practised at levels above t h i s rainimtjm depends
on the economic, p o l i t i c a l , cu l t u r a l and aes the t i c
values of the waste producing soc ie ty .
Pollutants.:
Wastes are not necessarily pollutants in them
selves but all have the capacity to be so - A waste
becomes a pollutant when it occurs in a wrong place.
It will be appreciated that production of waste is an
inevitable consequence of the first and second laws
of thermodynamics. The production of actual pollutants
is far from inevitable,
Fredrick Werner (1975) defined a pollutant as
"A substance or effect is normally considered to be a
pollutant if it adversely alters the environment by
changing the growth rate of a species, interferes with
the food chain, is toxic, or interferes with health,
comfort, amenities, or property values of people.
Generally a pollutant is a substqnce or effect intro
duced into the environment in significant amounts as
sewage, waste, accidental discharge, or as a by product
of a manufacturing process or other human activity. A
polluting substance can be a solid, semi-solid, liquid,
gas or sub-molecular particle. A polluting effect is
normally some kind of waste energy such as heat, noise,
or vibration.
Pollution ;
pollution is the result of the action or presence
7
of a pollutant in a part of the environment where it
is considered to have deleterious affects.
In the statement by Darling (1970) : 'Pollution
comes from getting rid of wastes at the least possible
cost.
Odum (1971) says in his own words "Pollution is
an undesirable change in the physical, chemical or
biological characteristics of our air, land and water
that may or will waste or deteriorate our raw material
resources.**
Industrial Wastes:
As a consequences of rapid industrialization in
the post—independence period prior to which our
economy was largely, agrarian, the problem of indus
trial effluent has grown into a significant magnitude.
Since a large majority of indxjstries is water based,
considerable volxme of wastewater emanate from the
indtistries. As the industrial effluents are as
varied in nature as the industry itself, the problem
gets further aggrevated as no standard procedure for
treatment can be recommended. Because of a variety of
reasons the industrial effluents are generally discharged
into water course either untreated or inadeqioately trea-
8
ted. The situation therefore has created a problem of
surface and subsoil water pollution. The pressure on
our water resources is therefore two fold.
(i) Requirement of large volume of water for the
industry and
(ii) Inavailability of clean water because of the
pollution due to the discharge of wastewaters.
In the light of the above it becomes therefore
imperative that the Industrial effluents are
adequately treated so as to become largely inno
cuous. However before the various methods of
treatment and disposal are considered it is
desirable to have a look at the nature of
effluents from various industries.
The growth pattern of some industries in India
which releases hazardous substances which are not bio
logically degradable indicates the increasing serious
ness of the problem is given in the following table.
Characteristics of the Industrial Wastes :
Unlike the domestic sewage, the industrial
wastes are very difficult to generalize. The charac
teristics of the industrial wastes not only vary with
Growth pattern of Some Industries in India :
Production x 10 tonnes
1950
NA
NA
0.25
200
18
I960
1.46*
1.15
1.23
580
153
1970
3.00
13.55
1.79
17,100
1,059
1980
1*0.e&
30.85
5.07
24,100
3,005
Pesticides
Dyes and Pigments
Pharmaceuticals
Organic Chemicals including Petrochemicals
Fertilizers (Nitrogenous and Phosphatic)
Steel ingots
Non-ferrous metals
Copper
Lead
Zinc
Caustic soda
15x10^ 3.4x10^ 6.5x10^ 8.0x10^
NA
NA
NA
11
8.500
NA
NA
101
9.30
1.86
23.41
304
18.80
11.40
52.70
457
+ DDT only ; NA = Not available.
Ref. : Sundaresan, B.B.-, Subrahmanyam, P.V.R.;
I.A.W.P.C. Newsletter, July 1983.
lo
the type of the industry, but also from plant to
plant producing same type of end prodixjts. Different
types of liquid wastes originate from various tjrpes of
industrial processes. The pollutants include the raw
materials, process chemicals, final products, process
intermediates, process by-products, and impurities in
raw materials and process chemicals. Broadly, these
pollutants can be classified as follows :
(i) Organic substances that deplete the oxygen
content of the receiving streams and impose a great
load on the biological units of the sewage treatment
plant.
(ii) Inorganic substances like carbonates, chlorides,
nitrogen etc. that render the water body unfit for
further use and sometimes incourage the growth of some
undesirable micro-plants in the body of water.
(iii) Acids or alkalis which make the receiving stream
unsuitable for the growth of fish and other aquatic life
there, and cause serious difficulties in the operation
of sewage treatment plants.
(iv) Toxic substances like cyanides, sulphides, acety
lene, alcohol, petrol etc. which cause damage to the
flora and fauna of the receiving streams, affect the
11
municipal treatment processes and sometimes endanger
the safety of the workmen.
(v) Colour-prodiicing substances like dyes, which
though not toxic, are aesthetically objectionable when
present in the water sijpplies.
(vi) Oil and other floating substances, which not
only render the streams unsightly but interfere with
the self purification of the same, and the operations
of the sewage treatment plants. A general view of the
natijre of effluents can be had from the following table.
Pollution Characteristics of Different
Industries
Industry Pollution Character- Suggested treat-is tics ment Methods
1. Paper and Strong colour Chemicals recovery pulp
loading on the R- values and the lowest possible detec
table amount of metal ions on the chromatopiates. It
is evident that TBA impregnated SG layers gave highly
compact spots over a wide range of loading amount of
the metal ions. 0.5 pg of Ni gave R„ equal to 0.9^
while it is 1.0 for 400 ug of Ni "*".
In order to bring out a more clear picture
regarding the separation of Zn "*" from Cd "*", Ni "*", and
70
Co , some TLC parameters such as AR- (R^ of separating
metal ion-R- of Zn ), separation factor (a) and reso
lution (Rs) have been calcialated. These data have been
presented in table 6. The values for a and Rs have been
calculated by using the following relationships.
(M » separating metal) ( i ) a = KZn/Kj^
/ 1 - R-
/ where K is a capacity factor which measures the degree
of retention of a solute compared to the solvent.
R : s 1/2 (d- -Hi2)
where AX is the distance between the centres of spots
and d-. , d„ are their respective diameters. Two solutes
are just separated if Rs is equal to 1. It is clear
from table 6 that a good separation of Zn from Cd ,
Ni and Co can be carried out by using the proposed
method. The AR- value is always greater than 0.5.
A high value of separation factor and well resolved
spots with R_ >, 5 are the added advantages of this
study.
The proposed method consisting the use of 40-50"/
TBA impregnated SG layer and a mixture of 1.0 M SF and
71
1.0 M FA in 8:2 ratio as developer is very reliable and
reproducible for achieving the separation of a particular
cation from others in general. It is particularly more
usefiiL if one needed sharper and clearer ternary and
quarteraary separations. The spots are so well formed
and compact that good quartemary separations are always
possible. It is a very reliable method to separate Zn
from over a reasonable pH range of sample solutions.
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76
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77
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78
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C H A P T E R - IV
USE OF ACIDIFIED SILICA GEL LAYERS AS AN
ADSORBENT IN CHROMATOGRAPHIC SEPARATION
OF SOME METAL IONS
83
C H A P T E R IV
INTRODUCTION
In c o n t i n u a t i o n of oxxr p rev ious work ^ ,
we have used ca rboxy l i c and mineral ac ids as impre-
gnants on s i l i c a ge l l a y e r s in o rde r t o unders tand t h e
r e t e n t i o n behaviour of some metal i o n s . As a r e s u l t
we have achieved some important s e p a r a t i o n s which a r e
d i s cus sed i n t h i s c h a p t e r . However, some more work
i s r e q u i r e d t o pu t t h e s e r e s u l t s fo r more p r a c t i c a l use .
In t h i s d i r e c t i o n , t h e q u a n t i t a t i v e s e p a r a t i o n of
d i f f e r e n t va lence s t a t e s of mercury i s i n p r o g r e s s .
The s e p a r a t i o n of Hg(II) from some metal ions on t h i n
l a y e r s of s y n t h e t i c i no rgan ic ion exchangers has been
31-36 e a r l i e r a t tempted by some workers-'^ -^ .
However t h e i r s t u d i e s s u f f e r t he fol lowing
l i m i t a t i o n s .
( i ) Effec t of anions on t h e s e p a r a t i o n of m e r c u r y ( l l )
from o t h e r ions has no t been examined.
( i i ) Loading e f f e c t of s e p a r a t i n g ions has no t been
s t u d i e d .
Therefore i t was thoughtworthwhile t o op t imize
t h e c o n d i t i o n for t h e s e p a r a t i o n of mercury ( I I ) from
s e v e r a l metal ions
&k
EXPERIMENTAL
Apparatus
Toshniwal TLC apparatus was used for the p re -
paucation of s i l i c a gel l aye r s .
Reagents
Silica gel G of BDH India and all other reagents
were of analytical grade.
Impregnants
Following aqueous impregnants whose concentra
tions are given in parenthesis were used.
(i) Oxalic acid (0,1, 0.5, 1.0, 2.0 and 10 /)
(ii) Citric acid (0.5 '/)
(iii) Tartaric acid (0.5 /)
(iv) Formic acid (0.5, 1.0, and 2.0 'A)
(v) Hydrochloric acid (O.l, 2.0, 5.0 and 10 '/)
(vi) Nitric acid (2.0 /)
(vii) Perchloric acid(2.0 and 5.0 "/)
Solvent Systems Used
The solvent systems used are given below.
85
Solvent System Composition EA-Acetone-FA-Water
10
8
7
2 : 1
6 : 1
8
10 : 1
k : 1
Preparation of silica gel plates:
Plain silica gel thin layers were prepared as
discussed earlier. For the preparation of acid impreg
nated silica gel layers 20 gram of silica gel was
shaken in a conical flask with 60 ml of 0.1-10 /. aqueous
solutions of various acids to obtain a homogeneous slurry.
The resultant slurry was spread over glass plates to
form a layers of uniform thickness ('~ 0.25 mm). The
plates were heated at 100 ± 5°C for 1 h, and then
cooled to room temperature by keeping in a closed
chamber.
Test Solutions and Detectors ;
Test solutions and detectors used were the same
as earlier.
86
Procedure
Plates were developed xjsing ascending technique
as discussed earlier and the ascent was kept 10 cm in
all cases.
RESULTS AND DISCUSSIONS
The results obtained have been shown in figs.
5-7 and tables 7-10. The silica gel layers impregna
ted with carboxylic and mineral acids provide some
new separations. Silica gel layers impregnated with
acids were found more selective to most of the metal
ions compared to plain silica gel layers. The R^
value of metal ions remained almost constant in the
range of 0.1 - 2 / oxalic acid impregnation. It is
evident from fig. 5 that oxalic acid impregnated
silica gel layers retained the metal ions more
strongly than the plain silica gel layers. Cr, Mn
and V are only the exceptions which showed strong
adsorption on plain silica gel layers. The chromato
graphic behaviour of metal ions on mineral acids and
carboxylic acids impregnated silica gel layers have
been summarized in fig. 6(a) and (b). The mobility
of the most of the cations was higher in formic acid
impregnated plates compared to oxalic acid impregnated
plates (fig. 6b) showing the stronger complexing
87
< I— ^c:>5^ii 11 o 2 < I M 2 O > - X I—»— < } — > o 2 : i j L U . o 2 o f ^ 2 o > X I—»—
Metal ions »
Fig. 5 :
Plot of AR^ (R^ on plain silica gel layers
Rf on Impregnated layers) Vs metal ions.
88
a)
'mpregnants:
o 2 / HCI
X 2 / HGO^
A 2/ HNO3
. 5/ HCIO,
(b)
< P > o l l 2 £ S z 5 . 5 M ^ S ^ f ^ x P f e ^ ^ 3
o 2/ FA
® 2 / Ox Ac
Metal ions
Fig. 6(a) and (b)
Mobility of metal ions on mineral acid and carboxylic acids impregnated s i l i c a gel l aye r s in ethyl ace ta t e -acetone-formic acid-water so lvent system.
89
tendency of oxalic acid. Amongst the mineral acids(Fig.7)
xjsed, perchloric acid and hydrochloric acid were found
better impregnants. The optimiam impregnant concentra
tion was found to be 5 percent for HCl or HCIO^ and
2 percent for oxalic acid. Almost all the cations
tailed on silica gel layers impregnated with 0.5 'A
oxalic acid, citric acid or tartaric acid. 5 percent
perchloric acid impregnated silica gel layers gave
more compact spots compared to 5 percent hydrochloric
acid impregnated plates. Ni "*", Cd^*, Zn "*" and Fe^*
tailed at all HCl concentrations (O.l - 10 percent).
Th " , Bi^*, Ag*, Pb " , Tl"*" , remained at the point of
application, while Cu " , Uo|*, Fe moved with the
solvent system at all HCl concentrations. However,
the R- of Co increases with the HCl concentrations.
The substitution of water by 1.0 M aqueous sodium
formate solution in solvent system leads to the
formation of tailed spots for most of cations. The
R- values of cations were found to be dependent on
the concentration ( /. volume) of formic acid or water.
Several important separations achieved on acid
impregnated silica gel layers have been summarized in
tables 7-lC.
The separation of Hg "*" from Hg " and of Th "
from UOp using 2 percent oxalic acid and 5 percent
perchloric acid as impregnants respectively was carried
50. Quresh i , M.', Mohammad, A.; Fat ima, N. ; J . Liq .
Chromatogr. , 8, 1279-1292, 1985.
5 1 . Qtireshi , M. ; Varshney, K.G.', Fat ima, N . ; Sep. «
S c i . 12 , 321-328, 1977.
32. De, A.K.i Pal, B.K.; Sep. Sci. 15, 1271-1275, 1980.
33. Sen, A.K., Ghosh, Ch.U.; J. Liq. Chromatog., 3,
71-79 (1980).
34. Sen, A.K., Das,S.B.; Ghosh, U. C., J. Liq. Chromatog.
8, 2999-3008, (1985).
lOA
35. De, A.K,; Chakraborty, P.; J. Liq. Chromatogr.»
4, 2223-2228 (1981).
36. Nangijneri, V.; Kumar, N.; Devi, y.P.; J. Assoc.
Off.Anal. Chem., 64, 792-732 (1981).
P 3593 F
Joiipiial of Planar Chromatograpliy —Modern TLC
DYNORPHIN (1-10)/SORBITOL IN SIMS BLOT nj/2 ,235
m/z 12 36 [] tlf'-'
.:^~,'
Secondary ion mass spectrometry in imaging analysis. See page 738
2/88 A Publication of iQj H t t t M g
Reversed Phase Thin Layer Chromatographic Separation of Heavy Metal Ions on Silica Gel Layers Loaded with Tributylamine
Mohammad Ajmal*, A. Mohammad, N. Fatima, and Akhtar H. Khan
Key Words:
Thin layer chromatography, TLC Heavy metal ions Tributylamine loaded silica Reversed phase
Summary
Chromatographic behavior of some heavy metal Ions on silica gel layers loaded with tritrntylamine has been studied in formic acid-sodium formate systems. Several important binary, ternary and quartemary separations have t>een achieved. Zn has t>een successfully separated from Cd, Ni, and Co. Some TLC parameters for Zn-Cd, Zn-Ni and Zn-Co separations have also t>een calculated.
1 Introduction
The discharge of heavy metals, which are nondegradable pollutants often contained in industrial waste water, has been the subject of great concern in recent years. Heavy metals cause adverse effects on living organisms, and some are lethal even at very low concentration. Therefore, the presence of such substance in water beyond permissible levels may constitute a chemical hazard and render the water unfit for many uses. Among the analytical techniques available, thin layer chromatography is an important tool for detection and separation of heavy metals in the field of environmental chemistry.
Reversed phase TLC offers some distinct advantages over normal phase TLC by providing several special features, such as organization of the hydrocarbon ligands on the silica surface, intercalation of solvent into the bonded layer, and the activity of residual silanois on the solid support. All these factors influence the selectivity of the medium in a specific manner. Thus, in reversed phase TLC the selectivity of a medium can be altered by varying the mobile phases or sor-bents, as well as by surface modifications involving reaction between silica support and reactive organosilanes of varying chain lengths.
Because of its simplicity and better resolution power, reversed phase chromatography has become a widely used method for chemical analysis of complicated mixtures. As a
M. Ajmal, A. Mohammad, N. Fatima, A. H Khan, Environmental Research Laboratory, Department of Applied Chemistry, Z H. College of Engg. and Technology, Aligarti Muslim University, Aligarh 202 002. India
result, a number of studies have been reported on the separation of metal ions using various mobile and slationary phases [1-14]. Most of these reversed phase studies are based on the use of paper and column chromatography and little attention has been paid to the use of TLC [15-1^ .
Separation of Zn(ll) from Cd(ll) is of great interest because of close resemblance in their chromatographic behavior. Several attempts have been made to achieve their mutual separation by using normal and reversed phase paper chromatography [19-21], ion exchange chromatography (22), solvent extraction [23), normal phase TLC [24], and by precipitation [25]. It is surprising that no work has been reported on reversed phase TLC for the separation of Zn(ll) from Cd(ll). It was therefore decided to establish optimum conditions for the separation of Zn(ll) from Cd(ll), Ni(ll), and Co(ll) by reversed phase TLC using tributylamine (TBA) as stationary phase on a silica gel (SG) support. Aqueous solvent systems containing variable concentrations of fonnic acid and sodium formate were used as mobile phases.
2 Experimental
2.1 Apparatus
A thin layer chromatography apparatus (Toshniwal, India) for the preparation of silica gel thin layers on 20 x 3 cm glass plates was used. Chromatography was performed in 24 x 6 cm glass jars. An Elico pH meter was used for pH measurements.
2.2 Reagents
Silica gel G from BDH, TBA from Fluka, sodium formate (SF) and formic acid (FA) from E. Merck (India) were used. All other reagents were of analytical grade.
2.3 Test Solutions and Detectors
The 0,1 M solutions of nitrates, chlorides, or sulfates of most of cations were prepared in 0.1 M solutions of the corresponding acids. Various known volumes of standard solu-
128 Journal of Planar Chromatography 1988 Dr. Alfred Huethig PuDlis^ers
RP-TLC o' Heavy Mel.il Ions
tions of metal ions were taken to study the effect of loading on tfie flf values. To study tfie effect of pH of metal solutions on the R, value of cations, the pH of the sample solutions were brought to the required value by the addition of either dilute NaOH or dilute HCI. Zn^' and Cd^* were detected with difhizone solution and other metal ions were detected by using conventional spot test reagents [26].
2.4 Preparation of Chromatoplates
2.4.1 Preparation of Plain SG Thin Layer Plates
SG was slurried with demineralized water in the ratio of 1:3 with constant shaking for 5 minutes. The resulting slurry was coated on clean glass plates with the help of an applicator to give a layer of 0.25 mm. The plates were air dried first and then kept at 100°±5''C for 1 h in an electrically controlled oven. Tlie plates were cooled to room temperature in a closed chamber before use.
2.4.2 Preparation of TBA Impregnated SG Thin Layers
Impregnated silica gel thin layers were prepared by two methods.
Direct Impregnation Method: 20 g of silica gel was shaken in a conical flask with 60 ml of 10-70% TBA solution in benzene (V/V) to obtain a homogeneous slurry. The resultant slurry was spread over glass plates to form a layer of uniform thickness (= 0.25 mm). Benzene was allowed to evaporate at room temperature. The plates were heated at 100 ± 5°C for 1 h and then cooled to room temperature in a closed chamtjer.
Indirect Impregnation Method: The plain SG plates were first prepared by adopting a method as mentioned above and then were impregnated by placing them in chromatographic jars for development containing a 10-70% TBA solution in benzene (V/V). Benzene was allowed to evaporate at room temperature and then the plates were heated at 100°± 5°C for 1 h in an electrically controlled oven. The plates were cooled to room temperature in a closed chamtjer and then used as such.
2.5 Solvent Systems Used
Aqueous FA(10"^ 10-^ 0.1. 1.0, 5.0. 10.0, and 20.0 M) Aqueous SF (10"^, 10-^ 0.1, 1.0, 2.0, 5.0 M) Mixtures of 1.0 M aq. FA and 1.0 M aq. SF (8:2, 6:4, 1:1, 4:6. and 2:8 ratio)
(0 (ii) (iii)
2.6 Procedure
The sample solution (3-5 MO was loaded on plain or TBA impregnated SG chromatoplates with the help of micropi-pettes. The spots were dried at room temperature t)efore development. The glass jars containing mobile phase were covered with lids and left for 10 minutes before introducing tfie plates for development. The plates were developed in the chosen mobile phase by the ascending technique with a solvent run to 10 cm in all cases, unless othenwise stated. After
development, the plates were air dried and the cations were detected by spraying appropnate coloring reagents The R, values were calculated from the values of R, (ft. ot leading front) and fly {Rt of trailing front).
3 Results and Discussion
The results of this study are summarized in Figures 1-4 and
Tables 1-6.
Table 1
Binary separations achieved on silica gel layers impregnated with 40% TBA in different solvent systems.
Solvent system Separations achieved {R^ - Rj)
1.0 M FA V(y-(0.3-0.15)-Ti'''(0.0-0.0) or Ap-(0.8-0.7) V(y*(0.3-0.15)-W*-(0.0-0.0) or Np-(1.0-0.8) AP'(0.6-0.5)-Ti*-(0.0-0.0) Fe'-(0.7-0.5)-Ti'-(0.0-0.0) Ti'*(0.0-0.0)-Ni^-(0.9-0.7) UOi*{0.8-0.6)-Ti"(0.0-0.0) or VO'*(0.35-0.2) Fe^*(0.0-0.0)-mixtures of Ni^'. Co'' Mn'-(1.0-0.8)-Cu="(0.3-0.2) or Fe'-(0.1-0.0) Mn^'(1.0-0.8y-Bi''(0.1-0.0) or Zn'-(0 05-0.0) UOf(0.25-0.22)-Co'-(0.8-0.7) Ap-(0.2-0.1)-Cu'-(0.3-0.26) or Cd'-(0.8-0.7) Ap-(0.2-0.1 )-Ni'-{ 1.0-0.9) Zn'*(0.28-0.17)-Cd'-(0.8-0.66) UO|-(0.36-0.33)-Zr^-(0.0-0.0) Ti''*(0.0-0.0)-Ap-(0.42-0.2) or Ta**(0.45-0.3) Se'-(1.0-0.9)-Pb'* or Bi '(O.O-O.O) Se'-(1.0-0.9)-Ti**(0.0-0.0) or Fe"(0.25-0.0) Se'-(1.0-0.9)-Zn''(0.25-0.1) U'*(0.75-0.6)-Zr'-(0.0-0.0) VO^*(0.3-0.0)-Zn^-(0.6-0.45) or Cd'-(0.6-0.4)
1.0 M S F
M .0 M SF + 1.0 M FA (8:2)
1 . 0 M S F +
1.0 M FA (4; 6) 1.0 M S F + 1.0 M FA (6:4)
Tr(0.66-0.52)-Tp-(0.0-0.0) Cr^*(0.53-0.45)-Ni^-(1.0-0.9) Se'*(0.68-0.50)-Bi'l0.08-0.0) or Pb'-(O.O-O.O) Zn'*(0.83-0.7)-Ni^-(1.0-0.9) Cd^'(0.7-0.5)-Nl'*(1.0-0.8) Fe''(0.75-0.4)-Ni^* + Co"(1.0-0.8)
Reversed phase chromatography on SG impregnated with TBA gave excellent results. The thin layers were of good quality. However, the plates prepared by direct impregnation proved superior to those obtained by indirect impregnation. The time of development ranged from 1-2 h depending upon the mobile phase composition. The spots were compact and well formed in all solvent systems and at ail percent impregnations (10-70%) of TBA. However. Cd^*. Ag*, Hg2**, and Hg^* showed some tailing («L -RJ > 0.3) in some solvent systems. The R, values of metal ions were found to depend upon the time and temperature of drying of the impregnated SG plates. The plates were quite stable in acidic developers and also in 1.0 M SF but at a higher pH of mobile phase the plates were deformed on drying. Specifically, the plates developed in 5.0 M aqueous SF (pH - 7.75) were deformed
Journal of Planar Chromatography VOL. I.JUNE 1988 1 2 9
RP-TLC of Heavy Metal Ions
Table 2
Binary separations obtained on silica gel layers impregnated with 60% and 20% TBA using different solvent systems.
% Impreg- Solvent system Separations achieved (ft, - R,) nation with TBA
Table 4
Quarternary separations achieved on silica gel layers impregnated with 40% TBA by using solvent system containing 1.0 M SF and 1.0 M FA In an 8:2 ratio (ascent 12 cm).
on drying. The effects of various factors on the chromatographic behavior of metal ions are given below .
3.1 Effect of Aqueous SF Concentration on the Mobility of Metal Ions
On the basis of their chromatographic behavior on SG layers impregnated with 40% TBA in varying concentrations of SF (0.001 to 5.0 M), metal ions can be classified into the following groups:
(0 Metal ions such as U0|*, Fe^*, AP*, Ag*. Pb^*, B\^\ 1\^\ and Ti** showed no mobility over the entire range of SF concentrations. The low R, value for these metal ions may be attributed to the formation of anionic/neutral complexes with SF similar to those reported by Oureshi et a/. [27] for rew cations. HgJ* and Hg^* produced tailed spots starting from the point of application.
(iO Ni^* and Co^* moved with the solvent front giving high R, (= 0.9) over the whole concentration range. The absence of sorption in these cases may be attributed to the lack of formation of anionic metal formate complexes.
(iii) Metal ions like Tl* and Cd^* showed an increase in mobility with the increase in SF concentration giving fl, equal to 0.9 in 5 M SF. The increase in R, value with the increase in SF concentration is probably due to increased complexation at higher pH.
(Iv) Cu^* and Zn^* did not move in solvents containing up to 1.0 M SF. However, a sudden increase in their R, values was observed in 2.0 M and 5.0 M SF.
All the melal ions were detected satisfactorily at all SF concentrations (0.001-5.0 M). The development time increases with the ncrease in molar concentration of SF until it reaches to 2 h in 5.0 M SF.
3.2 Effect of FA Concentration on the Mobility of Metal Ions
The study of chromatographic behavior of metal ions on 40% TBA impregnated SG plates in acidic developers containing
varying molar concentrations of aqueous FA (0.001-20.0 M) gave some interesting results. The main points emerging from this study are as follows:
(i) HgJ'' formed elongated spots at all FA concentrations while Bi^* and Cd^* produced tailed spots (starting from the origin) in 5-20 M and 0.001 M - 0.1 M FA, respectively.
(ii) Ag*, Pb^*, and Ti"* remained at the point of application at all FA concentrations used. Conversely, Ni^* and Co^* moved with the solvent front, probably due to the solvation of these ions/complexes by the mobile phase.
(iii) UOl\ Fe^\ A!'*, Bi^\ Zn^\ Cr^*, Cu^\ and Cd^* did not move in mobile phases containing up to 0.1 M FA. On further increase in acid concentrations, these metal ions show significant mobility giving ft, 0.7-0.9 in 1.0 M FA. The R, values reach a maximum (R, = 1.0) at higher FA concentrations {i.e. 5-20 M). The higher FA concentration was found unsuitable because of (i) spreading of spots, C") longer development time (iii), less sharp detection of most of the metal ions.
The increase in W, with increasing molar concentration of FA is attributed to the increase in the number of H* ions competing with the cations or cationic complexes for the exchange sites.
3.3 Effect of TBA Impregnation on the Mobility of Metal Ions
Figure 1 shows that TBA impregnated SG layers are more strongly sorbing than unimpregnated or plain SG layers for
l.OMSF • l-OMSF + IOM FA (1:1)
+0.8
.•0-6
I •0-6 ARf
• 0-2
00
-0.2
catlons Figure 1
Comparison of s«lectjvjtles of TBA-impregnated and unimpregnated silica get layers in different solvent systems.
most of the metal ions, as indicated by positive values of AWf. Here Afl( is the measure for the difference in the fl( values of metal ions on unimpregnated and impregnated SG layers, i.e. Afl, = fl, on unimpregnated SG layers - R, on impregnated SG layers. Thus, TBA impregnation enhances the selectivity of the plain SG layers.
Figure 2 shows the effect of the degree of impregnation of TBA on the R, values of metal ions in 1.0 M FA and in 1.0 M FA + 1.0 M SF (2:8) solvent systems. The R, values for only those cations which gave compact spots were taken for plotting the figures. It is evident from Figure 2 that, in 1.0 M FA, the R, values generally decrease with increasing degree of impregnation. However, Cd^* and Bi^* showed constancy of R, values at ail degrees of impregnation. Zn^* showed significant tailing (R, = 0.0-0.6) over 10-20% impregnation.
In solvent system containing a mixture of 1.0 M FA and 1.0 M SF in a ratio of 2:8, the plots (Figure 2) showed frequent fluctuations over the entire range of TBA impregnation. Interestingly, a few cations showed stronger sorption at 30% TBA impregnation. Detection of all metal ions was very clean and sharp at all degrees of impregnation but the spots were more compact at higher degrees. The shapes of these curves can be tentatively explained on the basis of the existence of a neutral, positive, or negative species as well as the possibie formation of less strongly adsorbed higher charged negative
complexes. Some other phenomena, such as the adsorption in the network of the support, precipitation in the network of the support, precipitation, hydrolysis, and solvent-solvent interactions, may play an important role affecting the sorption behavior of metal ions on impregnated SG layers.
3.4 Effect of Mixed Solvent Systems Containing Mixture of 1.0 M FA and 1.0 M SF on the Mobility of Metal Ions
It is clear from Figure 3a that 1.0 M SF is the best solvent for the separation of Zn^* from Cd^*, Ni^* and Co^* on 60% TBA impregnated SG layers. However, the separation of Cd^* from Zn^* in this solvent is also possible on 40% impregnated plates but the greater tailing of Cd^* decreases the resolution of its separation from Zn^* (Figure 3b). It is obvious from Figure 3b that 1.0 M SF behaves differently from 1.0 M FA as a mobile phase. Most of the cations move faster in FA and produce more compact spots compared to SF. Ni^* and Co^* show identical tjehavior in both the solvent systems and move with the solvent front. Figures 3c-d, summarize the chromatographic behavior of metal ions in solvent systems containing mixtures of 1.0 M FA and 1.0 M SF in different molar ratios. Evidently, most of the metal ions show relatively greater mobility and higher compactness in solvents containing tiigher percentages of FA.
_ j I 1 i _
r -o--
10 20 30 iO SO 60 70 V. impr«gr\Qtior\ w i t h T8A
10 20 JO 40 50 SO 70 ' / . . r r p r t g n o l i o n w i t h TBA
Rf 0
0
0
Rf 0
0
0.
s
c
4
2 -
0
-g,-- ' - g . - . ^ - . ^ : ^ ^
1 0
0 8
0-6
Rf 0 4
0 2
0 0
1*
- S - - 0 - - 0 -
" • - - o o — o I ^ t ^O-
~-c>-,o_ - 0 - - 0 - - < i > —
- - 0 - -
Tl
"^^^"^Q—^ --f—9 ^ -
Hg
10 20 30 4 0 50 60 70
V , imprtgnot ion wi th TBA 10 20 30 60 50 60 70
V . imprtgnotion with TBA
Figure 2
Plot of R, Vs percentage impregnation of TBA in t)€n7ene. - ® ® - 1.0 M FA; - i ' »•>- 1.0 M FA + 1.0 M SF (2:8) .
132 V O L 1, J U N E 1988 Journ.'^l of PInnnr Chfnrn.'i'' / j i .K'f ' .
RP-TLC of Heavy Metal Ions
1 OM SF
A-IOM SF»1 0MFA(«:2) B-IOM SF + 10MFA(2:8) C-)OM SF • )0M FA(1:))
A-VOMSF«).OH FA(S:4) B-lOM SF + 10MFA(4:6)
4 > O b . | Z o Z < - > N < u X X P p a . < 0 3 > -Utlons
Figures
Pkrt of R| n metal lone in different eoivent systems, a - 60% TBA impregnated SO layers. b ,cd • 40% TBA impregnated SG layers. • — • Compact spots; A — A TaBed spots virfth SL - n , > 0.4; O — O T a i M spots with R - RT < 0.4.
3.5 Effect of pH of Metal Solutions on the Separation ofZn^* from Ni**, Co**, and Cd**
Rgure 4 shows that the R, values of Zn^*, Ni^*, Co^\ and Cd * are independent of the pH of the sample solution in the pH range of 1-5. Thus a good separation of Zn^* from these metal ions can be obtained on 60% TBA impregnated SG
10
oe I 0 6(-
Rf0 4
0 2 •
00
Cd^ Ni *on4 Co?* - • m • •
2 3 t fH of fflttal tolution*
Figure 4
Plot of pH o< metal solutions M . R, on silica gel layers impregnated with 60% TBA In solvwil syslMn containtng l A i t SF and 1 . 0 M FA In an 8:2 ratio.
layers in mobile phase containing a mixture of 1,0 M SF and 1.0 M FA in 8:2 by using unbuffered sample solutions without adhering to the close control of the sample pH.
Enhancement of the selectivity of SG layers by impregnation with TBA provides an opportunity to achieve many analytically important separations. Many such separations have actually t>een realized and are tabulated in Tables 1-4. Separations such as Zn^*-Cd^\ AP*-CU^*, VCP*-TP*, VCP*-W*\
Th''*-Zr*\ Fe3*-TP^ AP^-Cu^^-Ni^^-Ti"*, Cr^^-BJ^*-Cd^^-Co^*, Zn^^-Cd^^-Pb^* and Zn^-'-Tr-Pb^* are worth mentioning.
Table 5 summarizes the results of the effect of loading on the fl( values and the lowest possible detectable amount of metal ions on the chromatoplates. TBA impregnated SG layers gave highly compact spots over a wide range of loading of the nrretal ions. 0.5 pg of Ni * gave R, equal to 0.94 while it is 1.0for400Mgof Ni *.
In order to present a clearer picture regarding the separation of Zn^* from Cd^*, Ni^*, and Co^*, someTLC parameters such as Afl, (ft, of separating metal ion - Rf of Zn^*), separation factor (a) and resolution (f?J have been calculated. These data are shown in Table 6. The values for a and Rg have t)een calculated by using the following relationships
(i) a
K' 1- f l ,
(M = separating metal)
where K' is a capacity factor which measures the degree of retention of a solute compared to the solvent.
fls M
1/2 (d, + dz)
where AX is the distance between the centers of spots and di, d2 are their respective diameters. Two solutes are just separated if R, is equal to 1. It is clear from Table 6 that a good separation of Zn^* from Gd^*, Ni *, and Go * can be carried out by the proposed method. The Afl| value is always greater than 0.5. A high value of separation factor and well resolved spots with H. > 5 are the added advantages of this study.
The proposed method, consisting in the use of 40-60% TBA impregnated SG layers and a mixture of 1.0 M SF and 1.0 M FA in a 8:2 ratio as developer is very reliable and reproduc-'Me for achieving the separation of a particular cation from others in general. It is especially useful if one needs sharper aix) clearer ternary and quartemary separations. The spots are so well formed and compact that good quartemary separations are always possible. It is a very reliable method for separating Zn^* from Cd^* over a reasonable pH range of sample solutions.
Journal cil Plan.ir Chromatopfaphy vol I .11 INF 19R8 133
RP-TLC of Heavy Metal Ions
Acknowledgment
The authors thank Prof A. U. Malik. Chairman, Department of Applied Chemistry, for providing facilities and the University Grants Commission (India) for financial assistance to N. Fatima.
References
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Ms received: November 10, 1987 Accepted by SN: January 5, 1988
134 VOL. I.JUNE 1988 Journal of Planar Chromatograptiy