STUDIES ON TITANIUM(IV) TUNGSTOSILICATE AND TITANIUM(IV

ACTA CHROMATOGRAPHICA, NO. 13, 2003
STUDIES ON TITANIUM(IV) TUNGSTOSILICATE
AND TITANIUM(IV) TUNGSTOPHOSPHATE.
II. SEPARATION AND ESTIMATION OF HEAVY
METALS FROM AQUATIC ENVIRONMENTS
Z. M. Siddiqi* and D. Pathania
Department of Applied Chemistry, Dr B.R. Ambedkar National Institute of Technology,
Jalandhar 144011, India
SUMMARY
Binary and ternary separations of heavy metals, e.g. Zn2+–Bi3+,
Mn –Pb2+, Cd2+–Pb2+, Mn2+–Bi3+–Mo6+, and Cr6+–Pb2+–Bi3+ on columns
of titanium(IV) tungstosilicate and Zn2+–Ni2+, Mo6+–Pb2+, Hg2+–Pb2+,
Zn2+–Cr6+–Bi3+, and Zn2+–Ni2+–Bi3+ on titanium(IV) tungstophosphate,
have been demonstrated. The adsorption and elution of important metal ions
such as Mo6+, Al3+, and As3+ on titanium(IV) tungstosilicate and Hg2+,
Fe3+, and Cr6+ on titanium(IV) tungstophosphate have been studied. Titanium(IV) tungstosilicate and titanium(IV) tungstophosphate have been used
for separation and estimation of Pb2+, Cr6+, Zn2+, Mn2+, Ni3+, Fe3+, and
Cd2+ in diverse real water samples such as river water, hand pump water,
and industrial effluents.
2+
INTRODUCTION
Ground water and surface water have always been useful and
unique sources of fresh water for domestic, industrial, and agricultural
purposes. Because of rapid industrialization and urbanization the world is
facing serious water pollution problems because of the harmful effects of
heavy metals. Heavy metals concentrations in water and aquatic ecosystems have been analyzed worldwide [1–4]. Selective separation of metal
ions present at very low levels in water is required for estimation and
removal purposes. Modified ion-exchange resins have recently been used
for selective separation of Fe2+ from Al 3+, Fe2+ from Hg2+, and Ag+ from
other metal ions [5–7]. Inorganic ion exchangers have been shown to enable
selective separation of metal ions from aquatic environments [8–10].
Selective binary separations of Cr6+from other metal ions on thin layers of
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titanic silicate and of Hg2+ from Fe3+ on impregnated silica gel layers have
been achieved [11,12]. In a more recent study in our laboratory, titanium
(IV) tungstosilicate and titanium(IV) tungstophosphate have been shown
to have promising characteristics as inorganic ion-exchange materials on
the basis of distribution studies of many metals and the separation of metal
ions from each other [13]. A variety of water samples from industrialized
cities have been reported to be contaminated by heavy metals at concentrations above permissible levels [14]. This study, an extension of our previous work, deals with the adsorption, elution, separation, and estimation
of metals, especially heavy metals, from different water samples.
EXPERIMENTAL
Reagents
All reagents were of analytical grade. Stock solutions (1000 ppm)
of individual elements were usually prepared in 2% HNO3 (high purity; E.
Merck).
Synthesis of Titanium(IV) Tungstosilicate (TiWSi)
As reported elsewhere [13], an aqueous solution of tungstosilicic
acid was added dropwise with constant stirring to an alcoholic solution of
titanium (IV) chloride, in 1:1 molar proportion. After complete addition of
the tungstosilicic acid the pH was adjusted to between 0 and 1 by addition
of 0.1 M HNO3 solution (pH was measured with an Orion pH meter). The
solution containing the precipitate was stirred for 1 h and then left
overnight. The precipitates were then isolated by filtration, washed with
distilled water, and dried overnight at 40°C in an oven. The material was
converted to the H+ form by treatment with 0.1 M HNO3 for 24 h, washed
with distilled water to remove excess acid, and finally dried at 40°C in an
oven.
Synthesis of Titanium(IV) Tungstophosphate (TiWP)
The preparation of TiWP was also performed as described elsewhere [13]. An aqueous solution of tungstophosphoric acid was added
dropwise with constant stirring to alcoholic solution of titanium(IV)
chloride, in 1:1 molar proportion. When addition of tungstophosphoric
acid was complete the pH was adjusted to between 0 and 1 by the addition
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of 0.1 M HNO3 solution. The rest of the process was as described above
for TiWSi.
Study Area
The study focused on the north of India. The state of Punjab is
most developed state in the northern region of India. The Jalandhar,
Ludhiana, Amritsar, Patiala, and Bathinda districts of this region were
selected, because they are most industrialized in terms of small-scale
industry. Effluent of these industries enters the water system directly,
because of a lack of a proper sewerage system, so monitoring of surface
and ground water in these districts was therefore undertaken [14]. For this
study water was sampled from different sources, e.g. rivers, hand pumps,
and industrial effluents; details of the samples are given in Tables I and II.
Sampling
Surface and ground water samples were collected from different
regions of the studied area. Standard methods of collection, preservation
and analysis were adopted [15,16]. Polythene bottles of 500 mL capacity
were used for collection of water samples. Bottles were soaked in 10%
nitric acid solution for 24 hours and then rinsed with distilled water. Then
bottles were dried at 103°C for two hours, cooled to room temperature,
capped and labeled. All samples collected from sites were filtered and
immediately preserved. Preservation was accomplished with 5 mL of HNO3
per 500 mL.
Sample Preparation for Metal Analysis
Water samples (250 mL) were digested with concentrated nitric
acid and hydrochloric acid on a hot plate. When volume had been reduced
to 10 mL the sample was transferred to a 50-mL volumetric flask and
diluted to volume with double-distilled water. The pH was adjusted to ~6
by addition of dilute nitric acid, if required.
Elution of Metal Ions
TiWSi and TiWP (1 g) were supported on glass wool plugs in two
different glass columns (30 cm × 2.7 cm diam.). Solutions of metal ions
prepared from standard solutions of the metals (for atomic absorption
spectrophotometry (AAS) analysis) were circulated many times through
the columns at a rate of 20 drops min–1 to ensure maximum exchange of
metal ion on the ion-exchanger. Metal ions not adsorbed were washed from
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Table I
Separation and estimation of heavy metals from water samples on TiWSi
Concn of
Estimated
Concn (M)
metal in concn of metal Volume of of HNO3
Metal ions
Details of sample
separated water sample ion eluted eluent (mL) used as
loaded (ppm)
(ppm)
eluent
Lake water, near
Cr6+
1.40
0.60
100
0.1
Nakodar, Jalandhar Pb2+
1.24
0.65
100
0.5
Handpump water,
Zn2+
1.00
0.25
100
0.1
Jalandhar
Pb2+
1.24
1.00
100
0.5
Industrial
Zn2+
1.71
0.62
100
0.1
effluent, Ludhiana
Pb2+
1.24
0.92
100
0.5
Ground water,
Mn6+
1.20
0.92
100
0.1
Amritsar
Fe3+
4.44
3.15
100
0.5
River water, near
Ni3+
1.24
0.45
100
0.1
Amritsar
Fe3+
4.44
4.10
100
0.5
Industrial
Zn2+
1.20
0.91
100
0.1
effluent, Amritsar
Fe3+
4.44
3.52
100
0.5
Metal industry
Mn2+
1.25
0.65
100
0.1
effluent, Patiala
Fe3+
3.03
2.65
100
0.5
Bein water,
Ni3+
1.20
0.68
100
0.1
Patiala
Fe3+
3.03
2.45
100
0.5
Industrial
Zn2+
1.44
0.46
100
0.1
effluent, Patiala
Fe3+
3.03
2.40
100
0.5
1.42
1.20
100
0.1
Tube well water
Mn2+
2.87
1.95
100
0.5
Bhatinda
Fe3+
Handpump near
2+
Zn
0.66
0.21
100
0.1
thermal power
Fe3+
2.87
1.60
100
0.5
plant, Bhatinda
the column and kept for analysis. Different concentrations of HNO3, as
eluent, were then passed through the column and the effluent was
collected as 10-mL fractions and tested for metals ions by AAS (Varian
SpectrAA.20 Plus). The elution curves are reported in Figs 1 and 2.
Binary Separations of Metal Ions
TiWSi and TiWP in the H+ form (mesh size 50–100 µm; 1 g) were
supported on glass wool plugs in separate glass columns (13 cm × 1.1 cm
diam.). The columns were washed with distilled water and mixtures of the
two metal ions to be separated were passed through the columns several
times, at a flow rate of 20 drops min–1, until exchange of H+ on the ion-
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Table II
Separation and estimation of heavy metals from water samples on TiWP
Details of sample
Industrial effluent,
Jalandhar
Industrial effluent,
Jalandhar
Industrial effluent,
Jalandhar
Industrial effluent,
Ludhiana
Industrial effluent,
Amritsar
Canal water,
Amritsar
Handpump water,
Patiala
Concn of
Estimated
Concn (M) of
Metal ions metal in water concn of metal Volume of
HNO3 used
separated sample loaded ion eluted eluent (mL)
as eluent
(ppm)
(ppm)
Zn2+
1.00
0.62
100
0.1
Ni3+
2.40
1.41
100
0.5
Zn2+
1.00
0.92
100
0.1
Cr3+
1.50
0.95
100
0.5
Zn2+
1.00
0.72
100
0.1
Pb2+
1.20
0.92
100
0.5
Zn2+
1.71
0.96
100
0.1
Ni3+
1.00
0.65
100
0.5
Zn2+
1.20
1.00
100
0.1
Ni3+
1.00
0.46
100
0.5
Zn2+
1.20
0.85
100
0.1
Cd2+
2.40
1.00
100
0.5
Zn2+
0.66
0.41
100
0.1
Cd2+
1.50
0.62
100
0.5
exchanger by metal ions was believed to be maximum. The columns were
again washed with distilled water to remove un-exchanged metal ions.
HNO3 at different concentrations was used to elute the metal ions from the
exchanger, and the metals ions thus collected were determined by AAS.
Metal ion solutions for AAS were either concentrated or diluted, as required, to ensure concentrations were within the limits appropriate for AAS
analysis. The separation curves for the heavy metal ions are shown in
Figs 3 and 4.
Ternary Separations of Metal Ions
The method employed was the same as for binary separations
except that mixtures of three metal ions were passed through the TiWSi
and TiWP columns. The elution curves are shown in Figs 5 and 6.
Separation and Estimation of Metal Ions in Water Samples
TiWSi or TiWP (1 g) were supported on glass wool in 1.1 cm i.d.
glass columns. Water samples containing mixtures of metal ions were passed
through the columns slowly (20 drops min–1) and recycled many times to the
adsorption of the metal ions. The columns were then washed with distilled
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Fig. 1
Elution patterns of metal ions on TiWSi
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Fig. 2
Elution patterns of metal ions on TiWP
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Fig. 3
Binary separation curves of metal ions on TiWSi
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Fig. 4
Binary separation curves of metal ions on TiWP
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Fig. 5
Ternary separation curves of metal ions on TiWSi
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Fig. 6
Ternary separation curves of metal ions on TiWP
water to remove unadsorbed metal ions. The metal ions adsorbed on the
exchangers were then eluted with different concentrations of HNO3. The
collected effluent was tested for the metals of interest by means of AAS.
The results are listed in Tables I and II.
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RESULT AND DISCUSSION
Figs 1 and 2 show the elution patterns obtained for Al 3+, Mo6+,
and As3+ on TiWSi and for Hg2+, Cr6+, and Fe3+ on TiWP. These results
can be used for estimation and recovery of these toxic metals in aqueous
media. Figs 3–6 show binary and ternary separation patterns achieved on
TiWSi and TiWP as column materials. These patterns show that Pb2+,
Bi3+, and Mo6+ were eluted from TiWSi columns with 0.5 M, 1.0 M and
1.5 M HNO3, respectively. From this it can be inferred that Pb2+ and Bi3+
can be selectively separated from metals ions which can be eluted with
0.1 M HNO3 before elution of Pb2+ and Bi3+ by use of TiWSi. Pb2+ and
Bi3+ were eluted from TiWP columns with 0.5 M and 1 M HNO3 whereas
elution of other heavy metals was achieved with a lower concentration of
HNO3 (0.1 M).
Table I shows the utility of TiWSi as column material for selective
separation of Pb2+ and Fe3+ from different water samples, probably
because of the higher distribution coefficient, Kd, of Pb2+ (as shown by its
elution by higher concentrations of HNO3) and Fe3+, as reported elsewhere
[13]. Table II shows the usefulness of TiWP for selective separation of
Zn2+, which has a low Kd value (and thus eluted by less concentrated
HHO3) from other heavy metals (eluted with 0.5 M HNO3) [13]. Other
metal ions, because of their reported presence in the water samples at
much lower concentrations [14], could not affect separation and estimation
of the metals reported in Tables I and II. These separations and estimations
were performed at pH ≈ 6; this should be considered at the time of sample
preparation. The results reported in Tables I and II are the averages from
five replicate analyses. Standard deviations were between 0.005 and 0.01.
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