removal of nickel from electroless nickel plating rinse water with di(2‐ethylhexyl)phosphoric...
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Removal of Nickel from ElectrolessNickel Plating Rinse Water with
Di(2-Ethylhexyl)phosphoric
Acid-Impregnated Supports
Hai Trung Huynh and Mikiya Tanaka*
Research Institute for Green Technology, National Institute of
Advanced Industrial Science and Technology (AIST),
Onogawa, Tsukuba, Ibaraki, Japan
ABSTRACT
Electroless nickel plating technology is playing an increasingly important
and indispensable role in many fields such as the electronic and automobile
industries. As a result, the treatment of the rinse water containing about
50 mg=dm3 of nickel is becoming a serious environmental problem.
Although this water is currently treated by the conventional precipitation
method, a method without sludge generation is highly desired. This
study explores the possibility of removing and recovering nickel from
the rinse water with di(2-ethylhexyl)phosphoric acid-impregnated supports
(D2EHPA-IS). Macroporous polymer and oil adsorbents made of synthetic
and natural fibers as the supporting materials were tested for the nickel
*Correspondence: Mikiya Tanaka, Research Institute for Green Technology, National
Institute of Advanced Industrial Science and Technology (AIST), Onogawa, Tsukuba,
Ibaraki 305-8569, Japan; E-mail: [email protected].
SOLVENT EXTRACTION AND ION EXCHANGE
Vol. 21, No. 2, pp. 291–305, 2003
DOI: 10.1081=SEI-120018951 0736-6299 (Print); 1532-2262 (Online)
Copyright # 2003 by Marcel Dekker, Inc. www.dekker.com
291
removal abilities from simulated rinse water. In the batch experiments,
more than 90% of the nickel can be adsorbed by these D2EHPA-IS without
pH adjustment. The adsorption of nickel reaches the equilibrium within
1.2 ks at 298K at a shaking rate of 140 rpm. The pH-dependency of the
nickel adsorption by the D2EHPA-IS shows that the nickel is adsorbed by a
cation exchange reaction. The adsorbed nickel can then be readily eluted
with mineral acids. Most of the IS can be used many times without losing
their adsorption abilities. In the column experiments, the breakthrough
curves of nickel for these supports indicate that the nickel–D2EHPA
complex formed at the high nickel loading region tends to dissolve into
the aqueous phase. These findings lead to the conclusion that most of the
studied D2EHPA-IS are effective for the removal and recovery of nickel
from an electroless nickel plating rinse water in batch mode.
Key Words: Nickel; Adsorption; Di(2-ethylhexyl)phosphoric acid;
Electroless nickel plating rinse water; Impregnated supports.
INTRODUCTION
Many researchers have made efforts to remove heavy metals from
industrial wastewater by using several methods such as chemical precipitation,
adsorption, solvent extraction, ion exchange, and reverse osmosis.[1–4] Some
of these methods are expensive and have limitations. Currently, the usual
treatment technology of metal-bearing wastewater is chemical precipitation.
However, this method often creates secondary problems with sludge
generation.[5]
Among the many methods mentioned above, solvent extraction and ion
exchange are known to be effective for metal removal. Although they offer
many advantages, there are several unsolved problems such as (i) the loss of
organics; and the contamination of the water with organics for solvent
extraction, and (ii) slow kinetics for ion-exchange.[6] Extractant-impregnated
resins have been shown to be effective adsorbents for the metal removal from
diluted aqueous solutions.[7] They combine the advantages of the solvent
extraction and ion-exchange processes.[8] Also, oil adsorbents made of
synthetic and natural fibers can adsorb an extractant used in metal solvent
extraction and are expected to be the supports of the impregnated metal
adsorbents. Thus, extractant-impregnated supports (extractant-IS) would be
widely applicable for the treatment of heavy metals in wastewater.
Electroless nickel plating is a typical surface finishing technology and
plays an important role in the high-tech industries. As a result, the rinse water
from the electroless nickel plating containing about 50 mg=dm3 of nickel is
becoming a serious environmental problem. The objective of this study is to
292 Huynh and Tanaka
explore the possibility of removing and recovering nickel from the electroless
nickel plating rinse water with di(2-ethylhexyl)phosphoric acid (D2EHPA)-IS.
Di(2-ethylhexyl)phosphoric acid was selected as the extractant, because this is
a typical organophosphorous acid and known to extract nickel at a pH greater
than 2.9.[9,10]
EXPERIMENTAL
Simulated Rinse Water and Reagent
The simulated rinse water was prepared by diluting the spent bath
discharged from an electroless nickel plating plant in Japan. Ion exchange-
distilled water was used throughout this study. Chemicals used in this study
were all reagent grade except for the extractant. Di(2-ethylhexyl)phosphoric
acid was the product of Daihachi Chemical Industry Co., and was used as
received. Various concentrations of sodium hydroxide and hydrochloric acid
were used as the pH adjusting reagents. As eluting reagents, 2 mol=dm3
hydrochloric and 1 mol=dm3 sulfuric acids were used.
Support
The thermally bonded fabrics, KFO Mat P-185 (KFO), made of poly-
ethylene and polypropylene, the non-woven fabrics, Static Resistant Oil
Sorbent HP-556 (OS), made of polypropylene, and the natural fiber, Oil
Catcher KT-65 (OC), made of kapok fiber, produced by Kyushu Filter Industry
Co., Ltd., 3M Co., Ltd., and Kakui Co., Ltd., respectively, were supplied in the
form of sheets. Before impregnation, all the fibers were cut into
0.5 cm� 0.5 cm pieces.
The macroporous resin Amberlite XAD7HP, supplied by Rohm and Haas
Co., is a polymeric adsorbent with an acrylic ester matrix. On a dry basis, it
has a specific surface area of more than 400 m2=g, a porosity more than 0.5, an
average pore size of 45–50 nm, and a pore volume of 0.5 cm3=cm3.
Impregnation Procedure
The D2EHPA-IS were prepared as follows:[8,11] The supports were
washed with methanol, dried, and contacted with 10 vol.% D2EHPA in ethanol
in the phase ratio of 50 cm3=g at 298K at a shaking rate of 140 rpm overnight.
The supports were then removed by filtration and washed with an excess
volume of water. Finally, the supports were dried in an oven overnight at
353K. The concentration of D2EHPA held in the supports was determined by
Electroless Nickel Plating Rinse Water 293
the difference in weight before and after the impregnation. In some cases, the
concentrations of D2EHPA in the IS were also determined by the digestion
with the mixture of sulfuric and nitric acids followed by the phosphorous
analysis by ICP-AES (Seiko SPS4000). The results agreed with each other
within �5%.
Adsorption and Elution Procedures
In the batch equilibrium experiments, the desired amount of each
D2EHPA-IS and 10 cm3 of the simulated rinse water with the liquid–solid
phase ratio of 50 cm3=g dried non-impregnated support (DNIS) except the
experiments for nickel adsorption isotherm, and the very small amount of the
pH adjusting reagent (less than 2 cm3 of the 1 mol=dm3 HCl solution per 1 dm3
of the rinse water), when necessary, were placed in a stoppered 50 cm3-conical
flask and shaken at a rate of 140 rpm in a water bath maintained at 298K for
more than 12 hours to ensure equilibrium. A small amount of the aqueous
phase was then removed and appropriately diluted in order to determine the
nickel concentration. The nickel concentration in the IS was calculated on the
basis of mass balance. The adsorbed nickel was eluted separately by
2 mol=dm3 HCl and 1 mol=dm3 H2SO4 with the liquid solid phase ratio of
50 cm3=g DNIS by vigorous vertical shaking for one hour. When the durability
for repeated use of the IS was investigated, the D2EHPA-IS after the
adsorption–elution cycle was washed with water until chloride ion was not
detected in the filtrate, dried at 353K, and submitted to another adsorption–
elution cycle.
In the kinetic runs, the contact of the two phases began under the same
conditions as those for the batch equilibrium experiments without adding the
pH adjusting reagent to the rinse water. During the experiment, the pH of
the aqueous phase was not kept at constant. At preset time intervals, the two
phases were separated, and the nickel concentration in the aqueous phase was
determined after appropriate dilution.
In the column experiments, 1 g of the D2EHPA-IS was packed in a glass
column with an inner diameter of 11 mm. The rinse water or the eluting
reagent was fed to the bottom of the column maintained at 298K, and the
effluent from the head was collected by a fraction collector.
The nickel concentrations in the aqueous solutions before and after
adsorption, and after elution were determined by ICP-AES. The pH values
in the aqueous phases were measured by a pH meter (Toa HM-60G). Sulfate,
phosphinate, and phosphonate ions, as well as lactic and propionic acids in
the simulated rinse water were analyzed using a capillary electrophoresis
apparatus (Otsuka CAPI-3200).
294 Huynh and Tanaka
RESULTS AND DISCUSSION
Composition of the Rinse Water
The composition of the simulated rinse water was measured, and the result
is shown in Table 1. The simulated rinse water is weakly acidic with high
concentrations of sodium, phosphonate, sulfate ions, and organic acids. Since
the nickel concentration in the spent bath was gradually changed due to
the slow precipitation of nickel phosphonate, the nickel concentration in the
simulated rinse water was varied from 20 to 50 mg=dm3; thus, the actual nickel
concentration will be described in the legend of each figure or table.
Batch Experiment
The relationship between the nickel adsorption percentage and equili-
brium pH is shown in Fig. 1. At the equilibrium pH of 3.9 for the D2EHPA-
impregnated OC and XAD7HP, and 4.2 for the impregnated KFO and OS
(these pH values are attained if the adsorption of nickel from the simulated
rinse water is done without pH adjustment), more than 90% of the nickel is
adsorbed. The nickel removal efficiency is abruptly reduced with decreasing
pH, suggesting that nickel is adsorbed by a cation exchange reaction. For
solvent extraction of nickel using D2EHPA,[10] nickel is not extracted at a pH
lower than 2.9. In addition, nickel is extracted from the simulated rinse water
using 48.5 g=dm3 D2EHPA dissolved in Shellsol D70 (Shell Chemicals) with
the phase ratio of 1 : 1; however, at the equilibrium pH of 3.9, the extraction
efficiency is only 50% in spite of the fact that the amount of D2EHPA per unit
Table 1. The composition and pH value ofthe simulated rinse water.
Component Concentration (mg=dm3)
Sodium 1020
Nickel 20–50
Iron <1
Zinc <0.1
SO42� 630
H2PO2� 230
HPO32� 1200
Lactic acid 550
Propionic acid 90
pH 5.3
Electroless Nickel Plating Rinse Water 295
volume of the aqueous phase was more than three times higher in the solvent
extraction (SX) than those in the IS. According to the nickel removal
percentages by adsorption and extraction, D2EHPA-IS are more effective
than SX using the same extractant.
The blank experiments show that OC itself adsorbs nickel to a slight extent;
that is, without pH adjustment, about 40% of the nickel is adsorbed at the
equilibrium pH of 5.0. This is probably because natural fibers (OC) have some
functional groups like ��OH. For other supports, nickel is not adsorbed at all.
The difference among the pH dependency of the nickel adsorption by
each D2EHPA-impregnated fiber (OC, OS, and KFO) is not found; however,
over the entire investigated pH range, nickel adsorption is reduced in the order
of the impregnated supports: OC>OS>KFO in accord with the decreased
order of the D2EHPA concentrations in the supports: OC>OS>KFO. On
Figure 1. The effect of equilibrium pH on the nickel adsorption. The nickel
concentration in the rinse water was 48.4 mg=dm3. The D2EHPA concentrations in
the IS (g=g IS) were 0.27 (KFO), 0.28 (OS), 0.39 (OC), and 0.37 (XAD7HP).
296 Huynh and Tanaka
the other hand, the pH dependency of the nickel adsorption by the D2EHPA-
impregnated XAD7HP is slightly less than those by the D2EHPA-impregnated
fibers. The reason for this is not clear, but would be related to the difference in
the structures of the fibers and XAD7HP.
Without adding the pH adjusting reagent to the rinse water, 100% of the
iron and zinc are adsorbed by all the IS, and due to their very low concentrations
we did not pay special attention to the adsorption of those metals hereafter.
The time courses of the nickel removal for the different D2EHPA-IS are
shown in Fig. 2. Under the present experimental conditions, the adsorption
equilibria are reached within 1.2 ks (20 min) for all the D2EHPA-IS, which
would be fast enough to remove nickel in the rinse water by batch mode. The
fibers seem to exhibit faster removal rates than the resin. This is probably due
to the diffusion resistance in the XAD7HP pores.
Figure 2. Time courses of nickel removal with D2EHPA-IS. The nickel concentration
in the rinse water was 46.3 mg=dm3. The D2EHPA concentrations in the IS (g=g IS)
were 0.23 (KFO), 0.48 (OS), 0.55 (OC), and 0.26 (XAD7HP).
Electroless Nickel Plating Rinse Water 297
Figures 3 and 4 show the adsorption isotherm of nickel with D2EHPA-IS.
The isotherm was obtained by varying the solid–liquid ratios. The pH of the
aqueous phase was not adjusted. As shown in Figs. 3 and 4, the amount of
adsorbed nickel increases with the rise in the aqueous nickel concentration,
particularly in the low nickel loading region. In the high nickel loading region,
the amount of adsorbed nickel tends to decrease with the rise in the aqueous
nickel concentration for the D2EHPA-impregnated fibers. This phenomenon,
though not clear for the D2EHPA-impregnated resin, is probably due to the
dissolution of the nickel–D2EHPA complex into the aqueous phase and will
be discussed more later.
The adsorbed nickel is readily and completely eluted with 2 mol=dm3
hydrochloric or 1 mol=dm3 sulfuric acids. The elution efficiency does not
Figure 3. Adsorption isotherm of nickel with the D2EHPA-impregnated fibers. The
nickel concentration in the rinse water was 47.6 mg=dm3. The D2EHPA concentrations
in the IS (g=g IS) were 0.43 (KFO), 0.29 (OS), and 0.60 (OC).
298 Huynh and Tanaka
depend on the kinds of supports and acids, and achieves more than 95%
(unbalance within 5% is due to the experimental error) for all the D2EHPA-IS
(Table 2).
The durability for repeated use of the investigated D2EHPA-IS was tested
at a low nickel loading (phase ratio was 50 cm3=g DNIS). For the D2EHPA-
impregnated OS, the nickel removal efficiency remarkably decreases, and the
IS became an inert adsorbent for nickel after the 5th cycle (Fig. 5). However, for
other IS, the change in the nickel adsorption percentages is not found, and they
can be used many times without losing their adsorption abilities, indicating that
the loss of D2EHPA is negligible at the low nickel loading region.
Figure 4. Adsorption isotherm of nickel with the D2EHPA-impregnated XAD7HP.
The nickel concentration in the rinse water was 43.3 mg=dm3. The D2EHPA concen-
trations in the IS (g=g IS) were 0.18 [XAD7HP(1)], 0.26 [XAD7HP(2)], and 0.37
[XAD7HP(3)].
Electroless Nickel Plating Rinse Water 299
Column Experiment
Due to the remarkable loss of D2EHPA for the impregnated OS (Fig. 5),
the column experiments were conducted only for the impregnated KFO, OC,
and XAD7HP. Breakthrough curves of nickel for these IS are shown in Fig. 6,
where the relative nickel concentration is the nickel concentration in the
effluent divided by the nickel concentration in the feed solution. The relative
nickel concentrations for the D2EHPA-impregnated KFO and OC exceeded
unity. For the D2EHPA-impregnated XAD7HP, at the lower D2EHPA content
(0.18 g D2EHPA=g IS), the relative nickel concentration does not exceed unity
and the shift of the breakthrough curve during the second cycle from that
during the first cycle is small; however, at the higher D2EHPA content
(0.37 g D2EHPA=g IS), the relative nickel concentration exceeds unity and
the shift of the breakthrough curve during the second cycle from that during
the first cycle is much larger.
One possible explanation for the fact that the relative nickel concentration
exceeds unity might be that the adsorption of other cation in the rinse water by
D2EHPA-IS caused the nickel elution. If that happened, however, the break-
through curves of nickel for the D2EHPA-impregnated XAD7HP in the
second cycle would be identical with those in the first cycle. Therefore, the
following two hypotheses can be formulated:
The first one considers the adsorption of sodium by the D2EHPA-IS and
the dissolution of the Na–D2EHPA complex thus formed into the aqueous
phase. The second one considers the dissolution of the Ni–D2EHPA complex
formed at the high nickel loading region into the aqueous phase.
Table 2. Nickel elution efficiency from the adsorbed impregnated supports. Thenickel concentration in the rinse water was 19.4 mg=dm3.
Elution efficiency, %
Extractant- D2EHPA Solid Ni
impregnated
support
concentration
in the IS, g=g IS
concentration,
mg=g IS
2 mol=dm3
HCl
1 mol=dm3
H2SO4
D2EHPA-KFO 0.26 0.68 95 97
D2EHPA-OS 0.32 0.64 97 96
D2EHPA-OC 0.46 0.49 99 96
D2EHPA-XAD7HP 0.18 0.63 99 96
Note: D2EHPA is di(2-ethylhexyl)phosphoric acid; IS is an impregnated support; and
KFO, OS, and OC are KFO Mat P-185, Static Resistant Oil Sorbent HP-556, and Oil
Catcher KT-65, respectively.
300 Huynh and Tanaka
Sodium can be extracted by D2EHPA dissolved in a nonpolar organic
solvent;[12,13] thus, the extraction of nickel and sodium from the simulated
rinse water by D2EHPA dissolved in Shellsol D70, and Shellsol D70 alone
was done at the various phase ratios, and the nickel and sodium concentrations
in the obtained organic phases were determined by the analysis of the aqueous
phase formed after stripping by 2 mol=dm3 hydrochloric acid with the phase
ratio of 1 : 1. The result shows that the sodium concentrations in the organic
phases at various phase ratios are almost constant, indicating that sodium is
not extracted or extracted to a very small extent under the conditions of the
present study (Table 3). This result rejects the first hypothesis.
For the nickel extraction using D2EHPA dissolved in a nonpolar organic
solvent, the formation of Ni–D2EHPA polymer complexes at a high nickel
Figure 5. Repeated usage of D2EHPA-IS. The nickel concentration in the rinse water
was 48.2 mg=dm3. The D2EHPA concentrations in the IS (g=g IS) were 0.57 (KFO),
0.26 (OS), 0.51 (OC), and 0.37 (XAD7HP).
Electroless Nickel Plating Rinse Water 301
loading region in the organic phase were reported by some authors.[14,15]
Especially, the Ni–D2EHPA complex proposed by Sato and Nakamura[15]
exists as a trimer, has the octahedral structure, and contains coordinated water
molecules. This complex is likely to have high solubility in an aqueous
solution. In the present study, in order to detect the Ni–D2EHPA complex in
the aqueous phase, several effluent fractions during the column experiment
with D2EHPA-impregnated OC at the flow rate of 2.1 cm3=ks were mixed with
Shellsol D70 with the aqueous to organic phase ratio of 5 : 1 by vigorous
vertical shaking for one hour. The organic phases thus obtained were stripped
Figure 6. Breakthrough curves of nickel at the flow rate of 1.67 cm3=ks. The nickel
concentration in the rinse water was 35.1 mg=dm3. The D2EHPA concentrations in the
IS (g=g IS) were 0.26 (KFO), 0.46 (OC), 0.18 [XAD7HP(1)], and 0.37 [XAD7HP(2)].
302 Huynh and Tanaka
by 2 mol=dm3 HCl with the phase ratio of 1 : 1. For the effluent fractions with
the nickel relative concentrations of 0.11, 0.55, 1.22, and 2.09, the nickel
concentrations in the aqueous solutions after stripping were 0.25, 1.18, 4.14,
and 14.7 mg=dm3, respectively. This fact qualitatively indicates that the Ni–
D2EHPA complex is present in the effluent, and its concentration increases
with the rise in the effluent volume. This result supports the second hypothesis
that the Ni–D2EHPA complex formed at the high nickel loading region
dissolves into the aqueous phase.
CONCLUSIONS
The adsorption properties of nickel from the electroless nickel plating
rinse water by the D2EHPA-IS have been studied at 298 K using synthetic
fibers (KFO and OS), natural fiber (OC), and resin (XAD7HP) as the
supporting materials. The results are summarized as follows:
(i) Under the batch contact, more than 90% of the nickel can be
removed within 1.2 ks by the D2EHPA-IS without pH adjustment
via a cation exchange reaction.
(ii) The adsorbed nickel can be readily eluted by mineral acids.
Table 3. The extraction of nickel and sodium from the simulated rinse water withD2EHPA dissolved in Shellsol D70. The nickel concentration in the rinse water was32.5 mg=dm3.
D2EHPA
concentration Aqueous to Equilibrium
Equilibrium
organic phase,
mg=dm3
in the Shellsol organic aqueous
No. D70, g=dm3 phase ratio pH Na Ni
1 10.5 1 : 1 4.7 23.7 11.7
2 10.5 5 : 1 4.9 19.8 23.4
3 10.5 10 : 1 5.0 26.7 23.4
4 10.5 15 : 1 5.0 23.6 17.1
5 0 1 : 1 5.3 23.6 0
6 0 5 : 1 5.3 21.4 0
7 0 10 : 1 5.3 22.8 0
8 0 15 : 1 5.3 23.8 0
Electroless Nickel Plating Rinse Water 303
(iii) As long as the nickel loading is low, the D2EHPA-IS can be used
many times without losing its adsorption ability except that using
OS as a supporting material.
(iv) When the nickel loading becomes high, the nickel–D2EHPA
complex tends to dissolve into the aqueous phase; thus, the
D2EHPA-IS lose their adsorption abilities.
Therefore, D2EHPA-IS using KFO, OC, and XAD7HP as supporting
materials can be used for the batch treatment of the rinse water in the low
loading region.
ACKNOWLEDGMENT
One of the authors, Hai Trung Huynh, gratefully acknowledges the
financial support provided by the Japan Science and Technology Cooperation
under the STA fellowship.
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