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  • Removal of Nickel from ElectrolessNickel Plating Rinse Water with


    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


    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:


    Vol. 21, No. 2, pp. 291305, 2003

    DOI: 10.1081=SEI-120018951 0736-6299 (Print); 1532-2262 (Online)Copyright # 2003 by Marcel Dekker, Inc.


  • 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 nickelD2EHPA

    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.


    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.[14] 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


    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 isbecoming 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]


    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.


    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, anaverage pore size of 4550 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 liquidsolid

    phase ratio of 50 cm3=g dried non-impregnated support (DNIS) except theexperiments 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 of50 cm3=g DNIS by vigorous vertical shaking for one hour. When the durabilityfor repeated use of the IS was investigated, the D2EHPA-IS after the

    adsorptionelution 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


    Composition of the Rinse Water

    The composition of the simulated rinse water was measured, and the result

    is shown in Table 1. The


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