Removal of Nickel from Electroless Nickel Plating Rinse Water with Di(2‐Ethylhexyl)phosphoric Acid‐Impregnated Supports

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<ul><li><p>Removal of Nickel from ElectrolessNickel Plating Rinse Water with</p><p>Di(2-Ethylhexyl)phosphoric</p><p>Acid-Impregnated Supports</p><p>Hai Trung Huynh and Mikiya Tanaka*</p><p>Research Institute for Green Technology, National Institute of</p><p>Advanced Industrial Science and Technology (AIST),</p><p>Onogawa, Tsukuba, Ibaraki, Japan</p><p>ABSTRACT</p><p>Electroless nickel plating technology is playing an increasingly important</p><p>and indispensable role in many fields such as the electronic and automobile</p><p>industries. As a result, the treatment of the rinse water containing about</p><p>50 mg=dm3 of nickel is becoming a serious environmental problem.Although this water is currently treated by the conventional precipitation</p><p>method, a method without sludge generation is highly desired. This</p><p>study explores the possibility of removing and recovering nickel from</p><p>the rinse water with di(2-ethylhexyl)phosphoric acid-impregnated supports</p><p>(D2EHPA-IS). Macroporous polymer and oil adsorbents made of synthetic</p><p>and natural fibers as the supporting materials were tested for the nickel</p><p>*Correspondence: Mikiya Tanaka, Research Institute for Green Technology, National</p><p>Institute of Advanced Industrial Science and Technology (AIST), Onogawa, Tsukuba,</p><p>Ibaraki 305-8569, Japan; E-mail: mky-tanaka@aist.go.jp.</p><p>SOLVENT EXTRACTION AND ION EXCHANGE</p><p>Vol. 21, No. 2, pp. 291305, 2003</p><p>DOI: 10.1081=SEI-120018951 0736-6299 (Print); 1532-2262 (Online)Copyright # 2003 by Marcel Dekker, Inc. www.dekker.com</p><p>291</p></li><li><p>removal abilities from simulated rinse water. In the batch experiments,</p><p>more than 90% of the nickel can be adsorbed by these D2EHPA-IS without</p><p>pH adjustment. The adsorption of nickel reaches the equilibrium within</p><p>1.2 ks at 298K at a shaking rate of 140 rpm. The pH-dependency of the</p><p>nickel adsorption by the D2EHPA-IS shows that the nickel is adsorbed by a</p><p>cation exchange reaction. The adsorbed nickel can then be readily eluted</p><p>with mineral acids. Most of the IS can be used many times without losing</p><p>their adsorption abilities. In the column experiments, the breakthrough</p><p>curves of nickel for these supports indicate that the nickelD2EHPA</p><p>complex formed at the high nickel loading region tends to dissolve into</p><p>the aqueous phase. These findings lead to the conclusion that most of the</p><p>studied D2EHPA-IS are effective for the removal and recovery of nickel</p><p>from an electroless nickel plating rinse water in batch mode.</p><p>Key Words: Nickel; Adsorption; Di(2-ethylhexyl)phosphoric acid;</p><p>Electroless nickel plating rinse water; Impregnated supports.</p><p>INTRODUCTION</p><p>Many researchers have made efforts to remove heavy metals from</p><p>industrial wastewater by using several methods such as chemical precipitation,</p><p>adsorption, solvent extraction, ion exchange, and reverse osmosis.[14] Some</p><p>of these methods are expensive and have limitations. Currently, the usual</p><p>treatment technology of metal-bearing wastewater is chemical precipitation.</p><p>However, this method often creates secondary problems with sludge</p><p>generation.[5]</p><p>Among the many methods mentioned above, solvent extraction and ion</p><p>exchange are known to be effective for metal removal. Although they offer</p><p>many advantages, there are several unsolved problems such as (i) the loss of</p><p>organics; and the contamination of the water with organics for solvent</p><p>extraction, and (ii) slow kinetics for ion-exchange.[6] Extractant-impregnated</p><p>resins have been shown to be effective adsorbents for the metal removal from</p><p>diluted aqueous solutions.[7] They combine the advantages of the solvent</p><p>extraction and ion-exchange processes.[8] Also, oil adsorbents made of</p><p>synthetic and natural fibers can adsorb an extractant used in metal solvent</p><p>extraction and are expected to be the supports of the impregnated metal</p><p>adsorbents. Thus, extractant-impregnated supports (extractant-IS) would be</p><p>widely applicable for the treatment of heavy metals in wastewater.</p><p>Electroless nickel plating is a typical surface finishing technology and</p><p>plays an important role in the high-tech industries. As a result, the rinse water</p><p>from the electroless nickel plating containing about 50 mg=dm3 of nickel isbecoming a serious environmental problem. The objective of this study is to</p><p>292 Huynh and Tanaka</p></li><li><p>explore the possibility of removing and recovering nickel from the electroless</p><p>nickel plating rinse water with di(2-ethylhexyl)phosphoric acid (D2EHPA)-IS.</p><p>Di(2-ethylhexyl)phosphoric acid was selected as the extractant, because this is</p><p>a typical organophosphorous acid and known to extract nickel at a pH greater</p><p>than 2.9.[9,10]</p><p>EXPERIMENTAL</p><p>Simulated Rinse Water and Reagent</p><p>The simulated rinse water was prepared by diluting the spent bath</p><p>discharged from an electroless nickel plating plant in Japan. Ion exchange-</p><p>distilled water was used throughout this study. Chemicals used in this study</p><p>were all reagent grade except for the extractant. Di(2-ethylhexyl)phosphoric</p><p>acid was the product of Daihachi Chemical Industry Co., and was used as</p><p>received. Various concentrations of sodium hydroxide and hydrochloric acid</p><p>were used as the pH adjusting reagents. As eluting reagents, 2 mol=dm3</p><p>hydrochloric and 1 mol=dm3 sulfuric acids were used.</p><p>Support</p><p>The thermally bonded fabrics, KFO Mat P-185 (KFO), made of poly-</p><p>ethylene and polypropylene, the non-woven fabrics, Static Resistant Oil</p><p>Sorbent HP-556 (OS), made of polypropylene, and the natural fiber, Oil</p><p>Catcher KT-65 (OC), made of kapok fiber, produced by Kyushu Filter Industry</p><p>Co., Ltd., 3M Co., Ltd., and Kakui Co., Ltd., respectively, were supplied in the</p><p>form of sheets. Before impregnation, all the fibers were cut into</p><p>0.5 cm 0.5 cm pieces.The macroporous resin Amberlite XAD7HP, supplied by Rohm and Haas</p><p>Co., is a polymeric adsorbent with an acrylic ester matrix. On a dry basis, it</p><p>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.</p><p>Impregnation Procedure</p><p>The D2EHPA-IS were prepared as follows:[8,11] The supports were</p><p>washed with methanol, dried, and contacted with 10 vol.% D2EHPA in ethanol</p><p>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</p><p>volume of water. Finally, the supports were dried in an oven overnight at</p><p>353K. The concentration of D2EHPA held in the supports was determined by</p><p>Electroless Nickel Plating Rinse Water 293</p></li><li><p>the difference in weight before and after the impregnation. In some cases, the</p><p>concentrations of D2EHPA in the IS were also determined by the digestion</p><p>with the mixture of sulfuric and nitric acids followed by the phosphorous</p><p>analysis by ICP-AES (Seiko SPS4000). The results agreed with each other</p><p>within 5%.</p><p>Adsorption and Elution Procedures</p><p>In the batch equilibrium experiments, the desired amount of each</p><p>D2EHPA-IS and 10 cm3 of the simulated rinse water with the liquidsolid</p><p>phase ratio of 50 cm3=g dried non-impregnated support (DNIS) except theexperiments for nickel adsorption isotherm, and the very small amount of the</p><p>pH adjusting reagent (less than 2 cm3 of the 1 mol=dm3 HCl solution per 1 dm3</p><p>of the rinse water), when necessary, were placed in a stoppered 50 cm3-conical</p><p>flask and shaken at a rate of 140 rpm in a water bath maintained at 298K for</p><p>more than 12 hours to ensure equilibrium. A small amount of the aqueous</p><p>phase was then removed and appropriately diluted in order to determine the</p><p>nickel concentration. The nickel concentration in the IS was calculated on the</p><p>basis of mass balance. The adsorbed nickel was eluted separately by</p><p>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</p><p>adsorptionelution cycle was washed with water until chloride ion was not</p><p>detected in the filtrate, dried at 353K, and submitted to another adsorption</p><p>elution cycle.</p><p>In the kinetic runs, the contact of the two phases began under the same</p><p>conditions as those for the batch equilibrium experiments without adding the</p><p>pH adjusting reagent to the rinse water. During the experiment, the pH of</p><p>the aqueous phase was not kept at constant. At preset time intervals, the two</p><p>phases were separated, and the nickel concentration in the aqueous phase was</p><p>determined after appropriate dilution.</p><p>In the column experiments, 1 g of the D2EHPA-IS was packed in a glass</p><p>column with an inner diameter of 11 mm. The rinse water or the eluting</p><p>reagent was fed to the bottom of the column maintained at 298K, and the</p><p>effluent from the head was collected by a fraction collector.</p><p>The nickel concentrations in the aqueous solutions before and after</p><p>adsorption, and after elution were determined by ICP-AES. The pH values</p><p>in the aqueous phases were measured by a pH meter (Toa HM-60G). Sulfate,</p><p>phosphinate, and phosphonate ions, as well as lactic and propionic acids in</p><p>the simulated rinse water were analyzed using a capillary electrophoresis</p><p>apparatus (Otsuka CAPI-3200).</p><p>294 Huynh and Tanaka</p></li><li><p>RESULTS AND DISCUSSION</p><p>Composition of the Rinse Water</p><p>The composition of the simulated rinse water was measured, and the result</p><p>is shown in Table 1. The simulated rinse water is weakly acidic with high</p><p>concentrations of sodium, phosphonate, sulfate ions, and organic acids. Since</p><p>the nickel concentration in the spent bath was gradually changed due to</p><p>the slow precipitation of nickel phosphonate, the nickel concentration in the</p><p>simulated rinse water was varied from 20 to 50 mg=dm3; thus, the actual nickelconcentration will be described in the legend of each figure or table.</p><p>Batch Experiment</p><p>The relationship between the nickel adsorption percentage and equili-</p><p>brium pH is shown in Fig. 1. At the equilibrium pH of 3.9 for the D2EHPA-</p><p>impregnated OC and XAD7HP, and 4.2 for the impregnated KFO and OS</p><p>(these pH values are attained if the adsorption of nickel from the simulated</p><p>rinse water is done without pH adjustment), more than 90% of the nickel is</p><p>adsorbed. The nickel removal efficiency is abruptly reduced with decreasing</p><p>pH, suggesting that nickel is adsorbed by a cation exchange reaction. For</p><p>solvent extraction of nickel using D2EHPA,[10] nickel is not extracted at a pH</p><p>lower than 2.9. In addition, nickel is extracted from the simulated rinse water</p><p>using 48.5 g=dm3 D2EHPA dissolved in Shellsol D70 (Shell Chemicals) withthe phase ratio of 1 : 1; however, at the equilibrium pH of 3.9, the extraction</p><p>efficiency is only 50% in spite of the fact that the amount of D2EHPA per unit</p><p>Table 1. The composition and pH value ofthe simulated rinse water.</p><p>Component Concentration (mg=dm3)</p><p>Sodium 1020</p><p>Nickel 2050</p><p>Iron </p></li><li><p>volume of the aqueous phase was more than three times higher in the solvent</p><p>extraction (SX) than those in the IS. According to the nickel removal</p><p>percentages by adsorption and extraction, D2EHPA-IS are more effective</p><p>than SX using the same extractant.</p><p>The blank experiments show that OC itself adsorbs nickel to a slight extent;</p><p>that is, without pH adjustment, about 40% of the nickel is adsorbed at the</p><p>equilibrium pH of 5.0. This is probably because natural fibers (OC) have some</p><p>functional groups like OH. For other supports, nickel is not adsorbed at all.The difference among the pH dependency of the nickel adsorption by</p><p>each D2EHPA-impregnated fiber (OC, OS, and KFO) is not found; however,</p><p>over the entire investigated pH range, nickel adsorption is reduced in the order</p><p>of the impregnated supports: OC&gt;OS&gt;KFO in accord with the decreasedorder of the D2EHPA concentrations in the supports: OC&gt;OS&gt;KFO. On</p><p>Figure 1. The effect of equilibrium pH on the nickel adsorption. The nickel</p><p>concentration in the rinse water was 48.4 mg=dm3. The D2EHPA concentrations inthe IS (g=g IS) were 0.27 (KFO), 0.28 (OS), 0.39 (OC), and 0.37 (XAD7HP).</p><p>296 Huynh and Tanaka</p></li><li><p>the other hand, the pH dependency of the nickel adsorption by the D2EHPA-</p><p>impregnated XAD7HP is slightly less than those by the D2EHPA-impregnated</p><p>fibers. The reason for this is not clear, but would be related to the difference in</p><p>the structures of the fibers and XAD7HP.</p><p>Without adding the pH adjusting reagent to the rinse water, 100% of the</p><p>iron and zinc are adsorbed by all the IS, and due to their very low concentrations</p><p>we did not pay special attention to the adsorption of those metals hereafter.</p><p>The time courses of the nickel removal for the different D2EHPA-IS are</p><p>shown in Fig. 2. Under the present experimental conditions, the adsorption</p><p>equilibria are reached within 1.2 ks (20 min) for all the D2EHPA-IS, which</p><p>would be fast enough to remove nickel in the rinse water by batch mode. The</p><p>fibers seem to exhibit faster removal rates than the resin. This is probably due</p><p>to the diffusion resistance in the XAD7HP pores.</p><p>Figure 2. Time courses of nickel removal with D2EHPA-IS. The nickel concentration</p><p>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).</p><p>Electroless Nickel Plating Rinse Water 297</p></li><li><p>Figures 3 and 4 show the adsorption isotherm of nickel with D2EHPA-IS.</p><p>The isotherm was obtained by varying the solidliquid ratios. The pH of the</p><p>aqueous phase was not adjusted. As shown in Figs. 3 and 4, the amount of</p><p>adsorbed nickel increases with the rise in the aqueous nickel concentration,</p><p>particularly in the low nickel loading region. In the high nickel loading region,</p><p>the amount of adsorbed nickel tends to decrease with the rise in the aqueous</p><p>nickel concentration for the D2EHPA-impregnated fibers. This phenomenon,</p><p>though not clear for the D2EHPA-impregnated resin, is probably due to the</p><p>dissolution of the nickelD2EHPA complex into the aqueous phase and will</p><p>be discussed more later.</p><p>The adsorbed nickel is readily and completely eluted with 2 mol=dm3</p><p>hydrochloric or 1 mol=dm3 sulfuric acids. The elution efficiency does not</p><p>Figure 3. Adsorption isotherm of nickel with the D2EHPA-impregnated fibers. The</p><p>nickel concentration in the rinse water was 47.6 mg=dm3. The D2EHPA concentrationsin the IS (g=g IS) were 0.43 (KFO), 0.29 (OS), and 0.60 (OC).</p><p>298 Huynh and Tanaka</p></li><li><p>depend on the kinds of supports and acids, and achieves more than 95%</p><p>(unbalance within 5% is due to the experimental error) for all the D2EHPA-IS</p><p>(Table 2).</p><p>The durability for repeated use of the investigated D2EHPA-IS was tested</p><p>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</p><p>IS became an inert adsorbent for nickel after the 5th cycle (Fig. 5). However, for</p><p>other IS, the change in the nickel adsorption percentages is not found, and they</p><p>can be used many times without losing their adsorption abilities, indicating that</p><p>the loss of D2EHPA is negligible at the low nickel loading region.</p><p>Figure 4. Adsorption isotherm of nickel with the D2EHPA-impregnated XAD7HP.</p><p>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)].</p><p>Ele...</p></li></ul>

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