On the basis of homogeneous liquid-liquid extraction (HoLLE) with Zonyl FSA to plating water containing 1 mg palladium, 96.6% of the palladium was extracted into the sedimented liquid phase. After phase separation, the volume ratio (Va/Vs) of the aqueous phase (Va) and the sedimented liquid phase (Vs) was 556 (50 mL → 0.09 mL). The assessment of the potential implementation of this procedure to wastewater treatment showed that HoLLE was satisfactorily achieved when the volume was scaled up to 1000 mL. Moreover, HoLLE was conducted to real palladium plating wastewater generated in the plating industry. 94.5% of the palladium was extracted into the sedimented liquid phase. After phase separation, the volume ratio (Va/Vs) of the aqueous phase (Va) and the sedimented liquid phase (Vs) was 500 (50 mL → 0.1 mL). In addition, HoLLE could separate palladium from coexisting metals in real plating wastewater. This knowledge is expected to lead to the development of new separation and concentration technologies of rare metals from real plating wastewater.
The multi-functionalization and miniaturization of electronic devices is accompanied by a growing density of their components. Highly efficient electronic devices contain many parts, such as connectors and sensors, involving precious metal plating. Gold plating is widely implemented in wiring and contact materials in the electronic industry because it provides excellent corrosion resistance and electric conductivity [
Recently, the potential use of plating wastewater as a metal resource has attracted considerable attention. Currently, most plating wastewater treatment procedures rely on sludge reclamation after pH adjustment. In Japan, plating industries have been reported to produce 50,000 tons of sludge per year, and almost all of this sludge is reclaimed [
Precious metal recovery from plating wastewater relies on economically and environmentally suitable hydrometallurgical technologies such as solvent extraction, which has been extensively applied at the industrial scale [
To lower the wastewater treatment costs, the volume of the plating wastewater is often reduced by heat treatment in a specialized facility. Therefore, an effective metal extraction system is required. To meet this requirement, in this study, an extraction system exploiting the high efficiency and recovery of HoLLE was developed for palladium plating wastewater.
Palladium plating consisting of dichlorotetraammine palladium (1 wt%), ammonium nitrate (15 wt%), and water (84 wt%) received from Ibaraki Plating Kogyo Co., Ltd. (Ibaraki, Japan) was used in this study. The palladium concentration of the plating water in this experiment was determined to be 4.34 g∙L−1 by inductively coupled plasma optical emission spectrometry (ICP-OES). Aqueous metal ion solutions were prepared by diluting 1000 mg∙L−1 standard solutions obtained from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). A Zonyl FSA (CF3(CF2)nCH2CH2SCH2CH2CO2H, n = 6 - 8, DuPont, Tokyo, Japan) solution was prepared by diluting the pure substance with an equivalent amount of distilled water. Nitric acid, hydrochloric acid, ammonia, and other basic chemicals were obtained from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). All the reagents used in this study were of analytical grade.
The following instruments were utilized in this study: an M-12 pH meter manufactured by Horiba (Kyoto, Japan), a 7780 centrifugal separator manufactured by Kubota (Tokyo, Japan), an XGT-5000WR X-ray fluorescence spectrometer manufactured by Horiba (Kyoto, Japan), and an ICP ULTIMA2 ICP-OES manufactured by Horiba (Kyoto, Japan).
A 1000 mg∙L−1 palladium standard solution was added to a 50 mL centrifuge tube such that 1 mg of palladium was placed in the tube. 13.4 M ammonia (1 mL) was then added to the centrifuge tube, and the volume was adjusted to 30 mL with distilled water. The pH of the solution was adjusted to 2.0 using 5 M nitric acid. Next, acetone (10 mL) and 50 v/v% Zonyl FSA (1 mL) were added to the mixture, and the volume was adjusted to 50 mL with distilled water. The solution was centrifuged at 2500 rpm for 30 min. After phase separation, the sedimented liquid phase was collected using a microsyringe.
Palladium plating water (30 mL) containing 1 mg palladium was added to a 50 mL centrifuge tube, and the pH of the solution was adjusted to 2.0 using 5 M nitric acid. Next, acetone (11 mL) and 50 v/v% Zonyl FSA (1 mL) were added to the mixture, and the volume was adjusted to 50 mL with distilled water. The solution was centrifuged at 2500 rpm for 30 min. After phase separation, the sedimented liquid phase was collected using a microsyringe.
The performance of HoLLE was evaluated for a palladium-ammine complex in weakly acidic aqueous media using Zonyl FSA. Upon the addition of 13.4 M ammonia, the orange-colored palladium standard solution instantly became colorless and transparent, suggesting the formation of the palladium-ammine complex. On the basis of palladium-ammine complex, phase separation was satisfactorily completed by HoLLE in weakly acidic aqueous media. After phase separation, approximately 100 µL of each aqueous and sedimented liquid phase were collected using a microsyringe. These solutions were then dropped onto a filter paper and analyzed by X-ray fluorescence. The results of the analyses are shown in
The ICP-OES analysis of the aqueous phase revealed that 100% of the palladium was quantitatively extracted into the sedimented liquid phase, indicating that it was possible to concentrate palladium via HoLLE using Zonyl FSA.
HoLLE using Zonyl FSA was reversible with the pH change in the solution, corresponding to below and above the pKa of Zonyl FSA [
Next, the effect of the water-soluble organic solvent on palladium recovery was evaluated because this organic solvent significantly contributes to phase separation. When dioxane, tetrahydrofuran, or acetone was added, the phase separation was satisfactory. This suggested that the formation of the sedimented liquid phase depended on the solubility of Zonyl FSA in the water-soluble organic solvent. The volume of the sedimented liquid phase amounted to approximately 100 µL in dioxane and acetone but was a little larger in tetrahydrofuran (approximately 130 µL). The palladium recovery was 94% in dioxane, which was lower than that in tetrahydrofuran and acetone. Consequently, acetone was chosen for the remainder of the experiment. The acetone concentration was then optimized when it was 0 - 30 vol.%. Insoluble matter, which was believed to be Zonyl FSA, was detected near the sedimented liquid phase when the acetone concentration was 0 - 2 vol.%. This insoluble matter persisted even when the sedimented liquid phase formed from 6 - 12 vol.% acetone. Because the sedimented liquid phase was satisfactorily formed in 16 - 30 vol.% acetone, the palladium recovery was evaluated in this concentration range. Approximately 95% of the palladium was extracted in the sedimented liquid phase for these acetone concentrations (
Finally, the influence of Zonyl FSA concentration on HoLLE was determined (
Phase separation | Recovery (%) | pH (Before separation) | pH (After separation) |
---|---|---|---|
× | - | 9.82 | 9.77 |
× | - | 8.99 | 8.89 |
○ | 100 | 1.99 | 2.68 |
○ | 100 | 1.85 | 2.30 |
○ | 100 | 1.66 | 2.01 |
○ | 100 | 1.40 | 1.63 |
○ | 100 | 1.24 | 1.42 |
○ | 100 | 1.02 | 1.20 |
The pH (Before separation) was measured before addition of Zonyl FSA and acetone. Added palladium weight: 1 mg, [Ammonia]T = 0.267 M, [Acetone]T = 20 vol.%, [Zonyl FSA]T = 1.00 vol.%.
increasing Zonyl FSA concentration, and was almost 100% above 1.0 vol.% Zonyl FSA. Therefore, the Zonyl FSA concentration was set at 1.0 vol.% for the remainder of the experiment.
Palladium recovery from plating water containing a palladium-ammine complex was performed under the HoLLE conditions optimized for pure palladium solutions. Similar to the pure palladium solution, HoLLE was performed with and without ammonia addition for the plating water. The phase separation occurred in the absence of ammonia because the palladium-ammine complex already existed in the plating water. Therefore, the extraction was performed without ammonia addition. The phase separation of plating water with 1mg palladium was achieved by HoLLE using Zonyl FSA (
These results suggest that the HoLLE-based approach effectively concentrated palladium from plating water.
To assess the applicability of this approach to industrial plating water, palladium was also concentrated from plating water by HoLLE. The total volume was increased to 1000 mL, which is twenty times higher than the original volume, whereas the remaining conditions were maintained identical to the optimized ones. Phase separation was satisfactorily completed (
This data showed that HoLLE resulted in high volume ratio and high recovery upon scale-up. Moreover, because of scale-up experiment without centrifugal separation, it was confirmed that phase separation was satisfactorily completed with only addition of reagents.
The palladium concentration of these plating water samples was 33.3 mg∙L−1, which was equivalent to 1 and 20 mg palladium in 30 and 600 mL solutions, respectively. Industrial plating wastewater results from a mixture of plating bath and rinse water bath and has been reported to contain 100 - 400 mg∙L−1 of metals in Japan [
confirms that HoLLE effectively extracted palladium from wastewater in plating facilities. In this concentration range, the recovery gradually decreased with increasing palladium concentration (
The sedimented liquid phase contained palladium and Zonyl FSA. Back-extraction by addition of a solvent [
To confirm the effect of coexisting metals, except palladium, HoLLE was performed to real palladium-nickel plating wastewater generated in the plating industry. Plating water and plating wastewater in palladium-nickel plating compositions in palladium-nickel plating are shown in
These results show that it is possible to simultaneously concentrate palladium and separate coexisting substances.
Palladium was extracted from plating water by HoLLE in the presence of Zonyl FSA. For plating water with 1 mg palladium, palladium recovery amounted to 96.6%, and the volume ratio was 556 (50 mL → 0.09 mL). Performance assessment for the potential use of this approach for wastewater treatment demonstrated that the phase separation was satisfactorily achieved at the scaled-up volumes. Moreover, this extraction approach was applicable
Plating water (mg∙L−1) | Plating waste water (mg∙L−1) | |
---|---|---|
Pd | 15200 | 29.6 |
Ni | 9280 | 17.7 |
Au | Not detected | Not detected |
Cu | 180 | 0.4 |
Weight in the plating waste water (mg) | Weight in the sedimented liquid phase (mg) | Recovery (%) | |
---|---|---|---|
Pd | 0.888 | 0.839 | 94.5 |
Ni | 0.531 | 0.130 | 24.6 |
Au | Not added | - | - |
Cu | 0.012 | 0.007 | 57.2 |
to plating wastewater at standard industrial concentrations, as well as the real plating wastewater. This knowledge is expected to lead to the development of new separation and concentration technologies of rare metals from real plating wastewater.
These results are related to special power supply location prefecture technology promotion work by the Ministry of Education, Culture, Sports, Science and Technology, Japan. The authors would like to express their appreciation to Ibaraki Plating Kogyo Co., Ltd. (Ibaraki, Japan) for providing palladium plating water and real palladium plating wastewater. Finally, the authors would like to thank Enago (www.enago.jp) for the English language review.
TakeshiKato,ShukuroIgarashi,OsamuOhno,ShotaroSaito,RyoAndo, (2016) Homogeneous Liquid-Liquid Extraction (HoLLE) of Palladium in Real Plating Wastewater for Recovery. Journal of Environmental Protection,07,277-286. doi: 10.4236/jep.2016.72024