Overview
Taniguchi and colleagues tested chitosan nanofiber hydrogel for selective recovery of palladium from tin-rich plating wastewater. This is in-scope mitigation and metal-recovery evidence, not chitosan occurrence evidence.
Key numbers
The English abstract states that the plating wastewater contained palladium 2 ppm and tin 200 ppm. The Japanese methods/results text reports untreated plating wastewater at pH 1.12 with Pd 1.89 ppm and tin (Sn) 218 ppm.
After pH adjustment to pH 4.0 and centrifugation to remove precipitated tin hydroxide, the Sn concentration in the supernatant decreased from 218 ppm to 16 ppm. The supernatant contained Pd 1.99 ppm before hydrogel adsorption.
For standard mixed solutions containing Pd, Au, and Pt, the CNF hydrogel adsorption rates were Pd 76.8%, Au 89.5%, and Pt 21.4%. For Pd standard solution at 10 ppm, adsorption increased with pH: 19.4% at pH 1.0, 85.3% at pH 2.0, 95.3% at pH 3.0, and 98.4% at pH 4.0. At initial Pd concentration 33.5 ppm, Pd recovery per gel weight was 41.0 mg/g.
Table 1 reports adsorption-isotherm parameters:
| Metal | Langmuir qm (mg/g) | Langmuir KL (L/mg) | Langmuir R2 | Freundlich KF (mg/g) | Freundlich n | Freundlich R2 |
|---|---|---|---|---|---|---|
| Pd | 0.0049 | 2.58 | 0.952 | 138.2 | 5.09 | 0.283 |
| Au | -0.0012 | -0.119 | 0.194 | 121.0 | 0.858 | 0.966 |
| Pt | 0.0048 | 0.0954 | 0.780 | 17.41 | 1.25 | 0.946 |
In 5 mL plating wastewater treated with 5 mg CNF hydrogel, the Pd adsorption rate was 89.5% and Pd recovery rate was 86.1%. The Sn adsorption rate was 90.1% and Sn recovery rate was 43.7%.
In the 500 mL scale-up experiment, wastewater/CNF hydrogel ratios of 2.5, 5, 10, and 50 gave Pd recovery rates of 43.5%, 52.8%, 50.4%, and 34.7%, respectively. Sn recovery rates at the same ratios were 9.04%, 1.93%, 0.84%, and 0.12%, respectively, which the authors interpret as selective Pd recovery under higher wastewater/CNF hydrogel ratios.
Methods (brief)
CNF hydrogel was prepared from chitosan nanofiber dispersion, PEGDA, and ammonium persulfate. Adsorption experiments used Pd, Au, and Pt standards and plating wastewater. Metal concentrations were measured by ICP-OES. Plating wastewater was adjusted from pH 1.12 to pH 4.0 with 1 M NaOH, centrifuged to remove precipitated Sn, then treated with CNF hydrogel.
Related evidence
Update history
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