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Highlights: [•] Low cost and environmentally green adsorption material. [•] Remarkable selectivity for adsorption of precious metals over base metal ions. [•] High efficient for preconcentration and separation of precious metals. [•] Superior performance over commercial anion exchange resin. [Copyright &y& Elsevier]

Abstract: A new adsorption gel has been developed by immobilizing N-aminoguanidine (AG), a chelating ligand, on persimmon tannin extract through consecutive reactions. Adsorption behavior of the gel was investigated for the adsorptive separation and recovery of precious metal ions from varying concentration of HCl medium. The adsorption isotherms of precious metal ions on the gel were described by the typical monolayer type of Langmuir model and the maximum adsorption capacities were evaluated as 8.90molkg−1 for Au(III), 2.01molkg−1 for Pd(II) and 1.01molkg−1 for Pt(IV). Real time applicability of the gel was examined for the recovery of precious metals from actual leach liquor of e-waste leached with chlorine containing hydrochloric acid. The gel was found to be highly efficient and selective for the uptake of targeted metal ions in the presence of excess base metal ions and also exhibited superior selectivity over commercially available anion exchange resins. [Copyright &y& Elsevier]

A tannin-based novel adsorbent, named “BTU-PTgel”,was prepared by immobilizing bisthiourea (BTU) ligand on persimmontannin (PT) extract. The adsorption behaviors of precious metal ionsalong with other coexisting base metal ions onto BTU-PT gel were studiedby batch and continuous column methods. The gel exhibited remarkableselectivity for precious metal ions such as Au(III), Pd(II), and Pt(IV)over base metal ions such as Cu(II), Fe(III), Ni(II), and Zn(II) in1–5 mol dm–3hydrochloric acid. The adsorptionof precious metal ions on the present gel was found to obey the typicalmonolayer type of Langmuir model, and the maximum adsorption capacityof the adsorbent was evaluated as 5.18 mol kg–1forAu(III), 1.80 mol kg–1for Pd(II), and 0.67 molkg–1for Pt(IV). Combination of ion exchange, electrostaticinteraction, and coordination through the thiocarbonyl group is themechanism of adsorption of precious metals on BTU-PT gel. In the caseof Au(III) adsorption, the adsorbed species was simultaneously reducedto elemental gold by abundant polyphenolic groups of the tannin matrix.Elution by using acidothiourea solution in continuous column experimentrecovered the adsorbed precious metals almost quantitatively. Theresults of a potential reusability test of the gel for consecutiveadsorption and elution cycles by continuous column experiment indicatedthat the gel was stable and regenerated with undiminished metal uptakecapacity up to five cycles. The real time applicability of the adsorbentfor the recovery of precious metals from real industrial liquor wasevaluated from actual acidic leach liquor of printed circuit boardsof spent mobile phones. The gel selectively adsorbed precious metalspecies but exhibited negligible affinity toward base metals presentin the leach liquor. The BTU-PT gel is a potential adsorbent for selectiverecovery of precious metals from acidic leachate of spent mobile phonescontaining elevated concentrations of base metals. [ABSTRACT FROM AUTHOR]

Abstract: An adsorption gel was prepared by crosslinking the persimmon tannin with concentrated sulfuric acid and adsorption behavior of Au(III) from acidic chloride media on the crosslinked gel as well as crude persimmon tannin powder was evaluated. The crosslinked gel exhibited 100% adsorption of Au(III) over a whole concentration range of HCl from 0.1 to 6.0M (M=moldm−3) while crude persimmon tannin powder achieved 100% adsorption only in the low concentration region of HCl. The maximum adsorption capacity of the crosslinked gel for Au(III) was evaluated as high as 7.7mol/kg whereas it was only 5.8mol/kg for the crude tannin powder. The phenomenon of adsorption coupled reduction is considered to be responsible for the high adsorption of Au(III). The reduction of Au(III) to its elemental form was confirmed by XRD and digital micrograph of the adsorbents after the adsorption of Au(III). The reaction kinetics at different temperatures for both adsorbents was evaluated in terms of pseudo-first-order and pseudo-second-order kinetic models. As revealed by the high activation energy (E a) value, adsorption of Au(III) on both the adsorbents was found to be a chemical phenomenon. [Copyright &y& Elsevier]

Persimmon tannin was chemically modified to prepare a quaternary amine type of adsorption gel, named as quaternary amine modified persimmon tannin (QAPT) gel. The QAPT gel has been used to investigate the adsorption behaviors for Au(III), Pd(II), and Pt(IV) from HCl media. It was found that the gel exhibited good selectivity towards precious metals over a wide concentration range of HCl. However, it exhibited poor affinity towards base metals such as Cu(II), Fe(III), Ni(II), and Zn(II). The adsorption isotherms of the gel for precious metal ions were described by the Langmuir model. The maximum adsorption capacities for Au(III), Pd(II), and Pt(IV) were evaluated as 4.16, 0.84, and 0.52 mmol g−1, respectively. Although the anion exchange is the main mechanism for the adsorption of anionic species of Au(III), Pt(IV), and Pd(II), adsorption of Au(III) is followed by subsequent reduction, which results in the extraordinary high adsorption capacity for Au(III). Adsorption behavior of QATP gel for Au(III) was also compared to that of the persimmon tannin, the feed material. [ABSTRACT FROM PUBLISHER]