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Inan effort to develop sustainable materials and methods for therecovery and recycling of precious metals, we recently developed twodifferent adsorbents by cross-linking pure cellulose with either epichlorohydrinor concentrated sulfuric acid and then modifying the surface with N-aminoguanidine functional groups. The adsorption behaviorof these sorption materials toward Au(III) from a multicomponent mixtureof Pt(IV), Pd(II), and some base-metal ions was studied in hydrochloricacid media. Both of the adsorbents exhibited outstanding selectivitytoward precious metals, with a selectivity order of Au(III) ≫Pd(II) > Pt(IV), over base metals in a wide range of acid concentrations.These materials contain a number of positive centers in HCl mediathat function as sorption active sites for chloroanionic species ofAu(III), Pd(II), and Pt(IV). The chloroanionic species of the correspondingprecious metals were thus adsorbed on these materials through anion-exchange-coupledelectrostatic interaction. The sulfuric acid cross-linked materialexhibited improved selectivity and greater adsorption capacity comparedto the epichlorohydrin cross-linked adsorbent. As equilibrium wasachieved within an hour with quantitative adsorption, the effectivenessof the sulfuric acid cross-linked material with regard to Au(III)was exemplified by the fact that 1 kg of the dry adsorbent materialhad a capacity to load 9.2 mol, that is, nearly 1.8 kg of Au(III).Moreover, the adsorbed Au(III) was subsequently reduced to the elementalform, yielding metallic gold particles, thereby demonstrating theconsiderable improvements in efficiency and effectiveness of the noveladsorbents for the recovery of gold in comparison to current commercialresins. [ABSTRACT FROM AUTHOR]

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]