Selective Recovery of Precious Metals from Acidic Leach Liquor of Circuit Boards of Spent Mobile Phones Using Chemically Modified Persimmon Tannin Gel

Abstract

A tannin-based novel adsorbent, named "BTU-PT gel", was prepared by immobilizing bisthiourea (BTU) ligand on persimmon tannin (PT) extract. The adsorption behaviors of precious metal ions along with other coexisting base metal ions onto BTU-PT gel were studied by batch and continuous column methods. The gel exhibited remarkable selectivity 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) in 1−5 mol dm −3 hydrochloric acid. The adsorption of precious metal ions on the present gel was found to obey the typical monolayer type of Langmuir model, and the maximum adsorption capacity of the adsorbent was evaluated as 5.18 mol kg −1 for Au(III), 1.80 mol kg −1 for Pd(II), and 0.67 mol kg −1 for Pt(IV). Combination of ion exchange, electrostatic interaction, and coordination through the thiocarbonyl group is the mechanism of adsorption of precious metals on BTU-PT gel. In the case of Au(III) adsorption, the adsorbed species was simultaneously reduced to elemental gold by abundant polyphenolic groups of the tannin matrix. Elution by using acidothiourea solution in continuous column experiment recovered the adsorbed precious metals almost quantitatively. The results of a potential reusability test of the gel for consecutive adsorption and elution cycles by continuous column experiment indicated that the gel was stable and regenerated with undiminished metal uptake capacity up to five cycles. The real time applicability of the adsorbent for the recovery of precious metals from real industrial liquor was evaluated from actual acidic leach liquor of printed circuit boards of spent mobile phones. The gel selectively adsorbed precious metal species but exhibited negligible affinity toward base metals present in the leach liquor. The BTU-PT gel is a potential adsorbent for selective recovery of precious metals from acidic leachate of spent mobile phones containing elevated concentrations of base metals.

Selective Adsorption of AuIII from Aqueous Solution Using 2,5‑Dimercapto‑1,3,4‑thiadiazole Modified Persimmon Tannin

“…The peaks at 1247 and 1059 cm -1 are attributed to symmetrical and asymmetrical C-O-C stretching vibrations. 6 These peak positions are consistent with the reported literature. 6 After grafting DMTD, significant changes were observed.…”

“…6 These peak positions are consistent with the reported literature. 6 After grafting DMTD, significant changes were observed. The peak that corresponds to the O−H stretching vibration at 3423 cm -1 shifted to 3428 cm -1 , the band was broader, and the intensity was slightly weaker; these observations indicate that cross-linking occurred at the hydroxyl group.…”

“…Further, DMTD-PT had a superior adsorption capacity (equivalent to 0.42 mmol g -1 ) for Au III and had a comparable adsorption capacity as that of the reported adsorbents of thiourea-modified Amberlite XAD ). However, it was lower than that of bisthiourea-modified BTU-PT (5.18 mmol g -1 ), 6 and this is probably caused by the significant difference in the N and S contents of the biosorbents.…”

“…3 Over the past decade, persimmon peels and residues, whose main composition is persimmon tannin (PT), 4 have attracted a great deal of attention among waste agricultural byproducts because of the plentiful resources and moderate conditions for chemical modification. 4 Relevant work has mainly focused on grafting amine-and thiourea (TU)-based modifiers on the PT matrix [5][6][7] to improve both adsorption capacity and selectivity for precious metals. It is imperative to develop new modifiers to provide more choices for modifying biosorbents for various purposes.…”

Tannins in Mineral Processing and Extractive Metallurgy

“…It was shown the that tannin gel could be successfully regenerated for up to 5 cycles of use. Finally, an industrial study was done using actual circuit board leach liquor and as indicated in the initial laboratory work, the BTU-PT tannin gel acted as a successful adsorbent for precious metals while not taking up base metals in solution [32]. Work done by Yurtsever and Sengil at Sakarya University in Turkey explored the use of a valonia tannin gel for the removal of silver ions from solution.…”