Selective Recovery of Precious Metals from Acidic Leach Liquor of Circuit Boards of Spent Mobile Phones Using Chemically Modified Persimmon Tannin Gel
Bibliographic record
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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".