Desorption Behavior of Cd, Zn and Pb Sorbed on Hydroxyaluminum- and Hydroxyaluminosilicate-Montmorillonite Complexes
Bibliographic record
Abstract
Abstract There is a clear gap in the understanding of the desorption patterns of metals sorbed on soils and clays, despite their importance in the mobility, transport and fate of metals in natural environments. In this study, we investigated the desorption behavior of Cd, Zn and Pb sorbed on montmorillonite (Mt) and on hydroxyaluminum (HyA)- and hydroxyaluminosilicate (HAS)-Mt complexes. At pH 6.5, 2.5 g L–1 of HyA-Mt and HAS-Mt sorbed almost all of the 10–6 M Cd, Zn or Pb, while Mt under the same condition sorbed ~48, 49 and 55% of the added Cd, Zn and Pb, respectively. Based on pH50 values, the selectivity of metal sorption on Mt was Pb > Zn > Cd, and on the complexes, it was Pb ≫ Zn = Cd. In general, larger fractions of sorbed metals were remobilized from Mt than from the complexes. Again, in comparison with Pb, larger fractions of sorbed Cd and Zn were remobilized from different clays. Reducing the pHs of the equilibrium sorption systems from a fixed point (6.5) to different points (6.0, 5.5, 5.0, 4.5, and 4.0) and from different points (6.5, 6.0, 5.5, 5.0, and 4.5) to a fixed point (4.0) both yielded hysteretic metal desorption patterns. The fractions of Cd and Zn desorbed through Na and Cu exchange from the clays, especially from the complexes, were very different, indicating the existence of cation exchangeable metal sorption sites of weak and strong affinities on the complexes. Based on the EDTA-extractable fractions of Cd and Zn from HAS–Mt and HyA-Mt, it appeared that HyA–metal bonds are stronger than the HAS–metal bonds. Compared with other agents, acetic acid remobilized the highest fractions of all metals irrespective of the type of clays, with a concomitant release of Al or Al + Si. The Pb-HyA/HAS-Mt bonds were, however, still much too strong to be broken substantially by this mechanism. The results accomplished in this study suggest further attention to the fundamental understanding of the mobility, fate, bioavailability and toxicity of the concerned metals in soils and related environments.
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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) | 0.000 | 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) | 0.001 | 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".