Sorption of cadmium on humic acid: Mechanistic and kinetic studies with atomic force microscopy and X-ray absorption fine structure spectroscopy
Bibliographic record
Abstract
Humic acids (HA) constitute a major fraction of the organic matter in soils and sediments. Little is known about the kinetics and mechanisms of Cd sorption by HAs, especially those pertaining to the surface features and structure of the Cd-humate complexes. We investigated Cd sorption by HA using the conventional batch method, N 2 -BET method, atomic force microscopy (AFM), and extended X-ray absorption fine structure (EXAFS) spectroscopy to gain a better understanding of the kinetics and mechanisms. Cadmium sorption by HA can be described by the parabolic diffusion equation. The increase in the apparent diffusion coefficient with an increase in the initial Cd concentration was less pronounced at higher initial Cd concentrations, apparently due to an enhancement in aggregation of the Cd-humate complexes. The HA before and after Cd sorption at Cd concentrations ≤ 10 –6 M in different reaction times was spheroidal in shape. The Cd-humate complexes formed at 10 –4 and 10 –3 M Cd gradually changed to resemble the shape of a bean with increasing reaction time, thereby substantially decreasing their specific surface. Cadmium ions raveled the spheroidal HA particles into a bean-like structure by coordinating to six O atoms from the functional groups of HA, with a Cd-O distance of 2.297(2) Å. The Cd-O bond strength decreased with increasing initial Cd concentration. Key words: Cadmium, humate complexes, conformation, atomic force microscopy, EXAFS
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 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 | 0.002 |
| 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 teacher head, 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".