Effect of humic acid coating on arsenic adsorption on ferrihydrite-kaolinite mixed systems
Bibliographic record
Abstract
The reactivity of the colloids formed in soil environments results from complex interactions between clay minerals, (oxy)hydroxides and organic matter of soils. The adsorption/desorption equilibria and kinetics of anionic and cationic species on/from natural colloids could substantially differ compared with their interaction with pure minerals. The objective of this study was to investigate the arsenite and arsenate equilibria and the kinetics of arsenite adsorption on ferrihydrite-coated kaolinite as influenced by the presence of humic acid coverage. The Langmuir adsorption maximum and affinity of arsenite and arsenate adsorption on the kaolinite-ferrihydrite system was reduced by the presence of the humic acid. The enthalpy of adsorption on the kaolinite-ferrihydrite system, measured with isothermal titration calorimetry, was –24.4 kJ mol –1 for arsenite and –39.9 kJ mol –1 for arsenate, and was only slightly decreased by the humic acid coating. The kinetics of arsenite adsorption was substantially influenced by the presence of the humic coverage, resulting in the decrease in the rate constant, the Arrhenius heat of activation, and the pre-exponential factor (indicative of the collision frequency of the sorbate and the sorbent). The hampering effect of the humic acid on arsenic adsorption was attributable to the blocking by the organic ligand of the adsorbing sites, coupled with the steric hindrance of the large organic molecules, which restricted the arsenic to approach the surfaces. Key words: Arsenic, adsorption, kinetics, kaolinite, ferrihydrite, humic acid
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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 | 0.002 | 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) | 0.000 | 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".