Abiotic reduction of 2-line ferrihydrite: effects on adsorbed arsenate, molybdate, and nickel
Bibliographic record
Abstract
The abiotic reduction of X-ferrihydrite (X-FH, where X = 0, As, Mo, or Ni at various Fe/X molar ratios) was investigated by reacting Fe(II)(aq) at solution concentrations of 0.5 mM or 10 mM and at target pH values of 8 or 10 (using lime water as a base) for 7 days. Under all reaction conditions tested, the measured pH was always lower than the target; this difference was greatest for As-FH (at up to 5 pH units). The control FH sample behaved as expected and transformed to lepidocrocite (LP) and goethite (GT) phases. For As-FH, the sample containing less As (Fe/As = 32.9) transformed to LP–GT phases but phase transformation in the sample with more As (Fe/As = 4.47) was inhibited. Solution concentrations of As were below the detection limit for the Fe/As 32.9 sample but As release was evident for the Fe/As 4.47 sample. For Mo-FH, phase transformation to LP–GT phases was observed at lower target pH (8) conditions under both reacting Fe(II)(aq) concentrations. At the higher target pH (10) and using 0.5 mM Fe(II)(aq), phase transformation inhibition was observed for Mo-FH varieties that contained both high (Fe/Mo 12.5) and low (Fe/Mo 31.5) concentrations of Mo. This is the first time an element forming an outer-sphere complex on FH (e.g., Mo) has been shown to retard phase transformation; such phenomena are usually observed for metalloids that form inner-sphere complexes with FH (e.g., As). Under all conditions, Mo was released into solution (up to 340 ppm) and under some conditions was then readsorbed by the solid phase. Finally, all Ni-FH samples exhibited phase transformation under the reaction conditions tested; however, magnetite (MG) and a green rust-like phase were observed in addition to the LP–GT phases. Under all reaction conditions, the largest amount of Ni was released into solution on the first day of reaction, after which the amount in solution decreased with time due to its readsorption into the solid phase.
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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 | 0.000 | 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) | 0.000 | 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".