CHARACTERIZATION OF ARSENATE-FOR-SULFATE SUBSTITUTION IN SYNTHETIC JAROSITE USING X-RAY DIFFRACTION AND X-RAY ABSORPTION SPECTROSCOPY
Bibliographic record
Abstract
Arsenic-bearing synthetic jarosite [KFe 3(SO4)2(OH)6] was characterized to elucidate the form of the arsenic. The XANES spectra indicate that the As occurs exclusively as As 5+ , nominally as AsO4, consistent with the valence state of the arsenic in the reagents used for the syntheses. X-ray-diffraction analyses show that at least 9.9 wt.% AsO 4 can be structurally incorporated in the jarosite. Cell refinements show that both a and c increase slightly as the proportion of AsO 4 increases. The EXAFS spectra indicate that the As–O interatomic distances are uniform at 1.68 A, and that the coordination numbers, 4.6 ± 1.7 to 5.4 ± 1.7, are indicative of tetrahedral coordination of the oxygen atoms around the central arsenic atom. The As–Fe interatomic distances are approximately 3.26 A, with the coordination numbers being around 2, confirming that AsO 4 substitution for SO 4 occurs in synthetic jarosite. The larger arsenate ions seem to be accommodated in the tetrahedral sites by the expansion of the unit cell and by deficiencies in adjacent Fe–O(OH) octahedral sites. The observed increases in the unit-cell parameter c with increasing arsenate-for-sulfate substitution are similar to those of selenate and chromate substitutions for sulfate in jarosite. We believe t hat the Fe occupancy affects the amount of arsenate substitution, which is limited to about 17 mole % AsO 4/(AsO4 + SO4). We contend that the charge imbalance caused by the substitution of arsenate is compensated by the partial protonation of the AsO 4 and SO4, which would be consistent with the ionic species actually present in the synthesis media.
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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 | 0.001 |
| 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 | 0.001 | 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".