On the precipitation and stability of scorodite produced from sulphate media at 950C
Bibliographic record
Abstract
Arsenic is a major contaminant in the non-ferrous extractive metallurgical industry and its disposal poses a serious environmental threat. Precipitation of arsenic from aqueous acidic solutions in the form of crystalline scorodite (FeAsO4.2H2O), which is a naturally-occurring mineral, is proposed as an arsenic fixation method. The production of scorodite is usually done in autoclave at high temperature and pressure. However, in a breakthrough at McGill University, a step-wise neutralization procedure has been developed where scorodite can be formed at ambient pressure (95°C). This work investigates the relation between precipitation conditions in sulphate media with the crystallinity, yield, and above all, solubility of scorodite produced. This work has investigated the effect of (1) type of seed, (2) type of base, (3) cationic and anionic additives, (4) Fe/As ratio, and (5) presence of Fe(II) in the precipitation media. It was found that crystalline scorodite can be produced via the use of various types of seed such as hematite and gypsum in addition to scorodite. The stability of the product was not found to be affected measurably upon change of base from MgO to CaO and in the presence of various cations (Cu, Zn, Ni, Co, and Mn) and anions (sulphate, nitrate and phosphate). Most solubilities measured were between 1 and 3 mg/L at pH 5. Solubilities as low as 0.5 mg/L were found when Fe(III):As(V) was 3:1 but the yield was low. Following these results, Fe(II) was added to the system and solubilities as low as 0.2 ppm were observed with yields of over 80% in a single precipitation step.
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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".