The design and application of sequential extractions for mercury, Part 2. Resorption of mercury onto the sample during leaching
Bibliographic record
Abstract
This paper examines the stability of Hg in a six-step sequential extraction scheme, focusing in particular on the first leach designed to extract ‘soluble’ Hg in sediment and soil samples. The recovery of Hg as a spike (Hg 2+ , equivalent to 15 ng g −1 in a sample), alone and mixed with a background granite ‘GG’, was found to be low and dependent on the time of extraction (15–60 min) in the following reagents: Ca(NO 3 ) 2 , NaNO 3 , KNO 3 , CaCl 2 and MgCl 2 . While the complexing action of thiourea stabilized Hg in solution (0.1M Ca(NO 3 ) 2 ), it also acted as an extractant itself and therefore could not be used to minimize resorption of Hg onto the sample during leaching. The minerals Hg 2 Cl 2 , HgCl 2 , HgO (red and yellow), HgS (synthetic and cinnabar) and Hg (0) were used alone and mixed with GG to evaluate the selectivity of the scheme. The reagents used in sequence are as follows: 0.01M Ca(NO 3 ) 2 (categorized as ‘easily soluble’, F1); 0.1M Na 4 P 2 O 7 (labile organic component, F2); 0.25M NH 2 OH.HCl/0.25M HCl (amorphous Fe and Al oxides, F3); 1M NH 2 OH.HCl/25% CH 3 COOH (crystalline Fe and Al, F4); 40% HNO 3 (non-labile organic component and elemental Hg, F5); and aqua regia (residual phase, containing sulphides (HgS), oxides, some silicates, refractory organics etc., F6). Alone, each mineral dissolved fully in the appropriate reagent, for example: HgCl 2 in F1 (soluble), HgO in F3 (with amorphous Fe/Al oxide phase), Hg (0) in F5, and HgS in the final aqua regia digestion. However, when mixed with GG, these minerals (except HgS) also dissolved in subsequent stronger leaches. For example, Hg in the sample HgCl 2 mixed with GG (total Hg concentration of 513 ng g −1 ) dissolved in F1, F2, F4 and F5. Thus, resorption in the initial leaches of a sequential extraction can confound the results for Hg and lead to incorrect results and interpretation of leaches purported to define the bioavailable component of Hg in environmental materials. New methods should be designed to minimize this phenomenon, using, for example, a flow-through system to achieve short contact times.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".