Mechanisms of the Reductive Immobilization of Hexavalent Chromium by Wheat Straw Biochar
Bibliographic record
Abstract
Biochar has received significant attention as an innovative sorbent for treating heavy metal contamination due to its high surface reactivity and sorption capacity, ease of manufacture and low production cost. Most studies involving chromium removal from solution by biochar have focused on removal rates and extent, which largely ignores the mechanisms of sorption and electron transfer that occur during Cr immobilization. For this reason, a comprehensive Cr-biochar study that couples adsorption and reduction kinetics to spectroscopic data to elucidate the Cr binding environment and speciation on the biochar was conducted. Wheat Straw biochar (WSBC), produced by the Alberta Biochar Initiative, was used to sorptively remove and subsequently reduce hexavalent chromium (Cr(VI)) from solution over the course of days at a range of acidic pH (between 2 – 3). Sorption and reduction kinetics were monitored and concentration-independent intrinsic rate constants for both phenomena were calculated. To understand the Cr binding environment on the surface of WSBC following metal reduction, synchrotron X-ray adsorption spectroscopy, synchrotron-based X-ray fluorescence mapping, Fourier transform infrared spectroscopy, Raman microscopy and scanning electron microscopy were performed. The results show that (1) the reduction and sorption of Cr(VI) with WSBC is possible, especially in acidic media, (2) that the distribution of Cr on the WSBC surface is heterogeneous, and (3) the Cr(III) binding to WSBC surfaces are dominated by O-containing functional groups, with hydroxyl groups comprising the majority of the Cr binding sites, followed by binding to carboxyl and carbonyl groups.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 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".