Overview
Wang and colleagues converted lignin-rich residue from a furfural manufacturing process into activated biochars and tested them as aqueous sorbents for Pb(II), Cd(II), and Cu(II). This is primary remediation-method evidence, not food or product occurrence evidence: the measured endpoints are biochar properties, adsorption kinetics, and isotherm capacities rather than concentrations in edible crops, ingredients, consumer products, or drinking water.
Key numbers
Biochar properties
Table 1 reports that both activation routes increased surface area and pore volume relative to hydrochar. Selected source-reported properties:
| Material | pHpzc | BET surface area (m2/g) | Pore volume (cm3/g) | Acidic groups (mmol/g) | Basicity (mmol/g) |
|---|---|---|---|---|---|
| Hydrochar | 9.8 | 13.2 | 0.068 | not reported | not reported |
| BC-H3PO4 | 3.5 | 680 | 0.65 | 0.692 | 0.21 |
| BC-ZnCl2 | 4.6 | 790 | 0.74 | 0.980 | 0.36 |
The acidic-group total above sums the Table 1 carbonyl, carboxylic, lactone, and phenolic groups. The authors attribute the higher adsorption performance of BC-ZnCl2 to its larger surface area, pore volume, and acid-group content.
Adsorption tests and kinetics
Batch adsorption tests used 0.6 g biochar in 100 mL aqueous metal-ion solution at 25 +/- 2 C. Initial concentrations for isotherms ranged from 0.5 to 5.0 mM for Pb(II), Cd(II), and Cu(II). Metal concentrations in filtrates were measured by atomic absorption spectroscopy.
For Pb(II), adsorption was rapid: the paper reports more than 90% of the equilibrium uptake in the first 30 minutes, with equilibrium at about 4 hours. Table 2 gives pseudo-second-order fit values for Pb(II):
| Biochar | Initial Pb concentration | Experimental q (mg/g) | PSO q (mg/g) | PSO k2 | PSO R2 |
|---|---|---|---|---|---|
| BC-H3PO4 | 100 mg/L | 11.5 | 11.8 | 0.0079 | 1.000 |
| BC-H3PO4 | 250 mg/L | 25.8 | 24.9 | 0.0019 | 0.999 |
| BC-H3PO4 | 500 mg/L | 39.7 | 39.9 | 0.0017 | 1.000 |
| BC-ZnCl2 | 150 mg/L | 51.2 | 51.1 | 0.0092 | 1.000 |
| BC-ZnCl2 | 370 mg/L | 60.9 | 60.7 | 0.0051 | 1.000 |
| BC-ZnCl2 | 600 mg/L | 65.3 | 65.2 | 0.0057 | 0.999 |
Isotherm capacities
Table 3 reports Freundlich and Langmuir fits. The authors state that Langmuir fits were stronger than Freundlich fits overall and that the BC-ZnCl2 material performed better for all three metal ions.
| Biochar | Metal ion | Langmuir qm (mg/g) | Langmuir K (L/mg) | Langmuir R2 | RL |
|---|---|---|---|---|---|
| BC-H3PO4 | Cu(II) | 7.2 | 0.54 | 1.00 | 0.002 |
| BC-H3PO4 | Cd(II) | 36.9 | 0.072 | 1.00 | 0.011 |
| BC-H3PO4 | Pb(II) | 44.8 | 0.014 | 0.99 | 0.324 |
| BC-ZnCl2 | Cu(II) | 27.5 | 0.15 | 0.99 | 0.105 |
| BC-ZnCl2 | Cd(II) | 50.4 | 0.036 | 0.98 | 0.495 |
| BC-ZnCl2 | Pb(II) | 63.5 | 0.089 | 0.98 | 0.134 |
The conclusion also reports BC-ZnCl2 uptake ranges across the tested concentration gradient: Pb(II) 23.1-72.1 mg/g, Cd(II) 6.8-55.6 mg/g, and Cu(II) 8.2-30.5 mg/g. Table 4 compares Pb(II) capacity with other sorbents and lists this study’s Pb(II) adsorption capacities as 42.7 mg/g for BC-H3PO4 and 72.1 mg/g for BC-ZnCl2.
Methods (brief)
Lignin-rich residue from a corn-cob furfural process was dried, milled below 100 mesh, hydrothermally carbonized at 250 C for 2 hours, washed, and then chemically activated. The H3PO4 route mixed hydrochar with 40% H3PO4 at a 1:6 hydrochar/H3PO4 ratio for 24 hours, activated at 500 C for 2 hours under nitrogen, washed to neutral pH, and dried. The ZnCl2 route mixed hydrochar with 40% ZnCl2 at a 1:10 ratio for 24 hours, activated at 500 C, boiled with 1 M HCl, washed until chloride-free, and dried.
Biochars were characterized by nitrogen adsorption/desorption, BET surface area, pore volume, FT-IR, Boehm titration, zeta potential/pHpzc, SEM, TEM, and XRD. Adsorption experiments varied pH, contact time, and initial Pb(II), Cd(II), or Cu(II) concentration; filtrate metal concentrations were analyzed by atomic absorption spectroscopy.
Implications
Certification: Do not use this source in any food, infant-food, supplement, cosmetic, or ingredient occurrence pool. It does not measure consumer-product concentrations or demonstrate a reduction in a food matrix. It is relevant only as remediation context for low-cost carbonaceous sorbents.
App: Context for water-treatment and upstream remediation notes. The key takeaway is that ZnCl2-activated lignin-residue biochar had higher Pb(II), Cd(II), and Cu(II) sorption capacity than H3PO4-activated biochar under controlled aqueous test conditions.
Courses: Useful for teaching the distinction between sorbent capacity and occurrence concentration, plus the role of pH, surface area, acid groups, and Langmuir/PSO model fits in remediation studies.
Wiki pages this source may touch
Verification notes
This page was built from the full PDF, including the synthesis methods, adsorption-experiment design, Table 1 biochar properties, Table 2 Pb(II) kinetic fits, Table 3 isotherm fits for Cu(II), Cd(II), and Pb(II), Table 4 Pb(II) comparator capacities, the conclusion, and the supplementary-materials note. The source uses dissolved Pb(II), Cd(II), and Cu(II) nitrate solutions; frontmatter uses the repo’s broader Pb, Cd, and Cu metal slugs while this page preserves ion-state specificity in prose and tables. Products and ingredients are intentionally empty because no food, ingredient, or consumer-product matrix was sampled.
Audit subagent (2026-06-02) flagged [[mitigation/agronomic]] as a semantic mismatch — the wiki’s agronomic-mitigation page covers pre-harvest food-crop interventions (cultivar selection, paddy water management, soil amendment for crops), not aqueous-solution sorption. Verified against wiki/mitigation/agronomic.md and confirmed; the link was removed. [[mitigation/remediation-evidence]] is retained as the closest existing destination even though that page is also food-crop-focused, since the “may touch” framing is speculative rather than a routing assertion.
The matrices slugs (lignin-rich-residue, corn-cob-residue, biochar, aqueous-sorption-test, wastewater-remediation) are remediation-domain proposals outside the project’s current food-matrix controlled vocabulary. A future taxonomy refresh should decide whether to formalize a remediation-matrix vocabulary or to route this source via a separate non-food remediation register. The routing audit’s malformed entry for this source is advisory (empty products/ingredients) and reflects the genuine absence of food/ingredient/product scope, not a defect.
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