Li et al. 2025 - Iris sibirica biochar for cadmium adsorption from wastewater

Li and colleagues pyrolyzed the root, stem, and leaf tissue of Iris sibirica L. (a wetland emergent plant) at 900 degrees C and tested the resulting biochars (BC_R, BC_S, BC_L) as aqueous sorbents for Cd(II). This is primary remediation-method evidence, not food or product occurrence evidence: the measured endpoints are biochar physico-chemical properties, batch adsorption kinetics, isotherm capacities, and mechanism partitioning rather than cadmium concentrations in edible crops, ingredients, consumer products, or drinking water.

Key numbers

Biochar physical properties (Table 1, page 6)

The three biochars differed substantially in surface area and pore structure. Source-reported values:

Raman ID/IG ratios were 0.91 (BC_R), 1.05 (BC_S), and 0.97 (BC_L), with BC_S showing the highest structural defect density (Figure 1d).

Equilibrium adsorption capacity (abstract; Section 3.2.1)

At pH 5.5, initial Cd concentration 20 mg/L, NaNO3 0.01 mol/L, 25 degrees C, biochar dose 1 g/L (0.02 g in 20 mL), 24 h equilibration, the source reports equilibrium adsorption capacities and removal efficiencies:

The abstract orders these BC_S (19.92) > BC_L (19.89) > BC_R (13.22).

Langmuir isotherm fitting (Table 3, page 13)

The Langmuir model fit the equilibrium data at 15, 25, 35, and 45 degrees C with R2 = 0.93-0.98. Maximum monolayer adsorption capacities Qmax (mg/g) and Langmuir constants KL (L/mg):

The authors highlight 2606.11 mg/g (BC_S at 45 degrees C) as the peak adsorption capacity (Section 3.4). Increasing KL with temperature was interpreted as evidence of endothermic adsorption.

Freundlich isotherm fitting (Table 4, page 13)

Adsorption kinetics (Table 2, page 12)

Second-order kinetics fit better than first-order for all three biochars, with BC_S showing the strongest improvement (first-order R2 = 0.663, second-order R2 = 0.964). Intra-particle diffusion fitted in three stages, with R2 > 0.83 for stages 1 and 2 across all biochars. Elovich parameters: alpha (initial sorption rate, mg/g min) = 0.192 (BC_R), 232.320 (BC_S), 1.139 (BC_L); beta (mg/g) = 1.737, 0.595, 0.265. BC_S had the highest initial sorption rate by orders of magnitude.

Mechanism partitioning (Figure 6, page 16)

The source separated Cd adsorption into ion exchange (Qcme), precipitation (Qcmp), and other (surface complexation and Cd-pi interaction; Qother) by sequential acid washing and elution treatments. Reported contributions:

Among exchanged cations (K+, Ca2+, Mg2+), K+ released most readily in exchange for Cd2+, with BC_L releasing the most K+ (up to ~25 mg/L for untreated material, Figure 5d). The authors note BC_L “could be used as a potash fertilizer additive based on high K+ leaching.”

pH and electrolyte sensitivity (Figure 3, pages 9-10)

Maximum Cd uptake occurred at pH 5.5-6 for all three biochars. Below pH 5, H+ competed with Cd2+ for binding sites. Above pH 7, Cd(OH)+ / Cd(OH)2 / Cd(OH)3- complexes reduced free Cd2+ and slightly suppressed uptake.

NaNO3 electrolyte effects (initial Cd 20 mg/L, pH 5.5, 0.01-1.00 mol/L NaNO3): BC_R uptake rose with electrolyte content up to 0.50 mol/L NaNO3 and then plateaued near 18 mg/g, while BC_S and BC_L hovered at 18.17-18.33 mg/g across the range. Zeta potential ranged -10 to -33 mV across pH 2-8, becoming more negative with increasing pH.

Recyclability (Figure 7, page 17)

BC_S retained Cd removal efficiency over five adsorption-desorption cycles, declining from 99.45% (cycle 1) to 87.96% (cycle 5).

Methods (brief)

Iris sibirica L. plants (six months old) were collected from a nursery in the Daxing district of Beijing, washed, dissected into roots (including rhizomes), stems, and leaves, oven-dried at 70 degrees C for 72 h, crushed, and passed through a 100-mesh sieve. Biomass powder (5.00 g) was pyrolyzed in a tube furnace at 900 degrees C for 120 min under argon flow (~200 mL/min), then annealed to room temperature within 200 min, and hand-ground through 100 mesh.

Batch adsorption used 0.02 g biochar in 20.00 mL Cd(II) solution prepared from Cd(NO3)2.4H2O (500.00 mg/L stock), with NaNO3 (0-1.00 mol/L) as background electrolyte, on a horizontal vibrator (HZX-Q100, China) at 200 rpm, 25 degrees C, pH 5.5, filtered through a 0.22 micrometer membrane. Cd, K, Ca, and Mg were quantified by ICP-MS (Agilent 7500cx, USA). Characterization: BET N2 adsorption (Tristar 3020 M), SEM (Hitachi SU8010), XRD (Bruker-AXS), FTIR (Bruker VERTEX 70, 4000-500 cm-1), Raman, Zetasizer Nano (UK), and ash determination per ASTM D1782-84 at 750 degrees C for 6 h. Each biochar sample was tested in triplicate.

The Cd source is a synthetic aqueous solution, not environmental or food samples. The biochars are the engineered adsorbent under test.

Implications

Certification: Do not use this source in any food, ingredient, beverage, or consumer-product occurrence pool. It does not measure Cd in food matrices; it measures Cd uptake by wetland-plant-derived biochars in synthetic aqueous solution.

App: Context for wastewater remediation and biomass valorization (wetland plant biochars as Cd sorbents).

Courses: Useful for teaching how feedstock organ (root vs stem vs leaf) and pyrolysis conditions shape biochar surface area, porosity, and Cd uptake mechanism; how mechanism partitioning (ion exchange vs precipitation vs complexation) varies across biochars; and why a Cd-loaded biochar is a remediation matrix rather than food-contamination evidence.

Wiki pages this source may touch

• remediation-evidence
• cadmium
• index

Verification notes

This page was built from the full PDF, including the abstract, Section 2 Materials and Methods (feedstock collection, pyrolysis at 900 degrees C, batch adsorption protocol, ICP-MS quantification, characterization suite), Table 1 biochar properties, Table 2 kinetic parameters, Tables 3-4 Langmuir and Freundlich isotherm parameters, Figures 3-7 (pH/electrolyte/Zeta potential, kinetic model fits, elution mechanism partitioning, recycling cycles), and Section 4 conclusions.

Products and ingredients are intentionally empty in frontmatter because this is a wastewater-remediation methodology study. The Iris sibirica biomass is the biochar feedstock, not a food ingredient; the wiki has no ingredients/iris-sibirica page and should not gain one from this source. The routing layer therefore records this source as advisory-malformed for missing products/ingredients, which is the expected behavior for remediation-only evidence and is not a defect to fix.

The abstract states the order BC_S (19.92 mg/g) > BC_L (19.89 mg/g) > BC_R (13.22 mg/g) but later (Section 3.2.1) reports BC_R 13.22, BC_L 19.89, BC_S 19.92 mg/g and removal efficiencies 66.1%, 99.45%, 99.60% respectively. These are consistent values; the abstract ordering is by qe descending. No internal contradiction.

Source-side anomaly in Table 1 (BC_L): the reported micropore area of 274.80 m2/g exceeds the BC_L BET surface area of 16.68 m2/g. Micropore area is physically a subset of total BET surface area, so these two values are mutually inconsistent. The wiki table reproduces the source values verbatim because the source prints them as shown; the inconsistency is a paper-side issue, not a wiki transcription error. Fresh-context audit subagent (2026-06-02) confirmed the verbatim reproduction matches the printed Table 1 and recommended disclosing the anomaly here.

Matrices vocabulary: biochar, aqueous-sorption-test, and wastewater-remediation are precedented slugs already used by other remediation source pages (e.g., wang2020-lignin-residue-biochar-heavy-metal-remediation, lin2025-coffee-waste-metal-dye-removal). iris-sibirica-biomass is a descriptive kebab-case feedstock token introduced by this paper and should be confirmed against the matrices controlled vocabulary on the next Karen review.

Page history

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