Li et al. 2025 - Iris sibirica biochar cadmium adsorption

Li and colleagues prepared biochars from the roots, stems, and leaves of Iris sibirica and tested them against cadmium-spiked aqueous solutions. This is primary remediation-method evidence for Cd(II) adsorption mechanisms, not food, ingredient, or consumer-product occurrence evidence.

Key numbers

Biochar preparation and characterization

The plant biomass was separated into roots including rhizomes (BCR), stems (BCS), and leaves (BCL), dried, powdered, sieved, and pyrolyzed at 900 degrees C for 120 min under argon.

The authors report Raman ID/IG ratios of 0.91 for BCR, 1.05 for BCS, and 0.97 for BCL. XRD showed SiO2 as the main component of BCR and KCl as the main component of BCS and BCL.

Cd(II) adsorption capacity and removal

At pH 5.5, 25 degrees C, 20.00 mL solution, 0.02 g biochar, 0.01 mol/L NaNO3, and an initial Cd(II) concentration of 20.00 mg/L, maximum equilibrium adsorption capacities were:

The authors report that adsorption increased as initial Cd(II) concentration rose from 5 to 500 mg/L. For initial concentrations not higher than 30 mg/L, BCS and BCL adsorbed Cd(II) more strongly than BCR.

Electrolyte effects were tested using NaNO3 from 0 to 1.00 mol/L. BCR adsorption increased with electrolyte concentration and stabilized near 0.50 mol/L NaNO3, while BCS and BCL stayed around 18.17-18.33 mg/g before declining when NaNO3 exceeded 0.50 mol/L.

pH experiments from pH 2 to 8 showed a strong increase in adsorption from pH 2 to 6. The authors identify pH 5.5-6 as the region where deprotonated carboxyl and hydroxyl groups favor Cd(II) retention.

Kinetics and isotherms

The adsorption processes fit second-order kinetics better than first-order kinetics for BCR, BCS, and BCL; BCS had R2 = 0.964 for second-order kinetics versus R2 = 0.663 for first-order kinetics. Elovich-model R2 values were 0.963 for BCR, 0.909 for BCS, and 0.914 for BCL.

Selected kinetic parameters from Table 2:

Langmuir and Freundlich isotherm fits both had R2 values between 0.93 and 0.99. The source reports the following Langmuir Qmax values (mg/g):

These Langmuir values are model-fitted high-concentration adsorption capacities, not measured environmental concentrations.

Mechanism and reuse

Elution experiments separated Cd(II) adsorption contributions into ion exchange, mineral precipitation, and other mechanisms such as surface complexation and Cd(II)-pi coordination. Ion exchange accounted for 32% of BCR adsorption, 54% of BCS adsorption, and 65% of BCL adsorption. Mineral precipitation accounted for 46% of BCR adsorption and was less dominant for BCS and BCL. Acid washing reduced Cd(II) adsorption by 71.93% for BCR, 75.06% for BCS, and 63.96% for BCL.

The authors conclude that BCS is the best of the three for Cd-containing wastewater because of its high adsorption capacity, BCR is better suited to acidic wastewater because precipitation dominates, and BCL may have fertilizer-additive relevance because of K+ leaching. In five adsorption-desorption cycles using BCS, removal efficiency decreased from 99.45% to 87.96%.

Methods (brief)

Cd(II) solutions were prepared from a 500.00 mg/L Cd(NO3)2.4H2O stock solution with NaNO3 as background electrolyte. Kinetic tests used 0.02 g biochar in 20.00 mL of 20.00 mg/L Cd(II) solution for 5-1440 min. Isotherm tests varied Cd(II) from 0 to 500 mg/L at 15-45 degrees C with 1.00 g/L sorbent for 24 h. Cd(II), K+, Ca2+, and Mg2+ were measured by ICP-MS. Biochar characterization included BET N2 adsorption, SEM, XRD, FTIR, zeta potential, pH, yield, and ash content.

Implications

Certification: Do not use this source in HMTc occurrence pools. The Cd values are removal capacities from deliberately spiked aqueous solutions.

App: Context for remediation and wastewater-treatment evidence where cadmium capture by plant-derived biochar is relevant.

Courses: Useful as a mechanistic example showing why adsorption-capacity numbers and contamination-occurrence numbers must not be mixed, even when both are expressed in mg/g or mg/L contexts.

Wiki pages this source may touch

• cadmium
• index
• wastewater-irrigation

Verification notes

This page was built from the full PDF, including the abstract, Materials and Methods, Tables 1-4, Figures 3-7, conclusions, supplementary-materials note, and data-availability statement. Products and ingredients are intentionally empty because the study used laboratory-prepared Iris sibirica biochars and Cd(II)-spiked aqueous solutions, not food, ingredients, or consumer products.

Page history

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