Deng et al. 2021 - Mg-modified corncob biochar for Cu, Pb, Cd remediation

Deng and colleagues prepared four magnesium-modified corncob biochars (5%, 10%, 15%, 20% Mg/biomass ratios) by impregnating dried corncob biomass with MgCl2 solution, ultrasonicating, drying, and pyrolyzing at 450 °C under nitrogen, then tested their adsorption performance for aqueous Cu(II), Cd(II), and Pb(II) in single-metal and binary-metal batch experiments. This is primary remediation-method evidence, not food, ingredient, or consumer-product occurrence evidence: the measured endpoints are sorbent properties, kinetic and isotherm fits, and binary-system selectivity, not concentrations in any edible matrix or drinking water.

Key numbers

Biochar physicochemical properties

Table 1 reports element composition, H/C, O/C, pHpzc, BET surface area, and pore volume for the five biochars:

Modification raised pHpzc from 8.00 (BC) to 9.88-10.02 (xMg-BC), increased H/C and O/C ratios (more oxygen-containing functional groups and lower aromaticity), and increased BET surface area up to 174.29 m2/g at 15% Mg loading before declining at 20% Mg loading where the carbon skeleton agglomerated.

Single-metal sorption capacities and kinetics

For 15%Mg-BC, the source-reported single-metal sorption capacities were Cu(II) 200.33 mg/g, Cd(II) 164.51 mg/g, and Pb(II) 448.5 mg/g (Section 3.2), about 6.37, 2.36, and 9.34 times higher than pristine BC, respectively. The optimal experimental conditions identified were biochar dosage 0.01 g in 50 mL solution and initial pH 5.0 at 25 °C with 24 h contact time. Sorption capacity rose sharply with initial pH between 2.0 and 5.0 and plateaued at pH 5.0.

Table 2 reports kinetic fits for 15%Mg-BC:

Cu(II) and Pb(II) kinetics fit the pseudo-second-order model best (R2 = 0.9753 and 0.9499), consistent with chemisorption dominated by cation exchange and precipitation. Cd(II) kinetics fit the intraparticle-diffusion model best (R2 = 0.9555); the IPD line did not pass through the origin, indicating that liquid film diffusion and surface adsorption also influenced the Cd(II) sorption rate.

Single-metal sorption isotherms

Table 3 reports Langmuir and Freundlich fits for 15%Mg-BC:

The authors identify the Langmuir model as the better fit for Cu(II) (monolayer adsorption on homogeneous surface) and the Freundlich model as the better fit for Cd(II) and Pb(II) (heterogeneous surface). The Langmuir-derived maximum capacities (Qm) for 15%Mg-BC were Cu(II) 300.20 mg/g, Cd(II) 178.97 mg/g, and Pb(II) 526.20 mg/g. The corresponding experimental equilibrium capacities at 24 h were Cu(II) 296.85 mg/g, Cd(II) 180.93 mg/g, and Pb(II) 527.67 mg/g. The affinity ranking on 15%Mg-BC was Pb(II) > Cu(II) > Cd(II).

Table 4 compares 15%Mg-BC Qm values against other modified-biochar sorbents reported in the literature; the comparator values are reproduced in the source for context and are not re-extracted here.

Binary-metal system

In binary-metal experiments at pH 5.0 (Cu/Cd 0-50/50 mg/L paired with Pb 100 mg/L fixed, etc.), all three metals showed reduced sorption due to competitive sorption. Cd(II) capacity dropped most sharply: from 133.23 mg/g to 34.6 mg/g with increasing Cu(II), and to 22.72 mg/g with increasing Pb(II). Cu(II) and Pb(II) declined more slowly with rising Cd(II) co-ion concentration: Cu(II) from 156.4 to 125.02 mg/g, Pb(II) from 292.27 to 258.05 mg/g. When Cu(II) and Pb(II) coexisted, both dropped sharply: Cu(II) from 156.4 to 80.9 mg/g and Pb(II) from 292.27 to 87.25 mg/g with increasing concentration of the coexisting ion. The authors interpret this as Cu(II) and Pb(II) competing for the same sorption sites on 15%Mg-BC.

Adsorption mechanisms (FTIR/XRD/XPS evidence)

After Cu(II)/Cd(II)/Pb(II) adsorption onto 15%Mg-BC, FTIR peaks at 3696 cm-1 (-OH stretch of Mg(OH)2), 3412 cm-1 (-OH), and 1618 cm-1 (C=O) weakened, the 1440 cm-1 C-H peak shifted to 1383 cm-1, and the 419 cm-1 Mg-O peak shifted to 453-456 cm-1, consistent with surface complexation, ion exchange, and precipitation. XRD spectra of metal-loaded biochars showed loss of the CaCO3 peak, weakening of the Mg(OH)2 peaks, and new peaks consistent with Cu(OH)2, Cu2(OH)2CO3, CdCO3, and Pb3(OH)2(CO3)2 crystals. XPS binding energies of Pb 4f at 138.2 +/- 0.1 eV, Cu 2p at 934.8 +/- 0.1 eV, and Cd 3p at 405.1 +/- 0.1 eV were assigned to Pb3(OH)2(CO3)2, Cu2(OH)2CO3, and CdCO3, respectively. Atomic-percent decreases of Ca and Mg with concurrent increases of Cu, Cd, and Pb after sorption support ion exchange as a co-mechanism. The authors propose four contributing mechanisms: precipitation as carbonate/hydroxycarbonate phases, surface complexation with -OH and -COOH groups, cation exchange with Mg2+ and Ca2+, and cation-pi bonding.

Methods (brief)

Corncob biomass was collected in Ya’an City, Sichuan Province, China (29 58’50” N, 103 1’23” S [the source-reported coordinate string is preserved as published]), milled to 1 mm particles. Five grams of biomass were soaked in 50 mL of MgCl2.6H2O solution at Mg/biomass mass ratios of 5%, 10%, 15%, or 20%, ultrasonicated for 2 h at room temperature, dried at 80 °C, and pyrolyzed in a muffle furnace under nitrogen atmosphere with temperature ramped from room temperature to 450 °C at 10 °C/min and held for 1 h. The pyrolyzed material was washed with deionized water, dried at 80 °C, and crushed through 40 mesh (0.45 mm) to give xMg-BC (x = 5, 10, 15, 20). Unmodified BC was prepared under the same pyrolysis conditions as a control.

Characterization used a Vario Macro Cube (Germany) elemental analyzer for C, H, O, N; ICP-OES (PerkinElmer Optima 8000, Waltham, USA) for Mg, Ca, and adsorbed-metal content; nitrogen adsorption BET (Quadrasorb 2MP, USA) for surface area and pore structure; FTIR (Nicolet iS20, Thermo Scientific, Waltham, USA); SEM (ZEISS Evo18 500, Jena, Germany); XRD (PANalytical X’Pert Powder, Almelo, Netherlands); and XPS (Esclab 250Xi, Thermo Scientific, Waltham, USA). The pHpzc was measured by salt-addition method with 0.1 M NaCl, 48 h incubation.

Adsorption experiments used 0.01 g biochar in 100 mL centrifuge tubes containing 50 mL of metal solution; initial concentrations were Cu(II) 50 mg/L, Cd(II) 50 mg/L, Pb(II) 100 mg/L; pH was varied 2.0-6.0 (above pH 6, metal ions precipitated and were excluded); dosage was varied 0.001-0.1 g; suspensions were shaken at 180 rpm at 25 °C for 24 h, filtered through 0.45 µm membrane, and analyzed by ICP-OES. Sorption-kinetic samples were collected at 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, 16.0, and 24.0 h. Sorption-isotherm experiments used 0.01 g of 15%Mg-BC with Pb(II) 50.0-150.0 mg/L and Cu(II)/Cd(II) 10.0-100.0 mg/L. Binary-metal experiments fixed one or two metals and varied the third over 0-50 or 0-100 mg/L at pH 5.0.

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. Its remediation relevance is to industrial wastewater or mining wastewater treatment, not drinking-water polishing at trace concentrations.

App: Context for water-treatment and upstream remediation notes. The headline finding is that 15% Mg/biomass loading on corncob biochar produces a sorbent with Langmuir Qm values of 300-526 mg/g for Cu(II), Cd(II), and Pb(II) under controlled aqueous test conditions (50-100 mg/L initial metal concentration, pH 5.0, 25 °C, 24 h).

Courses: Useful for teaching adsorption-mechanism reasoning across PFO/PSO/IPD kinetics and Langmuir/Freundlich isotherm fits, the role of surface functional groups and pHpzc, the trade-off between Mg loading and pore-structure collapse at the 20% level, and how FTIR, XRD, and XPS evidence converge to identify carbonate/hydroxycarbonate precipitation, ion exchange, surface complexation, and cation-pi bonding as parallel sorption mechanisms.

Wiki pages this source may touch

• remediation-evidence
• lead
• cadmium
• copper
• index

Verification notes

This page was built from the full PDF (15 pages), including the abstract, methods (Sections 2.1-2.6), Section 3.1 Table 1 (biochar physicochemical properties), Section 3.2 dosage/pH text, Section 3.3 Table 2 (sorption kinetics), Section 3.4 Table 3 (sorption isotherms), the binary-system text in Section 3.5, the mechanism evidence in Section 3.6 (FTIR/XRD/XPS), and the conclusion. Table 4 comparator literature values are referenced but not re-extracted because they are not findings of this study.

The source measured aqueous solutions of Cu(II), Cd(II), and Pb(II) prepared as CuCl2, Pb(NO3)2, and CdCl2 spikes; 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.

The matrices slugs (biochar, aqueous-sorption-test, wastewater-remediation) follow the convention established for the existing remediation-context sources (e.g., wang2020-lignin-residue-biochar-heavy-metal-remediation) and are remediation-domain proposals outside the project’s current food-matrix controlled vocabulary. The routing audit may flag empty products/ingredients as advisory; this reflects the genuine non-food scope of the study, not a defect.

Methods-section vendor and instrument names (Vario Macro Cube, PerkinElmer Optima 8000, Quadrasorb 2MP, Nicolet iS20, ZEISS Evo18 500, PANalytical X’Pert Powder, Esclab 250Xi) are retained per the Part 12 brand-firewall Exception 2 (scientific-method vendor/material names locked 2026-05-17).

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