Lignin-Sustainable Polymer for Mn(II) Biosorption from Aqueous Media

Area of Science:

• Biomass valorization
• Environmental chemistry
• Materials science

Background:

• Lignin, a renewable carbon resource from biomass, offers a sustainable alternative to fossil resources.
• Efficient utilization of renewable resources is crucial for the circular bioeconomy and environmental protection.
• Heavy metal pollution, such as Manganese (Mn(II)), poses significant environmental and health risks.

Purpose of the Study:

• To evaluate the biosorption efficiency of unmodified Tripidium bengalense (Sarkanda grass) lignin for Manganese (Mn(II)) removal from aqueous solutions.
• To investigate the adsorption kinetics, thermodynamics, and mechanisms of Mn(II) biosorption.
• To assess the recyclability and ecotoxicity of the Mn(II)-loaded lignin biosorbent.

Main Methods:

• Biosorption experiments using unmodified Sarkanda grass lignin.
• Optimization of operating conditions: adsorbent dosage, pH, and temperature.
• Kinetic, isotherm, and thermodynamic modeling of the adsorption process.
• Characterization of the biosorbent using FTIR, SEM-EDX, and TG/DTG analyses.
• Recyclability testing through multiple desorption-resorption cycles with 1N HCl.
• Ecotoxicological assessment using Sorghum bicolor L. germination tests.

Main Results:

• Optimal biosorption conditions achieved: 5 g/L adsorbent dosage, pH 6.5, and 20 °C, yielding a capacity of 12.52 mg/g.
• Rapid adsorption equilibrium within 30 minutes, fitting the pseudo-second-order kinetic model (R² ≥ 0.9998).
• Freundlich isotherm model best described equilibrium data (R² ≥ 0.9886), indicating chemisorption.
• Thermodynamic analysis confirmed a spontaneous and endothermic process (ΔG: -13.24 to -26.19 kJ/mol; ΔH: 11.21 to 14.83 kJ/mol).
• FTIR, SEM-EDX, and TG/DTG confirmed Mn-O coordination with phenolic hydroxyl and carboxylic groups.
• Lignin maintained >70% retention efficiency after three cycles; post-adsorption filtrates showed 100% seed germination, while Mn(II)-loaded lignin showed 0% germination.

Conclusions:

• Raw Sarkanda grass lignin is a highly efficient, scalable, and sustainable biosorbent for Manganese (Mn(II)) removal.
• The biosorption mechanism involves chemisorption and inner-sphere complexation.
• The biosorbent demonstrates excellent recyclability and effectively immobilizes heavy metals, rendering treated water safe.
• This study highlights lignin's potential in heavy metal remediation within a circular bioeconomy framework.