Cadmium adsorption performance and mechanism from aqueous solution using red mud modified with amorphous MnO₂

Area of Science:

• Environmental Science
• Materials Science
• Chemical Engineering

Background:

• Red mud (RM) is an industrial solid waste with limited applications.
• Cadmium (Cd²⁺) is a toxic heavy metal pollutant in wastewater.
• Effective and economical adsorbents are needed for heavy metal removal.

Purpose of the Study:

• To synthesize and characterize manganese dioxide modified red mud (MRM).
• To evaluate the efficiency of MRM for Cd²⁺ removal from aqueous solutions.
• To investigate the adsorption mechanism and thermodynamics of Cd²⁺ onto MRM.

Main Methods:

• Red mud was modified with manganese dioxide.
• Adsorption experiments were conducted to study the effects of dosage, pH, and initial concentration.
• Characterization was performed using SEM-EDS, XRD, BET, FTIR, and XPS.
• Adsorption kinetics, isotherms, and thermodynamics were analyzed.

Main Results:

• MRM exhibited a higher surface area and pore volume than RM.
• The equilibrium adsorption capacity of MRM for Cd²⁺ reached 46.36 mg g^-1, nearly triple that of RM.
• The pseudo-second-order kinetic model and Langmuir isotherm model best described the adsorption process.
• Maximum adsorption capacity was determined to be 103.59 mg g^-1.

Conclusions:

• Manganese dioxide modified red mud is a highly effective adsorbent for Cd²⁺ removal.
• The adsorption process is spontaneous, endothermic, and follows Langmuir monolayer adsorption.
• Adsorption mechanisms involve electrostatic attraction, specific binding, and ion exchange.
• MRM presents a promising, cost-effective alternative for industrial wastewater treatment.