Fabrication of Nanocomposite Zeolite Granules for Cadmium Stabilization in Contaminated Soils

Cadmium contamination of soil poses significant environmental and public health risks. Among the techniques used for remediation, the chemical stabilization of heavy metals using mineral amendments shows promise. Composite zeolite granules were synthesized through the in situ formation of a manganese dioxide phase onto the surface of natural zeolite granules (1–2 mm). Scanning electron microscopy and X-ray diffraction analyses confirmed the formation of the MnO₂ phase, which was identified as c-disordered hexagonal birnessite. The adsorption of cadmium onto natural and composite zeolite samples was investigated using two experimental setups. The first setup involved studies in a single-component cadmium solution, while the second setup used a multicomponent ‘soil solution’ prepared by equilibrating Cd-contaminated soil with water for one month. Batch adsorption experiments revealed that the adsorption of both materials could be best described by a pseudo-second order kinetic model. The maximum Cd adsorption capacities, as determined by the Langmuir model, were found to be 12.96 mg/g for natural zeolite and 16.09 mg/g for composite zeolite. In a multicomponent ‘soil solution’ with elevated concentrations of Cd, Pb, and Zn (0.07, 0.04, and 3.67 mg/L, respectively), the composite zeolite granules demonstrated superior Cd adsorption efficiency compared to the natural zeolite (100% and 43%, respectively). Furthermore, both materials showed high zinc adsorption efficiencies (~98%). These results highlight the potential of composite zeolite granules as an effective mineral amendment for the stabilization of heavy metals in contaminated soils.