Application of alumosilicate polymers based on metakaolin in adsorption of cadmium ions from wastewater

Alumosilicate polymers (geopolymers) based on metakaolin as precursor and alkaline activators of different concentrations (2M, 4M, 6M and 8M NaOH/Na2SiO3) were used to remove ions of cadmium from wastewater. Experiments were carried out in a batch process at room temperature (23 ± 1 ° C) for different operating parameters: adsorption time, pH value of solution, initial concentration of metal and mass of adsorbents. It was found that the optimum pH value for all adsorbents is above 6.0. The adsorption efficiency increases with increasing pH of the solution. With an increase in the initial concentration of cadmium, the adsorption capacity increases and reaches a value of over 200.0 mg/g. The experimental results have better agreement with Freundlich's adsorption isotherm (surface heterogeneity, hemisorption mechanism) and the pseudo-second order model (the principle of the chemisorption mechanism and adsorption rate depend on the adsorbent concentration). Alumosilicate geopolymer samples were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier-Transform Infrared Spectroscopy (FTIR).