Milled goethite nanocrystalline for selective and fast uptake of cadmium ions from aqueous solution

Abstract

The purpose of the present study was to evaluate the performance of milled goethite as an effective nanomaterial for the removal of Cd(II) ions from aqueous solutions. Goethite nanocrystallines powders were prepared by high-energy ball milling with a balls-to-powder mass ratio of 10:1 and for 40 h of milling. X-ray diffraction, Rietveld analysis, and vibrating sample magnetometer are used to characterize the obtained nanopowders followed by tests for toxic metals removal from aqueous solutions. In addition, batch of experiments were performed to determine the adsorption equilibrium, kinetics, and thermodynamic parameters of toxic heavy metal ions by milled goethite. Adsorption data were modeled using Langmuir model, Freundlich equation, pseudo-first-order and pseudo-second-order equations. The adsorption process was found to be highly pH dependent. The adsorption of heavy metal ions reached a maximum value rapidly within 6 min and the adsorption parameters were in good agreement with both the Langmuir and Freundlich isotherms. A maximum Cd(II) ion adsorption capacity was estimated to be 167 mg g−1 at 328 K and a pH of 7. The kinetics of the adsorption process was found to follow the pseudo-second-order rate law. The evaluation of the thermodynamic parameters of milled goethite revealed a spontaneous endothermic adsorption process. Besides, the positive values of the entropy suggest an increase of randomness at the solid–solution interface during the heavy metal ions adsorption.