Theoretical Research On Adsorption Of Heavy Metal Cadmium Ion On Goethite

Optimal geometries and charge distribution of hydration and hydrolysis species of Cadmium and free energies of hydration and hydrolysis reactions of Cd are investigated using Density Functional Theory (DFT). Chemical adsorption of water molecules and cadmium ion on (010) surface of goethite are studied using Semiempirical MOPAC method. Results show that1. The stability sequence for all hydration and hydrolysis species of Cd(II) is , which means the hydration species of cadmium are stably superior to the hydrolysis species and Cd(OH₂ )₆²⁺ is the most stable species among all. As the extent of hydrolysis enhances, it becomes more difficult for cadmium to bond water molecules in the first cell and the charge of cadmium decreases. According to theâ–³G298 of hydration and hydrolysis reactions, hydration of Cd(II) can take place spontaneously while hydrolysis can not. According to the NBO analysis, hydration can passivate Cd while hydrolysis can activate Cd.2. Dissociative adsorption of water, which both completes the coordination of the surface oxygen ions as well as increases the coordination of the under-coordinated Fe(III) surface ion, is favored over associative adsorption on the (010) surface of goethite. Molecular dynamic simulation results show liquid water molecules hardly interact with goethite surface after chemical adsorption of water molecules and have little influence on goethite surface.3. Hydrolysis adsorption of cadmium on goethite occurs in single corner, double corner and triple corner styles. The stability sequence of different adsorption structures is DC(b)>SC>TC>DC(a). Cd(II) ion is stabilized by the adsorption course.