Layered chalcogenide for Cu2 + removal by ion-exchange from wastewater

The layered chalcogenide, K 2x Mn x Sn 3−   x S 6 (x   =   0.5   –0.95), which exhibited excellent adsorption properties for removal of Cu 2   + from aqueous solution, was synthesized hydrothermally. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectrometer (EDS) were used to characterize the crystal structure, chemical composition and micro-morphologies of KMS-1 before and after adsorption. Cu 2   + can covalently bond with sulfur atoms after it exchanged with K + . The interlayer spacing of KMS-1 was changed from 0.851   nm to 0.592   nm after adsorption. The sizes of KMS-1 crystalline after adsorption changed to smaller. The effects of pH, reaction time, initial concentration, reaction temperature and coexisting ions on the adsorption of Cu 2   + by KMS-1 were studied. The pH was found to be a slight factor determining adsorption capacity at pH from 3 to 6. Kinetic data were fitted well to a pseudo-second-order kinetic model and the rate controlling steps were external film diffusion and intraparticle diffusion at different temperatures. The activation energy for the adsorption process was estimated to be 45.15   kJ/mol. The maximum adsorption capacity of KMS-1 was 164.7, 155.6 and 152.7   mg/g at a temperature of 10, 25 and 40   °C, respectively. The Langmuir adsorption isotherm was used to fit the adsorption equilibrium process. The alkaline and alkaline earth metal ions had slight effect on the removal efficiency of Cu 2   + and the degree of inhibition followed the order: Ca 2   +   >   Mg 2   +   >   Na + . The heavy metal ions had great effect on the removal efficiency of Cu 2   + and the degree of inhibition followed the order: Cd 2   +   >   Pb 2   +   >   Zn 2   +   >   Ni 2   + . The adsorbed KMS-1 can be considered as an excellent permanent waste storage without the risk of leaching of Cu 2   + .