Adsorption of Cadmium from Aqueous Solution onto Untreated Gypsum Rock Material: Equilibrium and Kinetics

The concentration of heavy metals exceeding from certain limit may cause risk and endanger ecosystems and human health. Water receives a considerable concentration of heavy metals from different anthropogenic and natural sources. A study was carried out to investigate the effectiveness of rock materials on the reduction of Cd from contaminated water. For this purpose, gypsum was applied to the contaminated water. The findings of the present study concluded that the adsorption of Cd was higher in finer rock material rather than coarse material due to the surface area. The finer grains contained a greater surface area than coarse grains. The isotherms of adsorption were constructed according to the mathematical linearization. The best-fitting followed the Freundlich and Dubinin-Radushkevich models, describing multilayer adsorption and chemical interaction, also confirmed by the pseudo-second-order kinetic model. The material removed a greater amount of Cd from contaminated water, especially at an increasing application rate.