The use of waste fondry sands in the removal of some dyestuffs from aqueous solution

Recycle of waste casting sand, which is a serious problem arising from the ever-growing casting industry, into high value-added products for a different industry by using it for the removal of cationic dyestuffs that are widely used in the textile industry, helps to protect our natural resources, save raw materials and contribute to the economy, and contribute to the environment will contribute to the conservation and reduction of waste. In the thesis study, the adsorption of cationic type Methylene Blue (MB), Crystal Violet (CV), Malachite Green (MG) and Basic Fuchsin (BF) dyestuffs on waste casting sand (Sample 4) and system sand (Sample 5) in a batch system was studied and adsorption equilibrium, adsorption thermodynamics and adsorption mechanisms were investigated. For this purpose, adsorption tests were performed at three different temperatures (25, 35 and 45 oC) at different initial concentrations of dyestuff solution. The experimentally obtained adsorption data were modeled by applying two-parameter (Freundlich, Langmuir, Dubinin-Radushkevich (D-R)) isotherm models and the isotherm constants were calculated. It was seen that the equilibrium data of both adsorbents were in accordance with the Langmuir Isotherm Model in terms of adsorption capacities within certain error limits. Maximum adsorption capacities of Sample 4 and Sample 5 are 41.01 and 39.33 mgg1, respectively for MG with initial concentration C0=500 mgL1. Adsorption Gibbs free energies (ΔGº), enthalpies (ΔHº) and entropies (ΔSº) were calculated using adsorption isotherms obtained at different temperatures. According to the calculations, it can be said that the ΔGº values for both samples are positive (ΔGº>0) at 25 °C and 35 °C, that is, the process does not occur spontaneously. At 45 °C, ΔGº values are negative for both sands (ΔGº<0). Therefore, it can be said that the process occurs spontaneously for this temperature and the adsorption is physical adsorption. In addition, the positive values of ΔHº for Sample 4 and Sample 5 (ΔHº>0) indicate that the system is endothermic.