Methyl violet removal by hydroxyapatite synthesis from waste egg shells

The most important factor causing water pollution, which is directly or indirectly a major problem for the ecosystem on Earth, is the dyestuffs used in most of the sectors. Using the waste eggshells, which are used in large quantities around the world, and the hydroxyapatite synthesized from these shells for dye removal can be recycled, and at the same time, converting them into cost-effective biosorbents will provide advantages in the long run. In this study, the biosorption of Methyl Violet (MV), a cationic type dyestuff, on waste eggshell (ES) and Hydroxyapatite (HAp) synthesized from these eggshells by chemical precipitation method was studied in a batch system. Optimum conditions (pH, biosorbent amount, contact time, temperature, and initial dyestuff concentration) were obtained by using the Central Composite Design (CDD) method in the experimental design. At the same time, desorption and toxicity studies of biosorbents were carried out. Maximum biosorption capacities (qmax) for ES and HAp at optimum conditions were found to be 24.916 mg/g and 47.069 mg/g, respectively. While the fit isotherm model for YK was determined as the Langmuir isotherm model, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherm models were determined as for HAp. It can be said that the kinetic model fit for both biosorbents is the pseudo-second-order kinetic model. It can be concluded that the thermodynamically evaluated biosorption processes occur with exothermic reactions in two biosorbents. In addition, the characterization of each biosorbent was performed using analysis techniques such as XRD (X-Ray Diffraction), FT-IR (Fourier Transform Infrared), and SEM (Scanning Electron Microscopy).