Abstract
In this study, hydroxyapatite@Mn-Fe composite was used as a novel adsorbent to eliminate Nile blue (NB) dye and hexa-valent chromium ion (Cr(VI)) from aqueous media. Different analyses such as FTIR, Map, SEM, EDX, BET, and XRD were used to study the characteristics of the composite. The highest sorption efficiencies of Cr(VI) and NB at pH 2 and 10 were 97.63% and 98.83%, respectively, which are significant values. Equilibrium and kinetic studies of the sorption process showed that the Freundlich isotherm model and pseudo-second-order kinetic model can better describe the equilibrium and kinetic behavior of the sorption process. According to the Langmuir model, the maximum sorption capacities of NB dye and Cr(VI) ion using the hydroxyapatite@Mn-Fe composite were 0.259 and 0.938 mmol/g, respectively. Also, the results of the thermodynamic study showed that the sorption process is favorable (Delta S degrees = - 34.2 kJ/mol.K for Cr(VI) and - 144.6 kJ/mol.K for NB), spontaneous (Delta G degrees <0), and exothermic (Delta H degrees = -27.99 kJ/mol for Cr(VI) and - 64.2 kJ/mol for NB). Moreover, the desorption process of both contaminants using the hydroxyapatite@Mn-Fe composite showed that the H2SO4 solution with a concentration of 3 mol/L can remove both contaminants separately with the highest efficiency. Furthermore, the reusability study indicated that the composite can be used in five reuse cycles without significant decrease in its efficiency. Besides, the composite was able to eliminate color, turbidity, COD, and BOD5 from the textile wastewater with removal efficiencies of 93.06, 81.61, 76.05, and 71.88%, respectively. To the best of our knowledge, hydroxyapatite@Mn-Fe composite was synthesized and used for the first time to remove Cr(VI) ions and NB dye. In general, the aforementioned composite is recommended for industrial wastewater treatment.