Facile synthesis of a magnetic chlorapatite composite with a high efficiency and recyclable adsorption for Congo red

In this study, a composite of magnetic core and chlorapatite (Fe3O4@CLAP) is synthesized and used to remove Congo red (CR) from aqueous solution. The Fe3O4@CLAP is characterized by various analytical methods to estimate the adsorbent features. The effects of initial solution pH, adsorbent dosage, and ionic strength on the dye removal are studied to determine the optimized operating conditions. The sorption kinetics fit well with pseudo-second-order model, and the intra-particle diffusion model curve shows that three diffusion stages exist in the process. In addition, the Langmuir, Freundlich and Temkin isotherm models are used to fit the experimental data, and the fitting results show that the data are well described by Langmuir isotherm. The maximum adsorption capacity of CR is 370.4 mg g−1, which is outstanding compared with existing reports. The thermodynamic analysis reveals that the adsorption process is exothermic with a spontaneous nature. Moreover, the desorption is achieved with 0.01 M NaOH and the removal efficiency of adsorbent still remains 82.5% after 5 cycles. Therefore, Fe3O4@CLAP is a promising adsorbent with a high adsorption capacity and excellent recyclability for removing CR from aqueous solutions.