Adsorptive performance of a synthesized Mg-Al Hydrotalcite compound for removal of malachite green: kinetic, isotherm, thermodynamic, and mechanism study

Abstract

ABSTRACT The use of new synthetised materials as adsorbents for wastewater disposal is gaining importance due to their outstanding advantages. A Hydrotalcite-like compound Mg-Al-CO3 (HT2) with a molar ratio of Mg/Al = 2 was synthesised by the constant pH co-precipitation procedure and then characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and volumetric analysis (BET). The adsorption capacity of the solid was estimated against a textile dye such as malachite green (MG). Approximately 98% MG (5.10−5M) was adsorbed onto 100 mg of Hydrotalcite in 60 min. The effect of MG concentration, the influences of pH, and contact time on adsorption, studied by a factor-by-factor approach, revealed that adsorption was influenced by all factors. A maximum adsorption of 98 ± 0.51% was achieved at 46 mg L−1 MG, 100 mg Hydrotalcite, 400 rpm in 60 min with a maximum adsorption capacity of 14 mg g−1. The nonlinear form of the kinetic and isothermal models was used to verify the experimental data. According to the error of the calculated values of R2 (Coefficient of determination), χ2 (Chi-square) and standard deviation (Δq (%)), it was found that the form of the second-order kinetic model and Langmuir isotherm model are the most suitable for the experimental data of HT2. However, thermodynamic studies and post adsorption characterisation data show that the adsorption of MG dye on Hydrotalcite is a spontaneous and endothermic physical process.