Red mud is an undesirable by-product of bauxite in Bayer process has been used as a low-cost adsorbent for the removal of Cd(II) from aqueous solution by batch mode of experiment. The red mud was activated by acid dilution followed by ammonia precipitation for better adsorption of Cd(II). To achieve optimum condition for adsorption, different variable parameters were studied. X-ray diffraction, SEM and EDX were used to characterize the adsorbent before and after cadmium adsorption. The maximum adsorption capacities of Cd(II) on activated red mud (ARM) were found to be 12.046 and 12.548 mg g −1 at temperature 293 and 303 K, respectively. Adsorption data of Cd(II) are best fitted to linearly transformed Langmuir isotherm with R 2 > 0.99. The pseudo-second-order model describes the kinetics of Cd(II) adsorption successfully to predict the rate constant of adsorption. Thermodynamic parameters reveal the endothermic, spontaneous and feasible nature of adsorption of Cd(II) onto ARM. The mass transfer study led to compute the external mass transfer coefficient (k f ) by the equation of McKay et al. and Weber-Mathews at temperature 293 and 303 K. The desorption efficiency of Cd(II) ions from ARM was 91.29% using 0.2-mol L −1 HCl.
Article Highlights• Pseudo-second order kinetic model primarily governed the phenol uptake process • The average effective diffusivity (6.4×10 -13 m 2 /s) of phenol was estimated using the Boyd model • The maximum uptake of phenol (54 mg/g) was obtained at 333 K • Overcome the difficulty of recovering the photocatalyst after use • The negative values of ΔG indicate that the sorption of phenol was spontaneous Abstract Mahua (Madhuca longifolia) seed activated carbon (MSAC) has been developed as an effective adsorbent for the removal of phenol from contaminated wastewaters. The prepared MSAC was characterized for various physicochemical properties, by Fourier transform infra-red (FTIR) and scanning electron microscopy (SEM) analysis. Laboratory batch experiments were performed to investigate the effect of MSAC dosage (w), pH, contact time (t), and initial phenol concentration (c o ) on sorption efficiency at optimal conditions. The maximum adsorption capacity of phenol was obtained at pH 6, t = 5 h and MSAC dosage = 1.2 g/l. The kinetics data of phenol adsorption was very well described by the pseudo-second-order kinetic model. The equilibrium adsorption data were best fitted to the Langmuir isotherm. The average effective diffusion coefficient 6.4×10 -13 m 2 /s was calculated from the experimental data. Thermodynamic studies confirmed the sorption process to be spontaneous and exothermic. The isosteric heat of adsorption of phenol was found to increase with an increase in the surface loading indicating that MSAC have more homogeneous surface.
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