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Adsorption of silver, thorium and nickel ions from aqueous solution onto rice husk

In this article, adsorption of metal ions such as silver (Ag(I)), thorium (Th(IV)) and nickel (Ni(II)) from aqueous solution onto rice husk (RH) was performed at room temperature. Adsorption of these metal ions (silver, thorium, and nickel) onto RH was demonstrated by using Fourier transform infrared spectroscopy and energy-dispersive X-ray. Morphology of RH was investigated before and after adsorption of these metal ions onto it by using scanning electron microscopy. The effect of different operational parameters (contact time, initial concentration of metal ion solution, weight of RH, pH, and temperature) on the percentage removal of these metal ions was explored in detail and compared. Experimental data for adsorption of these metal ions onto RH was subjected to Langmuir and Freundlich isotherm models. Results showed that adsorption of silver and thorium fitted well to Langmuir isotherm model (R2 > 0.99) whereas adsorption of Ni(II) fitted well to Freundlich isotherm model (R2 > 0.99). Adsorption kinetics study demonstrated that adsorption of these metal ions onto RH from aqueous solution fitted well to pseudo-second-order model. Adsorption thermodynamics investigation represented that adsorption of these metal ions onto RH was endothermic process. The values of Gibb’s free energy were –6.53 to –9.17 kJ/mol for Ag(I), –1.11 to –3.57 kJ/mol for Th(IV) and –0.89 to –1.40 kJ/mol for Ni(II). The negative values of Gibb’s free energy for these metal ions suggested that the adsorption process was spontaneous in nature. The regeneration of RH and recovery of these metal ions were also studied.