Application of NaOH-treated rice husk for adsorptive discharge of cobalt ions from wastewater

In this research, batch adsorption of cobalt ions (Co(II)) from wastewater onto NaOH-treated rice husk (TRH) was studied at room temperature. Several techniques such as Fourier transform infrared, scanning electron microscopy, and energy diffraction X-rays were used to prove adsorption of Co(II) onto TRH. The percentage discharge of Co(II) was increased with the contact time, amount of TRH, and temperature whereas decreased with an initial concentration of Co(II) solution. Nonlinear isotherms such as Langmuir, Freundlich, and Dubinin-Radushkevich were utilized to study experimental data for adsorption of Co(II) onto TRH. Results showed that experimental data fitted well to nonlinear isotherms. The value of Langmuir constant Q(m) was 9.35 x 10(-5) mol/g. Adsorption kinetics was studied by using pseudo-first-order model, pseudo-second-order model, Elovich model, liquid film diffusion model, modified Freundlich equation, and Bangham equation. Results exhibited that experimental data for adsorption of Co(II) fitted well to pseudo-second-order model having k(2) numerical value of 0.45 g/mg min. Thermodynamic analysis revealed that adsorption of Co(II) from wastewater was endothermic with a change in enthalpy (Delta H degrees) value of 15.406 kJ/mol and spontaneous process. Desorption of Co(II) from TRH was also investigated. Hence, TRH could be used as an excellent adsorbent for the discharge of Co(II) from wastewater.