Carmine Adsorption from Aqueous Solution by Crosslinked Peanut Husk

To observe the feasibility of the removal of carmine, peanut husk, an agriculture by-product, was crosslinked with epichlorohydrin in alkaline medium and used for adsorption of carmine from aqueous solution. Batch experiments were carried out to study the effects of various parameters such as initial pH, contact time, adsorbent dosage and initial carmine concentration, as well as temperature on carmine adsorption. The results indicated that adsorption equilibrium data could be more effectively described by Langmuir isotherm equation than by Freundlich equation. The maximum monolayer adsorption capacity of peanut husk from the Langmuir model was 6.68 mg/gat 323 K. The pseudo second-order model provided a better fit to experimental data in the kinetic studies. The mass transfer model such as the intraparticle diffusion was applied to the experimental data to examine the mechanisms of the rate-controlling step. It was found that the intraparticle diffusion is the significant controlling step under the experimental conditions but it was not the unique one. The thermodynamic parameters of the adsorption process were also calculated by using constants derived from Langmuir equations, which propose an endothermic physical spontaneous adsorption process.