Adsorption of Crystal Violet from aqueous solution onto NaOH-modified rice husk

In this study, equilibrium, kinetics and thermodynamics of Crystal Violet (CV) adsorption onto NaOH-modified rice husk (NMRH) was investigated. Experiments were carried out as function of contact time, initial solution pH (2–10), adsorbent dose (0.5–5 g) and temperature (293, 303 and 313 K). The adsorption was favoured at higher pHs and lower temperatures. Adsorption data were well described by the Freundlich model, although they could be modelled by the Langmuir model as well. The adsorption process followed the pseudo-second order kinetic model. The mass transfer model based on intraparticle diffusion was applied to the experimental data to examine the mechanisms of the rate controlling step. It was found that intraparticle diffusion was not the sole rate controlling step. The activation energy (Ea) of the system was calculated as 50.51 kJ mol−1. Thermodynamic parameters suggest that the adsorption is a typical chemical process, spontaneous, and exothermic in nature.