Optimization of cadmium(II) adsorption onto modified and unmodified lignocellulosics (rice husk and egussi peeling)

Abstract

The present study is based on the adsorption of cadmium (II) ions on rice husk and egussi peeling, unmodified and modified with nitric acid in aqueous solution, using batch technique. It was carried out as a function of contact time, dosage, pH and initial concentration. The equilibrium time was achieved within 25 minutes for unmodified rice husk (Glu NT) and 20 minutes for unmodified egussi peeling (Cuc NT) with an adsorbed quantity of 13.18 mg/g. In the case of modified materials, we obtained 15 minutes for modified rice husk (Glu HNO3) and 10 minutes for modified egussi peeling (Cuc HNO3) with an adsorbed quantity of 18.77 mg/g. The maximum biosorption occurred at pH 5.5 for all biosorbents. The adsorbent mass for maximum adsorption was 0.4 g giving an adsorption capacity of 62.02 % for unmodified adsorbents. In the case of modified adsorbents, the minimal mass at which maximum adsorption occurred was 0.4 g giving an adsorption capacity of 98.33 % and 0.6 g giving an adsorption capacity of 98.33 % for modified rice husk and egussi peeling respectively. The adsorbent/adsorbate equilibrium was well described by the pseudo-second order kinetic model and by Langmuir’s and Freundlich adsorption model. This models showed that the adsorption of cadmium (II) is a chemisorption process.