The sorption of cadmium(II) ions on mercerized rice husk and activated carbon

This work describes the removal of Cd(II) ions in aqueous solution by unmodified and base-modified rice husk (RH) as compared to that by activated carbon (AC). Mercerization of RH was carried out by using dilute solutions (0.013 M) of NaOH, KOH, and Ca(OH)2. The experiments were conducted in duplicate under 1-batch and 2-batch treatments. In the 1-batch treatment, a fresh 200 mg of each adsorbent was used to study the sorption of the Cd(II) ions from 100-mL solutions at an initial concentration of 5 mg L-1. The adsorption percentage increased in the order of unmodified RH (80.13 \pm 0.46%) < Ca(OH)2-modified RH (90.74 \pm 0.18%) < NaOH-modified RH (93.36 \pm 0.23%) \le KOH-modified RH (93.78 \pm 0.27%) < AC (98.4 \pm 0.18%). In the 2-batch treatment, a fresh 100 mg of each adsorbent was placed in 100-mL solutions at an initial concentration of 5 mg L-1 of Cd(II) ions for 30 min, and the resulting solutions were filtered. The filtrates were subjected to another fresh 100 mg of each adsorbent for an additional 30 min. The percentage removal of the metal ion using the 2-batch treatment for unmodified RH, base-modified RH, and AC was 97.71%, 98.00 \pm 1.00%, and nearly 100%, respectively.