Impact of pH on the Removal of Cadmium (II) Ions from Aqueous Solution using Rice Husk Ash as Adsorbent

Author(s): Virendra Kumar Yadav and Chitrasen Gupta

Abstract:

The removal of cadmium Cd (II) from aqueous solutions using rice husk ash (RHA) is fundamentally governed by the solution's pH, which modulates the electrostatic interactions at the adsorbent-metal interface. In highly acidic environments, a high concentration of hydrogen ions H+ acts as a primary competitor for available binding sites, imparting a positive charge to the ash surface. This results in electrostatic repulsion of the positively charged cadmium ions, significantly hindering removal efficiency. As the pH increases toward neutrality, the reduction in H+ competition facilitates the migration of Cd (II) ions toward the ash surface. This study investigated Cd (II) adsorption as a function of equilibrium time, adsorbent dosage, initial metal concentration, pH, and particle size using a batch system. Results indicate that removal efficiency is positively correlated with increasing pH levels. Specifically, modified rice husk ash achieved a maximum adsorption capacity of 0.396 mg/g (76.27% removal) at an optimal pH of 7.5, a contact time of 140 minutes, and an initial concentration of 0.192 mg/L. The adsorption data demonstrated a strong fit for both Langmuir and Freundlich isotherms. Ultimately, the findings confirm that modified rice husk ash serves as a more favourable and effective adsorbent than unmodified RHA for cadmium remediation.

keywords:
Adsorption, Rice Husk Ash, Aqueous solution, modified and unmodified adsorbent.

Pages: 174-179     |    20 View     |    1 Download