Montmorillonite-rice husk composite for heavy metal sequestration from binary aqua media: a novel adsorbent

Abstract

This work describes the sorption of metal ions using a montmorillonite-rice husk composite as a novel adsorbent. The adsorption capacity of the new adsorbent was compared with the unmodified, alkaline and acid treated montmorillonite. Scanning electron microscopy showed an increase in the porous nature of the adsorbent modified with rice husk. The Fourier transform infrared spectra showed an alteration of the structure of the montmorillonite-rice husk adsorbent. Brunauer–Emmett–Teller (BET) analysis showed a sharp increase in the surface area of the montmorillonite from 55.76 to 118.01 m²/g and the total pore volume from 0.0688 to 0.114 cm³/g. It showed a decrease in the average pore diameter from 49.35 to 38.64 Å and enhancement of the cation exchange capacity from 90.78 to 96.17 meq/100 g for the new adsorbent. The change in solution pH, initial metal concentration, adsorbent dosage, contact time and solution temperature affected the adsorption process. The Freundlich model gave a better fit than the Langmuir model in the equilibrium isotherm analysis for the acid, alkaline and rice husk treated adsorbents, while the latter was suitable for the unmodified form. Interestingly, the rice husk modified adsorbent recorded a higher adsorption capacity than the unmodified, acid and alkaline derivatives. Both the pseudo-first order and pseudo-second order kinetic models were applicable for the sorption on all the adsorbents and a thermodynamic study revealed a feasible, spontaneous and endothermic adsorption on the novel adsorbent.

Keywords:

• montmorillonite
• rice husk
• isotherm
• sorption
• thermodynamics