Peanut hull was converted into an adsorbent by Namasivayam and Periasamy [151] by treating it with concentrated sulfuric acid, followed by its carbonization in air and further treating with 1% sodium bicarbonate overnight. The treated material was used as an adsorbent for the removal of Hg(II) ions from aqueous solutions and the adsorption was found to conform to both Freundlich and Langmuir isotherms. Chamarthy et al. [152] also prepared an adsorbent from peanut shell by thermal treatment in presence of phosphoric acid or citric acid and used it for the adsorption of Cd(II), Cu(II), Ni(II), Pb(II), and Zn(II). Their study showed that phosphoric acid-modified shells adsorbed metal ions in larger amounts compared to citric acid-modified shells.