The effect of pH and ligands on the sorption of heavy metal ions by cellulose

Abstract

The adsorption of copper, lead, cadmium and zinc ions by cellulose suspensions has been examined at pH values ranging from 3.5 to 11. The chemical form of the metal ions has been changed by adding ligands such as oxalic acid, citric acid, tartaric acid, ethylenediaminetetraacetic acid, ethylene- diamine, glycine, cysteine and α,α'-bipyridyl. Stable anionic complexes were not sorbed by the cellulose, and at a given pH cationic complexes were sorbed less than hydrated ions. The presence of excess ligand generally served to mask the precipitation of the metal- hydroxy species which can occur in the pH 6-7 region.    

The amount of metal cation sorbed increased with pH. This has been attributed to increased ionization of acid functional groups having a pK_a value of around 4.4.    

The implication of the results, in respect to aqueous metal ion levels in natural systems, has been considered.