The sorption of ions heavy metals by technical lignins

Abstract

This study investigated the sorption of iron (III) and copper (II) ions from aqueoussolutions by various technical lignins, which are waste products from kraft, organosolv and hydrolysis wood processing. In order to understand the sorption mechanism of heavy metals, lignin samples were thoroughly characterized with respect to their elemental composition, their content of functional groups (OH and COOH), which was determined by 31Р NMR, and their molecular weight, which was determined by gel-permission chromatography. The obtained results suggest that lignins can be used for the efficient sorption of iron (III) and copper (II) from aqueous solutions. It seems that polar functional groups present in the lignin structure, especially aliphatic hydroxyl groups, have a major effect on heavy metal sorption capacity. The kraft lignin with the highest content of aliphatic OH groups demonstrated an adsorption capacity twice as high as that of organosolv and hydrolysis lignin. Being natural products, lignin adsorbents can easily be disposed of as ash residue after use and subsequent burning.