Metal removal from process water by lignin

Lignin obtained as a byproduct from the paper and pulp industry in the form of powder and beads (obtained upon polymerization) was used for the removal of trivalent and hexavalent chromium, lead and zinc from aqueous solutions. Metal uptake as a function of time and temperature was determined. It appears that oxygen functionalities such as phenols present in lignin may serve as sites for the metal cation exchange. The metal bearing lignin upon a wash with 10% sulfuric acid results in elution of copious amounts of metal. The dissolved metals in a concentrated form in the acid can be precipitated by addition of alkali resulting in the metal recovery.