Polymeric sorbents for removal of Cr(VI) from environmental samples*

Chromium (Cr) is an important raw material in some chemical industries including paint, pigments, textiles, leather tanning, steel fabrication, electroplating, cement preservation, and canning industries. Once in the environment, Cr exists in various oxidation states depending on pH and concentration. Trivalent [Cr(III)] and hexavalent [Cr(VI)] forms are the most common with Cr(VI) being the most toxic to biota. The review discusses various types of polymeric sorbents that have been prepared for the extraction of Cr(VI) from environmental samples, mostly aqueous samples. Sorbents are categorized into biosorbents, hybrid sorbents, synthetic polymeric, and modified natural polymeric sorbents. Most of the emphasis will be on the advantages and disadvantages of different synthetic polymeric sorbents. Important parameters that define the performance of the sorbents, that is, binding capacity, equilibration time, optimum sample pH, and selectivity, are compared.