Chemically Modified Polysaccharides for Hexavalent Chromium Adsorption

Over the last decades, adsorption has emerged as a potential separation process for the removal of heavy metals that are extensively released in effluents from different industries. Among heavy metals, Cr(VI) is relevant due to its high toxicity, and its required concentration limit between 50 and 100 µg/L in water for human consumption. Several adsorbents, including silica, zeolites, clays, and carbon, are expensive for this application. This literature review proposed the use of novel adsorbents based on polysaccharides, mainly chitosan and cellulose, generalizing the effect of pH, equilibrium, kinetics, thermodynamics, and mechanism on the adsorption efficiency. It is shown that chitosan and cellulose exhibit a competitive Cr(VI) adsorption capacity reaching up to 625 and 358 mg/g, respectively. Also, a general review of sorbent reusability and continuous-flow adsorption is provided as they are critical for the highly extensive operation where maximum continuous-flow removals of 350 and 93 mg/g are reported for chitosan and cellulose. The use of polysaccharides as sorbents in batch and semi-continuous systems is an area of great interest and an opportunity to direct the efforts to provide state-of-the-art sorbents and technology for the removal of hexavalent chromium from polluted water streams.