Adsorption-Desorption of Heavy Metal Ions

Adsorption and desorption studies on different types of adsorbents, including natural materials such as teak tree bark powder, rice husk, natural bentonite, different algae like Ecklonia maxima, Escherichia coli, Ascophyllum nodasum, Rhizopus nigricans, Cladophora fascicularis, goethite and soils of three nuclear power plant and artificial materials such as Fe oxide-coated sand, goethite pretreated with phosphate, dithizonemodified sodium trititanate whisker, modified nanometre sized TiO₂, Chromosorb 102 resins and poly(m-phenylenediamine) are summarized. The kinetics, thermodynamics, sorption/desorption mechanism of different metal ions on different adsorbents under different experimental conditions are discussed. It is found that desorbing agent is greatly dependent on the adsorbate used. All the metal ions are desorbed using acids like HCl, HNO₃ and H₂SO₄ in most of the cases, except Cr(VI). EDTA can be used to remove Pb²⁺ and Zn²⁺ in addition to acids. Since Cr(VI) is present in anionic form; it can be eliminated from the loaded adsorbents using bases like NaOH, Na₂CO₃ or NaHCO₃.