Sorption of Heavy Metal Ions from Aqueous Solutions: A Review

Sorption techniques are widely used to remove heavy metal ions from large volumes of aqueous solutions. Herein, the natural and some artificial materials, such as clay minerals, biosorbents, carbon-nanomaterials, metal oxides, are reviewed as adsorbents in the removal of different heavy metal ions, such as Ni(II), Cu(II), Pb(II), Cd(II), Cs(I), Eu(III), Th(IV), Cr(VI) from large volumes of aqueous solutions. The sorption kinetics and thermodynamics, the influence of environmental factors on the sorption, the possible sorption mechanism of heavy metal ions and the modification of adsorbents on the removal of heavy metal ions are discussed in detail. The sorption properties of the different adsorbents are also described. The different methods such as batch sorption techniques and spectroscopy techniques (such as XPS, FTIR, EXAFS, ATR-IR) in the determination of heavy metal ion sorption properties and sorption mechanisms are presented. Different models for the simulation of sorption isotherms and kinetic sorption data are given as a comparison to understand the sorption mechanism. Many amphibolous matters for further research and the necessity in the study of the selective adsorbents in multi-component sorption systems are also summarized.