Recent trends in Ni(II) sorption from aqueous solutions using natural materials

The use of materials of natural origin for the adsorption of heavy metal ions from aqueous solutions has gained attention in recent years among the scientific community. This is explained by the fact that nickel compounds, due to severe health consequences, are considered to be among the most dangerous to the environment. This article reviews the results of studies on the use of biosorbents for purification of aqueous solutions from nickel ions, and then attempts to classify them according to their origin. The characteristics of materials and their sorption capacity have been compared, and the removal mechanisms identified of which chemisorption and ion exchange are considered to be the most common. From the analyses, a major trend is the use of biomass; however, biosorbents from other groups also continue to attract the interest of researchers. Conducting laboratory studies can help select materials with high efficiency. The highest sorption capacity values for the materials in each group were: for waste products 56 mg Ni·g−1 (olive stone), for peat 61 mg Ni·g−1, for miscellaneous 225 mg Ni·g−1 (microbial flocculant GA1), for biomass 286 mg Ni·g−1 (Plantanus orientalis bark) and for composites/modified materials calcinated eggshells 769 mg Ni·g−1 (calcinated eggshells). However, for some materials the sorption phenomenon may be accompanied by precipitation in the presence of hydroxides, which significantly affects the sorption capacity achieved. There is a need to transfer these experiments to an industrial scale so as to verify their applicability. In such industrial scale applications, attention should be paid not only to the effectiveness of the material, but also to its availability, price, and ease of use, as well as the effect of the biosorbent in terms of changing the quality parameters of the aquatic environment.