Efficent removal of nickel(II) salts from aqueous solution using carboxymethylchitosan-coated silica particles as adsorbent

Three types of organo-mineral composites have been probed as adsorbents for the removal of Ni(II) ions from aqueous solution. Native Aerosil 200 silica particles have been encapsulated with carboxymethylchitosan (CM-CS) providing SiO₂+CM-CS, surface-silanized silica particles SiO₂NH₂+CM-CS were obtained by treatment with APTES and subsequent encapsulation by CM-CS. Alternatively, surface-carboxylated Aerosil 200 was coated by CM-CS affording SiO₂CO₂H+CM-CS. The materials have been characterized by various techniques. The effects of counter ions (Cl^-, Br^-, CH₃COO^-, NO₃^- and SO₄^2-), pH and initial Ni(II) concentration on the adsorption capacities have been systematically investigated. The maximum adsorption capacity q_m of CM-CS-coated silica was determined using the Langmuir adsorption isotherm. For SiO₂CO₂H+CM-CS, SiO₂+CM-CS and SiO₂NH₂+CM-CS, they decrease at pH 7 in the order 256mg/g>140mg/g>105mg/g. The adsorption kinetic fits well with a pseudo-second order model. These carbohydrate-derived biosorbents are excellent adsorbents with capacities superior to most other adsorbents reported in the literature.