In this book, the author studied the removal of Au(III) and Ag(I) on a chemically modified chitosan (R1) with Schiff's base of thiourea/glutaraldehyde in the presence of magnetite. The selective separation of Hg(II) using magnetic chitosan resin modified with Schiff's base derived from thiourea and glutaraldehyde (R1) has been studied. The removal of Mo(VI) as oxyanions from aqueous solutions was studied using magnetic chitosan resins chemically modified through the reaction with tetraethylenepentamine followed by glycidyl trimethylammonium chlorid to produce chitosan bearing amine (R2) and chitosan bearing both amine and quaternary ammonium chloride moieties (R3), respectively. Also the removal of reactive black 5 from aqueous solutions using magnetic chitosan resins (R2 and R3) was studied.