The formation of cobalt and nickel complexes on clay surfaces
Abstract Treatment of hectorite exchanged with cobalt or nickel with various ligands is investigated. Basic ligands such as 2,2′-bipyridyl,1,2-diaminoethane (ethylenediamine, en) and ammonia readily afford complexes of nickel(II) and cobalt(III). In the case of ammonia, evidence is obtained for the isolation of an oxidation intermediate on the clay. More quantitative studies including some typical groundwater ligands such as pentanoic and butanoic acids reveal that the weak acid ligands are effective in displacing significant quantities of exchanged cobalt and nickel to solution; by contrast, some basic ligands can “stabilize” the more labile ion pair sorbed fractions of the metal on the clay surface. Although [Ni(en) 3 ] 2+ is much more strongly sorbed than Na + or Ca 2+ , copper(II) ions release large quantities of nickel(II) to solution when aqueous [Cu(H 2 O) 6 ] 2+ contacts [Ni(en) 3 ] 2+ —hectorite. Tracer studies using 60 Co show that similar behaviour pertains at microscopic concentration levels to that observed with macroscopic concentrations.