Ion-exchange of amino- and aqua-complexes of nickel and cobalt in natural clinoptilolite

•Exchange of amino- and aqua-complexes of Ni and Co have to occur via smaller cations.•The attraction between the cation and ligands affect the complex-cations exchange.•These exchanges are favored by an increasing of the temperature.•The effect is especially notable for Ni possibly due to growing of site availability.

Natural clinoptilolite from Caimanes deposit (Cuba) modified to ammonium form was used for removal and recuperation of nickel and cobalt by ion-exchange from residual ammoniacal liquors of the nickel hydrometallurgical industry. Metal cations in these residual solutions exist in amino- and aqua-complex form, such as [Ni(H2O)6]2+, [Ni(NH3)6]2+ and [Co(NH3)6]3+. The subject of the present study is to analyze the influence both of the nature of these complex-cations and the temperature on its ion-exchange in the ammonia modified clinoptilolite. The main kinetic parameters associated with these exchanges were determined. An increase in the attraction interaction between the metallic-cation (Ni2+ and Co3+) and their ligands (H2O and NH3) affect the complex-cations exchange. Kinetic of theses exchanges is favored in the following order: [Ni(H2O)6]2+ > [Ni(NH3)6]2+ > [Co(NH3)6]3+. For steric reasons the exchange of these complex-ions from solution must occur via cations of smaller size, i.e. single Ni2+ and Co3+ and/or cations with a number of water or ammoniac molecules smaller than 6. The exchanges are favored by an increasing of the temperature, which is confirmed by a substantial raise of the rates of the diffusive processes and increased amounts of removed from the solutions ions of nickel and cobalt. This effect in the case of nickel is especially pronounced, probably due to increasing of exchange site
tm)s accessibility compared with exchange at low temperature.