Ammonium modified natural clinoptilolite to remove manganese, cobalt and nickel ions from wastewater: Favorable conditions to the modification and selectivity to the cations

Abstract The removal of manganese, cobalt and nickel from industrial ammoniacal wastewaters has been studied using natural Cuban clinoptilolite modified to ammonium form. Favorable conditions to obtain the ammonium-clinoptilolite form (NH 4 -CLI) were determined from detailed kinetic studies of NH 4 + ion-exchange in the clinoptilolite (CLI). Obtained NH 4 -CLI was characterized by IR spectroscopy and X-ray diffraction. NH 4 -CLI was used to remove Mn 2+ , Co 2+ and Ni 2+ from mixed aqueous solutions. The thermodynamic study on ion-exchange equilibrium between NH 4 + in solution and these metallic cations from metal-clinoptilolite forms was performed. Increasing the temperature promotes the NH 4 + exchange, which is controlled by the intracrystalline diffusion of ions inside the clinoptilolite. However, the activation energy of this process is not very high. This provides a wide temperature interval for the NH 4 -CLI efficient production. NH 4 -CLI removes Co 2+ and Mn 2+ by ion-exchange selectively at room temperature, being poorly selective to Ni 2+ , producing a well ions separation. Increasing the temperature greatly enhances the NH 4 -CLI capacity to remove these metal cations, which is substantially higher to Ni 2+ . The obtained values for the free energy variation and equilibrium constant lead to outline that the selectivity order of the metal-clinoptilolite forms by NH 4 + at room temperature is Mn-CLI > Co-CLI > Ni-CLI. Divergences in the behavior to these exchange processes are associated with difference in the interaction of cations with their ligands in solution as well as into zeolite framework, and accessibility at ion-exchange sites inside clinoptilolite.