Effect of temperature and pH value on cation exchange performance of a natural clay for selective (Cu2+, Co2+) removal: Equilibrium, sorption and kinetics

This work aims at investigating the strain effect, created by varying pH solution and continuous heating cycle, on the cation exchange process in the case of Na-rich montmorillonite sample in contact with bi-ionic solution with variable concentration, saturated respectively by Co2+ and Cu2+ cations. The ionic exchange process is characterized using XRD analysis obtained through the comparison of experimental XRD patterns with calculated ones, which allowed us to determine several structural parameters related to the nature, abundance, size, position and organization of exchangeable cation and water molecule in the interlamellar space along the c⁎ axis. Indeed, the proposed theoretical models, for the stressed samples, show that the structure presents an interstratified hydration character and proves the coexistence of more than two “crystallite” specie in the structure. The perturbation types have an obvious effect on the selective exchange process for all stressed samples, where the interlayer space is characterized by the coexistence of more one exchangeable cation.