Physicochemical characterisation of natural K-clinoptilolite and heavy-metal forms from Gördes (Manisa, western Turkey)

•As termed by us, the "rate of ion selectivity" differs from the "ion selectivity" of an ion-exchanged form.•Decrease in crystallinity is controlled by replacement of heavy metals in the clinoptilolite structure.•Peak intensities decrease in relation to increasing normality in the Ag+, Cd2+ and Co3+ forms, except the Cr3+ forms.•The temperature of adsorbed water loss in heavy-metal forms is consistent, that of water of crystallisation increases.

Physicochemical characterisation of natural K-clinoptilolite and heavy-metal (Ag+, Cd2+, Cr3+ and Co3+) forms was accomplished through ion exchange by batch, X-ray diffractometric (XRD), X-ray fluorescence (XRF), infrared-spectral (FT-IR), differential thermal analysis–thermal gravimetric (DTA–TG) and scanning-electron microscopic (SEM) methods. Increasing the normality in the cases of heavy-metal forms resulted in decrease in crystallinity and increases in unit-cell volume, rate of ion exchange, and percentage of ion selectivity. In this study, the order of ion-selectivity percentages (rather than ion selectivity) of heavy-metal forms was determined to be Ag+ > Cd2+ > Cr3+ > Co3+. This finding is consistent with the results of worldwide research on the order of ion selectivity in modified clinoptilolite.